FREDs? Replace 1N4003 rectifier diodes?

[Buckeye Sound]

I've never had to mess with rectifiers because they usually aren't an issue. My Music Man amp uses a bridge rectifier consisting of 4 - 1N4003 diodes, DO-41. I understand that I can replace these with FREDs which are faster? I'm trying to make more power available for the overdrive section of the amp. I've already upped the caps nearly 2x.

So, which FREDs should I use?!?! Are they drop in replacements. Please teach me about FREDs!!!

Thanks

PS here's a link to the schematic for my amp, and I'm trying to get faster power to V1. My amp is most like the last revision at the bottom of the scroll.

http://www.ernieball.com/mmonline/te...ps/1650-rd.pdf

[aletheian]

Huh? What are you trying to do? I think you are barking up the wrong tree there. Tell us your exact goal and maybe we can figure something out.

[Buckeye Sound]

sure. this is great amp. two channel one clean and one designed for overdrive with a 12ax7 tube. The overdrive channel isn't real usable because the lows are flabby and not well defined. I've added filter capacitance and changed plate/cathode setup on the 12AX7 to mirror Music Man's final revisions, but still not real usable (imo). So, someone on the Music Man site said he upgraded his rectifier using FREDs and this helped this problem.

[aletheian]

I don't think that FREDs are really going to do anything there, but they can't hurt. You can get them at just about any DIY tube audio place or mouser, Digi-key, etc. Just make sure the ones you get can take the voltage. A fred is just a fast recovery diode, so the switching time (in nanoseconds) does not produce RF hash noise. The 1n4003 bridge if just for the signal opamps, so they are very unlikely to efect the tightness of the lows.


Clarity in a dirty channel is all about controlling the low end before it goes to a clipping stage, so here are some simpler changes I would experiment with first:

--Solder a 100k resistor in parallel with C9 between the tube stages. That will give you a -3dB shelf at 150Hz and clean up the lows a bit.

--If you are using the version with the 560k/330k plate resistors, then I would tweak the cathode capacitors to shelf off some lows too... start at say .47uF for C10 and something a little bigger then that for C48--maybe .68uF and go from there. If you are using the version with grid leak bias and the huge 2M or 4M plate resistor... well then you are out of luck as far as sculpting the lows there.

Those are easy mods to do, and if you don't like the sound, you can undo them just as easily.

If i personally were trying to clean the low end of that channel up, I'd sculpt the EQ going into the tube stage a bit more (The capacitors in the feedback loop and ground leg of the inout opamp are to imit the highs and lows, respectively...lowering C1 will lower the bass, and raising C2 will lower the highs) and rewire the tone stack with a mid control, but that would change the tonalitu of the amp, and the sound of the clean channel since the opamp feeds both channels.