Crowther Audio - Prunes & Custard

Torchy · Post by **Torchy** » 07 Sep 2007, 20:14

Thats the only reason I could think of.

Nicely done schematic by the way, thank you

krome_magnon · Post by **krome_magnon** » 07 Sep 2007, 20:43

Torchy wrote:Thats the only reason I could think of.
Nicely done schematic by the way, thank you

Thanks. Disregarding the sketchy nature of some of the values, does it look like it follows the actual circuit?

I think I've followed it correctly, and the circuit makes sense as drawn.

CP10H brings up all sorts of crap on google, but no real details. I'd say something like a 1N4007 or similar diode would give polarity protection in that spot.

RLBJR65 · Post by **RLBJR65** » 07 Sep 2007, 21:46

CP104 maybe?

Electronic Devices Inc

Silicon Rectifier

V(RRM)(V) Rep.Pk.Rev. Voltage=1.2k

V(FM) Max.(V) Forward Voltage=2.0

@Temp. (?C) (Test Condition)=25

I(O) Max.(A) Output Current=150m

@Temp (?C) (Test Condition)=100

krome_magnon · Post by **krome_magnon** » 07 Sep 2007, 21:52

RLBJR65 wrote:CP104 maybe? ...

A likely candidate, and I could be right and pretty much any rectifier diode will go in it's place. It's not going to affect the audio path anyway.

analogguru · Post by **analogguru** » 07 Sep 2007, 22:42

Îf there would be written C10PH this would be a zener-diode 10V made by PH-ilips.

analoguru

kusi · Post by **kusi** » 08 Sep 2007, 10:07

hi guys,

thanks a lot for your work!

@krome_magnon:
i think one of the both 10k resistors at IC1b should be at pin6 of it.

could someone explain the theory behind this kind of clipping? lokks very intressting!

please excuse my english

regards, kusi

bajaman · Post by **bajaman** » 08 Sep 2007, 10:43

Hi kimosabi
you are correct

think one of the both 10k resistors at IC1b should be at pin6 of it

the board trace shows this.
I am still puzzled by the component around the second half of the dual opamp - I cannot see how it can be a 1Meg resistor from the Blacman's gut shot pics. I also thought it was a 390k, but it has an extra band on the body - is it an inductor by chance??
I also have issues with the resistors in the diode chains - I cannot see how the 56k resistor is correct - it looks like 21k to me (how did you measure it Richard - with a digital or analog meter??). The board trace gut shots show that the bottom two diodes and the 16k resistor on Krome Magnum's schem were never fitted as well!!!
I do not think there are three 16k resistors,(only two) - one of them looks more like a 15k to my eyes.
Anyway, I have posted a board layout based on the yellow traces and my guess at the correct values - I will update it once someone can actually verify the correct values
Ham and Mustard PCB and layout
cheers
bajaman[/url]

Bernardduur · Post by **Bernardduur** » 08 Sep 2007, 10:49

Isn't it JUST a 6 band resistor that read 390k Check here

Thanks for the layout!

bajaman · Post by **bajaman** » 08 Sep 2007, 10:59

Hi - thanks for the help Bernardduur - it is a 390k 1% resistor

enjoy the pcb layout
cheers
bajaman

bajaman · Post by **bajaman** » 08 Sep 2007, 11:13

After further checking - I now think that the 15k resistor is actually a 75k, and that the 56k is correct too.

snail · Post by **snail** » 08 Sep 2007, 11:17

Thanks a lot Bajaman!
Neat work!
Anyone knows any links to sound samples of the real thing?
I heard it once and then forgot where

snail

bajaman · Post by **bajaman** » 08 Sep 2007, 11:22

Perhaps Richard (theblackman) could measure these resistors and put us out of our misery - somehow, i don't think we are there yet - but getting closer

bajaman

krome_magnon · Post by **krome_magnon** » 08 Sep 2007, 13:42

The latest incremental update.

k**i wrote:@krome_magnon:
i think one of the both 10k resistors at IC1b should be at pin6 of it.

Well spotted, and I've corrected the mistake on the schem.

k**i wrote:could someone explain the theory behind this kind of clipping? looks very intressting!

Well it looks like...

The signal is fed into the second op-amp's inverting input and to that ladder of diodes.

When the signal is strong enough to pass through the first pair of diodes the portion of the signal strong enough to pass is fed to the non-inverting input, and therefore out of phase, with the main signal and cancels out some of the dry signal at the frequencies with enough amplitude to pass through the diodes.

If the signal is strong enough to pass the second pair they are fed to the inverting input and will add back into the original at the frequencies strong enough to get past 2 diode drops.

And so on, add, subtract, add, subtract at the various frequencies and amplitudes of the input signal.

bajaman · Post by **bajaman** » 08 Sep 2007, 13:58

NO
the first op amp has 100k feedback resistor
the second op amp has 390k feedback resistor
Still unsure about that 15k resistor in the diode ladder - it could be a 75k - hopefully theblackman will help us soon.
cheers
bajaman

krome_magnon · Post by **krome_magnon** » 08 Sep 2007, 14:20

bajaman wrote:NO
the first op amp has 100k feedback resistor
the second op amp has 390k feedback resistor
Still unsure about that 15k resistor in the diode ladder - it could be a 75k - hopefully theblackman will help us soon.
cheers
bajaman

Adjusted accordingly, I'll give it a rest until we get some more evidence

RLBJR65 · Post by **RLBJR65** » 08 Sep 2007, 16:46

krome_magnon I think the schematic is right but I still question some of the values. I cut the board sections from all 5 of the pics and pasted them into 1 pic. Really helped me instead of fliping though them. http://i10.tinypic.com/68mrwcn.jpg

Close pic http://i19.tinypic.com/4mrjc7b.jpg

The 16K resistors look like 20K to me. They are 5 band red black black red brown = 20K - 1%

I'll go along with the 56K if it's 6 band and the green has been scraped off Green blue black red brown red = 56K 1%

I can't tell if that is a 15K or 75K either. Violet? Brown? Looks more black than brown.

Jim777 · Post by **Jim777** » 10 Sep 2007, 00:39

Theblackman said he measured the 56k so I assume it's ok. I have doubts about a couple of things. The two 10k resistors coming from +/- of the second opamp to the 10u cap. On the pic they look like red red black black. 220ohms? The 10k resistor from the wiper of the level pot looks like brown black red, 1k.

theblackman · Post by **theblackman** » 10 Sep 2007, 00:40

hi guys, when I dismantled the P&C there were a number of components under the goop which had been damaged by my scraping, fortunately only the diodes were broken and easily replaced.

The resistors that you are asking about had some of the markings partially scraped off so I desoldered and measured with a DMM and made sure what was left of the markings agreed with the DMM reading.

And now I have broken my one month forum addiction cold turkey

If you are still unsure, please post an image of the circuit board with a circle around the disputed components and I'll see what I can do about finding their value. Cheers, Rich

bajaman · Post by **bajaman** » 10 Sep 2007, 00:44

Hi theblackman
As I requested in my PM to you, please measure and supply the values for the 6 resistors immediately in a vertical line below the 56k that you have already measured and posted - these values are critical to the circuit's operation, which is why Paul Crowther has scraped the bands of one end of them.
many thanks
bajaman

theblackman · Post by **theblackman** » 10 Sep 2007, 00:46

those are the ones I did measure with a DMM and posted them already on page one of this thread