Pre-Amplifier Questions
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I did some digging and I’ve found out that AliExpress sells a host of pre-made and DIY kits for amps, pre-amps, and power supplies. Many are clones of classic audiophile grade components that have an expired patent. Sometimes finding a power supply for the boards can be a pain because most of the boards featuring tubes have at least 3 different voltages. All of that said to get here. I purchased the Accuphase C3850 (Completed) preamp. It comes with a knob for selecting 1 of 3 inputs but it has no potentiometer for volume. I was wondering if you have to use a normal pot for volume or if using a tone control board would conflict with the operation of the preamp. Having bass and treble adjustments would be great but not if it would have a negative effect on the sound quality due to interference with the preamp board.
I’m also trying to learn about linear and switching power supplies and the role that each play. There is way more to the audio hobby that I ever imagined.
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Welcome to the seriously technical side of our hobby, a side I love and have been immersed in since single digits. If you’d like, I’ll give you whatever help, guidance, or excited influence I can to get you to your goal and beyond.
Amps, pretty much all amps, use different voltages for different stages / functions. Tubes need heater voltages and then high voltage to move the signal through the plate/grid/cathode structure, out to the output transformer. many tubes are 6 volt or 12 volt, but there are a number of others. For example, a 6V6 has a 6 volt heater while a 12AX7 has a 12 volt heater. That’s what the first number means with these tubes. Then you’ll need at least 250 volts, usually much more. This is why the power transformers have at least 2 windings.
Solid state may have low voltage for computer parts, slightly higher for relays and preamp sections, then something that gets closer to the wall voltage (1/2 that or more), either in a single ended supply or split (+ and – ) supply depending on amp design. Often, lower end amps have single voltage (maybe center-tapped) and then use various active devices (voltage regulators) to get the lower voltages needed.
To your actual question, I’ll refer to the generic schematic I found from Ubuy India. There are 3 possible spots to put the volume/tone board:
1. at the actual input (before the very first resistor)
2. after the resistor at the output of the op-amp (the triangle)
3. the line that comes off the “0.9V” line before the resistor that goes to ground.
My vote would be #2, as the signal has been buffered and most likely somewhat amplified for the next stage. Now, whether the board will cause other issues depends on what the quality of that board’s design and build, actually is. But, I’d probably go for something similar as well – volume and tone is important, regardless of your audiophile standing. Besides, you’re building it and you do what you want. Your decisions are right for you. Even if it doesn’t work out, you’ll have learned from it.I had started a thread in one of the prior forum iterations that had some links to stuff that can help one understand the jargon and theory behind the hobby. I’ll look for that later and link it if it’s still there.
Power supplies, we can talk about them a little later. That’s a hefty topic.
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Nope, can’t find the Reference / Help post that was there previously. I’ll have to restart that.
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I bought the dual 18 volt transformer that the seller suggested. I also asked them if I could use a tone board and they said “No.” They recommended a 50ka pot. It isn’t a deal breaker or anything. I bought this board to play with it and try to learn what differences pre-amps make. It seems like most of the tone boards or EQ boards I have are built with op-amps on them. Not quite sure what they do but it seems like it is the engine or processor of sorts. I have quite an assortment of parts to play with so I’ll follow their recommendations for now and see how it sounds with just a volume pot. Then I might play some later.
Thanks for your info. I’ll put it to use!
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