Fuzz Head with white noise?

Hey, I just picked up this used Keeley Fuzz Head for a buck 30 on ebay. I'm playing it through a SFDR. I just bought this amp last month and am going through a new pedal selection process. From my limited understanding, I think Fuzz pedals are sometimes a bit touchy with these amps, but this pedal, alone in line, has a "white noise" when activated. Not a hiss, not a hum, but WN. Not too awful, but I'd like it clean and it's the same in both normal and vibrato outputs. Is this the norm for a fuzz pedal with a DR?

That sounds odd. I had one for a while and don't remember any odd noises.
Inside is a trim pot to adjust the gain level. It may be turned too high up.
Axis29 has one and his trim pot seemed to behave different than the one I had so there may be some variability as to where to set it.
As a start, try 1/2 way up.

Thanks Lance. The trem pot was max'd out. Rolled it back to 1/2. With the pedal plugged into the normal channel, it sounds great. In the vibrato channel, still too much WN. The vibrato channel on these DR has a cap on the volume pot that makes it more treble-ie. I suspect that this may be the issue of running a fuzz pedal though these amps, at least in what little I've come to understand. I'm going to turn this over to Amp Central and see what comes up, thanks for the help

Lance beat me to it.....................:mad:
Enjoy it, I've had one for many many years, the one's without the graphics
http://img.photobucket.com/albums/v209/Rojelio/DSCF1633.jpg

I'll admit I do get some white noise from time to time. it usually has to do with the power source though...

Basically you are pushing the gain levels to the max. So, it kinda seems logical. The difference between the two channels on the DR are also tied into gain as well. The Vibrato channel has another gain stage... At lower gain levels, It is cleaner, but really the power source and power filtering make all the difference in the world.

I will say that used live, the level of noise is usually well hidden by the rest of the band. And it behaves so well at higher volumes and in live situations, I am more than willing to put up with any hiss or white noise I encounter!

I'll admit I do get some white noise from time to time. it usually has to do with the power source though...

The "final transistor stage" on most traditional style fuzzes is typically a huge source of noise, and it is also elevating the noise floor of any stages prior to it.

IDK what the specific circuit is in the FH, but I'm assuming it is probably Fuzz Face derived, especially if it is swapping out silicon and germ transistors. If it is just a pair strapped together like they are in the FF, it is pretty straightforward to do with some switching. Actually, it is almost as easy to simply have strictly a silicon and germ circuit, and just toggle between the two.

But regardless of the specific circuit topology, the final transistor is usually simply very crude by modern standards. Even with modern filtering tricks (internally), you are still at the mercy of the transistors selected in many cases. The transistors that are chosen for the "mojo vintage" vibe are typically noisier. Part of the appeal is a lower gain bandwidth, which translates to a higher noise floor that the transistors are incapable of "offsetting."

A trimpot was mentioned - there is a singular resistor in a FF that is typically modded from a stock value of around 330 ohms up to 680 or even 820 ohms to let you get the fuzz up to unity gain w/o having to really crank the level control. But there is another resistor that has to be changed to keep the bias proper, and exceeding a certain voltage will really ramp up the noise floor.

...Despite the standard biasing that is typically adhered to, which is between 4.5VDC to 5VDC on the "collector" terminal of the last transistor, a bit of noise can be eliminated by dropping the voltage lower. In the case of something like the EJ sig FF, it is biased at only 3VDC, and the noise floor is super low. As a plus, you get a much stronger fuzz effect, with more harmonics and those chewy octave-ish overtones.

That's just a basic rundown of MANY fuzz peculiarities. Even the Big Muff has a 4th transistor that is necessary simply to recover volume loss after the tone circuit. Depending on the transistor at "Q4," you can have a more or less hissy Muff fuzz.

So, the good news is that the FH does indeed have the trimmer in it, and cranking it down will kill some of that noise.

Aside from mods, transistor swaps, or modernizing the internal filtering, there is usually little that can be done.

...the DR.....

Even with the bright cap snipped, a DR still has a single 12 that can be a lot more harsh with a dirty signal, and it is obviously easier to run the power amp out of headroom versus the bigger BF/SF Fenders. The mid-sucked tone stack can also cause the bass to "compromise" the treble a bit. It is usually not an issue when the amp isn't run with dirt or fuzz pedals, but things can get ugly fast when they are used.

If someone uses pedals with a DR, I almost always recommend at least trying the following:

- put a 12AY7 in the 2nd preamp tube slot to smooth the gain of the vibrato channel

- try a darker/softer speaker in place of any traditional speaker that is really bright, beamy, and directional. You could try a spacer on the baffle if you want to keep the stock speaker, but it might just be easier to try something with just a more mild treble response. It rules out a lot of straight up C12N-derived speakers, but there are so many cool 12's to try that you might find something that is a much better fit...if you are a pedal user.

If you don't have an issue with someone finessing the amp to clip the bright cap and do some other internal maintenance, you may want to suggest that they replace the coupling caps from the phase inverter to the power tubes, from the oversized .1uF down to .047uF. You won't lose one shred of the DR magic, but it will almost always really improve the response, IF you use pedals.

While it may not be necessary, if someone is in there swapping that pair of caps, it still might be worth it to have the "input cap" on the phase inverter of a SF DR changed from .01uF down to the old BF value of .001uF - that will help quite a bit, too.

The bottom line with the DR is that it is really just pushing the limits, even without using pedals. The power section doesn't have the punch of the bigger Fenders, and the single 12 has more surface area to move than a single 10 in a Princeton Reverb, nor does it benefit from a pair of speakers like with the VR or bigger amps.

...With a normal dirt box like an OD, you can run a comp in front to smooth things out. But with most traditional style fuzzes, that simply doesn't work. If anything, putting almost any pedal in front of a trad fuzz will usually wreck things in a not pleasant way. It's not always the case, but just something I would suggest not adding as another tonal kink. It's easy to forget about this with all of the newer (relative to old fuzz designs) types of pedals.