Here is a disco mixer a put together a few years ago.
It is dual stereo in, 1 line input and one high gain mic input.
The mic input uses one stage of the triode.
The other triode amplifies all stages.
While there are two output sockets it is only mono out.
I have used it once in anger at a disco at the local cricket club.
Works a treat and sounds very clean.
It is dual stereo in, 1 line input and one high gain mic input.
The mic input uses one stage of the triode.
The other triode amplifies all stages.
While there are two output sockets it is only mono out.
I have used it once in anger at a disco at the local cricket club.
Works a treat and sounds very clean.
An externally hosted image should be here but it was not working when we last tested it.
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Your link isn't working for me. Can you please post it here, that way it will remain available to members who stumble across it in the future. Thanks.... 😀
Just bought some new website software and it keeps changing the picture filenames !! Why they cant just use the original name beats me.
I have fixed the link
Should have added it uses 2 transformers back to back for HT. It was cheaper that way instead of getting a special transformer. The mains voltage is dropped down then back up again.
It uses DC heater voltage.
I used a 12au7 valve.
It uses DC heater voltage.
I used a 12au7 valve.
For the stereo inputs I "or" them with 1k resistors into a 100k pot.
Line in goes into a 100k pot.
Mic input goes into 100k pot then into simple inverting valve stage.
Then all channels are mixed with 100k resistors into another inverting valve stage.
The insides should be more interesting. I can only see the one tube now, but I guess there are more.
It only needs one tube.
Its a double triode.
One half is used as the mic pre amp.
The other half is used to amplify all channels.
Ah ok. I made the wrong assumption there was some initial buffering or amplification, other than the mic's. Still, insides are always cool 😀
This was made on vero-board so isn't wonderful to look at.
It was my first valve design and I had hum problems so the vero-board ended up being hacked a bit to work. I changed the heater supply to DC to help get rid of hum but it didn't make a lot of difference.
The mains transformer drops the voltage down to 12VAC for the heater circuit.
Then I use an 18VAC transformer backwards to get back to over 200VDC.
Then I use an 18VAC transformer backwards to get back to over 200VDC.
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