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PostPosted: Sun Feb 04, 2018 6:20 am 
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Hi all,
During my Green Pony build I had an issue with how the gain structure sounded on my pedal. My pedal simply did not sound the same compared to some demo clips I found.

In the None-position I hardly hard any gain at all. It was more just like a clean boost.
In LED- and Si-position there was gain that I think sounded OK but in any of these positions there was quite a drop in volume, compared to the None-position.

So, I reviewed all my soldering’s, checked my component placement on the PCB, browsed through the BOYC forum, exchanging the OP-amps etc. but I couldn’t find the cause of the problem.

Finally I decided to remove the Gain pot and do dome measurement.
On VR1a it measured 244KOhm
On VR1b it measured 226KOhm

I am far from an electronic expert but I thought the pot looked quite asymmetric in the values and decided to change it.
I ordered four new pots and out of the four the one with the best match, according to spec, measured 236KOhm on both VR1a and VR1b. All the others measured < 236KOhm.

After installing the new pot the pedal sounds great and there is no issue with the lack of gain in the None-position and there is basically no drop in volume in LED- or Si-position. Maybe a tiny bit in the Si-position but I am happy and satisfied with how the pedal now sounds.

Now (finally) to my questions;
1. Could the asymmetric value in the original pot have caused the issue I had, or did my exchange of the pot fixed something else, a bad soldering for example? I have seen another post is this forum where the OP had issue with the lack of gain in the None-position as well and was not able to solve it. At least not since my last check. Could we suffer from the same issue with a bad pot?

2. Would a pot closer to spec. 250KOhm (or a pot with the tolerance pushing the value > 250KOhm) be even better? For instance, my Classic OD (TS808 clone) seems to have a bit more gain than my Green Pony.

Thanks in advance
/Pelle


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PostPosted: Sun Jan 20, 2019 7:32 pm 
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Joined: Wed Feb 15, 2006 11:04 am
Posts: 2376
Location: Indianapolis, Indiana - USA
pellestendahl wrote:
Hi all,
During my Green Pony build I had an issue with how the gain structure sounded on my pedal. My pedal simply did not sound the same compared to some demo clips I found.

In the None-position I hardly hard any gain at all. It was more just like a clean boost.
In LED- and Si-position there was gain that I think sounded OK but in any of these positions there was quite a drop in volume, compared to the None-position.

So, I reviewed all my soldering’s, checked my component placement on the PCB, browsed through the BOYC forum, exchanging the OP-amps etc. but I couldn’t find the cause of the problem.

Finally I decided to remove the Gain pot and do dome measurement.
On VR1a it measured 244KOhm
On VR1b it measured 226KOhm

I'd just rig your board up in a temporary way that you can sub in different value pots with some wire and alligator clips. When you find a value you really like, put that one in. I do this all the time in builds where the value of certain components is subjective. :)

I am far from an electronic expert but I thought the pot looked quite asymmetric in the values and decided to change it.
I ordered four new pots and out of the four the one with the best match, according to spec, measured 236KOhm on both VR1a and VR1b. All the others measured < 236KOhm.

After installing the new pot the pedal sounds great and there is no issue with the lack of gain in the None-position and there is basically no drop in volume in LED- or Si-position. Maybe a tiny bit in the Si-position but I am happy and satisfied with how the pedal now sounds.

Now (finally) to my questions;
1. Could the asymmetric value in the original pot have caused the issue I had, or did my exchange of the pot fixed something else, a bad soldering for example? I have seen another post is this forum where the OP had issue with the lack of gain in the None-position as well and was not able to solve it. At least not since my last check. Could we suffer from the same issue with a bad pot?

2. Would a pot closer to spec. 250KOhm (or a pot with the tolerance pushing the value > 250KOhm) be even better? For instance, my Classic OD (TS808 clone) seems to have a bit more gain than my Green Pony.

Thanks in advance
/Pelle

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Keep 'yer tips tinned, 'yer sponges wet, and TELL THEM KIDS TO SHUT THE HELL UP!!!


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PostPosted: Wed Jan 23, 2019 12:19 pm 
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Joined: Sun Jan 22, 2006 1:39 pm
Posts: 4129
Location: Moses Lake, WA
The LED and NONE settings don't clip as much as the Si, so it's not going to sound like there is as much distortion. Don't confuse gain with distortion.

A larger value pot for VR1b would provide more gain at IC1a, however, VR1a may not work very well for blending the dry signal if you used a larger value. Keep in mind that all the mods for the tubescreamer are applicable to the OD820 circuit. If you want more gain, the easiest way would be to decrease the value of R8.

Also, keep in mind that the circuit is running at +/-9v for a differential of 18v. This means you aren't going to get quite as much distortion out of it as a typical tube screamer. You could disconnect pin 4 of IC1 from -9v and connect it to ground, but you'd also need to connect R7 to 1/2v instead of ground for the correct bias voltage.

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Please do not PM me. email is prefered. keith@buildyourownclone.com


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