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GK rails in a pedal?

#281
wow. the distortion sounds a lot better with the 47K's for R4 and R5. i was previously using a 2K2 for R16, but after replacing R4&R5, I like a 1K there best (the lower the value at R16=more dirt).

it's actually really sounding like a pushed power amp now!
 
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#283
johnk_10 said:
wow. the distortion sounds a lot better with the 47K's for R4 and R5. i was previously using a 2K2 for R16, but after replacing R4&R5, I like a 1K there best (the lower the value at R16=more dirt).

it's actually really sounding like a pushed power amp now!
Click to expand...

COOL!!! I had a feeling we were not too far off.

Do you have that test mod in there, eliminating U1b?

-Frank
 
#284
yep. no U1B at all (no foldback).
here's a clip on how it sounds with the 47K resistor change, jumping Q4's collector to Q1's base (and removing the foldback section).
i'm really diggin' it now.

here's clip of it. it's bypassed for the first 13 seconds, and after that, just variable amounts of gain.

[Invalid or Expired Link Removed]
 
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#285
johnk_10 said:
yep. no U1B at all (no foldback).
here's a clip on how it sounds with the 47K resistor change, jumping Q4's collector to Q1's base (and removing the foldback section).
i'm really diggin' it now.

here's clip of it. it's bypassed for the first 13 seconds, and after that, just variable amounts of gain.

[Invalid or Expired Link Removed]
Click to expand...

That is a nice growl!
 
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#287
johnk_10 said:
yep. no U1B at all (no foldback).
here's a clip on how it sounds with the 47K resistor change, jumping Q4's collector to Q1's base (and removing the foldback section).
i'm really diggin' it now.

here's clip of it. it's bypassed for the first 13 seconds, and after that, just variable amounts of gain.

[Invalid or Expired Link Removed]
Click to expand...
i want.
 
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#288
johnk_10 said:
yep. no U1B at all (no foldback).
here's a clip on how it sounds with the 47K resistor change, jumping Q4's collector to Q2's base (and removing the foldback section).
i'm really diggin' it now.

here's clip of it. it's bypassed for the first 13 seconds, and after that, just variable amounts of gain.

[Invalid or Expired Link Removed]
Click to expand...

Nice!

Foldback can still work with it directly connected to Q4 collector. The GK amp has the foldback connected in this manner.

It sounds like LF353's will not work for U1b, so let's keep the collector of Q4 connected to Q1 base. If you want to reduce parts count, we could use U1b as an input buffer amp and get rid of Q7 and all of its circuitry.

Also, try a 50K pot for the input level to get rid of that scratchy noise.

-Frank
 
Last edited:
#289
boomertech said:
Nice!

Foldback can still work with it directly connected to Q4 collector. The GK amp has the foldback connected in this manner.

It sounds like LF353's will not work for U1b, so let's keep the collector of Q4 connected to Q1 base. If you want to reduce parts count, we could use U1b as an input buffer amp and get rid of Q7 and all of its circuitry.

Also, try a 50K pot for the input level to get rid of that scratchy noise.

-Frank
Click to expand...
IMO, it doesn't need the foldback at all but I still might give it a try.
i'll try a 50K pot and see if that helps.
 
#294
boomertech said:
Nice!

Foldback can still work with it directly connected to Q4 collector. The GK amp has the foldback connected in this manner.


-Frank
Click to expand...

so how would the foldback circuit be wired up then? would it still have D8 and the R31, with D7 connected directly to Q4's collector?



DirtyDuke said:
You know me and pre amps!!! Must have, like soon.....
Click to expand...
well, this one isn't a preamp, but rather, it's a power amp simulator.
 
#296
johnk_10 said:
IMO, it doesn't need the foldback at all but I still might give it a try.
i'll try a 50K pot and see if that helps.
Click to expand...

GK PWR TEST.jpg


The foldback connections shouldn't have changed with R24 at zero ohm, just keep R23 and R31 out of the circuit so U1b isn't mucking up the sound.

I'm not sure of what is happening with that input pot, 50K should have made it better if the pot was affecting bias for Q7. I need 3,000 mile test probes!! LOL

Anyway, you are much closer to the original GK circuitry than before with U1b removed. We can make a solid, no-scratch input buffer with less parts if you like.

-Frank
 
#298
boomertech said:
View attachment 533732

The foldback connections shouldn't have changed with R24 at zero ohm, just keep R23 and R31 out of the circuit so U1b isn't mucking up the sound.

I'm not sure of what is happening with that input pot, 50K should have made it better if the pot was affecting bias for Q7. I need 3,000 mile test probes!! LOL

Anyway, you are much closer to the original GK circuitry than before with U1b removed. We can make a solid, no-scratch input buffer with less parts if you like.

-Frank
Click to expand...

in that case I think that it's probably time to clean up the original schematic (V5?)




i should also add that it does sound bitchen after an OD/distortion pedal. I was running after my Bearfoot 3BOD and it added a lot of punch and girth to the tone.
 
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#300
johnk_10 said:
in that case I think that it's probably time to clean up the original schematic (V5?)




i should also add that it does sound bitchen after an OD/distortion pedal. I was running after my Bearfoot 3BOD and it added a lot of punch and girth to the tone.
Click to expand...

Before we get to V5, lets see if you like the foldback distortions... if there is little to no change in the sound we will just ditch the foldback circuit completely. I only put it in because we were searching for that 'rails' sound and no one had analyzed exactly where that 'rails' sound came from.

johnk_10 said:
I did draw up and built a Jfet input amp for it a while ago. maybe i'll bypass the one in it and jumper mine in there now.
Click to expand...

When we go to V5 I will use U1b for the input buffer. I have had discrete JFET front ends give me issues with picking up radio before... it has been less of an issue with a healthy opamp up there.

-Frank
 

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