yep. it is 1/2 of its Vpp.
BTW, here's the 'corrected' pcb layout:
John, are Q1 and Q2 correct? It still looks like the emitters are connected to D1 and D2.
-Frank
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An inexpensive audio transformer with DIY projects
- Thread starter boomertech
- Start date
John, are Q1 and Q2 correct? It still looks like the emitters are connected to D1 and D2.
-Frank
- Feb 16, 2008
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something's still not right. the waveshape changes but it has fizzy, weired decaying distortion with the knobs at any setting.
- Feb 16, 2008
- 21,240
- 23,634
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- John K Custom Basses
luckily they're socketed, so I just flipped them 180 degrees, but it still sounds exactly the same.
Pull Q1 and Q2 out of the circuit and see if you can get clean signal to pass thru the circuit.
-Frank
- Feb 16, 2008
- 21,240
- 23,634
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- John K Custom Basses
already tried that and there's no difference at all, with or without them.
Do you have an overlay for the PCB with the ref numbers from the schematic? I will look over PCB because it should be passing clean signal as long as you are not clipping the opamps with Q1 and Q2 out of circuit.
-Frank
C3 and C4 are on the wrong side of the 1K resistors. They need to connect directly to pins 4 & 8 on U1.
-Frank
-Frank
- Feb 16, 2008
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got it. thanks. I'll have it all ironed out by tomorrow.
sorry for being an idiot.
sorry for being an idiot.
got it. thanks. I'll have it all ironed out by tomorrow.
sorry for being an idiot.
You are doing just fine for brand new circuits.
Thanx for hanging in there!-Frank
And thankx to both of you for discussing this so openly on a public forum. I find it very interesting to see how a new circuit is developed, tested and improved. (Even though most of the tech talk sounds like Chinese to me).
Thanks! As of right now, this is an experiment to try out a concept with transformer saturation and a really cool soft clipping circuit. It all works out in theory, but the real test is how well it works in reality.
This is what John will look like at the end of this project.
-Frank
John, the load on U1b output may be too heavy for R4 and R5 to be 1K's. Please change R4 and R5 to 220R.
-Frank
-Frank
- Feb 16, 2008
- 21,240
- 23,634
- Disclosures
- John K Custom Basses
- Feb 16, 2008
- 21,240
- 23,634
- Disclosures
- John K Custom Basses
i made all of the changes/corrections on my test PCB. it still has an ugly/fizzy distortion with the fizzy decay, and the drive knob seems to be working backwards.
IMO, it has something to do with the final output stage or stages.
IMO, it has something to do with the final output stage or stages.
Last edited:
The drive control is different... as it increases gain for U2a it simultaneously decreases gain for U1b (Please check with o-scope). I did it this way so that if you only want clean/non-clipped signals affected by the transformer characteristics, you do not have to worry about over-driving the output opamp.
The output opamp may still be loaded too much. Change VR2 to 5K and change R17 to 10K. This will give a lighter output load on U1b and allow for more gain/level control there.
-Frank
The output opamp may still be loaded too much. Change VR2 to 5K and change R17 to 10K. This will give a lighter output load on U1b and allow for more gain/level control there.
-Frank
You should also have no tranny installed, no R26 installed and jumper 2-8 on tranny board.
-Frank
-Frank
- Feb 16, 2008
- 21,240
- 23,634
- Disclosures
- John K Custom Basses
it gets louder if you turn the drive down right now. is that how it's supposed to be?
okay, i'll try that next.
and yeah, there's no tranny installed yet for all of these tests with 2&8 jumpered.
Guys, thanks for sharing this process with us. It is very enjoyable.
In the first circuit you wouldn't have heard a volume change with the drive control. But since then I have added Q1/Q2 soft clipping circuit that places R23, R24, R25 and VR3 in parallel with the VR1a/R7 gain control for U2a. I also moved the VR2 level control from the output of U1b into the feedback loop. So you may hear some volume changes with the drive control, but you will need to make sure with your scope that when the drive control is increased, that U2a also has an increase in output level.
BTW, I haven't calculated or simulated all of the gain structure for the circuit with all of these gain variables now. But, we should be getting really close to passing clean signals thru this circuit.
-Frank
