Crowther Audio - Hot Cake Overdrive  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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greenskull
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Post by greenskull »

Well, okay. I built it up, but didn't experiment as threatened. I threw in a NE5534 and sounded good.. so I left it. As reported, the magic is at lower settings (halfway or less?), not full blast. Has a chimey buffered sound to my ears. The full on distortion didn't sound too great with passive humbuckers or single coils, BUT sounded killer with active humbuckers with gain all the way up... really smooth and saturated.
May still socket in the 220k resistor and change out the chip for a 741 to just make sure before boxing it up, but I'm liking the sparkley, low noise aspect right now, though.
Thanks for sharing the layout Torchy!!!!

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Post by analogguru »

guts from an original older version:
https://cgi.ebay.com/ws/eBayISAPI.dll?V ... otohosting
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.

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Post by bajaman »

Ha ha - notice the protection - one of Paul's business cards from Live Sound, Grey Lynn in Auckland, cut in half with white silicone rubber RTV underneath it. :wink: :lol:
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Jim777
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Post by Jim777 »

I was looking at that so called class A version trying to get my head round it. The opamp is biased at 3volts and the transistor base at 5.8v so with no input it doesn't look like the transistor is biased until the output goes over 6.4v. Then when it conducts it injects current into the emitter resistor of the current mirror transistor. So what's that going to do? Does it reduce gain on positive half cycles? It doesn't look like it's making the opamp run in class A. The common way I've seen for doing that is put a current source on the output to ground.

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Post by cbriere »

Jim777, i agree with your interrogations.... i will prototype this
pedal just to see what's the transistor will do to the overdrive
caracteristics of this circuit. asa i receive the tl071 part.
cbriere

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Post by bajaman »

I have NEVER seen an unmodified genuine Hot Cake with a class A transistor in it - and I have seen quite a few of them over the last 20 years or so :wink: :roll:
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vanessa
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Post by vanessa »

Is this the "To Build" pedal? Sounds like a lot of interest in it and I'm wondering if I need to break out the soldering iron for this one?

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Post by cbriere »

is there someone that can explain the output transistor function?

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Post by bajaman »

is there someone that can explain the output transistor function?
I believe it was a japanese mod - kaz may be able to help :?:
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Post by TMZ »

Layout for You.

Image[/img]

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Post by JHS »

The HC is a 30 year old design and Paul built a lot different versions over the years. The basic circuit design is always the same but he altered part values and the circuit layout over the years.

IMHO there exists no ultimate HC. 3 circuits are my fav. ones and the latest version is one of them.

It's a very simple design and IMHO very easy to modify to suit anyone.

JHS

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Post by bajaman »

You can get some interesting results by playing around with the frequency selective feedback components too (10k, 1k, 82n) - try 8k2, 560, and 150n for example. Also try decreasing or increasing the electrolytic in the drive control pot leg of the circuit. or - add a jfet buffer at the input ( check out the DIY projects section for details)
have fun :wink:
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chris_d
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Post by chris_d »

I just built this yesterday(from the the "'77 Old Cake" layout that Ulysses did) and i like it.

I am using it i guess like most do, for more like a low gain boost, maxxed level, half drive. For that purpose i like it, it is like a less squashed treble boost, nice sparkle when you roll of the volume, little darker grit when you roll it back up.

This is actually closer to the type of sound i was hoping to get out of the SHO i built a while back. I also really dig the feel and engagement of the SPST switch, much nicer feel/sound than the normal DPDT/3PDT clickpop action. True bypass is not something i normally care much about (unless the circuit is really dragging the signal down when it is off) anyhow, so i don't miss it here at all.

Thanks for this one guys!

-chris

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Post by sosodef »

do you guys like the buffer in the hotcake? I always liked it. I am not sure but at times it seems better than even the klon buffer.

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Post by modman »

Hot Cake revision Sept 2007 wrote: As of September 2007, The Hotcake now comes in only one version, and is internally presettable for "Normal" or "Bluesberrry" voicings, and also for the extended low frequency option for bass. The "Bluesberry" voicing of the Hotcake has a slightly less buzzy edge at the onset of distortion, and often works well when guitarists have amplifiers with extra extreme treble boost, like some Marshalls for instance.

Specificatons:
  • * Input impedance: 1 Megohm. (equivalent to a typical valve amplifier.)
    * Output impedance: less than 13k Ohm
    * Recommended minimum output load impedance: 100k Ohm.
    * Bypass type: Circuit converts into a high quality buffer with simple, quiet, seamless switching, using gold plated contacts.
    * Phase polarity: Non inverting.
    * Continuous current consumption: approx. 3.5 mA (LED on)
    * External power supply socket: 9-12VDC, 2.1mm, pin negative. Compatible with most popular AC adapters.
But more interesting, here's a letter from Paul Crowther on the switching, published by a user on TGP
Hi
The Hotcake has an unusual bypass system, and I shall paste in more info below. If you really want to go for total bypass, I recommend an external switching box.
Best regards,
Paul Crowther.
################################################## #
True bypass or not?
The true bypass thing really means that the signal does not pass through any electronics when bypassed, just switch contacts...the next best thing to unplugging the pedals altogether. True bypass can be noisy (big "click")
sometimes, and the switches usually just have tin plated contacts which can become unreliable when switching low level signal.

Pedals such as the Tube Screamer, and most Roland pedals use electronic bypass, which means that the signal goes into a buffer circuit at the input to the pedal, then through switching Fets (field effect transistors which can be used as an analog switch, but can introduce some distortion) , then at the output of the pedal there is another buffer circuit to protect th switching Fets from the outside world.

When I first started making the Hotcake, I had trouble finding a good DPDT switch, so I came up with a different idea which converts the circuit from a distortion to a high quality buffer. The distortion is basically enabled with a single switch to ground. By having a buffer in line with the guitar, the guitar electronics are isolated from being loaded with the guitar leads and other pedals between the Hotcake and the amp. This usually means that you get back a few highs, and some people hear that as "changing their sound."

The first person who told me that simply plugging in their Hotcake improved their guitar sound was our own Neil Finn, (Split Enz, Crowded House etc. )

I now use a latching relay with gold plated contacts for the actual switching, and that is super reliable as long as the battery is OK.

I have also made a "true bypass" system which I call "gold bypass". I use that with the Prunes&Custard pedal now, but with the Hotcake it is prone to instability (going into oscillation) because there is a lot of Level and
Gain available with the Hotcake, and for this type of switching, the input and output wires have to come
very close to each other at the relay contacts, and the guitar source impedance can be quite high, especially a passive electronics one (like a Strat or Les Paul), with the volume control backed off a little.

So...I rest my case.

Paul E. Crowther

from: Letter from P Crowther quoted on TGP by nashvillesteve 01-06-2006, 05:47 AM
Bajaman covered it so throughly, there's hardly anything to be added, perhaps maybe this short bio that's offline but still in Google's cache:
"Hello, I'm Paul and yes it was me who used to play drums for Split Enz at one time - quite a while ago now when I think about it! I was on the first two Enz albums - 'Mental Notes' and 'Second Thoughts'. Most of us were using our middle names, and mine is the Welsh name "Emlyn".
I've been a sound engineer now for many years and have been repairing other people's music gear for as long as I can remember. People are always bringing me their synthesizers, amps, mixing desks, mics, effects units etc asking me to fix them and sometimes modify them.
Back in 1976, I started to making a guitar distortion pedal called a 'Hot Cake'. I've sold quite a few of them over the years, even to guitarists from quite well known bands like Crowded House, Oasis, The Lemonheads, Pavement, Beck, The Tragically Hip, Ocean Colour Scene etc.
A recent idea which I am now making is a quite different sounding distortion which I have called a "Prunes & Custard". I use my prototype one quite a bit when I'm mixing FOH sound, and for recording. It is especially useful on bass and drum sounds, and for guitarists who really do want to try something different. Not for the faint hearted! A couple of Rhodes piano players are using them as well.
Contact Paul at croth@clear.net.nz"

from: Google chached version of this bio
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Post by modman »

analogguru wrote:
Also Analogguru mentioned a German pedal? that had a similar frequency dependant feedback system tone control like the Hot Cake uses.
Have a look at the Hawk Booster and - very similar - the Univox UEQ-375 Impersonator...

Never heard something about the Gronk Box or Herbert Box....must be something from the other side of the world. :wink:

analogguru
http://www.univox.org/effects/imp.html

http://tremolo.elektroda.net/Efekty/Imp ... Univox.gif
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Post by Greg »

Guys, anyone have an idea on what changes are made to the Bluesberry version.

Yes, I know it's a subtle change, but I'd still like to know... and considering the latest HC's come with sockets and the components to switch, I thought someone might know.

Thanks

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Post by modman »

Greg_G wrote:Guys, anyone have an idea on what changes are made to the Bluesberry version.

Yes, I know it's a subtle change, but I'd still like to know... and considering the latest HC's come with sockets and the components to switch, I thought someone might know.

Thanks
No hard info on that, but check JHS and Baja's comments earlier in this thread.
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Post by Greg »

modman wrote: No hard info on that, but check JHS and Baja's comments earlier in this thread:
http://www.phpbbserver.com/freestompbox ... boxes#2363
Thanks Modman.
I've read through all that pretty thoroughly.
To be honest, I have a bit of trouble getting my head around the tone setup on the HC.... what effects what, and how the frequency selective feedback works.
Maybe someone could talk me through it (10k, 82n and 1k) ??

It would be appreciated.

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Post by bajaman »

Maybe someone could talk me through it (10k, 82n and 1k) ??
Normally the 100k feedback resitor would be connected between the output terminal and the inverting input terminal of the opamp.
Varying the resistance between the inverting input and ground ( via the series capacitor to block dc bias and set low frequency gain structure), will increase or decrease the op amp stage gain in a high pass fashion.
Okay - here is the trick :wink:
We connect a series chain of 10k, 1k, and 82n from the op amp output to ground. This combination provides a variable frequency reactive filter on the output of the op amp.
At low frequencies - say 100hz, the 82n capacitor's impedance will be 19.4k ohms.
At high frequencies - say 10khz, it's impedance will be 194 ohms!!!
So - at high frequencies only 10% of the op amp's output signal voltage appears at the 100k feedback resistor, but at low frequencies 67% of the op amp's signal voltage appears at this point.
Because less feedback of signal is available at high frequencies, as the gain is increased the op amp goes into slew rate induced distortion a lot quicker at high frequencies than at low frequencies - this accounts for the clarity in the low end response when driven hard - the fundamental remains reasonably clean compared to the distorted top end response.
cheers
bajaman

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