Extreme TASCAM mods!

mshilarious

mshilarious

Banned
Anybody ever screw with their Portastudio? I've got my 424mkII open in front of me, looking the the mixer section. I'll probably take a pass on the tape section, although there is one kickass IC that is 64 pin thru-hole! It's probably bigger than a modern CPU! I would guess it controls the screen display, but anyway . . .

Back to the mixer section. I was thinking about patching in phantom power to inputs 1-2 using the V+ rail, I haven't measured it yet but looking at the caps it's probably 12 or 15V. I figure I'll remove the existing load resistors and run the phantom across 3.3K resistors and see how that goes. It should run electrets OK. I'm not going to bother with a case mod, so it will be unswitched.

The rest of the board looks generally OK . . . I might swap a few electros, but I ain't recapping the whole thing. The opamps are all NJM4565, in a 8-SIP package . . . not much to be done with that package anymore, although I see Mouser has 5532s in 8-SIP . . .

So far I have cleaned the faders :o
 
I've done a lot of mods on TASCAM mixers and reel-to-reels, but decided to leave my 246 portastudio alone for now. If you wanted to upgrade the op-amps on your 424 you could replace the 456x with NJM4580, which is the latest and best performing in that series. My 246 currently has 4560s and 4562s.

I still like the 5532s myself and if could take a couple xanax before desoldering the 8-sip ICs I might even try it. ;)

I would take input/output and meter measurements first, so I could tweak everything right back to where it was, and avoid having to realign the dbx NR circuits.

Mods are a lot of fun... I enjoy it. I've done a couple mods on my portastudios... adding a punch in/out switch to the original TEAC 144 and adding a switch to disable dbx on track 4 of a 244 for use with sync code.

~Tim
 
Beck said:
I've done a lot of mods on TASCAM mixers and reel-to-reels, but decided to leave my 246 portastudio alone for now. If you wanted to upgrade the op-amps on your 424 you could replace the 456x with NJM4580, which is the latest and best performing in that series. My 246 currently has 4560s and 4562s.

I still like the 5532s myself and if could take a couple xanax before desoldering the 8-sip ICs I might even try it. ;)

I would take input/output and meter measurements first, so I could tweak everything right back to where it was, and avoid having to realign the dbx NR circuits.
Click to expand...

See, that's why I don't want to screw with the tape board at all. I'm just looking at pre and EQ.

I don't think I'll bother with 4580, that's a chip I'm used to yanking out. I'll give a go at 5532 after I read the spec sheets again, try it on two channels and see what I get . . .
 
mshilarious said:
See, that's why I don't want to screw with the tape board at all. I'm just looking at pre and EQ.

I don't think I'll bother with 4580, that's a chip I'm used to yanking out. I'll give a go at 5532 after I read the spec sheets again, try it on two channels and see what I get . . .
Click to expand...

Let the rest of us know the results. I've got a couple of these laying around. :D
 
mshilarious said:
See, that's why I don't want to screw with the tape board at all. I'm just looking at pre and EQ.

I don't think I'll bother with 4580, that's a chip I'm used to yanking out. I'll give a go at 5532 after I read the spec sheets again, try it on two channels and see what I get . . .
Click to expand...

IMO, replacing the 456x with 5532 can really sweeten the EQ on some consoles, so it's worth a shot.
 
mshilarious said:
Anybody ever screw with their Portastudio? I've got my 424mkII open in front of me, looking the the mixer section. I'll probably take a pass on the tape section, although there is one kickass IC that is 64 pin thru-hole! It's probably bigger than a modern CPU! I would guess it controls the screen display, but anyway . . .

Back to the mixer section. I was thinking about patching in phantom power to inputs 1-2 using the V+ rail, I haven't measured it yet but looking at the caps it's probably 12 or 15V. I figure I'll remove the existing load resistors and run the phantom across 3.3K resistors and see how that goes. It should run electrets OK. I'm not going to bother with a case mod, so it will be unswitched.

The rest of the board looks generally OK . . . I might swap a few electros, but I ain't recapping the whole thing. The opamps are all NJM4565, in a 8-SIP package . . . not much to be done with that package anymore, although I see Mouser has 5532s in 8-SIP . . .

So far I have cleaned the faders :o
Click to expand...

I converted mine to 2" 24 track and it sounded awesome until I woke up.
 
Beck said:
IMO, replacing the 456x with 5532 can really sweeten the EQ on some consoles, so it's worth a shot.
Click to expand...
I realize this thread is just shy of 20 yrs old, but I have wanted to improve the built-in pres on my 246 for many years. My pipe dream is to also replace the TS inputs with 48v phantom power enabled XLRs as well. However I would settle for just getting the pres sounding like they are premium. Thoughts?
 
In fairness, the snag is that the preamps on this gear - in fact, most gear from the 70s and 80s had pretty OK preamps, and the limitations of the medium mask anything extra in the quality stakes?
 
The bigger problem is what you are wanting to do is not an easy task on a 246…or a 244 or a 144. They each have a similar input amp circuit. Its unbalanced, so in order to make it balanced you have to add a complete additional amplifier circuit. Or I suppose you could transformer balance it. But good quality transformers are not cheap. And I don’t know about the 246, but there’s NOwhere on a 244 to shoehorn in a set of transformers. On the positive side it’s not a completely garden variety circuit…it has a discrete transistor input stage using two 2SK68A transistors. There’s a part you can get that upgrades the two parts onto one die with higher quality parts…you have to do some monkey-business to make it fit because the pinout of the upgraded part is not at all compatible with the factory layout on the PCB. But even with that it’s still unbalanced. The 456x is not a bad part. I’m not that familiar with what’s compatible with the 456x…and it’s circuit dependent. So if you wanted to try different parts there you’d want to measure DC offset at the outputs before and after swaps in-circuit to see if whatever you put in there is happy…and you can recap with better quality caps…maybe something you can do replacing select 5% carbon film resistors with 1% metal film…like by select I mean feedback resistors. And if you want lower noise step 1 is recap the power supply. But to Rob’s point, with the limitations of the medium, and unless you chase this upgrade ideology all the way through the device, record amp, playback amp, output amp, it’s pretty questionable at best whether or not you’ll enjoy any noticeable benefit. And the audio power rails are +/-12V. Which is pretty standard for most all “portastudios”…but that means you’re still going to have the same headroom as the factory preamp. Now, don’t get me wrong…I’m not trashing on your idea, or on the format or anything. I’ve made it pretty clear I have a soft spot for cassette…currently have here in various states of condition from non-functional to fully restored, a couple Audio Technica AT-RMX64s, and a bevy of Tascam gear…122, 122B, several 244s, and a 238. And I have an experiment I’d like to do someday with the 244…do all the stuff I mentioned above. I analyzed the whole signal path and power circuits, consulted with some smart people, and bought parts to refine/upgrade the whole signal path. I’d like to do this someday and compare stock to upgraded version back-to-back. So naturally I understand where you are coming from, but it’s a huge question mark how far you have to go to get any beneficial results. And converting the input amp from unbalanced to balanced would be a bit of a project.
 
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