SS vs Tube Reverb Driver and Recovery. Preferences?

[bob p]

AC15C1 Schematics (Rev 2).pdf

What's Up with the current Vox AC15C1?

I had recently given some thought to buying one when I had a time-limited $300 coupon for gear from GC. I looked around for a schematic to verify what Vox is currently selling as an AC15 and I had trouble finding them from Vox. The best schem that I could find was the attached schem that was drawn independently. The opamps in the signal path gave me pause. sigh.

Look at the signal path. Vox is using a solid state tremolo oscillator, which doesn't seem like a bad idea to me. It's probably more reliable than a tube based oscillation generator, in addition to being cheaper to produce. Since it's not in the signal path I don't see it as a problem. In many ways this could be viewed as a step in the right direction, using SS components as needed to provide reliability while supporting a tube signal path.

Then I noticed the opamps that are used to mix the Normal and Top Boost channels (U1A on page 1) and drive the reverb unit (B) and to provide reverb recovery and drive into the PI (U5A on page 2).

We've seen the use of SS reverb send and recovery before (think cheap Fender amps).

Not having been fond of any of the cheap amps that I've played with SS reverb drive/recovery, and being an old fart who's used to tube based send and recovery for the spring reverb unit, I thought I'd ask people about their opinions on the sound of the opamp-based reverb drive/recovery units.

Does anyone make one that sounds good? How do you think they compare?

I was giving some thought to buying an AC15 just for the hell of it, but the opamps in the signal path kind of killed that vibe for me. It seems that the amp companies are committed to doing this with their low-cost / entry-level amps, and I've never liked the tone of their reverb units. Unfortunately, it's getting harder and harder to buy a low-powered all-tube amp. It seems as if the manufacturers are equating low power with low cost, and pushing us into a corner.

[stokes]

Not a fan of these SS reverbs but I'm also not a big fan of onboard reverbs in general,either.I have a couple of outboard 6G15 clones I've built,so the built in reverbs,even tubed,dont do it for me.When using the onboard reverbs I always feel that its inadequate anyway,so maybe the SS is just another trade off.I think that maybe the fact that we are so connected to tubes,"tube snobs" if you will,we tend to be biased against anything SS and maybe the SS reverbs arent as "bad" as we think.

[bob p]

I don't think it's my imagination -- I think that the SS reverbs are as bad as we think -- I think that the solid state reverb systems just don't sound as good as tube reverbs -- especially if they get overdriven. SS circuits just don't clip as softly as tubes, and I can hear the "edge" that clipping the opamp it puts on a mildly clipped tube signal. I guess that puts me in good company with the tube snobs.

I agree with you that the outboard 6g15 type reverb units in front of an amp do sound better than the AB763 reverb units. I'm thinking that my next amp build is going to be built in a BF/SF type chassis, but the normal channel is going to be replaced with an onboard 6g15 that goes before the main amp, like the Vibro-King.

I was really hoping that it would be possible to pick up an inexpensive amp to leave in a practice space that has decent reverb. i haven't found one yet.

[Justin Thomas]

I'm thinking that my next amp build is going to be built in a BF/SF type chassis, but the normal channel is going to be replaced with an onboard 6g15 that goes before the main amp, like the Vibro-King.

DO EET! EET'S ZEE BEEEESSSSST!

More to your point, I don't care for the SS reverbs either. I've not made a point of trying the pedals (except for the Boss - bluh), but the ones in "cheap Fenders" just don't do it for me. It reminds me of the reverb that they add to mixing boards for vocals... too short, too long, to clean, too hifi, too digital, too... sterile. I kind of like the idea that I can "play" the reverb in my Prosonic a little bit. But MY favorite reverb was the ones that came in my several vintage small Ampegs - a 63 Reverberocket & 67 Reverberocket II. I never had to turn them past 12:00, but they were just LUSH. Got mushy under driven or fast playing, put for serious ambience on a slow passage, wow... my Dual Showman Reverb sounded bigass through 2x15s, too. Why did I let that amp go?!?!?!

That said, one place I DO think SS reverb can work is in a full-on SS amp... <IF> they do it right, which of course adds to the cost...

Justin

[J M Fahey]

It is not a Tube vs SS thing but manufacturerīs greed/cheapness which results in lack of drive.
Reverb tanks, like some Ladies, like to be driven hard.
A classic Blackface/Silverface parallel 12AT7 provides between 1 and 2 W RMS and is the reference standard.
Fender standalone Tube Reverb uses a power pentode (which is "stronger" than a triode) offering 2 to 3 W RMS and is king of the hill.

Early SS reverbs used boosted Op Amps and were very good, think Lab L5 , which must have easily fed around 1W RMS or more into a tank, but later manufacturers saw they could get away with dropping the mid power (TO126/TO220) or mid/low power (TO92) boosters and settled on puny absolutely inadequate unboosted Op Amps.

A TL072 or similar used as a "power" amp, which of course it is not (they can barely drive headphones) provides some ludicrous 50mW RMS or so, definitely not even 100mW RMS.
Mediocre results are guaranteed.

But again,itīs a cheap design problem, not Tube vs SS .

Early Roland and Yamaha amps used an 8 ohm tank and a car radio type chipamp which could also drive them hard, with good results.

On the contrary, many Tube designers cheapened and washed out the classic Fender design, by using a single 12AX7 triode (quite inadequate) as power amp, instead of way higher current parallel 12AT7 ... I guess they must have less than 500mW available ... so still being "tube" they canīt meet classic Fender reverbs.

A colleague in SSGuitar, PHATT from Australia, designed and built a killer reverb circuit ... +/-35V rails and a couple TO220 transistors (think TIP31/32 or similar) which *smashes* the springs, you can hear the reverb sound coming out of the amp chassis itself, no speakers involved

Just by faint memory, I think early Kustom reverbs were also boosted Op Amps driven ... and those amps werenīt laking in Reverb at all (check CC Revival records).

[Justin Thomas]

I'm willing to admit that maybe what I don't care for is the execution...
Then again, I still hate digital just because, well, digital.

Justin

[J M Fahey]

Oh, digital is completely different.
I was talking springs

[g1]

I agree with JM that it may not be 'tube reverb' we like so much, but particular tube reverb circuits, specifically the Fender 'classic' transformer driven ones.
I mention the transformer part because even the Ampeg V type use a 3.5W driver tube and I don't think it compares with the classic Fender reverb. However, it is capacitor coupled into a high impedance tank, so maybe it is not getting the higher drive?