Crowther Audio - Hot Cake Overdrive

bajaman · Post by **bajaman** » 06 Jul 2007, 23:27

Here you go

Crowther Hotcake exposed 1
Crowther Hotcake exposed 2

enjoy
Steve

invictus · Post by **invictus** » 07 Jul 2007, 00:00

wohooo! talk about hot! great pics bajaman. thanks!

.

bajaman · Post by **bajaman** » 07 Jul 2007, 00:59

Hey Hey

I traced this way way back in 1984

Sorry if it's a bit rough

It is an amplifier designed and manufactured right here in ChCh NZ, by Bill LeGros and Mike Lewis (Holden Sound Industries), and sold under the name of HOLDEN Graphic 208 ( 200w rms into 8 ohms - although many local musos found they could run it into 4 ohms and get 300w rms (with some forced air cooling!!)
They were one of the most popular bass guitar amplifiers throughout the 80's and early 90's on the local music scene.

Check out Channel 1 - do you see the bypass switching system for the distortion

is that familiar

- It should be: it is the same as the early Crowther Hot Cake switching system

Cheers
Steve

theblackman · Post by **theblackman** » 07 Jul 2007, 03:50

great stuff bajaman! thanks!

soulsonic · Post by **soulsonic** » 07 Jul 2007, 07:24

I really like the footswitch board with the latching relay. Could someone provide a schematic of that bit? It's hard to make out exactly how it's wired up. I understand how the latch works with pulses, but how does the LED stay on - is it tied to a pole of the relay or is it held on a different way? Is the footswitch momentary?

bajaman · Post by **bajaman** » 07 Jul 2007, 07:52

Hi soulsonic and interested other folks

In the first page of this thread analogguru posted a lin "this" - check it out - R12 allows a bias voltage to turn on transistor Q1 which then allows current to flow through the LED, lighting it up

The relay is DPDT as mentioned in an earlier post - in the bypass state, one pole of the relay is connected to the base of the transistor. This turns the transistor off and consequently no current flows and the LED goes out.
The switch S1 is a latching not momentary type. The other pole of the relay effectively turns the boost function on and off - check out the Holden Graphic DC208 schematic in an earlier post in this thread

I am not sure of the missing resistor values in analogguru's schem, but they should not be difficult to find by experimentation - plenty of data in this thread on other posts too
Cheers
Steve

bajaman · Post by **bajaman** » 07 Jul 2007, 08:00

Oh yeah - it is not true bypass

soulsonic · Post by **soulsonic** » 07 Jul 2007, 09:05

This is a very interesting circuit. I wonder, why go through the trouble of using a relay and a latching footswitch if it's not going to be true-bypass? And if you're using a latching switch, why bother with a latching relay? I understand latching relays have superior performance relating to contact "bounce", but still it seems to me this whole arrangement can be done more efficiently.

soulsonic · Post by **soulsonic** » 07 Jul 2007, 09:11

I'm looking at it some more:
Hmmm... no bypass at all? It just switches between being distorted and being relatively clean? Is this pedal intended to be like a preamp you have on all the time? I know very little about the history and intention of this circuit, but it looks fun to build. I'd like to know what to expect from it.

bajaman · Post by **bajaman** » 07 Jul 2007, 09:43

similar type of bypass

https://i197.photobucket.com/albums/aa2 ... hic208.jpg

bajaman · Post by **bajaman** » 07 Jul 2007, 09:47

Hey soulsonic and others

Have you figure the bypass out yet

That's right - it converts the op amp to run as a non inverting buffer

Cheers
Steve

ps: my previous post refers to the switch on channel 1 input- it is clearer there

analogguru · Post by **analogguru** » 07 Jul 2007, 21:56

The schematic of the Hotcake 2003 has slightly been updated (cosmetics).

And here is the:

Crowther Hotcake 1977 schematic

enjoy,
analogguru

Igloo · Post by **Igloo** » 08 Jul 2007, 14:22

Hi Guys..
Looks like I'm a little late for the party...but sure glad I found my way here!
So my first post at the new site

These two are the Hotcake schems that I have had...from different souces.
I have put them both on the one page

And so I put this together this afternoon...

bajaman · Post by **bajaman** » 08 Jul 2007, 21:25

Welcome Hemi ( half of 100

)

The unknown capacitor you refer to IS critical to the hot cake operation - without it (470pf ceramic) , you will get very bad high frequency oscillation.

The schematics you post are close BUT not perfect - please check out analogguru links in a previous post on this thread, for the CORRECT and VERIFIED schematics, for the current and first model hot cakes.

Cheers
Steve

Igloo · Post by **Igloo** » 09 Jul 2007, 17:16

I have updated the posted schems so the top on now has the values.

To my tired eyes, it looks excatly the same as the posted 2003 one.. minus the relays etc.

Oh..lists a 50k pot for the presence.

Anyhow, I have based the layout on it, so hopefully alls well.

Do you see any errors?

Torchy · Post by **Torchy** » 10 Jul 2007, 00:13

Actually that top schematic is mine - I traced it from my Hotcake but left out the switching etc.

Here ...

daz · Post by **daz** » 12 Jul 2007, 00:49

That schemo is the early version with buffered bypass and mid-lift switch.

analogguru · Post by **analogguru** » 12 Jul 2007, 01:28

That schemo is the early version with buffered bypass and mid-lift switch.

Interesting.... and what is this (from the first part of this thread) ?

analogguru

bajaman · Post by **bajaman** » 12 Jul 2007, 02:23

Hi guys
analogguru's 1977 and 2003 Hot cake schematics ARE correct - I have personally VERIFIED
Cheers
Steve

jt · Post by jt » 15 Jul 2007, 14:06

Hi,great forum.
One question about Hotcake.Is the zener diode used for reverse polarity protection?
if so couldn't be substituted with a 1N400x?

Crowther Audio - Hot Cake Overdrive [traced]