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Hohner International Modular Effects Series "Valve Overdrive"

I got this from my brother a few years ago before I knew one end of a soldering iron from another. It's never worked and as I just found it again I haven't tried to fix it yet and as you can see the DPDT has been removed . It's a bit weird, it's as if it is incomplete as there are traces on the pcb that go nowhere.


http://www.b3ta.cr3ation.co.uk/data/jpg/img1058.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1053.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1050.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1054.jpg

The small cap is marked 56p, box cap is a WIMA .1u 100v, upright electro is a 10u 16v and there appears to be a black diode next to the electro between the jacks, IC is LM324N


if you want any more pics etc just ask

Nice pics!

If you are lucky the only reason it doesn't work is because the switch was removed and no one jumpered the connections.

Not uncommon to see missing componets on a board. Maybe they originaly had a buffer or? They also could have used the same board for more than 1 effect.

Only thing missing are the pot values they are shaded by the shafts. The one on top looks like 102A (10K) not sure though can you read them?

It's a bit weird, it's as if it is incomplete as there are traces on the pcb that go nowhere.

The traces are there because they made another type of pedal with the same pcb.

So the most important thing is to get some solder wick.
with this remove all of the unecessary solder around the switch area because they are causing shorts. There is an additional short near the 470µF capacitor and the 100k resistor and a second one between pin 11 and 12 of the LM 324.

After this you are ready for the next step:
There is a resistor near the LED with blue, grey and ?. The third ring can be brown or orange. It appears to me that this is brown, what would mean a value of 680 Ohm, a lot of power consumtion. If you have a multimeter please measure the value.

Then connect a 9V-battery to the pcb and measure the voltage across the black thing - it is a zener-diode. The voltage should be around 5V.

The potentiometers must be in the Mohm range. As far as I coould recognize there is something written like "2. MO RA" or so. This can be 2 Mohm or even 20 Mohm.

With the above information I can finish the schematic for further discussion.

analogguru

Some pictures of the reassembled pedal would be great too, the pictures I have seem to be from the same pedal (I think they came from eBay):
http://filters.muziq.be/model/hohner/hfx/valveoverdrive

I have the "Chorus Flanger" (not working), "Instant Funk" (envelope filter) and power supply from this series.

Thanks guys

Here's another couple of backlit pics
http://www.b3ta.cr3ation.co.uk/data/jpg/img1061.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1060.jpg

There is a resistor near the LED with blue, grey and ?. The third ring can be brown or orange. It appears to me that this is brown, what would mean a value of 680 Ohm, a lot of power consumtion. If you have a multimeter please measure the value.

that one is 680R, but the one that connects to the LED is the 2.2k next to it

Then connect a 9V-battery to the pcb and measure the voltage across the black thing - it is a zener-diode. The voltage should be around 5V.

There is only a drop of .2v across it. I'm getting 9v across it

The potentiometers must be in the Mohm range. As far as I coould recognize there is something written like "2. MO RA" or so. This can be 2 Mohm or even 20 Mohm.

they both read 2M0 2A . They both read over 2M , my multimeter reads just to 2M so I assume they are just over that - they get to 2M by about 3/4 of their movement.

DiscoFreq wrote:Some pictures of the reassembled pedal would be great too, the pictures I have seem to be from the same pedal (I think they came from eBay):
http://filters.muziq.be/model/hohner/hfx/valveoverdrive

That is my pedal, I think one of my first posts on harmony central was asking if anyone knew about it and possibly how to fix it and I probably put those pics up there, maybe that's where you found them? I'll try and find the footswitch and knobs and put it together

Thanks!

Those backlit pictures are great btw, not possible for all boards, but probably a lot easier to trace

Hanglow wrote:

Then connect a 9V-battery to the pcb and measure the voltage across the black thing - it is a zener-diode. The voltage should be around 5V.

There is only a drop of .2v across it. I'm getting 9v across it

9V is too much, maybe broken. Then you have to look, what is written on this diode.
Remove the 100µF electrolytic and look what you can see. If this is not sufficient, remove the diode too - take care, that the marking on it doesn´t get removed.

Discofreq wrote:I have the "Chorus Flanger" (not working), "Instant Funk" (envelope filter) and power supply from this series.

Time to test your new camera....

analogguru

Right I removed the electro, and when I did I could see that the casing of the diode is cracked. I can clearly see a 4v3 on one side, would a 4.3V zener make sense? There are other numbers but some wear so the are not clear

Discofreq, unfortunately I won't be able to take a pic of the reassembled pedal just yet - I used the DPDT in my multiface and the knobs are on a preamp I made for a mate. And I don't know where the back is either

If I get it working then I'll try and put it back in it's proper state

analogguru wrote:Time to test your new camera....

It didn't arrive yet :p

Anyone had any luck yet working out the schem? I had a shot, my first attempt at a schem ever and tried using jschem. Bloody thing crashed and I didn't save it , not that it was complete or in any way acceptable quality

I have just found this thread. I traced this pedal back in the 80s hence the hand drawn schematic.

I traced this from a friends pedal, it ate batteries like there was no tomorrow. I modified his with the low current mod (bottom right of schematic).

I built a clone but on mine I ran it from directly from 3v (2 X AAA batteries) and dispensed with the 4.3v zener and series 650R resistor. The batteries then lasted years.

Another mod I did on mine was a treble boost by changing the 1M gain resistor to a pot with the wiper going to earth via a 0.01uf capacitor. IIRC it added a load of hiss, I will have to dig out my pedal and check it out.

fred

DeltaFred - You've drawn a different pedal. The one at the top of the thread uses an LM324 quad op-amp and back-to-back diodes. Yours is more like the old Anderton "tube sound fuzz" that became the EH Hot Tubes....

mictester wrote:DeltaFred - You've drawn a different pedal. The one at the top of the thread uses an LM324 quad op-amp and back-to-back diodes. Yours is more like the old Anderton "tube sound fuzz" that became the EH Hot Tubes....

Thanks for pointing that out.

It was definitely a Hohner, and in the style of the one in the first post gut shots, that is what prompted me to post it. It is at least 15 years since I last saw the original and what it's name was escapes me. I will drop the guy an email and see if he can remember (his nephew now uses it).

I have located my clone and the chip is dated 1979 so it was probably shortly after that when I traced it.

Hanglow wrote:
The small cap is marked 56p, box cap is a WIMA .1u 100v, upright electro is a 10u 16v and there appears to be a black diode next to the electro between the jacks, IC is LM324N

dooh

Hanglow wrote:Hohner International Modular Effects Series "Valve Overdrive"

I got this from my brother a few years ago before I knew one end of a soldering iron from another. It's never worked and as I just found it again I haven't tried to fix it yet and as you can see the DPDT has been removed . It's a bit weird, it's as if it is incomplete as there are traces on the pcb that go nowhere.


http://www.b3ta.cr3ation.co.uk/data/jpg/img1058.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1053.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1050.jpg
http://www.b3ta.cr3ation.co.uk/data/jpg/img1054.jpg

The small cap is marked 56p, box cap is a WIMA .1u 100v, upright electro is a 10u 16v and there appears to be a black diode next to the electro between the jacks, IC is LM324N


if you want any more pics etc just ask

Hi,

made a trace.

Just for interest in another CMOS overdrive I downloaded the gutshots and
started to trace (When I saw, it's not a CMOS overdrive, I countinued
tracing.)

So it's a simple diode clipper, no tubescreamer-like lowcut before clipping,
moderate overdrive I guess.

Well, it is interesting, circuit is similiar to the CMOS-version, which was
traced by “deltafred”.



@Hanglow :

--- There is, possibly, a shortcut/tin bubble between pin 4 (9V) and pin 3 (~4.3 V).

This shortcut is a bypass for the resistor 680 Ohms and will kill the
Z-Diode, because the Z-Diode 4.3V is connected with 9V directly.

--- There is, possibly, a shortcut between the output (AC-signal, DPDT B2)
and the output of the OPA (4,3V+Signal).


Is it a noisy pedal? (Hi-Impedance-non-inverting OPA-circuits was blamed for being noisy.)


Have a nice day.

Torsten

That's definitely an interesting way of drawing a circuit diagram