Bass Pre-amp Build HPF/Compressor

[Lauri]

RV1 is a bias balance pot. If the triodes in ECC82 aren't matched well then the compressor might thump and RV1 can be used to adjust the current difference. RV2 is output volume pot. Center taps of the transformer should be left unconnected.

I updated the first version of the compressor so it should work better with 300V supply voltage. Couple of the resistor values are different and I added 22V zener diode to the side chain to limit the maximum amount of compression.

instcomp.pdf

[Wardy]

Thanks Lauri,

Been reading a lot on vari-mu compressors and this looks like it might turn out out just great. I appreciate your help. I have another question that arose as I was going through all the parts to see what I already had in stock etc.

The capacitors C6 and C7 seem very large like power supply smoothing caps. I'll be running from a dc to dc booster starting with a regulated 24v supply. I'll drop to 12.6 DC to run the heaters. go straight off the regulated supply to the side chain and then boost the 24v to about 300v for the plates. Do they need to be this big? also C5 appears on the input to SC1 but not on SC2 - is this correct?

many thanks

Steve

[Lauri]

C6 and C7 are power supply filter caps. They can be smaller. C5 is there to block DC current from going through the output transformer.

[Wardy]

Hi Lauri,

Once again sorry for any stupid questions. I have most of it together now but can you tell me what B2 is? B1 is marked as 300v but is B2 different? should it be a different voltage? maybe the circuit was taken from one using a different power supply?

Many Thanks

Steve

[Wardy]

Making some progress with this now although its turning out to be quite a lot more complex than I initially thought.

Progress 23-9-25.pdf

[Wardy]

Hi Gang,

Need some advice please. I have most of my preamp together but am struggling with noise from the SMPS. I can use a modified V Pump converter from Tubetown at 300v and it is silent. However it cannot take a 24v input and I need 24v to drive the sidechain on the compressor circuit. My goal is as follows.
24dc in - goes to a booster for 300v, also a reducer to 12.6v for the heaters and also goes straight to the sidechain of the compressor circuit.
I can achieve all the voltages no problem and the preamp works. (I haven't wired in the compressor circuit yet) However I can't achieve 300v form the dc dc converter without motorboating. I can get it to about 200v and I have already added 4 rc filter stages. As I dial down the volyage the motorboating slows down and evetually stops and turns into a high frequency noise but barely noticeable.
The tubetown modules are silent without any additional filtering but as I say won't take 24v which I also need.

So question is 1, does anyone know of a quiet dc dc booster that can tak 24v in and produce 300/350v out?
2. How can I make the booster i have properly quiet for this?
I am using the attached booster but have tried another similar with same results.

many thanks


Steve