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Built a Diamond Drive and a Plexi Plus and put them into a 1590BB for a dual British amp-in-a-box pedal.
I had very high hopes, and the Plexi Plus lived up to them, the Vox sounds fantastic, but I’m a tad disappointed that the Diamond Drive can’t be dialed back much at all. It DOES sound like a cranked Vox, but it’s like it’s on 9.7 on the gain when all the way down, and 10 when cranked. I want to check out the schematic and see where I can change a couple of components to give some “less gain” while retaining the ability to get the “more gain” stuff, too.
That said, the tones from both of these circuits are fantastic and definitely sounds like the two amps they’re designed to emulate. The Plexi uses the SMD J201s from the shop here, and they were pretty easy to set up with legs and socket.
YouTube Demo: https://www.youtube.com/watch?v=spTqoxBeCUg
Very nice and thanks for sharing!!
Can you take a voltage reading for the Drain leg of each Q of the Diamond Drive and report? Sounds like it is running a hot Bias.
Thanks Barry,
Q1 = 5.60
Q2 = 9.30
Q3 = 4.67
Q4 = 9.31
Q5 = 4.95
Also, I set the bias as described in the build docs, then tried to tweak by ear, and it goes into cutoff before it cleans up very much, so that was my first thought as well. I need to double check my resistor values, but I think I got them all correct. Also, I used the “standard” value for the pots, not the one recommended for “more distortion”.
Thanks Cybercow!
Hello there! Noob here, but not new to building pedals. I had the same issue as OP: sounds glorious, but drive only goes from 9.7 to 10, as you said it. Checked drain of all 5:
Q1: 5.88
Q2: 9.41
Q3: 4.86
Q4: 9.4
Q5: 4.7
any suggestions?
I checked the resistors with a multimeter, and all were in spec (except a few that were half the value, but I removed one and tested and it landed in value, so I suppose those change while in the pcb).
If you are using the old TO-92 style thru-hole components, as it looks like the OP has, the tolerances of those parts is highly suspect these days unfortunately. I have found that sometimes I need to stray greatly from the recommended biases, based on the sounds of the particular transistors. I got the advanced meter from small bear which allows you to test the transistors, and that helps a bit, but sometimes you need to increase the drain quite a bit to reduce the gain pushing through the circuit.
Ah ok, so the issue might be with the J113s, is what you’re saying. So on this circuit, there is a trimmer for adjusting bias for Q5, are you saying adjust that? Or should I be looking at adjusting the bias of another transistor?
I don’t have the greater multimeter, but after doing a couple builds I’m starting to see the need of something that can test transistors.
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