Audio Technica AT-RMX64 Story…

[sweetbeats]

So my affinity for the Philips Compact Cassette 4-track multitrack format, and over a decade of curiosity and fascination with the Audio Technica AT-RMX64 all-in-one mixer/multitracker came to a head a little while ago…got my mitts on a straight all-original specimen for a price far less than the insanity that is the current market. It looks like it will clean up really nice, appears to have relatively low hours on it, and came with the factory soft case and original owner’s manual. All that considered, it was a steal at $350 including shipping. it looks like this:

And, no, for that price with the cosmetic condition it’s in and the included accessories it’s not 100% functional…needs a little work…

1. Needs a new reel table drive tire, and as a result it doesn’t currently PLAY and ain’t so good in FFWD or REW either.

2. Pinch roller is *okay*, but could stand a replacement.

3. Several input channels pass signal only intermittently

4. Two meter lamps are out

That’s what I know so far.

For issue #1, I believe the transport, made by Sankyo, is closely related to the transport in a Nakamichi BX-150…looking at pictures of the BX’s Sankyo-made transport and studying the service manual for that machine, it appears to me the reel drive assembly is the same as the AT…those tires are readily available. So I’m going to order one of those at some point and see if I’m correct.

For issue #2 I disassembled the pinch roller assembly in order to test a theory: that the roller is the same as a Tascam 244 (and likely other Tascam units). I was right…same roller specs. And I happen to have a brand new Athan 244 roller here…I’m commandeering it for the AT-RMX64. I *highly* recommend the Athan rollers…got mine off of eBay. Poly instead of rubber, brass hub, and precision mini bearings. It…is a thing-a-beauty. Stock AT on the left, Athan on the right:

[EDIT] I spent some time perusing Athan’s offerings and see now they have a pinch roller for a “Nakamichi Sankyo Transport”. The dimensions match the factory AT-RMX64 pinch roller exactly, so I believe the Athan roller is a perfect match for the AT-RMX64. I have a couple messages out to them to verify, but here is a current link to the product: https://www.ebay.com/itm/2751181460...le5cs0tQ9u&var=&widget_ver=artemis&media=COPY

Issue #3…the plug-in input and mix buss modules are cool. What’s not as cool is what looks like mini-Molex edge connectors to interface the motherboards. Logically I can understand why they picked them, but I think they’re going to need some exercising, DeoxIT-izing and maybe some solder joint re-flowing. The boards are all phenolic resin instead of glass fiber…these intermittent signal issues might not be such an issue with more robust glass fiber boards but…ya can’t have it all. But if you have an AT-RMX64 and signal is dodgey, but you can make it happen by pushing or tapping various places along the affected channel on the dress panel or controls, it’s probably related to the edge connectors.

Last but not least, issue #4, the meter lamps, no sweat. There’s a nice thread right here on this forum started by @famousbeagle where he details a number of issues including meter lamp replacement. I took a gander…easy-peasey, and I think I even have some new meter lamps around here…somewhere.

Here’s a YouTube video that’s nearly 40 minutes of me going on and on about the AT and comparing it to other 4-trackers, looking at the some of the guts, etc…it seemed like 10 minutes when I was recording:

 

[sweetbeats]

So *why* the lore around the AT-RMX64…and why my long-standing fascination…it is NOT the most portable…at nearly 50lbs and with a bigass footprint it is the most ungainly cassette 4-track all-in-one you can sag a table with. It is not the most sophisticated by any means…neither the mixer nor the transport. Many period and later generation Tascam units have handy semi-inline monitoring features, handy device-specific routing/assign/source features, etc. And many units from a number of manufacturers have multipoint auto-locate functionality, auto-punch/rehearse, etc. The Tascam 644 and 688 blew the cap off in this regard. Nonna any of that on the AT-RMX64. It does do RTZ, but that’s it. And it doesn’t have dbx noise reduction. It has Dolby B and C. I’m not sure how I feel about that. I betcha Audio Technica couldn’t get the licensing at the time…too many other big names in the Portastudio game, including Teac, maybe pressured dbx to not allow more manufacturers to use their circuit. That’s complete conjecture. I just like the sound of cassette 4-track with dbx, and it gets the job done regarding the tape noise floor. Anyway, I may be totally wrong there about why no dbx on the AT, and maybe I’ll love the Dolby.

So what then…why the AT…well, it is the ONLY all-in-one cassette multitracker with plug-in mixer modules, and top-load at that. The 244 comes close, but they’re not plug-in (connectorized, yes…plug-in no…), and they come out through the bottom…have to remove the whole bottom half of the plastic case, etc…still cool, but not like the AT. It is by far the most robust chassis, and the most serviceable…hands down. It kills in the metal vs plastic department. I also like that it has a direct drive servo capstan but using all through-hole components rather than the problematic Tascam assembly with SMD components that invariably fail (238, and later generation 122…can’t recall if it is the mkII or mkIII). And the con I listed above regarding the relative lack of sophistication of the mixing console, well, in some ways that’s a plus. It is truly a full-featured straight-ahead 6 x 4 mixing console, XLR mic inputs on all 6 input channels, insert points, phantom power, two aux busses each globally switchable pre/post, two fully assignable returns, and 4 separate mix busses that feed individual outputs and corresponding tape tracks with their own record level controls. This means no brain straining around how to get signal to tape tracks. It’s very straight-forward; a very functional and well-built small format mixing console. Oh! And individually source selectable VU meters with post-fade peak indicators, and by source selectable I mean each meter can either source the corresponding mix buss or tape track, and if a track is in record ready and the corresponding meter is set to source “TAPE” it is monitoring the post record level signal so you can preview levels to tape. Very handy. There are also peak LEDs at the input stage, so good faculties around level and peak monitoring…unbalanced and balanced mix buss outputs…And by golly there are 4 headphone output jacks, with some source selection options. And yes I’ve saved the best for last, the EQ. Over my years of using and messing around with dozens of different mixing consoles both analog and digital, recording and mixing music, reading and studying how others do it, I’ve determined one of the most powerful tools to have is a sweepable HPF. This is a rare filter typically found only on high-end consoles, but is an absolutely invaluable tool for cleaning up mixes, and also managing signal energy to your recording. At first glance the EQ on the AT looks like a typical 2-band sweep EQ…maybe peaking or shelving…I really am not a fan of EQ filter sections with only peaking filters. Like, a hi shelving filter, in my experience, is much more useful than a hi peaking filter. Well, the EQ bands on the AT have push-pull pots. The lo band is either swept peaking or switches to a swept HPF. And the hi band is either swept peaking or shelving. This is arguably the most powerful 2-band EQ ever. I think it’s the most powerful EQ on any all-in-one cassette multitracker period. But the next most important question is how does it sound? Like, who cares about functionality if it sounds like ass. You won’t use it if it doesn’t sound good. Over the years I’ve become accustomed to my own internal determinant for if an EQ sounds good or bad or “meh” to me…if an EQ filter section makes me smile when I use it, if it is easy to get good sounds out of it, and makes me want to use it…does what I tell it to do without a fuss and sounds good, then I think it’s a good EQ. My first experience with that was on a British Soundtracs MX series console I used to have. Then the next time was my Studer 928 console. The AT is experience #3. I’ve done little experimenting with it so far because I’ve got things to fix on it, but I spent some time playing back a raw mix from a Yamaha AW4416 and A/Bing the mix straight off the monitor outputs of the AW compared to that signal input to 2 channels of the AT with EQ applied assigned to a pair of mix busses and monitored via a headphone out…I just did a little HPFing and hi shelving…conservative…but it sounded significantly better. It was literally, for me, an out-loud “no way” moment. If you’ve done any interweb reading on the AT you’ll see references to rumors the signal path and specifically the EQ section was designed by ex Neotek folks…for what that’s worth. I don’t know if that’s true. Nobody has verified that, and I’m not going to be the kreep that cold-calls the guy who was at Neotek at the time. It doesn’t really matter. It sounds good.

So the AT is, IMO, completely unique in a sea of 80s and 90s all-in-one cassette multitrackers.

I know there’s no shortage of threads around the interwebs of people begging for help getting schematics. Unobtanium. I’ve looked everywhere, talked to everybody I can…nada. Three years ago I was emailing with Michael Dewenter of transanalog.com. He told me he has schematics, but at the time he had just moved and all his shop stuff was packed up. I kept checking for awhile but he wasn’t in a position to help, I moved on to other things. Now, present day, I can’t get the guy to respond. So if anybody has leads on even just schematics I’d love it. Short of that, curiosity will probably get the best of me and I’ll start trying to reverse-engineer the modules, starting with the input module.

Anyway, stay tuned.

 

[sweetbeats]

I forgot to post this picture earlier…the heads…it really does look like it’s had relatively low use. A bit dusty. Somebody had a dog with some longer hair…anyway, heads:

And this is cool…I had a suspicion but wasn’t sure…these three PCB assemblies up above the transport assembly…

Are also plug-in cards…

Those are, from left to right, the record amp, playback amp and bias amp PCB assemblies.

It really is important to approach removing and inserting these PCB assemblies thoughtfully. The mini Molex type edge connectors require a fair amount of extraction and insertion force, and the thin phenolic boards means there’s risk for flexing and damage to joints or traces. Again, the phenolic resin base material is really common, it just wouldn’t be my choice for a motherboard or plug-in board. They are all well protected in the very sturdy chassis, it’s just an issue when extracting or inserting. I wonder if the designers intended for glass fiber, and the bean-counters value engineered that intention…

A few of the trimmers on the record amp PCB assembly are accessible from the top edge (when installed). All the rest are facing the front of the machine, so one would have to make extender cables in order to tweak the trimmers. There aren’t a lot of them though…like the bias traps and bias level trimmers are obvious to me. The four facing up on the record amp PCB I suspect are record level trimmers. And then there are four way down on the motherboard you can access through a slot in the sub-chassis panel of the record amp PCB. Maybe those are playback level trimmers? There are also trimmers on the four mix buss modules…sucks not having a service manual, but given time and gumption a guy could figure out what’s what.

 

[sweetbeats]

So I ended up ordering a replacement pinch roller specific to the AT-RMX64 from Athan. It is slightly different than the 244 roller. I think the 244 roller would work, but I think the specific roller is better. For more info on the pinch roller issue specific to the AT-RMX64 as well as some related discussion see this thread here: https://homerecording.com/bbs/threads/cassette-pinch-roller-carnage….419339/#post-4731041

For future reference the part at Athan is marketed under the title “Nakamichi Sankyo Transport.” I put that together since the AT-RMX64 transport was manufactured by Sankyo, and appears very similar to the Nakamichi BX-150 transport, which is one of the machines in the comparability list for the above Athan roller. Plus the dimensions seemed to match. It is an exact match, only much higher quality than the factory roller…a more precise fit, etc. I suggested to Athan they also market the part for the AT-RMX64 as well as the Nakamichi decks. I don’t know if they’ll do that or not, so for future readers who are interested or in need of a replacement pinch roller for their AT-RMX64, and are wanting the best, you can find it under the Nakamichi Sankyo Transport product title. Anyway, here it is:

 

[sweetbeats]

I’ve decided to partially disassemble the transport assembly to more safely replace the reel table drive tire, and also clean off old lubricant, and apply new to the reel table spindles, and headblock mechanism.

I captured a short video with some details about the transport assembly:

 

[sweetbeats]

The headphone amp on this thing is pretty burly…makes sense since there are a total of four headphone output jacks…but the amp chip is one I’ve not run across…a Sanyo LA4500. Here it is after I removed the substantial heat sink:

Cleaned up the old thermal paste, put new paste on and put it back together. Had to see what it was.

The specs are pretty impressive on it…5.3W…that may not seem like a lot but for a headphone amp? Yes.

 

[sweetbeats]

Another interesting bit of info: as I suspected from the specifications, the AT-RMX64 audio circuits are powered by +/-15V rails. This is probably the most common among professional and semi-professional audio gear…higher power means higher headroom. Of course there’s plenty of gear with higher audio power rails than +/-15V, but +/-15V is the most common, and the point I want to make is I know of no other Philips Compact Cassette multitrack machine, either all-in-one “Portastudio” or standalone machine, that has +/-15V rails for audio…they’re all +/-12V IIRC, or even less. Which is fine. But it means the Audio Technica mixer is better suited for real-world mixing situations in addition to mixing for the onboard multitrack section, which dovetails with the features of the mixer, the inputs and outputs, etc. It’s the most “serious” mixing console of any all-in-one mixer/cassette multitracker. The Tascam 688 has more inputs, busses and summing outputs, and online monitoring features…like, it’s a more flexible mixer, but it’s also an 8-track machine instead of 4-track so one would expect more channels and busses, it has no phantom power, has lower headroom, is far less robust a build, and most importantly it does not sound as good.

 

[famous beagle]

I can't wait to see this one up and running. I was really upset when I had to let mine go; I very much wanted to make it the centerpiece of my cassette recording projects. It's such a unique beast, and I really loved the sound of the onboard preamps!

 

[sweetbeats]

I can't wait to see this one up and running. I was really upset when I had to let mine go; I very much wanted to make it the centerpiece of my cassette recording projects. It's such a unique beast, and I really loved the sound of the onboard preamps!

I didn’t even try the preamps before I tore it apart lol…so typical. What I was really interested in was the EQ. And I liked it. Curious to try the preamps too of course. Just looking at the component topology on the input boards the preamp circuit looks similar to anything you’d find in a decent low to midrange budget mixing console of that era, like what you’d encounter in a Soundcraft 200 or 400 series, Soundtracs MR/MX, Tascam M-500 series…it’s a pretty common circuit. But this isn’t to say it’s bad. And definitely a higher quality circuit than any other all-in-one cassette machine.

 

[sweetbeats]

So I worked on this a little bit this week…got the transport refurbished…this is how it’s looking at the moment:

That’s after disassembly, cleaning off old lubricant, applying new lubricant, installing a new reel table drive tire and servicing the drive assembly, and installing the new Athan pinch roller. I didn’t *completely* disassemble the thing…maybe about 65%…enough to get most of the old lubricant off of the plates the slide against each other on the face, and, really, a lot of the disassembly is driven by getting the reel drive motor and drive assembly out. You see, all the parts are small. And a mix of plastic and some metal parts. And the old drive tire requires some measure of force to get it out of the wheel. And things being as the are when assembled, I was concerned about clear access to the wheel and tire and worried what if a tool slipped and damaged something else…and I wanted to see if I could apply a little superglue to the hub that goes on the motor shaft…more on that below…so I just wanted the whole assembly dismounted and out of the transport chassis. And to get it out you have to remove the reel table assemblies, and the capstan shaft/motor/servo assembly, and the headblock motion assembly. So…the reel table assemblies have to come off first.

Like most cassette transports the reel table assemblies are spring-loaded and retained on spindles by a small nylon (I believe) washer…very small. It services the function of a circlip, snap-ring, e-clip, etc. But it’s small enough that none of those retainers can be used so it’s this little nylon washer you have to kind of pry up and pop off, and if you’re not careful they like to go flying. The ones on the reel table assemblies are black. They aren’t as hard to find if they launch themselves during removal as the even smaller retainer that’s on the reel drive wheel, which is natural color nylon. You don’t have to ask me how I know that. I’ll just say the carpet in my workspace is similar in color to natural nylon…I’ll never get that time back. Anyway, you have to have nimble fingers and good eyesight to carefully remove those retaining washers. So the retaining washer comes off and then the reel table assembly just slides right off it’s spindle. Underneath is a Teflon washer, and then under that a leaf spring. The lubricant was mostly all still in good shape. This AT-RMX64 really is clean and seems little used…just needs refreshing due to age. Even though the lubricant was decent I wanted to clean the parts anyway and apply new lubricant. They used it pretty sparingly…a little on the face of the leaf spring, a little between the Teflon thrust washer and underside of the reel table assembly, then just a little at the nose under the retaining washer…so things are still clean after all these years. Note the takeup reel table assembly has a radial silver/black pattern on a label attached to the underside of the table…tach sensor circuit. So make sure you reinstall the takeup assembly on the takeup side, supply side on the supply side. Anyway, this is the transport with the reel table assemblies removed:

So then there are two screws that fasten the headblock motion assembly to the transport chassis, one at the back and one at the front, then one 11mm nut at the front on the nose of the capstan shaft/motor/servo assembly…remove all of those…I did clip the one zip tie that holds the wire bundle to the transport motion assembly PCB…allowed a bit more wiggle room to pivot stuff aside as each assembly was unfastened. And note, when you remove the capstan assembly retaining nut, that releases tension on a spring plate on the front that holds a small ball bearing captive…this keeps the slide plates on the front under some pressure for consistent motion action, but the ball bearing allows the whole mess to glide nicely. Anyway, back to the rear, you could desolder wires too to get even more working room as you remove assemblies, but experience has taught me, especially with small phenolic resin PCBs, if you can leave stuff intact, do it. And handle things gently. Okay, so then with the capstan and headblock motion assemblies removed, you can get to all three screws that hold the reel table and drive assembly to the transport chassis. Here’s the carnage that results:

Here is a closer shot of the capstan assembly. Again, I really appreciate the through-hole components here, and the surface-mount stuff is all larger form-factor…like 1/4W SMT resistors…I always prefer through-hole stuff, but this alternative is way better than the Tascam direct drive servo assembly on the 238 and I think the 122mkIII…a bunch of SMT electrolytic caps and tiny resistors, diodes, etc. A fella could actually work on the AT-RMX64 assembly:

And here’s the headblock motion assembly…genius…worm-gear to camshaft that actuates reed-type contacts. No belt, no problematic gear-reduction assembly or radial cam gear…this is the smartest design of any tape deck I’ve worked on which is a few. I removed the camshaft, which was easy, wiped off the little bit of old lubricant…applied new, put it back together…rubbed some paper in between the contacts on the reed switches, but there was no evidence of carbonization or anything. Ready for the next 40 years:

And finally I removed the reel table drive wheel, removed the old tire, which wasn’t in terrible shape. But the assembly wasn’t doing its job either, and the old tire does feel a bit more slick than the new part, which, again, is found searching for the tire for a Nakamichi BX-150. I inspected the rest of the drive assembly and decided to leave it alone. There isn’t any lubricant in the pivoting assembly anyway…just plastic parts on polished metal pins. I also mentioned applying some superglue…I’ll have to watch this over time…the drive hub on the motor shaft…well, it looks like the hole in the center could be just a hair bigger, because the part is cracked. Maybe you can see it in this pic:

So it probably won’t help, but I applied a little bit of superglue and worked it into the crack, thinking *maybe* it will slow the progression of the crack, if it’s even still progressing. Here is the assembly back together:

And from there I reassembled everything along with the new pinch roller…should be good to go.

Next I’ll be refurbishing the cassette bay door release mechanism…lubricant is all gummed up there…needs cleaned and relubricated…and then I can put the transport back in, and then focus on removing all the input, output and amplifier module assemblies, and inspecting and servicing those. I’m also slowly working through exterior cosmetic refurbishment, cleaning off old adhesive (never, EVER, ever-ever use masking tape for labeling, and especially don’t leave it on there for 100 years…the adhesive hardens into this almost mastic-like substance that’s dry, but *stubborn*…), cleaning knobs and switch caps, polishing the painted metalwork, and replacing the meter lamps. Then we can put the whole mess back together and see what we have.

ALSO expecting an original hard copy sales brochure to arrive any day now. It’s 12 pages. It’s different than the owner’s manual or specifications booklet you can find in pdf form online. This was a detailed sales brochure and I’m hoping it might reveal some interesting info about the AT-RMX64.

 

[famous beagle]

Phenomenal work, as always!

 

[sweetbeats]

Phenomenal work, as always!

Thanks!

Yeah I really think 90% of the issues people have with the transport on the AT-RMX64 is simply the need for a new reel table drive tire and a new pinch roller. The parts were about $60 shipped I think, and that includes the premium Athan pinch roller. The rest of the transport is simple, well-designed and maintenance-free, and like I mentioned above *should* last longer than equivalent Teac/Tascam transports because of the smarter headblock motion assembly, and the direct drive servo capstan that is devoid of SMT electrolytic caps and other small form factor SMT components.

 

[Slouching Raymond]

A very solid, well layed out 4-track. I missed this thread.

 

[RFR]

A very solid, well layed out 4-track. I missed this thread.

Well, looks like you done found it.

It’s a very well laid out machine. And thanks for @sweetbeats for dissecting it for us. Some of us geek types like that kind of stuff. Plus it creates a ‘forever’ internet archive of information that no manual can match.

 

[Robbie Stiefel]

Thanks!

Yeah I really think 90% of the issues people have with the transport on the AT-RMX64 is simply the need for a new reel table drive tire and a new pinch roller. The parts were about $60 shipped I think, and that includes the premium Athan pinch roller. The rest of the transport is simple, well-designed and maintenance-free, and like I mentioned above *should* last longer than equivalent Teac/Tascam transports because of the smarter headblock motion assembly, and the direct drive servo capstan that is devoid of SMT electrolytic caps and other small form factor SMT components.

Man.... This is so freaking encouraging. Very little info at all on this machine. This -including your YouTube video- is BY FAR the most exhaustive deep dive into this fabled machine. Believe it or not I actually scored a true NOS machine back in 2020. it was in orignal factory shipped box covered in plastic. It has a price tag on it but literally was NEVER plugged in. It was from the UK and the seller was the son of a gentleman who owned an pro audio store and decided to stash one aside for himself but never got around to using it. The I/O is really nice on this machine and I dig that the FX returns can be adjusted pre/post EQ and fader. I do wish the direct outs were balanced and that you could tap in post EQ but oh well... The only other quirk I cant figure out is why the balanced XLR subouts are not able to be panned. Those outs are reserved for unbalanced RCA and unbalanced 1/4". Kinda odd or am I missing the reason for that?

Please please keep working on this thing and I cant wait to hear what you think of the pres and what your take away is after digging into them. Yes the EQ really is fantastic. I also have very very much enjoyed the sound of the pres. Hopefully someone will cough up a copy of the service docs.

-Robbie

 

[Smithers XKR]

So I worked on this a little bit this week…got the transport refurbished…this is how it’s looking at the moment:

View attachment 125795

That’s after disassembly, cleaning off old lubricant, applying new lubricant, installing a new reel table drive tire and servicing the drive assembly, and installing the new Athan pinch roller. I didn’t *completely* disassemble the thing…maybe about 65%…enough to get most of the old lubricant off of the plates the slide against each other on the face, and, really, a lot of the disassembly is driven by getting the reel drive motor and drive assembly out. You see, all the parts are small. And a mix of plastic and some metal parts. And the old drive tire requires some measure of force to get it out of the wheel. And things being as the are when assembled, I was concerned about clear access to the wheel and tire and worried what if a tool slipped and damaged something else…and I wanted to see if I could apply a little superglue to the hub that goes on the motor shaft…more on that below…so I just wanted the whole assembly dismounted and out of the transport chassis. And to get it out you have to remove the reel table assemblies, and the capstan shaft/motor/servo assembly, and the headblock motion assembly. So…the reel table assemblies have to come off first.

Like most cassette transports the reel table assemblies are spring-loaded and retained on spindles by a small nylon (I believe) washer…very small. It services the function of a circlip, snap-ring, e-clip, etc. But it’s small enough that none of those retainers can be used so it’s this little nylon washer you have to kind of pry up and pop off, and if you’re not careful they like to go flying. The ones on the reel table assemblies are black. They aren’t as hard to find if they launch themselves during removal as the even smaller retainer that’s on the reel drive wheel, which is natural color nylon. You don’t have to ask me how I know that. I’ll just say the carpet in my workspace is similar in color to natural nylon…I’ll never get that time back. Anyway, you have to have nimble fingers and good eyesight to carefully remove those retaining washers. So the retaining washer comes off and then the reel table assembly just slides right off it’s spindle. Underneath is a Teflon washer, and then under that a leaf spring. The lubricant was mostly all still in good shape. This AT-RMX64 really is clean and seems little used…just needs refreshing due to age. Even though the lubricant was decent I wanted to clean the parts anyway and apply new lubricant. They used it pretty sparingly…a little on the face of the leaf spring, a little between the Teflon thrust washer and underside of the reel table assembly, then just a little at the nose under the retaining washer…so things are still clean after all these years. Note the takeup reel table assembly has a radial silver/black pattern on a label attached to the underside of the table…tach sensor circuit. So make sure you reinstall the takeup assembly on the takeup side, supply side on the supply side. Anyway, this is the transport with the reel table assemblies removed:

View attachment 125798

So then there are two screws that fasten the headblock motion assembly to the transport chassis, one at the back and one at the front, then one 11mm nut at the front on the nose of the capstan shaft/motor/servo assembly…remove all of those…I did clip the one zip tie that holds the wire bundle to the transport motion assembly PCB…allowed a bit more wiggle room to pivot stuff aside as each assembly was unfastened. And note, when you remove the capstan assembly retaining nut, that releases tension on a spring plate on the front that holds a small ball bearing captive…this keeps the slide plates on the front under some pressure for consistent motion action, but the ball bearing allows the whole mess to glide nicely. Anyway, back to the rear, you could desolder wires too to get even more working room as you remove assemblies, but experience has taught me, especially with small phenolic resin PCBs, if you can leave stuff intact, do it. And handle things gently. Okay, so then with the capstan and headblock motion assemblies removed, you can get to all three screws that hold the reel table and drive assembly to the transport chassis. Here’s the carnage that results:

View attachment 125801

Here is a closer shot of the capstan assembly. Again, I really appreciate the through-hole components here, and the surface-mount stuff is all larger form-factor…like 1/4W SMT resistors…I always prefer through-hole stuff, but this alternative is way better than the Tascam direct drive servo assembly on the 238 and I think the 122mkIII…a bunch of SMT electrolytic caps and tiny resistors, diodes, etc. A fella could actually work on the AT-RMX64 assembly:

View attachment 125804

And here’s the headblock motion assembly…genius…worm-gear to camshaft that actuates reed-type contacts. No belt, no problematic gear-reduction assembly or radial cam gear…this is the smartest design of any tape deck I’ve worked on which is a few. I removed the camshaft, which was easy, wiped off the little bit of old lubricant…applied new, put it back together…rubbed some paper in between the contacts on the reed switches, but there was no evidence of carbonization or anything. Ready for the next 40 years:

View attachment 125807

And finally I removed the reel table drive wheel, removed the old tire, which wasn’t in terrible shape. But the assembly wasn’t doing its job either, and the old tire does feel a bit more slick than the new part, which, again, is found searching for the tire for a Nakamichi BX-150. I inspected the rest of the drive assembly and decided to leave it alone. There isn’t any lubricant in the pivoting assembly anyway…just plastic parts on polished metal pins. I also mentioned applying some superglue…I’ll have to watch this over time…the drive hub on the motor shaft…well, it looks like the hole in the center could be just a hair bigger, because the part is cracked. Maybe you can see it in this pic:

View attachment 125810

So it probably won’t help, but I applied a little bit of superglue and worked it into the crack, thinking *maybe* it will slow the progression of the crack, if it’s even still progressing. Here is the assembly back together:

View attachment 125813

And from there I reassembled everything along with the new pinch roller…should be good to go.

Next I’ll be refurbishing the cassette bay door release mechanism…lubricant is all gummed up there…needs cleaned and relubricated…and then I can put the transport back in, and then focus on removing all the input, output and amplifier module assemblies, and inspecting and servicing those. I’m also slowly working through exterior cosmetic refurbishment, cleaning off old adhesive (never, EVER, ever-ever use masking tape for labeling, and especially don’t leave it on there for 100 years…the adhesive hardens into this almost mastic-like substance that’s dry, but *stubborn*…), cleaning knobs and switch caps, polishing the painted metalwork, and replacing the meter lamps. Then we can put the whole mess back together and see what we have.

ALSO expecting an original hard copy sales brochure to arrive any day now. It’s 12 pages. It’s different than the owner’s manual or specifications booklet you can find in pdf form online. This was a detailed sales brochure and I’m hoping it might reveal some interesting info about the AT-RMX64.

Lovely machine, total admiration for your restoration. Nice one

 

[sweetbeats]

Man.... This is so freaking encouraging. Very little info at all on this machine. This -including your YouTube video- is BY FAR the most exhaustive deep dive into this fabled machine. Believe it or not I actually scored a true NOS machine back in 2020. it was in orignal factory shipped box covered in plastic. It has a price tag on it but literally was NEVER plugged in. It was from the UK and the seller was the son of a gentleman who owned an pro audio store and decided to stash one aside for himself but never got around to using it. The I/O is really nice on this machine and I dig that the FX returns can be adjusted pre/post EQ and fader. I do wish the direct outs were balanced and that you could tap in post EQ but oh well... The only other quirk I cant figure out is why the balanced XLR subouts are not able to be panned. Those outs are reserved for unbalanced RCA and unbalanced 1/4". Kinda odd or am I missing the reason for that?

Please please keep working on this thing and I cant wait to hear what you think of the pres and what your take away is after digging into them. Yes the EQ really is fantastic. I also have very very much enjoyed the sound of the pres. Hopefully someone will cough up a copy of the service docs.

-Robbie

Yeah for sure I’ll continue working on it until it’s completed, posting updates here as I go and also likely additional video content on my YouTube channel.

Regarding the unbalanced direct outs, are you talking about the insert points? It’s not very common at all with a small format mixer for the insert patch points to be balanced. I really only see that when the internal signal path is balanced all the way through. The AT-RMX64, like many, many devices, is unbalanced -10dBv signal internally.

Regarding pre EQ insert sends…I was thinking about this. I am interested in identifying how to tap the post EQ point in the signal path on the input modules. It would be an easy mod.

And can you clarify what you mean by no panning on the XLR sub 3 & 4 outputs?

[EDIT]

Oh! Okay I re-read your post and looked again at the mixer features…I understand what you’re referring to now. Yeah it’s unique how the PAN function only associates with SUB 1 & 2 and not 3 & 4 as well. It’s actually a nice little feature because it allows SUB 3 & 4 to work well as additional sends if you want to use them that way…like you have a main buss and two mono alt busses, and you can have an input assigned to SUB 1, 2 & 3, set the PAN for your stereo mix on SUB 1 & 2 but have an additional post fade feed on SUB 3 that isn’t impacted by changes in the placement of the signal in the stereo field on SUB 1 & 2. This affords some creative flexibility with the SUB busses…which is supported by the fact the tape track record amp inputs are pre SUB fader and have their own record level pots. This allows the mixer to function independently in a live tracking situation, for instance, where you are mixing FOH and recording. But…yes…not sure why they put the balanced outputs on the SUB 3 & 4 busses…I would have put them on SUB 1 & 2.

I looked closer at this because I thought if the balance amp was its own separate PCB assembly, like on a lot of period Teac/Tascam stuff, one could swap inputs to the PCB and have SUB 1 & 2 feed the balance amp. So I looked at the backplane, but it’s just jack PCBs back there and ribbon cabling to the motherboard by the output modules. So then I thought “Hm…if the output modules use the same PC board and are just populated differently depending on which SUB module it is, then one might be able to populate the empty balance amp section of the SUB 1 & 2 PCB assemblies…then it would be a matter of putting in some jumpers on the motherboard…so…some modification…but in theory you could drive the XLR outs with SUB 1 & 2.”

Nope.

Each SUB module is a different PCB assembly altogether. Here is SUB 1 and SUB 3:

So no go there. One solution, since there are no direct SUB buss inputs, is to take the output of your SUB 1 & 2 stereo mix, and patch it to the dedicated return inputs and assign those to SUB 3 & 4. That leaves your dedicated returns unavailable for other things, and uses up all your SUB busses, but in a pinch in certain situations this is one solution, and with six full input channels there is potential to use a couple of those as full-featured returns. I suggest the dedicated returns for this relay of SUB 1 & 2 to SUB 3 & 4 because it’s the shortest most clean pathway to do this.

 

[sweetbeats]

Well, looks like you done found it.

It’s a very well laid out machine. And thanks for @sweetbeats for dissecting it for us. Some of us geek types like that kind of stuff. Plus it creates a ‘forever’ internet archive of information that no manual can match.

Thanks for feeding the animals.

I often wonder if anybody else has any interest in the same weird vein of “tear it apart and see how it’s made” that I do. And I know a lot of times my posts are long and too detailed and most of the young bucks move along because it’s too much to read. So I’m resigned to the fact 95% of the time my posts are just for me so I have somewhere to go to remember what I did and how I went about it. Because nobody else cares. But thanks for letting me know this stuff is of interest. At least to you lol.

 

[RFR]

Thanks for feeding the animals.

I often wonder if anybody else has any interest in the same weird vein of “tear it apart and see how it’s made” that I do. And I know a lot of times my posts are long and too detailed and most of the young bucks move along because it’s too much to read. So I’m resigned to the fact 95% of the time my posts are just for me so I have somewhere to go to remember what I did and how I went about it. Because nobody else cares. But thanks for letting me know this stuff is of interest. At least to you lol.

I’d bet there are more interested than you think.
And with your long detailed posts, you’re archiving info.
Very valuable stuff you’re doing.

 

[sweetbeats]

I made a new video focusing on tips and tricks for safe removal of the mixer input and output modules, as well as some more deep-dive discussion on the guts: