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?

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?

Abebibocombi wrote: Thu Jan 27, 2022 3:11 am 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, ...

A buddy had two of these and had one running well enough to record with and the other just functioning as a mixer.
I will see if he has schems still and report back!

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!

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.

brownreasontolive wrote: Thu Jan 27, 2022 9:54 am

A buddy had two of these and had one running well enough to record with and the other just functioning as a mixer.
I will see if he has schems still and report back!

thanks ! yep let me know !

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.

Restoring a stereo receiver and could use some advice or experience on tuning up the tuner. I posted more about it in the hi-fi thread here:
http://premierrockforum.com/viewtopic.p ... 4&p=793369

Anyone know any good books on passive crossover network design?

Back in the day Electro harmonix made a thing called the Hot Foot that let you control the knobs of a pedal with a foot controller. Does anyone still make those things? Seems like I could build one with a old volume pedal and a drill snake attachment, but I'd rather just buy one.