Fortin - Grind Pedal

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bmxguitarsbmx
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Post by bmxguitarsbmx »

I have both grind and 33. They are on loan because my amps are really too tight to boost. I thought the 33 said OPA2604, but maybe it said "OPA604" (single version of OPA2604). I'll track them down this weekend and confirm.

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sledgehammer
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Post by sledgehammer »

Anyone built the vero version? Mine works "okay" - all pots are doing what they should do and the preamp is amplifying the signal. But i got quite some high frequency hiss when turning the treble up (tested with different power supplies and battery the behaviour stays the same). Any ideas how to improve this?

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Post by mnemonic »

sledgehammer wrote:Anyone built the vero version? Mine works "okay" - all pots are doing what they should do and the preamp is amplifying the signal. But i got quite some high frequency hiss when turning the treble up (tested with different power supplies and battery the behaviour stays the same). Any ideas how to improve this?
It’s a baxandall eq and the high band is centered at 10khz so it certainly can add hiss and feedback, especially in higher gain situations. I don’t think I ever go higher than like 1:00 with the treble. It’s nice to add a bit of extra brightness or bite, but it can get out of hand and brittle easy.

I guess you could alter the part values around the treble control to lower the centre frequency into a more usable range for guitar.

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Post by Leito79 »

bmxguitarsbmx wrote:I have both grind and 33. They are on loan because my amps are really too tight to boost. I thought the 33 said OPA2604, but maybe it said "OPA604" (single version of OPA2604). I'll track them down this weekend and confirm.
Did you got them back? Some pictures of their circuit boards will be awesome!!!

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Post by audioguy »

Any chance someone's done a single layer, etch-at-home version?
J0K3RX wrote:I believe you guys are right about the grind/33 being a TC Electronic integrated pre clone, makes sense :thumbsup

nice layout & scematic here..
http://www.rullywow.com/wp-content/uplo ... e-v1.0.pdf

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Post by Optical »

I got a couple of Rullywow Chuggapre boards a week ago.
Just waiting on a couple of bit to arrive then I'll try it out

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Post by Optical »

bmxguitarsbmx wrote:I have both grind and 33. They are on loan because my amps are really too tight to boost. I thought the 33 said OPA2604, but maybe it said "OPA604" (single version of OPA2604). I'll track them down this weekend and confirm.

Any update?

bmxguitarsbmx
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Post by bmxguitarsbmx »

Hey Optical!

Grind is Burr Brown OPA604AP (single op amp) and Texas Instruments LT1054IP (Charge Pump). 33 is gone [smilie=a_damnit.gif]

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Post by Optical »

Ok, much as we thought. So just another TC integrated pre clone with probably a component value tweak to the filter center frequencies...
Are you able to read the cap values?

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Post by Optical »

Some filter frequency info on the 33 pedal in this video at 28mins https://www.youtube.com/watch?v=i86Zx0L8yf0

130Hz -10dB; 390Hz 0dB; 950Hz 7.5dB; 2.2kHz 5.8dB; 4.9kHz+ 5dB

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temol
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Post by temol »

Has anyone experienced problem with TC pre signal clipping (blocking, oversaturating) when bass and level pots are set past 15 o'clock?
With bass at noon and level at 15 o'clock it's ok. Checked 9V and 20V power supply. Little less clipping present with 20V, but still.

T.

bmxguitarsbmx
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Post by bmxguitarsbmx »

Temol,
Are you using the Rullywow chugga board?
I get clipping from my Chugga as well.

I'm changing R11 to 820k from 1M. We'll see how much that changes it.

820k is from this scheme here:
Attachments
tcpre original scheme maybe.jpg

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temol
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Post by temol »

I'm using the same schematic and PCB that I designed myself. No charge pump.

T.

bmxguitarsbmx
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Post by bmxguitarsbmx »

temol wrote:I'm using the same schematic and PCB that I designed myself. No charge pump.

T.
Cool.

I increased headroom by lowering the value of R4 and R10, but keeping the ratio the same. This limits the amount of cut or boost the circuit can do, and also limits how hard Q2 slams against the rails trying to make up for the op running out of headroom. My values are R4=47k and R10=110k in reference to the last schematic I posted. Hope that is useful, YMMV. I have also found that the LM741 outperforms both the tl071 and the opa604. Again, YMMV. Mine is crunching along smoothly atm.

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temol
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Post by temol »

bmxguitarsbmx wrote: I increased headroom by lowering the value of R4 and R10, but keeping the ratio the same.
I'll definitely try this out. Thank you.

T.

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Post by Belanger88 »

temol wrote:
bmxguitarsbmx wrote: I increased headroom by lowering the value of R4 and R10, but keeping the ratio the same.
I'll definitely try this out. Thank you.

T.
I’m using my own PCB as well which has a pump and I’ve found using a LF356 was the best out of all the single ic’s I tried. TL061, LM741, LF351, LF441,NE5534 among a few others.
Success is no accident. It is hard work, perseverance, learning, studying, sacrifice and most of all, love of what you are doing or learning to do.

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temol
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Post by temol »

I've replaced 741 with a LF356. It's a bit different in character (tonally) but no improvement with clipping. I've also reduced values of R4 and R10 by half. Slight improvement, clipping starts with higher volume and bass settings, but still present.

T.

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Post by bmxguitarsbmx »

With 20V supply you can barely get 2.5Vpp out of it. Yiy. I actually walked away for the last couple weeks.

The only reason I see for the BJT is to eliminate the unity gain dry signal. Which, I can see why that makes it brutal. That BJT sure clips hard though (Maybe where the magic is)

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Post by DevouredDeth »

I have also embarked down the integrated preamp path. I found some old forum postings in the seven string forum and other extreme metal boards of people shelling out loads of cash to only get a lemon of a pedal that sounds super flubby and tinny. Most people have manged to get it to sound ok at higher voltages like 25V or higher. I recently tried a charge pump for 33V and things are better but the clipping is still bad. Looks like their charge pump in version one is also running at 33V. Maybe I will change some resistors out like you guys have done.

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temol
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Post by temol »

I suspect that we might have two problems here - clipping inside the preamp and overloading input of the next device. I've checked this with two jfet preamps and ended up with a slightly different results. One of the preamps required slightly higher volume/bass levels before I could hear there is something going on.

T.

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