"AA1165" finished (finally)

[tubeswell]

Finally got around to finishing the Weber 6A14 kit I got last Oct (that I initially had a few teething probs with) this afternoon. (Its been sitting in my to-do pile for a few months while I've taken pecks at it now and again.) Anyhow its all finished and its all good.

Schematic attached (and soundbyte. FWIW the settings for the lead track were: vol-2, treb-7, bass-2, verb-3, speed and depth about 4 each, the rhythm track was dry - the thing was just dumped straight into garageband - with "RobO" drummer composed by moi - using the on-board mic on the mac - apologies for the recording quality and the musicianship )

The speaker is the Weber Sig 12S option with the kit and the OT is the 6k6 Pr Z that came with the kit.

The Weber PT got tossed out and replaced with a beefy NZ-made thing (values shown) with lots of iron (so it won't heat up - in fact I had it on for 2 hours this afternoon and the iron was only luke-warm). I reverted to the BFPR bias supply circuit (tapped off one side of the HT winding).

I did one of my own boards in the end and ended up changing the layout around quite a bit.

The trem is modified with the IRF820 source follower. The values are as shown. This gives quite a nice trem with no glitches.

Taking a cue from Merlin's excellent grounding article, the grounds are quite different from a BFPR ground return scheme. Every component on the board (and elsewhere in the amp) has its own separate grounding point going to the relevant filter cap ground return.

The filter cap can got tossed out and I put in separate filter caps and wired them with the grounds shown in the schematic and it is as quiet as a mouse.

There is an extra 10uF filter cap for the V1 tube (where the TS and vol pot grounds attach to).

The verb recovery triode and cathodyne triode and cathodyne driver triode grounds all go to the same 22uF filter cap ground. (The B+ supply for these stages is parallel with the B+ supply for the V1 stages.)

The 12AT7 grounds (incl the 12AT7 grid load resistor), and the RT secondary ground, together with the grounds for the entire LFO circuit, all return (by separate wires) to the same ground point (the screen node cap ground), because they all take their supply from the screen node.

[dai h.]

sounds good!

[Wombaticus]

Now that is one groovy sounding amp!

[imaradiostar]

Sounds good! I like the changes to the grounding scheme and the individual caps. The can cap has always bugged me on Fender amps.

Would you mind sharing your layout?

jamie

[tubeswell]

I haven't drawn up a layout (yet), I just worked off the schematic. I'll have to have a go at drawing the layout when I get around to it. Here's a pc of the board. The filter caps are in dog boxes on the underside.

[Wombaticus]

I haven't drawn up a layout (yet), I just worked off the schematic. I'll have to have a go at drawing the layout when I get around to it. Here's a pc of the board. The filter caps are in dog boxes on the underside.

Looks sweet, congratulations!

Incidentally, since we are both fans of trems coupled with MOSFET followers --- an interesting idea that will improve the tremolo performance even more is to include the IRF820 source follower in the phase shift loop. That way you are driving the phase shift loop with the low impedance output from the follower. Check out the vibroverb custom shop reissue (which did it with tubes, but the idea would be identical): http://support.fender.com/schematics...Reverb_0A4.pdf I'm gonna try this out next time I do a trem, and see if it helps it sustain really slow LFO speeds.

[tubeswell]

Looks sweet, congratulations!

Incidentally, since we are both fans of trems coupled with MOSFET followers --- an interesting idea that will improve the tremolo performance even more is to include the IRF820 source follower in the phase shift loop.

Isn't that what I did? Or did you mean something else? (Edit - Oh I see, they're running the RC phase-shift network of the CF cathode instead of from the LFO stage's plate. That looks nifty)

[imaradiostar]

Thanks for the pictures. I have some pt's with limited filament current so I may attempt one tube reverb and a solid state them with a mosfet oscillator and source follower. Isn't that what some newer fenders are doing?

[tubeswell]

tubenit is fond of one tube reverb, but I've never tried it. He sent me some clips a couple of years ago of some of his 1-tube reverb amps and they sounded nice, but I like more boing in reverb (which the BFPR has got plenty of). You really only need 100mA on the HT and about 2.5A on the heater (including the lamp) to make one of these go (and a 3A 5V winding if you want a 5U4, but you could do it with about 300-0-300 HT if you used FW SS).

[Wombaticus]

.... a solid state them with a mosfet oscillator and source follower. Isn't that what some newer fenders are doing?

Not sure about Fender, but I've done this as a power-tube bias wiggler trem with good results (after a period of tweaking).. To my mind there is almost no good reason to use a tube for an LFO, or for the follower. In my case, I used a LND-150 enhancement mode MOSFET for the LFO, since it can be biased almost like a tube, and direct coupled this to a STF3NK80Z (for our purposes, a bit like an evolved IRF820... it has the advantages of a fully insulated package and built in gate protection). I'd do the actual circuit slightly differently if I were to implement it again (the way I did it is somewhat subject to changes in gain as the circuitry heats up) , but I know for sure that it works and that the sound is very rich and swampy...and indistinguishable from a tube. Players who've tried out my tremolux 5G9 w/ MOSFET trem have uniformly been astonished when I tell them the dirty secret.