Orpheum Fuzz Squeal

[Jamforthelamb]

Hey All,
I have a recently built Orpheum that's squealing. I've searced, and tried some of the fixes that are on board (removing the "tone" pot, replacing R3 with a 100k pot, tried many different transistors) and it still squeals. Anyone have some tips to tame this beast ?

http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album18/album144/album109/ORPHEUM_FUZZ_VERO.gif.html

[Jamforthelamb]

bumpity

[John Lyons]

Make sure your input and output wires are not too close to each other.
Is this on a breadboard or?
It's probably oscillation...what transistors are you using?

John

[Jamforthelamb]

I've been using a variety, 2n3904s, 5088s, and a few others.
I've tried to use ones with lower hfe, but I most of them aren't very close to the 120 that dragonfly used in his build.

[nightingale]

Hi,
I have an original one that squeals when the battery is getting low. Maybe around 7v or so.
My original one has pretty low gain transistors in in. If I remember correctly they were around 150hfe.
hope this helps,
ry

[Jamforthelamb]

I tested the battery I was using and it's at 8.6 volts.

I'll see if I have something a little lower. I think most of the stuff I have been using has been at 200 and above.

[Jamforthelamb]

Tried the lowest ones I have (100 and 20) no difference.

I took some voltages, and they don't look right at all.
Q1
E:7.9
B:8.5
C: 8.5

Q2
E: 8.0
B 7.8
C 8.5

I'm going to double check all my soldering (again). I already checked my resistors, and they are all correct. The only major difference is that my 22k resistors read at 17k.

[Dragonfly]

Tried the lowest ones I have (100 and 20) no difference.

I took some voltages, and they don't look right at all.
Q1
E:7.9
B:8.5
C: 8.5

Q2
E: 8.0
B 7.8
C 8.5

I'm going to double check all my soldering (again). I already checked my resistors, and they are all correct. The only major difference is that my 22k resistors read at 17k.

Your voltages are way off.

Check your grounds.

The emitters of BOTH Q1 and 2 should be 0v, as theyre both directly connected to ground.

[John Lyons]

Yes, your voltages are of. Maybe missing a ground I think.
The voltages should be something like this:

Q1
C 6.4v
B .5v
E 0v

Q2
C .8v
B.5v
E 0v

John

[Jamforthelamb]

Ok, it's time for another embarrassing mistake moment.  I had the input and ground wires reversed on the input jack  .

No more squeal, I need to check the voltages again to see where they are at. One thing I noticed is that it sound nothing like . It's not nearly as fuzzy. I've tried several different trans. and it doesn't make that much of difference. Right now it sounds a lot like the fuzz on The Ventures "2000 lb bee" if anyone is familiar with that. Really trebely with a little buzz.

I'll post the voltages soon.

-jftl

[Jamforthelamb]

Ok,

Here's the new voltages

Q1
C:6.18
B:0.60
E:0.0

Q2
C:4.31
B:0.56
E:0.0

Seems to me I still have a problem at the collector of Q2. These readings were taken with the originally called for 10meg resistor at R3, not the mod of using a 100k pot in the same position.

-jftl

[Jamforthelamb]

I also found that the cap I pulled out of the 2000pf (or .0022) bag is actually a 330pf. I changed it out to the proper cap, but the collector on Q2 didn't change any. I haven't ran a guitar through it yet to see if it helped the sound. Hope to test it tonight.

-jftl

[Jamforthelamb]

I changed the cap out, and now I have squeal again. It seems like it has the fuzz I was looking for now, but it's hard to tell with the oscillation/squeal problem. I think the problem is the collector on Q2 seeing to much voltage. What do I have to do to get that down ? I really would like to get this project done since I have many more to do (as always  ).

Thanks!
-JFTL

[smnm]

This thread made me look at my orpheum fuzz again, as I've never really been happy with it.
I checked the schematic with the vero layout and it seems like the layout has a mistake - the input cap C1 on the schem is 0.1uf, but 0.01 on the layout.

I don't know if this has any bearing on your problem, it might even make it worse, but I'm sure it'll make mine a lot louder
When I get a chance I'm changing that cap - or I might just rebuild it with the pot in place of R3

schem is in this thread
http://www.diystompboxes.com/smfforum/index.php?topic=52296.msg394802

[Jamforthelamb]

Hey All,
Still having this problem. I put the pedal down for a little while to take a break, but I've come back to it now just because I would really like to get it done. Any suggestions ?

Thanks!
-jftl

[John Lyons]

Print out the schematic and get a red pen.
Trace the schematic against your build.
Every time you come to a new part make sure it's the same on your build and mark the schematic in red so you can see what you have already checked.
For what It's worth, the stock schematic is pretty thin and out of control.  If you bread board it you can switch out parts and get it to sound a lot fuller and still get to cool out of control sound...

John

[Sir H C]

I have a couple originals.  If you have squeal, then I would suggest the smallest cap from the base to the collector you can get away with, this will kill, or at least lower, the high frequency gain of the stage.  Also try putting a big cap across the battery terminals, that might tighten up the battery supply lines and keep it from squealing.  Does it squeal with the gain back a bit or just full out?  Sometimes it is best to get it to the squeal point, then pull back to the no squeal as you are at the maximum gain.

[Jamforthelamb]

John: I already did that. I usually do my builds that way (with the red pen). That's how I found that the cap I had put in was the wrong one because the place I had ordered it from put it in the wrong bag.

Sir H C: I don't have the "gain" control on this (I believe it's wide open all the time), I removed it as a suggested mod from another thread. I also replaced the bias resistor on Q2 with a pot. I'll try your suggestions and post my results. Thanks!

JFTL

[John Lyons]

The Orpheum circuit I like is much different from the stock one we're talking about but in the stock circuit the low gain setting sounds is really  in contrast to the high gain setting.
I'd put the gain control back in personally. The lower gain setting is something I don't think I'd cut out completely.
Too much versatility to be without.

John

[Jamforthelamb]

Hi John,
I may try that once I get it fully operational. All the stuff for it is still there, so all I have to do is re-connect the pot.

JFTL