sweetbeats
Reel deep thoughts...
When both STEREO and MONITOR out jacks are connected to loads, what are they? Are they both connected to the Adcom?
Tascam 388 Story...
- Thread starter sweetbeats
- Start date
Gaspardeden
New member
I always appreciate a good constructive critic. Thanks for your honesty! My skills improved since then, because obviously I had to improve in order to keep on working on the machine. After all, I did recap the entire machine so I picked a little experience along the way. I use top quality instruments, hakko soldering station, never go past 700, and also use a Hakko desoldering gun which changed my life. Since then I havent lifted a single trace. At first I was working with rudimentary tools and was very impatient.
Honestly I really can’t recall which ones I swapped. I will open it and inspect it and get back to you on this one.
Thanks for your insight sweetbeats. This is no surprise to me, I’ve been expecting that kind of outcome. This is really sad but I have to give up to a certain point. I havent been careful enough and havent been well enough supervised. I learn a lot from that. AND the 388 is especially finnicky, it is very complex. I would say that for the moment I can finish my album on it but if only I could fix the motor issue it would really help. The issue is degradating, yesterday the problem would happen twice, sometimes thrice in a row. I can live without DBX and collapsing tracks.
As soon as I finish that album I might consider another tape machine. Something like an MCI. But yea, I got to finish what I started.
sweetbeats
Reel deep thoughts...
Try this…does the Adcom have another set of inputs so you can have both the RCA STEREO and MONITOR outputs connected to the Adcom? If so try that. It doesn’t matter what inputs they are, I just want to know what happens with the hum if both sets of outputs are connected to the same device. Oh…and do either the Adcom or headphone amp have grounded power cords?
So the gremlins seem to have moved on...I did try exactly what you suggested. The Adcom has six inputs plus a phono channel so I was able to run both the MONITOR and the STEREO outs to the Adcom and had no noise. I went back and tried the initial hook up again AND HAD NO NOISE!
I did go through and clean all the contacts on both the MONITOR out and the RCA IN on the headphone amp. I guess its possible I wasn't making good contact on one of the connections? I just put everything through its paces again tonight and there is no additional noise. Sorry I wasted your time Sweetbeats...
It took me a minute to figure this MONITOR section out so I thought I'd share for anyone else that is following and may have struggled with this...
In order to use the MONITOR section gain and pan controls the RED L/R under each channel assign needs to be up (off) in order to use the Gain and Pan controls. If you push even one down, all eight monitor channels quit and you'll only hear that channel you engaged. I've been through the manual several times and have struggled to figure this out. It's nice having that flexibility with running a signal to a headphone amp. I can adjust the mix in the headphones wo adjusting my overall mix on the faders. So if I want more drums in the headphones i just turn them up in the monitor section and leave my fader alone.
I did go through and clean all the contacts on both the MONITOR out and the RCA IN on the headphone amp. I guess its possible I wasn't making good contact on one of the connections? I just put everything through its paces again tonight and there is no additional noise. Sorry I wasted your time Sweetbeats...
It took me a minute to figure this MONITOR section out so I thought I'd share for anyone else that is following and may have struggled with this...
In order to use the MONITOR section gain and pan controls the RED L/R under each channel assign needs to be up (off) in order to use the Gain and Pan controls. If you push even one down, all eight monitor channels quit and you'll only hear that channel you engaged. I've been through the manual several times and have struggled to figure this out. It's nice having that flexibility with running a signal to a headphone amp. I can adjust the mix in the headphones wo adjusting my overall mix on the faders. So if I want more drums in the headphones i just turn them up in the monitor section and leave my fader alone.
sweetbeats
Reel deep thoughts...
Well it’s not really a waste of time because of the issue was there once it might return…this kind of thing is not usually related to dirty contacts because it would be the shield of the RCA connector, which has gobs of surface area relative to just about any other connector type. The surface would have to be so corroded or oxidized to break contact. Here’s what I’m guessing is happening when the hum occurs: neither the Adcom or the headphone amp have three conductor power cords, right? The 388 doesn’t either. Depending on how the jack shields of all those devices bond to the chassis, the “ground” (which because of the two-wire power cords is potentially different for each device because none of them reference a common “earth”…their individual “ground” is floating), may or may not be completely isolated between one or more of the devices. You can check this by getting out your DMM, turning on all the devices, and touching one probe to one device and the other to the other and measuring for voltage. If it is anything but zero, there is a voltage differential between the ground of each device. And now if the jack shields float from the chassis in one or the other device or there is a high impedance path to the chassis, that voltage differential now allows your cable to be a powered antenna and lock up hum, RF or UHF interference and induce it to the signal conductor. To mitigate this all you typically have to do is run a wire between the chassis of the two devices with the chassis voltage differential. Some devices even have a threaded lug on the back for this purpose. If you *really* want to do it right you have all devices’ chassis reference a common ground, typically the ground prong in your grounded power outlet. This is best because it avoids loops…everything ties back to a common reference. So check some of that out if it comes back. I suspect it’s not a matter of something that’s broken, it’s a simple matter of dealing with the common problem of proper grounding and “pin 1” or jack shield reference to the chassis.
To take it a step further, turn to page 31 in the manual. The MONITOR mixer monitors PGM groups and tape tracks. That is it’s purpose. But the 388 employs automatic source switching depending on the status of L-R assign switches, the CUE/PGM switch, the INSERT switch, the track arming switches and the current state of the transport. It’s kinda fancy…cleans up the control surface negating the need for mechanical source switches, but it can be confusing and aggravating if you don’t understand how to use the controls that are there. Personally I like to do my own switching, but the auto-switching is what makes it nice for rolling punch-ins and the like…it affords the machine the ability to let you listen to the track and then automatically switch to the input when you punch. This was not new technology…but Teac bundled it with global mode switching as well for different stages of the recording process. So study the chart on page 31 because it lays out exactly what the MONITOR mixer source is depending on the state of the controls listed above. They could have done a better job explaining it. And don’t get caught up in trying to understand why the terms CUE, PGM and INSERT were used. IMHO some of that isn’t very intuitive. But that’s just me. But try and make friends with it because it’s a nice feature block.
sweetbeats
Reel deep thoughts...
@Gaspardeden
Ah. This explains a lot. I appreciate the additional background info and I’m sorry if I was quick to judge. Like you I too did some ugly looking work…and it still happens sometimes…sometimes it’s unavoidable…and it took me a long time to understand better technique and good equipment…trial and error. And yes the ugly work accelerated my skill-building with repairing my own damage lol!
I wish I had a desoldering gun…not in the budget. I do have a nice spring-loaded vacuum sucker, and honestly the thousands of solder joints I’ve desoldered with that type of tool I don’t know if I could get used to a desoldering gun, but I think it would be helpful when working on double-sided glass fiber PCBs…and that’s the only thing that’s in my Studer console. I kind of dread the day I really have to recap it.
Okay, fair enough. If you do get a chance to retrace your steps on that do post what you determine here. We can at least do a little forensics to establish the scope of what might have happened when that was done. Maybe it was inconsequential to any of your ongoing issues and you can put that behind you.
Your transport issue I’m sure is really annoying. I’m sure you want to have reliable operation. You’ve worked really hard to get there, and my goal isn’t to discourage you, but to offer an opinion that maybe will help save you from long term aggravation. Servo transport issues are difficult to resolve when they are intermittent like that. And what you have to do is start working through how the servo system works and checking that each part of the system is doing what it’s supposed to do. The problem is by the time of the 388 Teac stopped including any operational theory in their service manuals. You look at a manual for a 244, 234, 58…dozens of pages of detailed walk through of how the thing actually works…how the circuitry does what it does and it references each component…”leg bone connected to the hip bone” style. You can go to the Theory of Operation section with schematics in-hand and literally walk through what’s happening in the circuits and how it works. And there is detail of “you should see this happen or measure X-Y-Z when you press such and such a button” or “when the transport is in mode X you should see a square wave of X frequency on your scope when you measure between test points X” and you can actually understand why you should see that square wave. And then when you don’t see that you already have an idea of what might be in a failure state and you can check it out. It’s extremely valuable. It’s like the ultimate troubleshooting section. The 388 manual has none of this. It’s one reason I prefer the original first generation 122 cassette deck over the mkII or mkIII generations…original 122 service manual? 122 pages…mkII service manual? 52 pages. What’s missing? Allll the “here’s HOW it works and WHY it works” stuff. And for me, an unschooled untrained hobbyist electronics technician, I don’t have a hope or a prayer to fix stuff like what you’re struggling with on my own stuff if I don’t have that information…and even if I do it’s often times too much. So trying to do that over messaging when I don’t have the machine in front of me? That’s really hard. This is why I like mixers more than tape machines, lol! No motors or servos. And also why I like my old relay logic discrete component machines with no servos like my Ampex MM-1000 or 3M M64. They’re just easier to understand.
I will say though often times intermittent problems or problems that crop up with increasing frequency the longer a machine is being used or is powered have to do with heat and poor continuity. Poor continuity in a relatively high current circuit like with motors and servo systems can create a lot of heat through high impedance problem areas…cracked traces, solder joints that got super-heated during an event and need reinforced and reflowed…you said you got a replacement reel servo board…so maybe that’s not it…but you talked about smoke and such…have you inspected the joint PCBs? And sure it could be a control PCB issue too. So maybe it’s worth looking closely at those, under good light and magnification. Also running the transport with the machine tipped on its side and the bottom cover removed, gently probing or manipulating PCB assemblies and connections to see if you can either make the problem happen or make it stop. There’s also freeze spray to super chill a component. If you study the circuit and there are components that seem like they are getting hot you can chill them in operation and see if that temporarily resolves the issue, and that tells you maybe the component is at the end of its service life and/or you need to improve the continuity of the component to the board or neighboring components. So there’s a couple ideas.
Ah. This explains a lot. I appreciate the additional background info and I’m sorry if I was quick to judge. Like you I too did some ugly looking work…and it still happens sometimes…sometimes it’s unavoidable…and it took me a long time to understand better technique and good equipment…trial and error. And yes the ugly work accelerated my skill-building with repairing my own damage lol!
I wish I had a desoldering gun…not in the budget. I do have a nice spring-loaded vacuum sucker, and honestly the thousands of solder joints I’ve desoldered with that type of tool I don’t know if I could get used to a desoldering gun, but I think it would be helpful when working on double-sided glass fiber PCBs…and that’s the only thing that’s in my Studer console. I kind of dread the day I really have to recap it.
Okay, fair enough. If you do get a chance to retrace your steps on that do post what you determine here. We can at least do a little forensics to establish the scope of what might have happened when that was done. Maybe it was inconsequential to any of your ongoing issues and you can put that behind you.
Your transport issue I’m sure is really annoying. I’m sure you want to have reliable operation. You’ve worked really hard to get there, and my goal isn’t to discourage you, but to offer an opinion that maybe will help save you from long term aggravation. Servo transport issues are difficult to resolve when they are intermittent like that. And what you have to do is start working through how the servo system works and checking that each part of the system is doing what it’s supposed to do. The problem is by the time of the 388 Teac stopped including any operational theory in their service manuals. You look at a manual for a 244, 234, 58…dozens of pages of detailed walk through of how the thing actually works…how the circuitry does what it does and it references each component…”leg bone connected to the hip bone” style. You can go to the Theory of Operation section with schematics in-hand and literally walk through what’s happening in the circuits and how it works. And there is detail of “you should see this happen or measure X-Y-Z when you press such and such a button” or “when the transport is in mode X you should see a square wave of X frequency on your scope when you measure between test points X” and you can actually understand why you should see that square wave. And then when you don’t see that you already have an idea of what might be in a failure state and you can check it out. It’s extremely valuable. It’s like the ultimate troubleshooting section. The 388 manual has none of this. It’s one reason I prefer the original first generation 122 cassette deck over the mkII or mkIII generations…original 122 service manual? 122 pages…mkII service manual? 52 pages. What’s missing? Allll the “here’s HOW it works and WHY it works” stuff. And for me, an unschooled untrained hobbyist electronics technician, I don’t have a hope or a prayer to fix stuff like what you’re struggling with on my own stuff if I don’t have that information…and even if I do it’s often times too much. So trying to do that over messaging when I don’t have the machine in front of me? That’s really hard. This is why I like mixers more than tape machines, lol! No motors or servos. And also why I like my old relay logic discrete component machines with no servos like my Ampex MM-1000 or 3M M64. They’re just easier to understand.
I will say though often times intermittent problems or problems that crop up with increasing frequency the longer a machine is being used or is powered have to do with heat and poor continuity. Poor continuity in a relatively high current circuit like with motors and servo systems can create a lot of heat through high impedance problem areas…cracked traces, solder joints that got super-heated during an event and need reinforced and reflowed…you said you got a replacement reel servo board…so maybe that’s not it…but you talked about smoke and such…have you inspected the joint PCBs? And sure it could be a control PCB issue too. So maybe it’s worth looking closely at those, under good light and magnification. Also running the transport with the machine tipped on its side and the bottom cover removed, gently probing or manipulating PCB assemblies and connections to see if you can either make the problem happen or make it stop. There’s also freeze spray to super chill a component. If you study the circuit and there are components that seem like they are getting hot you can chill them in operation and see if that temporarily resolves the issue, and that tells you maybe the component is at the end of its service life and/or you need to improve the continuity of the component to the board or neighboring components. So there’s a couple ideas.
This make sense! The Adcom does have a 3 prong power cord it's model Adcom GFP-815. But working to get the other two to be grounded makes sense. Or at least connected to the Adcom. The phono jack has a threaded ground post..can I tap off that?
I'll spend some time with page 31 of the manual. I really appreciate the assign functions and flexibility of the mixer section is. I just want to wrap my head around everything it can do.
Side note, I finally looked up your page and subscribed to your YouTube channel. Looks like a ton of great info on there. I appreciate all you share with the audio community!
Brian
sweetbeats
Reel deep thoughts...
Here’s what I would do…if you’re using a grounded power strip or power distribution unit, I would see if there’s a way to connect ground wires to that. My Monster Power Pro rack mount power distribution units have a big threaded ground post on the back. And before that set your DMM to resistance and on each device measure the resistance between the RCA shields on the jacks to the device chassis…make sure the shields actually strap to the chassis “ground”, and if they do, and they should, then add the wire from the chassis to your central ground point. On the Adcom check resistance from the jack shields to the ground prong on the power cable.
You *could* use the Adcom as your central grounding point, but your non-grounded devices aren’t plugging into the Adcom for power. So if you source power somewhere else, and get ground from the Adcom, there’s still potential for differentials. Does that make sense? And if you have multiple power distribution centers like me, then each device that plugs into each distribution unit gets it’s ground from its respective distribution unit, and then each distribution unit plugs into wall outlets that are as close together as possible and on the same circuit breaker. So in my case the wall outlets ultimately become the central ground point.
And thanks much for subscribing to the YouTube channel! My material is a bit folksy and geeky…and no flash and dance…but at least there’s some content.
lagoausente2
New member
Hello Sweetbeats, I´m after a Tascam 488.., maybe you can give me a light..,
thank you a lot.
thank you a lot.
Good evening Sweetbeats... Had a crazy busy week but finally back in the studio and, as you predicted, the noise is back.
If I only plug in the monitor outs to the headphone amp everything is quiet. The minute I plug the stereo out going to the Adcom the noise comes through the monitors AND headphone amp.
Im trying to check the voltage between units based on what you wrote in a previous post: You can check this by getting out your DMM, turning on all the devices, and touching one probe to one device and the other to the other and measuring for voltage. If it is anything but zero, there is a voltage differential between the ground of each device.
So two basic questions:
1. The only time I don't get 00.0 is when my meter is set to 200m Is this the correct setting? (DC Voltage?)
2. is touching the cabinet enough to read what I'm looking for?
Ive been using the screw on the front of the 388 next to "phones" jack thinking it's not painted but the Adcom and Headphone amp have painted surfaces everywhere.
with the common (black) on the 388 and touching the cabinet of either the Adcom or Headphone Amp with the red probe I'm getting readings of 00.6 or 00.7
So I guess the first question is "Am I using the correct setting on my DMM?" (just for reference... its a Gardner Bender GDT 3190)
Sorry for such a NEWB question
Brian
If I only plug in the monitor outs to the headphone amp everything is quiet. The minute I plug the stereo out going to the Adcom the noise comes through the monitors AND headphone amp.
Im trying to check the voltage between units based on what you wrote in a previous post: You can check this by getting out your DMM, turning on all the devices, and touching one probe to one device and the other to the other and measuring for voltage. If it is anything but zero, there is a voltage differential between the ground of each device.
So two basic questions:
1. The only time I don't get 00.0 is when my meter is set to 200m Is this the correct setting? (DC Voltage?)
2. is touching the cabinet enough to read what I'm looking for?
Ive been using the screw on the front of the 388 next to "phones" jack thinking it's not painted but the Adcom and Headphone amp have painted surfaces everywhere.
with the common (black) on the 388 and touching the cabinet of either the Adcom or Headphone Amp with the red probe I'm getting readings of 00.6 or 00.7
So I guess the first question is "Am I using the correct setting on my DMM?" (just for reference... its a Gardner Bender GDT 3190)
Sorry for such a NEWB question
Brian
sweetbeats
Reel deep thoughts...
Does the Adcom, 388 or MH-40 have ground lugs next to where the power cord enters the chassis?
Sorry those pics are so big! I just find it odd that the noise/hum is only when the main stereo outs (either RCA or XLR) are connected to the preamp. The instant I unplug those from the 388, the monitor feed to the headphone amp is silent. With the mains plugged in I hear the hum/noise through the headphone amp as well as the main room monitors.
For what it's worth, I'm running this through an Adcom GFA 545ii amp.
No noise with CD, Interface or Cassette its only when I get to the channel the 388 is plugged into. I tried plugging the 388 into a different input on the preamp just to rule out a bad preamp channel and I get the noise in any input I use.
If I unplug the monitor outs (RCA connections) the noise/hum stays present in the main room monitors. So it seems like its a problem with the main Stereo outs but not sure how to really diagnose/fix that.
I appreciate you helping me think through this and I'll try anything at this point if it means I don't have to lug this 100lb beast anywhere.
Brian
For what it's worth, I'm running this through an Adcom GFA 545ii amp.
No noise with CD, Interface or Cassette its only when I get to the channel the 388 is plugged into. I tried plugging the 388 into a different input on the preamp just to rule out a bad preamp channel and I get the noise in any input I use.
If I unplug the monitor outs (RCA connections) the noise/hum stays present in the main room monitors. So it seems like its a problem with the main Stereo outs but not sure how to really diagnose/fix that.
I appreciate you helping me think through this and I'll try anything at this point if it means I don't have to lug this 100lb beast anywhere.
Brian
sweetbeats
Reel deep thoughts...
Think of it this way…
When you have two outputs from the 388 connected, my hunch is that it completes the loop, and there is a differential between your devices because the 388 and the MH-40 are floating. Instant antenna.
What about your rack-mount power distribution unit? Any ground post on that?
When you have two outputs from the 388 connected, my hunch is that it completes the loop, and there is a differential between your devices because the 388 and the MH-40 are floating. Instant antenna.
What about your rack-mount power distribution unit? Any ground post on that?
There is not, I've been looking for anything that has a spot to connect an extra external ground wire and keep coming up short.
If your theory is correct, wouldn't the noise stop if I unplug the monitor output? Wouldn't that break the antenna? Because as of now, the noise is present only when the main stereo outs are plugged in. (Whether or not the monitor outs are connected.)
If I unplug the monitor outs (RCA connections) the noise/hum stays present in the main room monitors. So it seems like its a problem with the main Stereo outs.
sweetbeats
Reel deep thoughts...
Could be.
If it was me I’d still test the hypothesis there is a ground differential, and the issue can be mitigated by addressing the ground differential.
If you want to do this quick-and-dirty set your DMM to resistance and measure from the ground prong on the Adcom power cord to a screw head on the back of the chassis. Keep probing until you find a fastener on the exterior that is a dead-short with the ground prong. Get two lengths of wire. Any wire. Speaker wire. Hookup wire. Solid core wire. Doesn’t matter. Any wire. Twist and loop one end of each of the two wires under that fastener you found on the Adcom. Add a washer if you need something to better clamp the wires. Measure resistance from the Adcom power cord ground prong to the other end of each of the two wires and verify it’s a dead short. If not, get an internal toothed washer and put that between the fastener head and the wires on the Adcom. Once you have a dead short from the ground prong to each wire end, twist and loop each distal wire end and fasten under any screw on the bottom panel of the 388 and the MH-40. I know for fact binding the wire to any part of the bottom panel connects the wire to the chassis and audio ground of those devices. Test it out and see if that mitigates the noise in the STEREO buss outputs.
Sweetbeats, your description was spot on and easy to follow.
I checked resistance from a chassis screw on the Adcom preamp to the ground prong on the AC plug and made sure it was s dead short.
Then I attached two wires form that screw and re-tested to the ground prong to the end of each wire and it shorted out.
Then I attached one wire to the bottom of the 388 and one to the bottom of the headphone amp and........drum-roll please.....still have the hum/noise
So I turned to my computer to write this post and left the hum/noise running next to me. I have my computer, with a usb cable, connected to an interface. From that interface i have a set of outputs going into one of the six channels the on the Adcom. (#2 to be exact) when I select #2 and play a youtube video its perfectly silent (except for the content)
When I go back to #6 (the 388) channel on the Adcom preamp, I, of course, hear the hum but as I'm typing and clicking my mouse the hum seems to react to those movements.
Every mouse click gives a little small burst of static sound. So somehow the 388 is reacting to another input on the preamp, So then I unplugged everything else that was going into the preamp leaving only the 388 and the noise/hum is still there. Obviously, it's not reacting to mouse clicks etc with nothing else plugged into the preamp.
So one last mystery piece of the puzzle... My rack mount power supply has two lamps that pull out to illuminate the equipment below. Those lamps have an on/off switch and a dimmer knob to adjust their intensity. As I sweep the knob from low to high I get a flanger-type sound to the hum noise. It's subtle but its definitely reacting to turning that dimmer knob.
After I re-capped the power supply card it was very quiet and then this crept in. I assume if I somehow have AC leakage the monitor out would have made that same noise? This is 100% the Stereo out that the hum is generating from. And when those are connected, the hum runs through the monitor section. When unplugged, the monitor out is quiet.
I wanted to confirm that it was quiet so I fired up the headphone amp and the noise was there too
!!! So I unhooked all the make-shift grounding we did and now its silent, from the monitor outs, again.
I'm pulling out what little hair I have left. I won't blame you if bail on this thread. It's been fun trying your diagnosis ideas and I've learned a lot. I'm secretly hoping something else I mentioned here will spark something you didn't think of before.
Thanks for hanging with me.
Brian
I checked resistance from a chassis screw on the Adcom preamp to the ground prong on the AC plug and made sure it was s dead short.
Then I attached two wires form that screw and re-tested to the ground prong to the end of each wire and it shorted out.
Then I attached one wire to the bottom of the 388 and one to the bottom of the headphone amp and........drum-roll please.....still have the hum/noise
So I turned to my computer to write this post and left the hum/noise running next to me. I have my computer, with a usb cable, connected to an interface. From that interface i have a set of outputs going into one of the six channels the on the Adcom. (#2 to be exact) when I select #2 and play a youtube video its perfectly silent (except for the content)
When I go back to #6 (the 388) channel on the Adcom preamp, I, of course, hear the hum but as I'm typing and clicking my mouse the hum seems to react to those movements.
Every mouse click gives a little small burst of static sound. So somehow the 388 is reacting to another input on the preamp, So then I unplugged everything else that was going into the preamp leaving only the 388 and the noise/hum is still there. Obviously, it's not reacting to mouse clicks etc with nothing else plugged into the preamp.
So one last mystery piece of the puzzle... My rack mount power supply has two lamps that pull out to illuminate the equipment below. Those lamps have an on/off switch and a dimmer knob to adjust their intensity. As I sweep the knob from low to high I get a flanger-type sound to the hum noise. It's subtle but its definitely reacting to turning that dimmer knob.
After I re-capped the power supply card it was very quiet and then this crept in. I assume if I somehow have AC leakage the monitor out would have made that same noise? This is 100% the Stereo out that the hum is generating from. And when those are connected, the hum runs through the monitor section. When unplugged, the monitor out is quiet.
I wanted to confirm that it was quiet so I fired up the headphone amp and the noise was there too
!!! So I unhooked all the make-shift grounding we did and now its silent, from the monitor outs, again. I'm pulling out what little hair I have left. I won't blame you if bail on this thread. It's been fun trying your diagnosis ideas and I've learned a lot. I'm secretly hoping something else I mentioned here will spark something you didn't think of before.
Thanks for hanging with me.
Brian