Mods to Kelsey console

HI, I'm looking to do some mods to this little cheapo Kesley mixer, beyond a recap bypass caps thing.. and would appreciate Some chiming in with any small Tweeks to the circuit, to lower noise, increase gain ect.. goal being making it a descent mobile box O pres and summing box... here is the schemo of the input ..there is an LM394, all other ic''s being 4559's
thankyou for any input..

That is the second Kelsey I have seen in 40 years.

The first one had no single stinky detail (except stupid power supply layout), but missed in SO many ways that I put it in back of an unused studio and never touched it again. Some things are worth fixing; others are just time-sinks.

I hope you find a more optimistic reply.

PRR said:

I hope you find a more optimistic reply.

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Not from me.

Traded my 8-ch Kelsey in excellent condition for a 16-ch turd in about 1982, needed more channels in a hurry. Not one of my better horse trading deals.

The main problem was the busssss-wiring, Grooves in all the PC board edges, with actual solid wire in a straight line between all boards, soldered onto pads. Hard to remove without cutting these wires to get slack, and then patching in more wire pieces. Vibration and banging around would constantly lift solder pads. Then upgraded to a Biamp 16-ch, and WOW, TWO fixed mids, I'm really styling now.  ,

PRR, if you want to see your third Kelsey, that same turd, just go to my shed. Couldn't  even get $100 for it on ebay, 100 percent working. 

Gene

I do realize it's a bit of a boat anchor..An experiment for sure...
I mod ,repair, and build a fair bit of gear .. Sinking time and parts into this is not an issue with in reason....However My theory does lack  So I was hoping someone with a far better know of circuits could take a peak at the schemo and see if there were some little things that could be done to tweek it, especially in the pre's..
I have a good desolder station and iron, scope and such.. the desks construction is not an issue..
I'll probably beef up the psu,  pop in opamps and compensation caps..to start

LeeharveyOsmond said:

HI, I'm looking to do some mods to this little cheapo Kesley mixer, beyond a recap bypass caps thing.. and would appreciate Some chiming in with any small Tweeks to the circuit, to lower noise, increase gain ect.. goal being making it a descent mobile box O pres and summing box... here is the schemo of the input ..there is an LM394, all other ic''s being 4559's
thankyou for any input..

Click to expand...

I don't really know you if you could improve it beyond what it really is.
LM394 was used in SSL 4K consoles, 4559 used in a lot of circuits also with good results

You could to do some replacements in one channel only at first an then compare with other channels to check if you get any improvments at all.
You can try replacing the LM394 with MAT02EH (low noise version) and replace the 4559's with NE5532AP
Do some measurments and tests and check if you find improvments

Besides that maybe just check if the PSU/Filtering can be improved

If you have the time and are doing this for fun, go on, otherwise PRR resumed the stituation quite well

LeeharveyOsmond said:

HI, I'm looking to do some mods to this little cheapo Kesley mixer,

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I don't know about the construction, but according to the schemo, there is not much you can do, unless you're ready to change the whole topology, LM394 is fine, 4559's are fine (actually as good as 5532 in this circuit).
I don't see local decoupling caps on the schemo, only two 22uF 'lytics; if that is really the case, I would think it worth doing, putting two 100nF ceramic caps close to each opamp, referenced to a solid good ground.

LM394 are hard to get, so maybe harvest those from the PCBs and put them in a good circuit?

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LeeharveyOsmond said:

HI, I'm looking to do some mods to this little cheapo Kesley mixer, beyond a recap bypass caps thing.. and would appreciate Some chiming in with any small Tweeks to the circuit, to lower noise, increase gain ect.. goal being making it a descent mobile box O pres and summing box... here is the schemo of the input ..there is an LM394, all other ic''s being 4559's
thankyou for any input..

Click to expand...

Doesnt look like there is much you can do with that circuit topology. Maybe change the EQ points to your liking and then add some balanced line inputs and call it a day.

I have a stock of LM394's, $4.25 ea.

Bill Wilson