Diezel VH4 Pedal  [schematic]

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

Re: Diezel VH4 Pedal

Postby temol » 14 Dec 2017, 09:46

RockKenny wrote:What kind of 7660 do you use? I mean firs letters.
I have oscillation with ICL7660SCPA.


Just 7660SCPAZ. Not SCPA but SCPAZ. No letters before digits. Bought it here, check the picture of the chip.

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Re: Diezel VH4 Pedal

Postby temol » 22 Dec 2017, 12:46

Any ideas where to buy C25k potentiometers (split shaft preferably) in decent price and (would be nice) in EU?

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Re: Diezel VH4 Pedal

Postby Jan1966 » 22 Dec 2017, 13:02


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Re: Diezel VH4 Pedal

Postby Ichabod_Crane » 17 Jan 2018, 17:13

I'm beginning to study this pedal, and I have some doubts and questions about it.
I know about some oscillation problem and I'm a bit worried.

I even know about the 560pf cap, which can replace the 47pf, but maybe getting the sound muddy.
I'll pay attention to the 7660 version, too.
I never did, but I could use the shielded cable, if I need.

I prefer and I would like make the board by myself and not to buy a PCB. I probably gonna build (not within few months) the veroboard layout by Guitar FX, and it's clear, I would make a perfect working pedal and the veroboard layout results verified, but did someone build it with none of this problem?

And now a technical question. I see the charge pump, and also a 12v regulator, right? The PSU of this pedal can be 12v or 18v. I suppose the pedal receive 12v or 18v, adjust it at 12v and the charge pump turn into 24v. Is it correct?
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Re: Diezel VH4 Pedal

Postby PittedPanda » 18 Jan 2018, 06:15

Thanks for all the hard work guys.

I just built this pedal from bajaman's PCB design.

I had horrible oscillations when gain was above 60%. This disappeared completely after changing C10 from 47pF to 22000pF mylar cap. It did decrease the overall gain quite a bit though.

I tried the 7660S and LT1054 in IC4. It was overall noisier and loudy with LT1054 but did not decrease tendency to oscillate.

No different in sound or oscillation between 12V or 18V sound.

I tried twisting +/- leads and tidying the wiring. No difference.

It seems the oscillations and some related pre-oscillation noise change threshold based on: Gain knob, Depth knob, Mid knob, and general position of PCB relative to pots. Beyond my ability to sort out why.


Now, the pedal works fine but there is a loud whooshing hum when master volume is up. Even with noise gate in front and guitar disconnected.

Also there is some ground-related hum/buzz that goes away when I play or touch my guitar strings.

So of the 4 noise types (oscillation sequel, pre-oscillation noise, ground-hum, and volume-related-whooshing), 2 were fixed by tidying wiring in increasing C10.

So questions:
1. How can I decrease Ground-hum and whooshing?
2. Should I put a ferrite bead in R1 as was on the original?
3. Should I build a buffer onto a daughter board before the input?
4. How can I make the master volume knob less touchy? (With it going into my FX return, I can only use 0% to 5% without bothering neighbors).

Thank you all in advance. I tried to trouble shoot this the best I could before posting but I've reached my wits end trying to figure this out solo :)
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Re: Diezel VH4 Pedal

Postby plush » 18 Jan 2018, 14:00

Ichabod_Crane wrote:And now a technical question. I see the charge pump, and also a 12v regulator, right? The PSU of this pedal can be 12v or 18v. I suppose the pedal receive 12v or 18v, adjust it at 12v and the charge pump turn into 24v. Is it correct?


Yeah, kinda...
7660 has an input operating range of something up to 12 volts. So, guys from diesel decided to use voltage regulator to protect 7660 chip. Some people use zener diodes for it, some prefer linear regulators. Both of them can be easily omitted if you plan to use the pedal with regulated power supply not exceeding 12v voltage.
I suppose, this pedal feeds of 9 volts normally, you can try and feed it with 12 volts, but it won't make any reasonable change.
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Re: Diezel VH4 Pedal

Postby Ichabod_Crane » 18 Jan 2018, 19:14

Well, I assume that if the Diezel works after the power section at 24v (in case of 12v/18V PSU) instead 18v (in case 9v PSU) the pedal will have more headroom, so a bit of volume and maybe a bit of more clear and bright sound. Actually, I don't have experience with this kind of stuff, but is this what I read around.

I'm sorry, PittedPanda. This is right the things I wouldn't get with my build. :(

So, I come back to ask:

Ichabod_Crane wrote:[...]
Did someone build it (the Guitard FX veroboard layout) with none of these problems?
[...]


Thanks! :wink:
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Re: Diezel VH4 Pedal

Postby temol » 18 Jan 2018, 21:50

And there it is, finally finished. Proper pots (Presence and Deep), decal.

Image

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