Tascam M-308 mixer distortion on 2 buss channels

WhinyLittleRunt

WhinyLittleRunt

Member
I was cleaning up my M-308 today trying to decide whether or not I need it and want to move it along, and so I was running things through the board and testing, etc. One function I never tested when I bought the board 5-6 years ago was the assign switches, because until I bought my 388 I actually had no idea how to use them. So in testing I'm finding that busses 3 and 4 are distorting and clipping tremendously. But these busses 1-4 also have 2 tape returns on each channel strip, and they have on/off switches on each one, so in order for the input channel to pass through the buss channel, you have to turn it on. There are 2 switches per channel, which also work for the tape returns (I've attached a pic to make it easier). So, for channel 4, as an example, if I turn on the upper channel, it doesn't distort but the needle pegs immediately. If I turn on the lower channel, it distorts. You can use either one. 3 does a similar thing. 1 and 2 are working fine.

I'm not sure what to look for... I've reseated whatever I could and de-oxed connectors inside but this model isn't set up like a 38 R2R where the cards come out. It's more like everything is attached to the top panel and you take off a buss strip that connects everything together rather than the cards themselves... I'll try maybe to re-flow solder on the connections but other than that, any theories?





EDIT: I tried re-flowing the solder on the connection to busses 3 and 4 and that made zero difference. And these cards are not easy to get to on this deck.
 
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I think you're confusing your terms here as the 4 recording busses, (orange faders) are outputs to feed to a multitrack recorder. The 8x2 tape return sub mixer section above those faders is an independent mixing system that feeds to either the stereo buss or to the auxiliary cue busses. They may appear to be tied into the 1-4 buss master faders but they are indeed a separate system.

Now, as to why 2 of those channels are distorting is a bit of a mystery to me at this moment. All I could suggest is to recheck the level settings to ensure you're not over-driving any one stage before it passed on to the next stage. Also, if 1 and 2 are clean, make sure you have the same setting on 3 and 4. Also check on the back panel to see if anything is switched differently on the balanced/unbalanced slide switches for the buss outputs.

The main idea I'm trying to forward here is to absolutely, positively rule out user error before you warm up your soldering gun.

Cheers! :)
 


This will probably explain better...

(Disclaimer: please pardon the excessive breathing and the dryer in the background; that mic is super sensitive apparently!)
I am basically showing the channel routed to the stereo faders first, then I am testing each of the assign switches. You can only hear your signal through the PGM faders/section if you turn on what appear to be the tape returns, but the signal will flow to each of these from the input strip and most of them are working, but the last 2 are messed up somehow and distorting wildly. The levels are set differently on the last two because I knew they'd distort and blow my ears out. And please tell me I'm worried about something that is a non-issue in most every day uses for this board, because I just want to make sure it is 100% functional because I am trying to sell the board eventually.
 
Thanks for posting that video.

OK, so I have a much clearer idea of what you're doing there and have to admit I forgot that that 8x2 sub mixer has a second function beyond just monitoring tape returns when you need the main mixing strips for other things like virtual tracks, etc.

It is a rarely used feature to be sure as I know when I had my M312B mixers, I never even once needed to use that section of the board to overdub or mix down so, odds are, whoever buys the board from you will also likely never need it.

All that said, yeah, there definately is an electrical problem there and I would suspect its an internal calibration pot that got messed with by the previous owner. If you have the manual with the schematics, try to hunt down that board's diagram and see if there are in fact internal calibration pots which have been cranked and turn them back down to where ever they're set on the first two channels which are clean. If there are no internal pots, I'm not sure what else to suggest at this moment.

Cheers! :)
 
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