Quantum Broadcast Mixer

So, a client of mine asked me to look at a channel on his Quantum Audio Labs mixer. He wanted to add the direct out option to the channel strip. The board layout already had the space for it. Umm, okay. He had full schematics and board layout info. Excellent!

Quantum Audio Labs Series 22

Up until this, in my electronics history, I had not heard of this manufacturer. But the internet yielded a plethora of info all indicating how great this manufacture’s products sounded. Quantum, it turned out, made mixers for the radio broadcast industry and eventually the recording industry as well, although the meat and potatoes was broadcast. And as happens with company’s is long out of business.

After determining the parts list and cost, even if it didn’t work, not a great deal of money wasted, parts were ordered and the board populated. A couple of wiring points added and the commensurate output wire with XLR was done. Cool! As I did not have the capability to test out the channel I gave back to the customer who, in a few days, said it worked perfect. A much better sound and lower noise floor than going thru the mixer buss.

Direct out option section
Direct out option section populated

Okay, that project done! Oops! He wants a second channel done and can I add a pad for the mic input that is switchable. Another umm… okay. After studying the schematic and conferring with the client, who is pretty knowledgeable about this mixer, it seamed straight forward. Just take an existing switch and use it to drop in and out a resistor pad to knock down the signal feeding the input transformer. “no problem”! There again off to the internet to find out how other designers dealt with mic pad’s. And in little time had an example on how to achieve the circuit.

Turned out to be pretty simple, as long as you have the right type of switch. Lucky for the client the switch that was available on the channel was exactly the type needed. Now, to remove said switch and cut traces on the board so as to not interfere with other process’s in the channel circuits. This switch is no longer used as it was to activate a “cart” system in a radio studio. It started a cartridge playback unit which was used to play commercials and the DJ would activate that at the appropriate time. Suffice it to say that the majority of radio stations haven’t used cart players in many years. It’s all computer based now.

This client was so happy with the added direct out option and pad switch, he wants four more channels done. GREAT!

send and return for mic signal
Pad switch w/resistors

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