Hearthrob or Schaller trem schematic?

[eurekaiv]

Does anyone have a schematic for this pedal?  All the links to the schaller schem are dead and I guess there never was one for the "hearthrob."    I built one over the weekend and while it does sound nice I'm thinking I need to tweak it a bit.  It also has some pretty annoying box pop even with the pulldown resistors that from reading about doesn't really have a solution.

[John Lyons]

Search for the schematic for the schaller in the gallery.
If you don't find it email me and I'll send it to you.

john

[eurekaiv]

Well, as luck would have it the link to the Schaller schem I found elsewhere started working again right after I posted this.  I guess the server was down this mornign or something.  In any case, thanks for the quick reply.  I've added the image to this post in case someone else is looking for it also.

[sixstringphil]

Please let us know if you find a solution for the on/off pop on this circuit. Myself and several others were unable to completely eliminate it.

[John Lyons]

The input is only 47K above ground so there shouldn't be any pop there
as the input is always connected to ground (no DC to build up there) .

The output could use a pulldown after the 4u7 output cap to ground, that should do it.
Is this how you have it guys? Still pops?

john

[eurekaiv]

I actually stuck the drop down on the input out of habit but I'm going to add one to the output and see if it gets any better.  From reading various old posts it seemed that neither eliminated it completely only lessened the severity.  I'm gonna try a couple things to see if I can get a tad more volume out of it as well.  Mine sounds just a touch below unity gain right now.

[eurekaiv]

Drop down on the output gets rid of it most of the time but it still will pop every now and then and sometimes pretty loudly.   

I added a 1uf cap across R4 and was able to get the output to unity gain with the depth at about 3/4 up.  It loses a touch of signal still when full clockwise and it doesn't quite chop as much with the extra gain but I think it improves the tone of the pedal personally, it's not quite so dark.  Is C8 the cap that controls how choppy the signal will be?  If so would I lower it or raise it to get a little more square wave out of it?

Another interesting observation... hit this thing with a bunch of volume from a fuzz pedal or something similar and it starts to sound more like a Univibe then a tremolo.  Pretty neat...

[John Lyons]

Are you measuring any DC voltage on the outside of C2?
Strange that the pop is intermitant/erratic.

A 1uf would make the gain of Q2 louder in the high end.
Not sure why it would change the chop though.

[Chris S]

I'm debugging this myself at the moment. I don't have any popping but I do have a very very significant drop in gain, about 1/4 volume - hence it still needs debugging and might start to pop once this is fixed. I replaced R1 and R2 with a 100k log pot which works fine but it's still not up to unity. I've used the slightly different layout below which has a few changes to the schaller one, I used 4 2N5089s instead of 2n5088s (i had them lying around). The depth only seems to work when it's around half way - sounds great there, so I think there might be a problem with the depth and volume. Any suggestions to where I should be looking to debug would be appreciated

[eurekaiv]

Are you measuring any DC voltage on the outside of C2?
Strange that the pop is intermitant/erratic.

A 1uf would make the gain of Q2 louder in the high end.
Not sure why it would change the chop though.

I'll have to measure when I get home from work. As for the cap, the larger the value the less the trem effect seemed to be passing.  I started with a 4.7 and while it sounded good as a booster, turning it all up had the effect seem more subtle.  It obviously wouldn't be changing the actual amount of chop but did seem to change how much of it you could hear passing through.

Oddly enough, I tried using 3 BS170s and a BC109 like the original and couldn't get the pedal to work at all.  It would only work with 3 5088s in Q1, Q3, and Q4. The BC109 worked fine in Q2 but sounded really weak.  I found this puzzling as the only changes I could find in this MarkM layout vs. the original were the 10uf cap on the speed switch and the 25k "Dwell" control.

I should have breadboarded this. A friend had me etch him a board and since I always do a few at a time I had a board laying around I thought I'd stick some parts in.  Not doing that again.   

[John Lyons]

Here are the differences in the Schaller/hearthob schematics.
There are 6 changes parts/values.
I should really check this again. If you see anything wrong please let me know.

I'd like to shift the range even faster as an option for a wilder stutter trem.
I like the way it is for sure but as an option...
Can anyone walk me through this?
thanks

john

[John Lyons]

B U M P

[eurekaiv]

I stopped fussing with mine after replacing the 47n with a 22n.  It does seem a touch choppier though it could be my imagination since it's impossible to do a side by side with only one build and no bread-boarded version.  As for the speed, mine will go so fast it pretty much doesn't even sound like a tremolo anymore, I'm not sure you could coax any more high speed chopp out of it.  That seems like a job for a repeat percussion unit but I haven't built one of those yet.  I do have the boards etched though. 

[John Lyons]

Ok, so C8 does set the high end of the speed?


john

[eurekaiv]

I think C9 and R13 on the switch deal with the speed or "frequency" as it's called in the schem. I'm not sure which is which on my build but in one position I can select a slower range then in the other though they do have some overlap.  You might be able to get a faster rate by playing with the values around that switch but I'm not sure really since I haven't much idea of how this circuit works except for the single amplifier stage.  From reading some back posts here and elsewhere it seemed that C8 was the "smoothing" cap and so I tried a lower value to make it a touch choppier and that seemed to help.  I think the pedal sounds pretty good now for my setup but of course YMMV.