Caline CP-29 White Heat  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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phatt
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Post by phatt »

CheapPedalCollector wrote: 17 Dec 2022, 06:32 Thanks phatt, excellent info.

I think the pulldown resistor in the input is just to stop the switch from clicking from capacitive buildup of voltage since the LED is also going through it, or maybe backwards charge potential on the input cap, I remember popping being some issue with it.
Yes R1 is just a discharge path for any floating voltage when switching, the anti pop thing. 2M2 is Way to high to have any effect on the input Z of U1A and it's isolated via C5.
CheapPedalCollector wrote: 17 Dec 2022, 06:32 I'll try building the circuit with a buffer transistor and see how much less noise it makes, should be able to lower R2/R6 also to 4.7k and 100k to retain the same gain but less noise yes?

I really need to buy a copy of art of electronics...
Regards to R2 & R6.
No this one does the gain by altering the resistance of R3.
(not ideal in my experience as all the gain might be close to the end of the sweep)
Better to make R6 a 500k pot and just ground R3. R3 does not have to go to Vb it can go to either Vb or Comm.
Frankly just use the values of the TS circuit then tweak till you find a sweet spot.
With the buffer you will need to up the value of C5 to 1uF or higher, see TS circuit.
Experiment by changing values of C4 & C6.
Also R3 but below around 500R it may just squeal like a pig be warned.

I was lucky that someone gave me a copy of a free sim program and *Art of Electronics*. Circuit maker Prg was very basic but for pedals it was all I needed to see just how it works.
BTW, All this was before I had internet. (shows my age group :wink: )
So I had a breadboard on the bench and a sim program on the screen.
So change a value on the screen and then do it to the actual circuit.
Really sped up my understanding.
I've worn out 5 breadboards in the last 30 plus years.
and I'm too old now to go back to uni to learn stuff I may never have time to use.

So now i have a good pedal and Amp setup and tend to play guitar far more than soldering stuff. :shred:

I urge anyone wishing to learn how to make pedals,, get yourself familiar with sims, They won't tell you everything but nothing like a plot on the screen and then hear it live to speed up just where tone is won and lost. :thumbsup
Phil.

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jhergonz
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Post by jhergonz »

wow! i learned so much in this thread. Thanks guys.

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CheapPedalCollector
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Post by CheapPedalCollector »

Manfred wrote: 17 Dec 2022, 08:02 What about the value of C5, do you keep it or adjust it?
I would play with it to keep the same frequency response, I think they chose this value so it's a bit more flat vs .047 which has bass roll off when using a 7 string, I always forget these days that 7 and 8 string is a bit more popular than 25 years ago.
phatt wrote: 17 Dec 2022, 10:42 Regards to R2 & R6.
Ahh yes I meant R3/R6, I'm prone to typos haha.

In regards to tube screamer, I get squealing in them a lot when I build them, the circuit layout seems to be sensitive.

I'm also too old to go to college, even if I could afford it. I can read though, I'll have to make it a priority to purchase it soon, first I need a new scope.

I think I will use another TL072 for input/output buffers as this provides a better impedance to the guitar than discreet transistors that aren't in a bootstrapped configuration, and it's less parts. I never really liked the buffers in the TS and other maxon/boss pedals done that way, I like the original narrow box TS buffers that use another 1458 which sounds better to me for some reason.

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Manfred
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Post by Manfred »

CheapPedalCollector wrote: 17 Dec 2022, 06:32
I'll try building the circuit with a buffer transistor and see how much less noise it makes, should be able to lower R2/R6 also to 4.7k and 100k to retain the same gain but less noise yes?
Sorry ,I forgot to answer your question.
With a buffer in front of it you can decrease the value of R2/R6 to 4.7k and 100k.
Regarding the noise, the noise value is not reduced by a factor of 10, but only by a factor of about 3,
because of the square root function in the calculation.
Have a look at this website:
https://www.beis.de/Elektronik/Nomogram ... Noise.html

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Post by Manfred »

I made this PCB layout in accordance with the schematic in the post above.
Caline White Heat PCB Layout.JPG
Ready-to-Print PDF-files:
Caline White Heat PCB Component Side.pdf
(10.54 KiB) Downloaded 79 times
Caline White Heat PCB Component Side enlarged.pdf
(11.07 KiB) Downloaded 74 times
Caline White Heat PCB Solder Side.pdf
(2.52 KiB) Downloaded 91 times
Sprint-Layout6.0 file:
Caline White Heat Own.zip
(10.88 KiB) Downloaded 87 times
Gerber and Drill files:
Caline White Heat Gerber & Drill Files.zip
(8.17 KiB) Downloaded 85 times

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Post by mauman »

CheapPedalCollector wrote: 17 Dec 2022, 19:53 .. I'll have to make it a priority to purchase it soon, first I need a new scope...
+1 on Art of Electronics 3rd edition, you can get a discount from the publisher Cambridge Univ. Press sometimes if you sign up for their promotional emails. If you get it elsewhere, beware of counterfeits, the author's website shows some bought from dubious sources that have been copied and poorly printed.

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Post by CheapPedalCollector »

Thanks for the tip, I was going to buy it from Amazon, but if I can get a discount on it from the publisher that's even better.

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Post by IleaneKrasley »

CheapPedalCollector wrote: 17 Dec 2022, 19:53
Manfred wrote: 17 Dec 2022, 08:02 What about the value of C5, do you keep it or adjust it?
I would play with it to keep the same frequency response, I think they chose this value so it's a bit more flat vs .047 which has bass roll off when using a 7 string, I always forget these days that 7 and 8 string is a bit more popular than 25 years ago.
phatt wrote: 17 Dec 2022, 10:42 Regards to R2 & R6.
Ahh yes I meant R3/R6, I'm prone to typos haha.

In regards to tube screamer, I get squealing in them a lot when I build them, the circuit layout seems to be sensitive.

I'm also too old to go to college, even if I could afford it. I can read though, I'll have to make it a priority to purchase it soon, first I need a new scope.

I think I will use another TL072 for input/output buffers as this provides a better impedance to the guitar than discreet transistors that aren't in a bootstrapped configuration, and it's less parts. I never really liked the buffers in the TS and other maxon/boss pedals done that way, I like the original narrow box TS buffers that use another 1458 which sounds better to me for some reason.
Thank you for answer!

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mictester
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Post by mictester »

nooneknows wrote: 04 Dec 2020, 11:59
CheapPedalCollector wrote: 29 Nov 2020, 12:54 They did that to reduce PSU noise.
ok, but how? I don't understand the purpose of adapting the impedance, a buffer doesn't reduce hum by itself as far as I know
Look at the electrolytic capacitors - one (effectively) across the 9V supply, and another at the voltage reference point for the ½V rail. The op-amp provides a big input impedance, so any supply hum will be filtered out by the electrolytic from the junction of the biasing resistors, and a very low output impedance, providing a quiet "virtual earth" at ½V to bias the signal-carrying part of the dual op-amp. With a good quality op-amp (NOT a 4558 or 1458) like the TL072 they've used, this will be a low noise pedal. I don't much like the lowered input impedance (the 47kΩ going to the non-inverting input of the op-amp) - this will tend to roll off the top end of many pickups. I'd go for at least 220kΩ in that position to prevent treble loss.

This circuit is ripe for modification - you could add clipping diodes from the output of the audio op-amp to the ½V rail to give DOD250-type clipping, or you could shape the frequency response with frequency-dependent feedback, to give treble boost or bass boost, and there are lots of other things that you could easily try.....
"Why is it humming?" "Because it doesn't know the words!"

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Post by IleaneKrasley »

CheapPedalCollector wrote: 17 Dec 2022, 19:53
Manfred wrote: 17 Dec 2022, 08:02 What about the value of C5, do you keep it or adjust it?
I would play with it to keep the same frequency response, I think they chose this value so it's a bit more flat vs .047 which has bass roll off when using a 7 string, I always forget these days that 7 and 8 string is a bit more popular than 25 years ago.
phatt wrote: 17 Dec 2022, 10:42 Regards to R2 & R6.
Ahh yes I meant R3/R6, I'm prone to typos haha.

In regards to tube screamer, I get squealing in them a lot when I build them, the circuit layout seems to be sensitive.

I'm also too old to go to college, even if I could afford it. I can read though, I'll have to make it a priority to purchase it soon, first I need a new scope. By the way, talking about college is you need some help with your stadies you can use https://essays.edubirdie.com/law-dissertation-help this service for law dissertation writing help or other.

I think I will use another TL072 for input/output buffers as this provides a better impedance to the guitar than discreet transistors that aren't in a bootstrapped configuration, and it's less parts. I never really liked the buffers in the TS and other maxon/boss pedals done that way, I like the original narrow box TS buffers that use another 1458 which sounds better to me for some reason.
No worries about the typo, happens to the best of us!

When it comes to tube screamers, I understand that the circuit layout can be quite sensitive, and you often encounter squealing issues when building them.

Regarding college, I totally get it. If it's not feasible for you, reading up on the subject is a great alternative. You might consider purchasing a new scope to help with your projects.

For input/output buffers, using another TL072 sounds like a good choice. It provides better impedance for your guitar compared to discrete transistors without a bootstrapped configuration. Plus, using the TL072 means fewer parts, which is always convenient. I'm with you on the original narrow box TS buffers using another 1458 – they have a certain sound that appeals to you, and that's what matters.

Keep up the good work, and happy building!

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Post by mictester »

nooneknows wrote: 04 Dec 2020, 11:59
CheapPedalCollector wrote: 29 Nov 2020, 12:54 They did that to reduce PSU noise.
ok, but how? I don't understand the purpose of adapting the impedance, a buffer doesn't reduce hum by itself as far as I know
If the half rail is sourced from an op-amp (as here) the capacitor from the non-inverting input to ground is made much more effective, leading to a quieter and more stable midrail. This approach is frequently used in professional audio design, because of the improvement this provides. If you look at (for example) the EHX Soul Preacher circuit, they use an active midrail supply - using a transistor in their case - done for the same reason. It provides a "stiffer" midrail, and will be quieter than just using a couple of resistors in series from supply to ground.
"Why is it humming?" "Because it doesn't know the words!"

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Post by mictester »

IleaneKrasley wrote: 29 May 2023, 08:20
For input/output buffers, using another TL072 sounds like a good choice. It provides better impedance for your guitar compared to discrete transistors without a bootstrapped configuration. Plus, using the TL072 means fewer parts, which is always convenient. I'm with you on the original narrow box TS buffers using another 1458 – they have a certain sound that appeals to you, and that's what matters.
Using an op-amp on the input of an effect can be problematical unless it's properly protected. You'll frequently see reverse-biased zeners, diodes or LEDs used at the inputs of op-amps to protect the op-amps from the vagaries of the outside world. It's very easy to destroy the input stage of an unprotected FET-input op-amp (like the TL072, for example).

That said, the TL072 (and its relations) are good choices for buffers - they can have a nice high input impedance to prevent loading effects, and their output impedance is reasonably low. They're also easy to stabilise, provide a very low noise contribution, and are easy to configure for gain, filtering and so on. They're also inaudible in use - they don't affect the "tone"!
"Why is it humming?" "Because it doesn't know the words!"

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