Tascam 388 - Hi Pitch sound from headphones / stereo out,

38869420

Member
Me again!

So further on the same problem of my 60hz hum, there's also a high pitched sound when I crank the outputs, which is audible in my mixdowns. I swapped the tape over to my spare 388 and luckily it's not on the recording, just in the monitoring & recording down of the audio. Anyone have any idea what this could be?

Did the same with my spare 388 and its just the hiss you can hear.
 

38869420

Member
Might try and swap the monitor pcb with my back up unit. I’ve found the monitor SW pcb in the schematics but not the monitor pcb. Anyone know where it is?
 
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sweetbeats

Reel deep thoughts...
The monitor PCB is the mixer section card to the farthest right...the one with the record arming switches on it.
 
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sweetbeats

Reel deep thoughts...
No...no. Sorry...there was a typo in my post I just corrected. It’s one of the vertical mixer section cards, the right-most one just to the left of the transport. It’s the one that has the record arming switches.
 

38869420

Member
Ah got it, thanks! Can I get to that one through the top panel, or need to flip it over? Havent delved deeper than the cards up under the lid
 

sweetbeats

Reel deep thoughts...
You can’t get to any of the mixer section cards through the top, or at least it’s a very bad idea...they are all attached to that mixer section dress panel...you’d have to remove all the knobs and all the pot nuts and then the screws that fasten the mixer dress panel to the chassis...then all the screws that hold the faders to the dress panel and then they fall inside...then as you pull the dress panel off all the mixer section cards sort of tweak position and then you’re never getting that mixer dress panel back on without going underneath and removing the buss PCBs and pulling all the cards out putting them back in one by one...and then reattaching the faders. Yech.

SO...flip it on its side, remove the bottom panel, take pictures and use blue painters tape or whatever to label each connector as you remove it from the monitor PCB so you know how it goes back in, then remove the screws on the dress panel that hold the monitor PCB to the panel and you should be able to pull it free. What I can’t recall is if the buss PCB, that skinny board that goes alllllll the way across the bottom of all the mixer section PCBs, also connects to the monitor PCB. If it does then removing that is first after you pull the bottom panel off. Be very gentle and careful removing it or you will crack solder joints...start at one end, gently lever it up to get a little movement and then do the same for each connection point along the PCB working just a little at a time. When you get to the other end rinse and repeat until the PCB is free.
 

38869420

Member
Wont get a chance to do this till the weekend, but was wondering could this also be the cause of my left channel recording out at about 6db higher than the right on the stereo & monitor outs?
 

sweetbeats

Reel deep thoughts...
That’s too broad a question to answer without more information, and without doing troubleshooting. And I’m not sure what “this” is when you say “could this be the cause...”
 

38869420

Member
Sorry, meaning the monitor card. I've read before of people having issues with the 388 mixing down unevenly, favoring the left or right more. I've never worried about it as I can just pan it flat when mastering, but wondered if the monitor card would affect the balance of the output in both the Stereo Outs, Monitor outs and the Headphone outs (to a slightly lesser extent, just checked it with a meter.
 

38869420

Member
Ok, so i've been spending a bit of time with the machine trying to figure out some hum issues, trying to figure out if it's the machine or cables and the hi pitch sound went away for a day. It's now back, but only comes on after operating for a bit. I'll give details on what's happening.


All faders down, inputs in RMX, Assign L R buttons pressed down
then when you push the Stereo Master up, you hear the hi pitch whine with a slight hum under it.
Removing all cables from the back slightly dulls the sound but it's still there
when plugging my patch bay input back into input 1, the sound gets louder. Not when I plug into any of the other channels though. This is with all the faders still down and the Stereo Master & Monitor up.
Turning the channel faders up doesn't change the volume of the hi pitch sound

Then, as I disengage the LR buttons it decreases in volume till I take the last one off, then it comes back
Push the MON button down to CUE and it decreases dramatically in volume, but is still there
Funnily enough, it goes down in volume when I turn up the MONITOR Gain knobs. Mainly knob 8.

Also, decreases in volume when I plug the Monitor outs (through a patch bay) into my audio card to try and capture the sound

From metering it in my DAW, the hi pitch sounds are peaks at 8100Hz and 16200Hz. This is a screenshot of all the noise with the Stereo Master & Monitor cranked and with the signal boosed in Logic
 

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38869420

Member
Ok I’m adding more for reference. Got both the cards out and cleaning up the ‘good’ one (AU machine). Interesting that the Australian one seems like an older revision. It also has these white jumpers on the underside of the board. Any clues to what they’re for? The US one is definitely brighter and nicer but I’ll swap this AU pcb into the US machine and see how it goes. Their serial numbers are the same but followed with a 01 on the AU and 02 on the US machine.

if it works and removed the high pitched noise then I’ll check all the caps on the US board and hopefully find the culprit.

also, a Capacitor (the biggest one) on channel 8 in my US machine looks weird, like it’s got a plastic sleeve around it. Any ideas what that’s about? Pic attached.
 

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sweetbeats

Reel deep thoughts...
The -01 and -02 designators on the PCB assemblies are exactly what you have identified...revision numbers. What was revised and exactly how they are different you’ll never know unless you reverse engineer them, which wouldn’t be time well spent. Functionally they should operate the same, but I suspect part of what was captured in the revision was changes to the traces to eliminate the jumper wires. Jumper wires are fine and you’ll typically find those in PCB assemblies...quite common. Sometimes it’s a stranded and jacketed wire like that, other times it’s just a bare solid core “staple” jumper. Don’t sweat it.

Unless I’m misunderstanding what you are referring to with the cap with the sleeve, every aluminum electrolytic cap in your 388 has a plastic sleeve on it. You’re talking about the black plastic with the white printing on it? The cap body itself is literally a shiny metal aluminum can, the plastic is a shrink-wrap with the info printed on it which also insulates the can from possible short circuit.

Your high-pitched noise issue...really perplexing. I’m not clear...does the symptom occur even when literally nothing is connected to the 388? If so, tell me again in what outputs you can hear the noise? Go through EVERY output including insert send, buss outs, tape outs, AUX and EFF outs, monitor, stereo...everything. That’s my first step, where can I hear the problem, and under what conditions. Make notes. Then start doing stuff to see what you can do to change the sound whether it’s the nature of the sound or the level of the sound...what controls effect the sounds. Once you have that clearly identify you can start to isolate from what board the problem may originate, and then it’s time to get out the scope. A high-pitched sound like that may sometimes be an artifact of a much higher frequency noise you can’t hear stemming from an active component oscillating.
 

38869420

Member
thanks! I’ll swap the cards today and report back.

re: Cap:
Here are pics of what I mean. Like the Cap is surrounded by clear plastic. It’s the only one on both of my machines. Never had trouble with this card though and it’s not bulging but wanted to pull it out to have a look. Is this a normal service thing?

I’ll put it all back together with just the swapped monitor cards and see where we’re at with the squeal. Don’t really want to remove another bus pcb in a hurry though lol
 

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38869420

Member
Ok, popped it all back in. Swapped the Monitor PCB with the other machines, cleaned up some spots on the back with Isopropyl & Carefully dexoxit-ed (wrapped them in cloth when I sprayed to clean up any excess) all the snap on connectors and the inputs for the bus pcb and whatever else I could reach. Popped it all back together and tested it out.

The whine is gone! Going to run it all day today to test it out but there's a few things i've noticed on my first test without anything plugged in but the monitor outs & headphones;

No high pitched whine
No crackling channels (channels 2, 3 & 6 would crackle and pop, like weird static when turned up with no signal going through
No low hum on most channels, so basically they all just sound nice, clean and quiet
Channel 8 (the one with that weird cap case on it) is the quietest channel. I turned them all up max, along with the outputs to hear the noise. On Mic input they all made a similar hiss but channel 8, which was much quieter. Same when swapped to Line. Checked playback off a tape and all channels play back properly. Must check signal going into this input to make sure it's all working right.

Now to attach all the inputs & test as I go
 

38869420

Member
In more good news, there was an issue where the left channel was outputting hotter than the right. That’s fixed too, so must be isolated to the Monitor PCB
 
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