5F1 Champ w/ Capacitor Coupled One-Tube 6BM8 Reverb (Eric Barbour/Ampeg-style)

[pietro_moog]

cool, thanks.
about the reverb pot, i mean,do you have pin1 going on ground and the 33k resistor on pin3 (wired as a volume pot) or is this reversed (like it looks on the schematics)?

[dchang0]

If I recall correctly, yes, when facing the back of the reverb pot with the pins pointing upwards, the left-hand pin (pin 1) goes to ground. The right-hand pin (pin 3) goes to the 33K resistor.

[pietro_moog]

thanks. i was 99.9% sure, but i thought to ask you.
you were right, the cathode cap on the second stage is maybe too much.
tomorrow i'll finish this thing and i'll see what to do about it.

[pietro_moog]

do wanna ear the funniest thing? i completed the amp, checked 2 times, found a couples of errors, everything mended.
time to place the tubes. then my 5y3 fell. 1000 pieces.
now i'm here trying to find a JJ 5y3 on the net, but it seems there's none in EU, just in USA. wtf? the factory s in EU!
i'll have to use a TAD one.

[dchang0]

Ouch--sorry man! Hope you get your replacement soon!

[dchang0]

Got the 8FB3C1B tank in and installed it right away. There's no appreciable difference in tone due to the higher impedance. It's just a tiny bit less nasal-sounding (upper midrange) and a little smoother across the guitar frequency range. So those of you in the US that can't find the 8F tanks easily can just as easily use the 8EB2C1B tank that's much easier to find.

The long decay IS however, much nicer than the medium decay, so for those of you who want more "outer space" and "surf," he 8FB3C1B tank is the way to go.

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To those of you who wish to build this circuit and want less midrange out of the reverb, this confirms that you'll have to play around with the coupling caps (500pF, .47uF) to shape the tone to your liking since the improved impedance match did not result in tonal improvements as it usually does with some other reverb circuits.

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BTW, a special thanks to H. Park over at Belton/Accutronics. They were totally awesome in shipping me one unit for testing purposes quickly and exceptionally well-packed. It's amazing how fast I got the unit all the way from Korea!

[greekie]

Looking forward to read your comments when you're done guys!

[dchang0]

$20 shipping turned out to be for Global Express Mail, so it is priced appropriately and not an overcharge.

[pietro_moog]

so, i've made it.
i have to say i expected more of it. the reverb is very very subtle, but sweet. yeah, long time reverb surely will sound richer.
how can i add gain to the reverb? the grid resistor? anode?

and btw, i have tons of noise out of that and it's a pain. but maybe my build is unlucky.
do you have noise too?

you were right, the cap on the second stage cathode is too much.

[dchang0]

I've got nearly no noise, no hiss, no hum. The biggest source of noise during the build was the placement of the reverb tank. I believe it was Chuck H that suggested I try turning the tank various directions and moving it around, and the hum completely disappeared. It was coming from the power transformer.

As for the reverb gain, try messing with the grid leak resistor on the recovery stage (currently 220K in the schematic--I am running 470K in my build). Next, increase the size of the mixing resistor (currently 100K in the schematic) to as high as 3.3M.

All it takes is a little tweaking of the passive mixer resistors to get the level you want. I actually find there to be a bit too much reverb for me--I run the reverb pot at 5/10 most of the time.

Hang in there--you're only a couple of inexpensive resistors away from the tone you want!

[dchang0]

Okay, I got tired of trying to get my friend Larry (wicked awesome session guitarist) to take some time out of his busy schedule to record some sound clips, so I just noodled around some of my own.

The gear:

one 5F1 Champ with 6BM8 one-tube reverb w/ Orange Drop and Atom caps, carbon comp resistors, Alpha audio-taper pots, Mercury Magnetics output transformer, 8FB3C1B Accutronics tank, and 10" Weber Alnico Signature 10S speaker in a special Mojotone tweed cabinet with custom-cut 10" speaker baffle. Tubes are JJ except for the 6BM8, which is a new Electro Harmonix.

one 1980 Les Paul Custom with EMG 81 at neck and EMG 60 at bridge

one Shure WH30 vocal mic, pushed right into the grillecloth, about halfway between edge and center of cone

no pedals


Here's the guitar at 3/10 volume, amp at 10/10, reverb at 5/10--this is where I usually hang.

5f16bm8reverb1.mp3

Notice the low noise floor--you can hear the ambient room noise over the amp itself.

Here's the guitar with reverb at 0/10, amp at 10/10, guitar at 10/10.

5f16bm8reverb2.mp3

The amp is very dry without reverb, almost stale. That's most likely the EMGs.

[pietro_moog]

thanks man. now i see why fender uses a gain recovery stage after reverb.
i'll try a few resistors and a new pot.
so you don't use that much reverb, just a tiny bit to sweeten the sound,am i right?

last, yeps, my noise is coming just from the reverb stages. i'll try to move the tank.
thanks man, you're making this very easy to me.

[dchang0]

Okay, this is guitar 10/10, amp 10/10, reverb 2.5/10.

5f16bm8reverb3.mp3

This is guitar 4/10 (on the edge of breakup), amp 10/10, reverb 2.5/10

5f16bm8reverb4.mp3

[dchang0]

Guitar at 4/10, amp at 10/10, reverb at 5/10:

5f16bm8reverb5.mp3

Guitar at 4/10, amp at 10/10, reverb at 7.5/10:

5f16bm8reverb6.mp3

Guitar at 4/10, amp at 10/10, reverb at 10/10:

5f16bm8reverb7.mp3

This had a little more noodling including fingerstyle and a bit of guitar at 10/10 at the very end. What you hear is the over-the-top spacey-tone I was talking about--something you won't find in other one-tube reverb circuits because their drive current is too low to crank the springs hard enough. Considering how much spacey/surfey tone we're getting out of this, it means that the driver side is definitely strong enough for our needs--for more overall reverb wet-to-dry ratio, just mess with the passive mixer.

[dchang0]

LOL--wow, you must want a TON of reverb.

A an extra recovery stage may not be necessary to get the sound you want. Have a listen to the impromptu recordings I just posted. As you can hear, the wet signal is always just a bit below the dry signal in the mix, even when the reverb knob is cranked to 10/10. All you have to do is play with the voltage divider between the 100K reverb pot, the 100K mix resistor, and the little 33K send resistor hanging off the reverb pot till you get the ratio of wet-to-dry that you want.

You could try the Fender Princeton Reverb's choices of 3.3M for the mix resistor, 100K (linear) for the reverb pot, and 470K send resistor. That should really crank your reverb levels up! Be sure to add the 10pF capacitor in parallel to the 3.3M mix resistor to pass the high frequencies.