Sound differences from different dual op amps in SS amps

[Enzo]

How can we suggest things when we do not yet know what you mean by "better."?

[Slobrain]

More tube like with a sweeter tone... more natural sounding as opposed to SS... lol

[J M Fahey]

More tube like with a sweeter tone... more natural sounding as opposed to SS... lol

Ouch !!! , still somewhat "poetic" definitions

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More tube like

No way, tubes and SS clip VERY VERY different, you will not get an inch closer by swapping parts, even by changing their values.

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a sweeter tone

same here .
Most you can do is to soften annoying attack/icepick/harshness by carefully cutting a little top end, and as Phatt from SSGuitar found and experimented, cutting some top before distortion also helps, I guess by avoiding such frequencies being hard clipped.
But this must be done very carefully, it's very easy to end up with dull or lifeless sound, not what was expected.

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more natural sounding as opposed to SS

Well, here's the opposite way: ss is far more transparent, distorts less, has flatter response, wins on all objective parameters, it's tubes which lie to us ... although often in a flattering way ... but that's something else.

Now to the main point: I'm happily surprised by your interest on learning and improving your amp, so I suggest you download read and reread Teemuk's book on SS amps, the most authoritative and well researched book about SS amps in the Planet, no kidding.

Among a lot of other very good stuff, you'll find lots of examples and analysis on circuits and ways to improve sound.

Book about solid-state guitar amplifiers

[Leo_Gnardo]

More tube like with a sweeter tone... more natural sounding as opposed to SS... lol

There's enough juice in the power supply to run a couple of pre tubes, I'm sure. I think you see where I'm going...

Juan, I agree with you on Peavey's saturation control, that's exactly what it's meant for. Besides whacking up some gain, there's a pair of back-to-back silicon diodes in there for an authentic fuzz effect. It does sound kind of "hard." Here's a Leo Gnardo mod secret: just bridge those silicons with a pair of 1N34 or similar germanium diodes. That'll soften up the fuzz a bit, make it more ear-friendly. One of my clients went head over heels for this tone.

History of op amps will show you Philbrick's tube op amps of long ago. Definitely too big to sub into an existing amp, plus their design requires a negative 150V supply. I think you'll find an article in one of the Vacuum Tube Valley magazines about these.

[Slobrain]

Hey Juan,

I just uploaded the book on SS and will read it. Actually I'm not trying to get the distortion channel sounding better but the over all clean sound of the amp. I use pedals to get my distortion and just use the amp loud and clean. Yes, it is very similar to a bandit 65 as I've looked over both schematics and only see minimal changes in the front ends of both. This amp clean doesn't sound as good as the bandit 65 clean so that was what I was wanting to change. I know I'll never get it to sound as good as my Marshall or my old 67 Fender Bandmaster which has been modded to a louder and cleaner amp. I'm just shooting for easy improvements to get it a little more pristine clean.

Regarding changing out the diodes that clip the distortion channel that Leo mentioned, sounds like using the germanium diodes would change it to sound a bit more like a MXR distortion + which isn't a bad idea if I decide to get to the distortion channel later in time.

Thanks for the input guys, its helped a lot. I guess I'll have to look at the schematics a bit and try to see where I can add some twists of my own.

Cheers

[Slobrain]

There's enough juice in the power supply to run a couple of pre tubes, I'm sure. I think you see where I'm going...

Juan, I agree with you on Peavey's saturation control, that's exactly what it's meant for. Besides whacking up some gain, there's a pair of back-to-back silicon diodes in there for an authentic fuzz effect. It does sound kind of "hard." Here's a Leo Gnardo mod secret: just bridge those silicons with a pair of 1N34 or similar germanium diodes. That'll soften up the fuzz a bit, make it more ear-friendly. One of my clients went head over heels for this tone.

History of op amps will show you Philbrick's tube op amps of long ago. Definitely too big to sub into an existing amp, plus their design requires a negative 150V supply. I think you'll find an article in one of the Vacuum Tube Valley magazines about these.

So changing the diodes to the 1n34 did this make it sound similar to the MXR distortion +?

[Leo_Gnardo]

So changing the diodes to the 1n34 did this make it sound similar to the MXR distortion +?

I can't say for sure sounded like MXR dist+ but it did for sure sound 'softer', not as harsh as typical Peavey saturation. As I recall the MXR is kind of barky too. I sure didnt' have one to compare side by side.

Took less effort hitting guitar strings to get into the fuzz zone, too, hard to play quietly enough to avoid it. Germaniums break over at 0.3V while silicon 0.6V. That explains the ease of getting fuzzy, and why you can just tack the Ge's over the siicons, you don't have to remove them, saves a lot of hassle hauling circuit board out of the amp. The volume level won't get high enough to hit those silicon diodes with the germies in parallel.

If anything it's reminiscent of very old fuzzbox tones from the mid 60's. All it takes is a pair of Ge diodes & a couple gator clip leads, you'll know in 5 minutes whether it's for you or not. If your ears agree, warm up the iron & solder 'em in.

[J M Fahey]

They are both "Op Amp at max gain possible driving 2 diodes", like 90% distortions out there, but the Peavey uses Si diodes (louder and harsher) , uses wider band 4558 (also perceived as harsher) and, most important, makes no effort to tame that, so the following amp gets the nasty squarewave as is.

The MXR Dist+ uses narrower bandwidth (at max gain) LM741 , uses Germanium instead of Si diodes for lower level and more rounded shoulder, but MOST IMPORTANT AND ALWAYS IGNORED : strongly cuts top end by adding a 1000pF cap in parallel with diodes and another in parallel with input .
In my book 2 cascaded 6dB/oct filters in series, even if not contiguous, still add up to 12dB/oct , which combined with 741 own rolloff add up to 18dB/oct well within the audio band and that is easier to hear, much more that expected differences in the tens of kHz range.



Yet people waste tons of electronic ink and paper worrying about pedal colour, script vs. block logo, whether a carbon zinc battery is better than an alkaline one , 741 brand or vintage, etc.

Oh well, as many Church Fathers noticed, over 1000 years ago: "the sin is its own punishment".

[pdf64]

The thing about that 1nF cap is that the source impedance from the diodes (when signal level is such that they're clipping hard) will probably be quite low (obviously way less than the 10k feeder resistor), so the effect of the cap shouldn't be as much as it seems to be in practice; any thoughts on that?

[Slobrain]

Well I installed 4 NE5532P dual ops in the amp tonight and I did notice it somewhat did improve the tone slightly. I could only try this at low volume not to get my neighbors mad. Maybe tomorrow I can crank the amp up a bit more but it seemed to slightly improve the tone stack and the cleans are a tiny bit more pristine. I cant really tell though until I put the amp thru some volume but the harshness wasn't as pronounced as before. For a 120 watt amp it just doesn't seem to be putting out all that much volume. Not sure why? but for an amp that's already 33 years old I cant complain. The main reason I bought it was someone loaded it with a 1974 made celestion creamback and I wanted the speaker for another use.


I went ahead and ordered some OPA 2134PA to try but these will take a while to get as I ordered them from japan.

[Leo_Gnardo]

I'd have to say that's a fair test and review. Peavey & lots of other manuf's state their buitar & bass amp power at some unknown distortion level, likely 10 or 20% distortion (well into clipping) not some fraction % like hi fi. Because you guitarists luuuuv distortion, don't you? Measure it properly, just a pinch below clipping, you'll probably find it's really under 100W.

Juan's comments very much to the point about filtering within fuzz & OD boxes. ( I know Enzo . . . but the matter keeps coming up. And it DOES apply to amps as well as kickboxes. For tone differences in amps, not so much wacky collector item prices.) A slight change in component value, even if it's just one - you have a different tone and the chase is on. At one recording session, the record co's A+R guy came trotting in with his newest buy, an authentic TS808 he just dropped $450 on. The artiste, a well known rock star who DOES have his ears on, compared it side by side with the latest version, after Mr. A+R left, so he wouldn't feel insulted if there was a bad review. Rockstar said all it took was a tiny move of the tone control, and one sounded exactly like the other. There's the diff between a $450 and a $75 box. 2% of the turn of a knob.

Here's today's offering for your comedy entertainment: Klon Centaur gold pro overdrive

[J M Fahey]

The thing about that 1nF cap is that the source impedance from the diodes (when signal level is such that they're clipping hard) will probably be quite low (obviously way less than the 10k feeder resistor), so the effect of the cap shouldn't be as much as it seems to be in practice; any thoughts on that?

Good catch.
I also spent many nights thinking about the same, and yes, it does not affect much the already clipped signal, for exactly the reason you mention, but it works before it clips (meaning at lower levels) so it behaves as if it were in an earlier stage than it actually is.
Many think that its effect shouldn't be important, but Phatt in SSG experimented a lot on that and found that restricting highs before distortion also contributed to smoother sound.

I guess, may be wrong, that clipping those highest harmonics is not needed to get more sustain (the main effect of using a distortion) and only "muddy the highs" or "intermodulate highs too much" or some other useless effect, so keeping them out actually helps.

It still adds to the input 1000pf to get 12dB/oct pre-distortion-filtering .

Op Amp rolloff is also pre-distortion.

I keep ceaslessly going back and minutely analyzing old, classic, very simple circuits, "the Truth is there, often in plain sight" but we fail to recognize it.

Sometimes it takes some Lateral thinking or looking at circuits with very naïve, Childlike eyes, without preconceptions.