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Re: Small questions that don't fit anywhere

631 by Abebibocombi
Hey, i'm posting this as a small question but it's no so small, sorry.

I am trying to repair an Audio-Technica RMX64 cassette recorder, especially the mixer section (I don't really care about the cassette part, although it would be nice to try it, I mainly bought this for the mixer section). Some tracks worked well, others didn't have any signal, others had very low signal some tracks didn't send audio to the subs, etc... I took the channel strips out and contact cleaned everything, and it worked a bit better, but still quite a lot of troubles.

So yesterday i took it apart more thoroughly, took out the channel strips, unplugged all the cables from the two motherboards, etc. But i forgot to take any picture of how the this was wired before I unplugged everything. Now i put it back up together, but I must have mixed up some stuff. All i can hear when i turn the mixer on and plug headphone is a buzz, which wobbles when I turn some buttons randomly.

I guess i could use it as a sort of synthesizer then, but if anyone has one and could open it and take a picture of how the mother board on the mixer section is wired, that would be awesome.

And also i am looking for schematics / parts list for the RMX64. I found the user manual and some block diagram thing, but no real service manual (eventhough I asked directly audio-technica but they didn't have it).

I know that's a long shot, but you never know !

Re: Small questions that don't fit anywhere

632 by Adam_I_III
The Yamaha preamp I just bought had been modded with a 'mix 78' board and 2 extra Jacks.

Previous owner reckoned he didn't know about it.

I tried connecting stuff (in and out) to the Jack's, but nothing. 8 channel mic preamp is what it is. There were no extra controls for the extra board. I'm struggling to work out what the board would be for. Took it out anyway.

It was connected to all the channels. Maybe a summed output that doesn't work?
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Re: Small questions that don't fit anywhere

633 by Tom Wanderer
My first thought would be an effects loop, but you should have gotten a signal from the 'send' if that were the case. Looking more closely at the IC and the electrolytic caps, it might have been something more sophisticated.

How many leads connect to the jacks? Is it possible they are TRS inserts and were shorted (passing no signal) if hooked up with a mono TS cable?
Last edited by Tom Wanderer on Thu Jan 27, 2022 9:54 am, edited 1 time in total.
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Re: Small questions that don't fit anywhere

635 by Adam_I_III
Tom Wanderer wrote: Thu Jan 27, 2022 9:49 am My first thought would be an effects loop, but you should have gotten a signal from the 'send' if that were the case. Looking more closely at the IC and the electrolytic caps, it might have been something more sophisticated.

How many leads connect to the jacks? Is it possible they are TRS inserts and were shorted (passing no signal) if hooked up with a mono TS cable?
I missed a bit of tiny writing on the board (because I'm old and blind!)

It's this:

4078 Mixer Amplifier - Low Noise Mixing Amp


1 - 10 input mixing amplifier for interstage mixing where noise is a major consideration. The gain can be altered by reducing or increasing the value of the feedback resistors R7 and R8.

Low noise is achieved by the use of selected low noise op-amps NE5534AN and it is essential that if replaced, a similar low noise device is used to maintain the performance of the circuit.

Stock no. 01-140 4078 Price: £17

Was very, very skilfully fitted! I don't know why a person would want a summed output from 8 channels with arbitrary control over the levels using the gain knobs, but somebody obviously did!

Funny.

Thanks!

Re: Small questions that don't fit anywhere

636 by Kniferide
Adam_I_III wrote: Thu Jan 27, 2022 11:50 amI don't know why a person would want a summed output from 8 channels with arbitrary control over the levels using the gain knobs, but somebody obviously did!
These types of mixer/preamps are often racked up in the closet of small events spaces, plugged into a 70 volt system with a few cheap Guitar Center wireless mics so drunk best men can give terrible toasts at weddings. Some times there is a 1/8" to xlr adapter that goes into 2 mic channels so the Maid of honor can plug in an iPod shuffle with a sweet playlist she made that has "Uptown Funk" on it. The distortion and noise are part of the charm.
Was Japmn.

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Re: Small questions that don't fit anywhere

638 by jirbling rake
Seeing love for the Schist Modi and JDS Labs DACs on here. Have any of you experience with the Cambridge Audio DacMagic 100? https://www.cambridgeaudio.com/usa/en/p ... acmagic100

Other DAC recommendations for computer digital audio to home stereo receiver paths too, if you got 'em.
"I got to tell you, if I went to a show and an opening band I never heard of lugged a Super Six on stage, I am paying attention." - Owen
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