Guild Foxey Lady

[azrael]

I recently modified a couple of EHX Big Muffs, one of them was an NYC Reissue that I modded to Guild Foxey Lady (GFL) Specs. I skipped the Foxey Lady tonestack values, going with a flat-mid tone stack with a pot to control the mid scoop. I also added a Boss-style power jack. Another difference is the use of glass capacitors. I found several in them the right value for the .12uF caps for the GFL, thought it would be fun.


However, I am experiencing an extranormal amount of hum and noise. I've noticed the GFL has more gain than a normal BMP, as 12 o'clock is well above unity gain.
Is this a normal effect of the GFL? Is it just noisy? Or is there something else wrong here? I'm going to try a few things...a supposed "noise gate mod", which invloves putting a 100K trimpot in parallel with the 100K resistor coming off Q2, and I'm going to clean up the 3PDT wiring.

Any other thoughts would be appreciated, of course.

[John Lyons]

The noise is "normal" I'm not really sure how to remedy it though.
I've built 3 and they all had it. 2N5089s in mine.

[azrael]

That's what I feared. Well, looks like I'll be trying the "noise gate mod". I'll let you know it works out.

EDIT: I still have the stock transistors in this one...2N5088. I have some other transistors that would work in the circuit...some Fairchild SE4010's, I believe. You think those'll affect it?

[John Lyons]

It's something inherent in the circuit.
I know another guy who built one with the
same noise issue. Basically low level hiss
in my builds.
There really isn't much difference than
the other big muff variations so I'm not
sure where to go with this...

[azrael]

Yeah, that's the think that gets me. All the circuits are very similar. I also modified a current Russian BMP reissue into a Civil War reissue, and changed out a lot of the bad tolerance parts. MUCH quieter. I'm wondering, which component difference is it that makes this circuit so noisy?

I'm not much for understanding every part of how a circuit works, but I think I can see why it has so much more gain on tap. The resistors between each buffer/amplification/clipping stage is smaller in the GFL, so that would give it more output.


I've also built a Triangle-era BMP, and that one wasn't this noisy. It shares some of the same component differences with the GFL, too. Hmm...

[Tonemonger]

Try raising the value of the caps betwtween collector and base to 560pf , pretty sure thats why they are there in the first place.
Also try a small one across Q4 ( maybe 220pf).
If this is too severe (ie-chops off too much top end ) try a sequence like 560 for Q2/470 for Q3/330 for Q4 or viceversa.
I cant remember the values off the top of my head but I've built a few BMPs and little BMs and done something like this to all of them.
Lower gain transistors would probably help too , I mean hey it's not like it's , not going to fuzz !!

[azrael]

I thought those caps were strictly to block high end? How would they affect hum?

I may try lower gain transistors...Which stages need high gain transisotrs more? I would assume Q1 and Q4?

[Tonemonger]

Yes , you are correct on both counts !
Sorry , I did'nt read your post properly and notice the mention of hum and a boss power supply.
Therein lies your problem I'd say . The above circuit has no secondary filtering of it's own so I guess adding a diode and a largish value electro in parallel with the battery/supply terminals should fix (1N4001 and something like 220uF ?).
I'm sure there's better info. on the subject somewhere on this site than I could offer !
Regarding the transistors I think most old fuzzes could do with lower gains -they probably were originally .
Here there is 2 clipping gain stages chained together, The harder you drive them , the harder they are going to clip and ,your note attack gets squashed and your squared off wave has sharper corners.
It's like when you read reviews that say things like "I really dug the way this pedal opened up when I rolled back the volume control"
or something like that .
Why not just make them better in the first place ?
Well thats what the boutique market is all about really-hand selecting and 'tuning' each pedal.
IMO lower gain transistors is probably a good place to start and yeah stick the biggest in Q4.

[John Lyons]

I guess I misread the original post as well...
You should not be getting hum per se.
The noise I get and others have gotten is
hiss...more hiss that any other muff variants.
Not really a white noise but more like a pink
noise (a more full frequency rushing noise/hiss).

I don't believe the caps across the diodes will make
a lot of difference as there are a few other BM variants
with the larger 560p caps and they are quiet. I know
they will cut down on higher frequencies and his but
to the detriment of the sound of the Foxey Ladey.
Transistors... maybe but those other variants are quite
with the same hfe transistors.

Hmmm...

[col]

Go with the bigger caps across the BC junctions of the transistors. I just held small value caps across each of the existing ones, increasing the value until it cut down the noise and then soldered them onto the existing cap. As you are adding them in parallel you are summing the capacitance. You really do need to use the minimum value possible as they significantly affect the overall tone, sustain and output. I also cut down wire lengths to a minimum and grounded everything to the back of one of the pots, that really made a big difference.

Good luck, easily the best of the BM family IMO

[Gus]

Hum and noise,  Hum can be caused by circuit layout and grounding and power supply and not being in a metal box.  Noise can be shielding ,power supply, transistors (sometimes you can get a noisy transistor(s)) related.

The BMP types often have two diode limited middle stages this tends to limit the max peak to peak to the tone and final gain stage.   Different tone control values load the 3rd stage differently also look at the final stages gain.  The BMP schematic linked in the first post has 22K resistors in the tone control and a final gain stage of about 10K/2K or X5 inverting. The GFL has 33K and 100K resistors in the tone control and a final gain of 12K/3.3K or about x3.6 inverting.

The way the BMP is designed the transistors should bias up fine with higher Hfe ones

Now the gain in the first three BMP circuits is a combination of the collector/emitter resistors and the C to B feedback network and the base to ground and series input resistors in Q1s case the source Z before it is a part of the gain setting.

Lots of things that can be adjusted in a BMP type circuit.

[azrael]

To clarify, I've tried it with a power supply (not Boss, I used the 2.1 Boss style jacks...but I power my pedals through a super quiet Voodoo Labs PP2) and a battery. Identical results. It's all grounded right, and it's in the enclosure. And the pedal wasn't this noisy before (Reportedly. When I received it, it was broken, haha. Lotta snapped wires, etc...)

Tonemonger: Since I am using a regulated and isolated power supply, I would assume the power filtering is not necessary? I will try my SE 4010's in Q1-3, then, and leave Q4 alone.

John Lyons: A rushing kind of wave is a good way of putting the noise. That's what it kind sounds like. It bother me simply because of what you said, it's more a full frequency thing; it's very noticeable. This pedal is not for me, but personally, I wouldn't use this at a gig ATM....way too noisy.

col: I checked with a multimeter, everything that should be going to ground IS going to ground. However, I suppose a star ground method can't hurt. I don't readily have a lot of small caps like this available, so I may have to figure out something else before I'm prepared to change the tone of the overall circuit.


Maybe it's because the GFL completely removes one of the high pass caps? That's a big difference between it and other BMPS...Hmm...I find that's integral to the sound, though....

[John Lyons]

Not all the BMs have that cap on Q1 base to collector) so I don't think that's it.
I don't think it's something "wrong" as my 3 builds have the higher noise and
a freinds have the same thing. It's something to do with the circuit and the higher
gain and circuit deviations for other big muff circuits.

John

[azrael]

That's true. It's got A LOT of gain on tap with the volume control.

I tried the "noise gate" mod I mentioned earlier...that trimpot on the 100K resistor off Q2. It works. Much quieter. Much of that "insane gain" we mentioned is gone, and we're left with something more along the lines of a normal BMP. However, it still sounds like a Foxey Lady.

Thoughts?

[azrael]

Just an update, got them back to the owner, seems to like 'em quite a bit. The Foxey Lady's noise gate mod worked like a charm.

[John Lyons]

So you just replaced the 100k with a trimpot and set it until it gates?
If not then can you explain..
thanks

john

[azrael]

Actually, I just soldered it in parallel with it, on the side of the board with the traces. This allows it to be accessible from the NYC's battery shelf.

However, I suppose you could just replace it. I set it to taste, until the noise was manageable, with volume and sustain set to noon.

[John Lyons]

Hmm ok, so it's a 50k resistoance at max now...
I'll have to try it.

thanks

John

[azrael]

Alright, cool. Let me know what you think!

[bloxstompboxes]

I realize this is an old thread but I have a noise issue with the 3 knob foxey lady. Mine is only on the tone control and is not scratchy but maybe staticy? I only hear it when I turn the tone control and the noise is pretty steady. It stops immediately when i stop turning the knob. I immediately thought it was a bad pot and swapped it out but the noise is still there. Anyone have any suggestions as to the culprit? I used the schematic from fuzzcentral to build it. I am at work now but pretty sure I didn't do any part substitutions. It otherwise sounds great. Is this just an inherent problem with this pedal's design? Thanks in advance!