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Hello, I'm new to this board. I've built a couple amps (including a 6V6 18watt) but i'm always interested in new ones (such as the matchless EL84 amps). Anyways, I have a quick technical question. I recently finished a BF Deluxe build and while i like the clean tone the transition into OD is rather abrupt and slightly buzzy (which may be inherent in the amp?). Any ideas for smoothing this out? It's a stock BF non reverb.

Hey MooreDogger,

Welcome

What tubes and speaker do you have in there?

I have a westinghouse 12ax7, a westinghouse 12at7, EH 6V6s, and a BBQ 10A125. I've tried different tubes with no success.

I have a '63 BF AA763 Deluxe-Amp, and it's easy to find "the zone" on that amp where you can ride the fine line between almost clean and overdriven, so I'd say your complaint is not a necessary characteristic of the design.

How much capacitance are you using in the power supply? I wonder if it might be a little stiff? It's been a while since I've looked inside, or at the schematic, but I think the first two sections are 16uF+16uF, if I recall correctly.

hmmmm, i think that may be the only thing that i haven't tried yet to fix it but now that you mention it my filter cap values are a little high (40uF i believe). When i can get my hands on some lower valued ones i'll give that a try. thanks!

And get rid of those EH 6V6GTs and throw a set of JJ 6V6S or NOS 6V6GT Tubes in it. Deluxes, unlike Deluxe Reverbs are known mainly for their cleaner tone. Put a good Clean Boost in front of her.

CR ><>

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Right at the edge of breakup, Fenders are cool. Turn it up from there, and they can get farty with blocking distortion. Part of the problem is with the use of a LOT of negative feedback in the amp, which keeps things clean clean up to a point; beyond that point things degrade fast and can get farty and buzzy, or distort for half a second on the initial attack, and then clean up.

One great thing to try in your amp is wiring a 100K or 250K pot as a rheostat in series with the NFB loop. If you have an extension jack (generally a superfluous feature), you can remove the jack and install the pot in it's place on the back panel. Basically interrupt the NFB connection that is fed off the output jack and put the pot in series.

Turned all the way down, the amp is stock as there is no additional resistance in the NFB loop. From there you can turn up this pot to introduce additional resistance and lower the amount of NFB to taste. Less - feedback will allow a smoother transition to overdrive, in addition to introducing a bit more "rawness" to the mix. I have this on my 71 DR and had it on my old 68 SR (gone now).

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"A noble spirit embiggens the smallest man..." - Jebediah Springfield

I have an amp that I did that with as you turn it up you are increasing the resistance in the NFB. My main observation is that it behaves sort of like an extra volume control. The increase in volume as you turn it is rather substantial. The tone does get a wee bit less 'refined' lets say, as you are removing the damping effect of NFB. Jeff

Thanks guys! I'm gonna try your suggestions over the next few days. I got a chance to gig with the amp this past weekend and while it sounded really good clean and could get some usable sounds with pedals i much prefer the complexity of an amp that sounds amazing right at the edge of breakup. I'll report back when I get a chance to fiddle.

Voltages have a lot to do with the harshness. Try to get your first 12ax7 voltages under 150. Lower voltages on the 12at7 pi will also help the breakup. Are you running a 12at7 or 12ax7 pi. The 12ax7 is harsher. This will cost you some headroom volume but it will be smoother.