Crowther Audio - Hot Cake Overdrive  [traced]

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jdix123
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Post by jdix123 »

I tried replacing the op-amp for an actual TI071, it sounds really good! Also, I went in and fiddled with the components on the board, made sure they weren't touching, etc. Made a HUGE difference! I'm so excited with how it turned out! :D

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andregarcia57
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Post by andregarcia57 »

as wiring diagram in the original DPDT?
1 4
2 5
3 6

thanks

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bc108
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Post by bc108 »

Bump thread for this timeless gem.
Built the 03' version, NICE fuzzy OD: that's true the similar grain' with the BD2.

Used TL081, I'll try TL071.
A25K in reverse (as the old version?); 220R to lug 2, and lug 1 to ground: nice sweep.

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Post by bluegrasser12345 »

Hotcake devotee here, resurrecting an old thread and paging Bajaman and Soulsonic! I'm having hard time wrapping my mind around the buffer/bypass operation - I'm building the 2003 schematic but using something like the 1977 bypass/buffer setup.

In the 2003 schem above with relay bypass (and Soulsonic's "mojocake"), it appears that when acting as a buffer the outside lugs of the drive pot are shorted, leaving no path to ground for the 220R, 1k, 470p, and 22n. As I understand this leaves only the 10k and 100k resistors in the feedback loop, and no path or resistance out of the loop to ground/vref. If this is the case, how is the gain of the opamp set by just those resistors in the loop?

In the 77 version does the 220k resistor to Vref come into play in bypass somehow? If I'm building the 2003 schem but with simple bypass, am I better off just shorting the gain pot, or lifting gain 3 and adding the 120k resistor to ground?

Hope that makes sense, and thanks a ton!

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aionios
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Post by aionios »

We were sorely missing any info on the post-2003 models, including the XLF and Bluesberry variants, so I traced a post-2008 Hotcake which includes internal switches for XLF and Bluesberry modes. Crowther goops these pedals pretty effectively, so it was a pain, but hopefully worth it!

Crowther Hot Cake (2008) Schematic
Crowther Hot Cake (2008) Schematic

Some interesting stuff going on with the offset null pin - I've never seen this pin used in a pedal before. I asked around at DIYSB and got some good explanations of how it works, so check out this thread if you're interested.

Full tracing journal:
https://aionfx.com/news/tracing-journal ... -hot-cake/

PCB available here:
https://aionfx.com/project/anomaly-vintage-distortion/

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The G
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Post by The G »

Just an outburst of my OCD, the version is 2008 or 2014 (like in the DIYSB thread)?

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Post by aionios »

It's the 2008 revision, but the specific model I traced was from 2014. As far as I understand, the next revision after 2008 was the 2020 one that released this summer, with toggles on the outside.

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Post by obbarius »

Not much happening in this thread anymore, but hopefully someone can help me with a quick question. There are some amazing resources here - thanks for all the efforts. I'm new to this, built a quick begginer's fuzz pedal, that didn't sound great and moved on to this one for something i actually need and should sound good. I spent a lot time googling and deciding on capacitors. I got the impression they were more important to the sound than resistors etc. I tried to find Wima capacitors, but had to look elsewhere for some values.

The pedal seems fine, except the overdrive is nowhere near as powerful as what you hear from the real Crowther pedal. It's as if i'm getting too much clean signal through, and not enough clipped signal / overdrive. It also sounds a little more fuzzy than the real thing, although not by a huge amount. The sound isn't bad, just not as good and powerful as the Crowther pedal. I've tested connections, and that all seems ok. I can set the pots so pedal on/off doesn't change the sound at all. Volume and presence sound like they're working as they should - only the overdrive sounds off.

My suspicion is that the fact that my capacitors have a max. vvc of 400-1000 volts is a problem. I've read different opinions on this - some say it anything above max. circuit voltage times two is fine, some say that when your circuit is at 4-5 less than capacitor max. voltage, the actual capacitance value drops. I can't seem to find good capacitors for the required capacitance values with max. voltage of about 40v-60v though.

TL/DR
- Is using capacitors of max. voltage much higher than required a problem in general?
- Could using capacitors of max. voltage 400-1000 in this circuit cause the overdrive to be "weak"?
- If my capacitor max. voltage values aren't the problem - any hints where to look?

Hope my explanations make sense, and that someone can help.

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modman
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Post by modman »

obbarius wrote: 06 Jun 2021, 12:07The pedal seems fine, except the overdrive is nowhere near as powerful as what you hear from the real Crowther pedal. It's as if i'm getting too much clean signal through, and not enough clipped signal / overdrive. It also sounds a little more fuzzy than the real thing, although not by a huge amount.
What schematic/layout did you use to build from? And what are you comparing your pedal to? Note also that the original pedals are not true bypass, they use a buffered bypass.
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obbarius
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Post by obbarius »

Ok, so i didn't mention this, because it's not the schematics from this thread, but a conversion to vero board found here:

http://tagboardeffects.blogspot.com/201 ... e.html?m=1

I wanted to ask here, because it seemed like a better place to get a good answer to the general question, but of course the schematic matters. I've read through the entire discussion on that page though, and people tend to agree that it sounds right - the version without buffer just has problems with oscillations with presence and gain maxed out, which i've also experienced.

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aionios
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Post by aionios »

obbarius wrote: 06 Jun 2021, 12:07 TL/DR
- Is using capacitors of max. voltage much higher than required a problem in general?
- Could using capacitors of max. voltage 400-1000 in this circuit cause the overdrive to be "weak"?
- If my capacitor max. voltage values aren't the problem - any hints where to look?
Can't comment on what may be the issue, but I can definitely confirm that the voltage rating of the capacitors will have nothing to do with their performance. Very rarely will a film capacitor even see the full supply voltage - for example, most film capacitors are 50V or higher, but when used as a signal coupling cap they will only see a fraction of a volt going through them. Doesn't matter if it's rated for 50V, 500V or 5,000V, it will provide the same capacitance.

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obbarius
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Post by obbarius »

aionios wrote: 06 Jun 2021, 16:05
obbarius wrote: 06 Jun 2021, 12:07 TL/DR
- Is using capacitors of max. voltage much higher than required a problem in general?
- Could using capacitors of max. voltage 400-1000 in this circuit cause the overdrive to be "weak"?
- If my capacitor max. voltage values aren't the problem - any hints where to look?
Can't comment on what may be the issue, but I can definitely confirm that the voltage rating of the capacitors will have nothing to do with their performance. Very rarely will a film capacitor even see the full supply voltage - for example, most film capacitors are 50V or higher, but when used as a signal coupling cap they will only see a fraction of a volt going through them. Doesn't matter if it's rated for 50V, 500V or 5,000V, it will provide the same capacitance.
Ok - thanks for taking the time to set that straight:)

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Post by modman »

obbarius wrote: 06 Jun 2021, 15:56 Ok, so i didn't mention this, because it's not the schematics from this thread, but a conversion to vero board found here:

http://tagboardeffects.blogspot.com/201 ... e.html?m=1

I wanted to ask here, because it seemed like a better place to get a good answer to the general question, but of course the schematic matters. I've read through the entire discussion on that page though, and people tend to agree that it sounds right - the version without buffer just has problems with oscillations with presence and gain maxed out, which i've also experienced.
I built two or three Hotcakes after my friends like them too much, just to have one for myself. They were all true bypass version and they did not oscillate though it's kinda fuzzy from a certain point onwards. Maybe there was a problem with that vero layout. Fixing problems that resulted from a bad layout by putting in a buffer is a great idea, but it takes you further away from the original Hot Cake.

That there are sonic differences is unavoidable, but the voltage rating on the caps are not important, as pointed out above.
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obbarius
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Post by obbarius »

modman wrote: 07 Jun 2021, 14:20
obbarius wrote: 06 Jun 2021, 15:56 Ok, so i didn't mention this, because it's not the schematics from this thread, but a conversion to vero board found here:

http://tagboardeffects.blogspot.com/201 ... e.html?m=1

I wanted to ask here, because it seemed like a better place to get a good answer to the general question, but of course the schematic matters. I've read through the entire discussion on that page though, and people tend to agree that it sounds right - the version without buffer just has problems with oscillations with presence and gain maxed out, which i've also experienced.
I built two or three Hotcakes after my friends like them too much, just to have one for myself. They were all true bypass version and they did not oscillate though it's kinda fuzzy from a certain point onwards. Maybe there was a problem with that vero layout. Fixing problems that resulted from a bad layout by putting in a buffer is a great idea, but it takes you further away from the original Hot Cake.

That there are sonic differences is unavoidable, but the voltage rating on the caps are not important, as pointed out above.
True - i'm not so concerned about the oscillation right now - i would rarely crank it all the way up anyway - but it just seemed odd that the general concensus was that the sound was otherwise very close to the original, and i have this very weak drive, while the rest of the circuit seems fine.

I did notice that the resistance across my 50k presence pot, went from 0 to about 15-17k before dropping to about 14-15 again while turning. Shouldn't it go between 0 and 50k as my volume and drive pots do?

THe way the presence pot affects the sound seems fine, and i can't see how this weird resistance pattern could affect the overdrive (yes, i'm sure it's the presence pot and not the drive:)

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aionios
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Post by aionios »

If the pot is measured in-circuit, without disconnecting one side of it, the measurement doesn’t mean anything since the rest of the circuit is loading or paralleling it. If you want to see if it’s working then you would have to desolder it before measuring. Pots are very hardy though so it is unlikely to be the issue.

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Post by obbarius »

aionios wrote: 08 Jun 2021, 11:37 If the pot is measured in-circuit, without disconnecting one side of it, the measurement doesn’t mean anything since the rest of the circuit is loading or paralleling it. If you want to see if it’s working then you would have to desolder it before measuring. Pots are very hardy though so it is unlikely to be the issue.
Of course - completely forgot about that. Thanks.

Would it be possible to check the voltages around the TL071? I mean can you say that with x resistance from y pot, the voltage on pin z of the TL071 should be around q?

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Post by aionios »

Yep, in fact I’m not sure the voltage would change at all with pot rotation (it usually doesn’t, but this circuit is a bit odd in several regards) so it should be clear if something’s wrong without needing to know the exact pot positions.

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Post by obbarius »

aionios wrote: 09 Jun 2021, 12:22 Yep, in fact I’m not sure the voltage would change at all with pot rotation (it usually doesn’t, but this circuit is a bit odd in several regards) so it should be clear if something’s wrong without needing to know the exact pot positions.
Ok. I don't want everything served to me on a platter, but as a beginner, how do i go about checking voltages in the circuit? Is there a good way to do it, or is it simply a matter of calculating resistances and checking voltages for path?

I'm also interested in tips for mapping a schematic (like the ones in this thread) to a vero board or something similar. Is there a method, that's easier for beginners or is it simply a matter of trying to arrange everything connected in lines?

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Post by Nocentelli »

obbarius wrote: 12 Jun 2021, 09:43
Ok. I don't want everything served to me on a platter, but as a beginner, how do i go about checking voltages in the circuit? Is there a good way....
use a multimeter set for dc voltage up to 20v, put the black/negative lead on circuit's ground and touch the red probe to the +9v supply rail (with the circuit connected to the power supply/battery), note down the voltage and then touch each opamp pin in turn with the red probe tip (black probe always connected to ground as the reference point), noting their voltages.
obbarius wrote: 12 Jun 2021, 09:43
I'm also interested in tips for mapping a schematic (like the ones in this thread) to a vero board or something similar. Is there a method, that's easier for beginners or is it simply a matter of trying to arrange everything connected in lines?
There isn't really a particular method, but trial and error experimentation in attempting to do a vero of a simple circuit will quickly show you a few rules, conventions etc. There is a guide at tagboardfx that |V|ark put together which is more like a description of the conventions/principles he tries to stick to in his layouts, then a walk-through of him drawing up a layout for a circuit explaining a why he's done what he's done at each step:


http://tagboardeffects.blogspot.com/201 ... e.html?m=0
Last edited by Nocentelli on 12 Jun 2021, 13:13, edited 1 time in total.
FiveseveN wrote: 16 Dec 2021, 19:40 For the love of Maxwell, de Forest and Shockley, why are all the components uncomfortably perched and flapping in the breeze like that?

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Post by Intripped »

This is the first time I read Mark and not ivlark... Excuse me for the OT

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