Best sounding SS amp you all have encountered?

[Steve Conner]

R.G., I beg to differ about the output impedance. (Maybe we should take this discussion to the new solid-state forum that doesn't exist )

I think it will basically be the output impedance of the transistor as a common emitter, which tends to infinity. Ie, the output stage is a voltage controlled current source, and the control voltage is what comes out of the driver secondary winding. But the negative feedback through the bias network will lower the output impedance.

As for the requirement for tight coupling, I think that may be because the leakage inductance of the transformer is in the output stage's local feedback loop, betwee the bias network and the base. If it needed multifilar winding, I guess it would be about impossible to use a tube driver like I suggested.

Arthur B, I have an interstage transformer for a Fender 300PS kicking around here. (And an output transformer too, evil cackle.) But the ratio of a tube interstage transformer is totally wrong for a TV output stage.

[daz]

Yeah, i heard that too about the pre being modeled after a rat. And actually i can believe it because it has that sound to a degree tho more refined so that it's tighter. I always felt rats are fantastic sounding when used right and when they are tweaked a bit. But they're very tempermental in a few ways including which amp you use and how clean the amps is. The pignose sounded to me like a rat in it's ideal enviornment with a few tweaks. I think i also recall Rivera being involved but memory is kinda foggy. I remember also having a lab series and a boogie MK3 at the same time and setting them side by side and trying to get the boogie and LS to sound as thick as the pig, but nothing i did would let them get close. That was one amazingly thick sounding amp.

Hey Daz,
I have read that either Lee Jackson or Paul Rivera maybe built this amp for Pignose. Lee worked there when the crossmix was put out in maybe 1978.
The crossmix was supposed to have a distortion circuit similar to a rat pedal for the thick sound it had. Yeah, those 70's pacers were pretty aweful sounding, I had one too

BTW, This thread is turning out nice, many cool posts on old SS maps.


SLO

[TD_Madden]

My Gibson G-55 ('71 I think) has a decent tone......I have a Reverend 1250 in it and it's not TOO SS'y.....not real loud, either. The funky parts (phaser and harmonic-something) I just keep turned off...even the single-spring internal reverb isn't all that cheesy......

[gtrboy]

Ampeg Ss For Shred, Lab L Series For Rock, And A Roland Jc120 For Clean.

[RickyD]

Anybody else play an Acoustic 150? That was a very powerful ss amp, super cleans. And the for bass players among us, I suggest a moment of silent respect for the Acoustic 370, which was the fattest baddest bass amp on the planet until the SVT came along.

Worst SS amp? Late '60's, I think, 1967 Gibson GSS100. Very trick looking with 2 - 2x10's, sounded terrible.

[R.G.]

R.G., I beg to differ about the output impedance. I think it will basically be the output impedance of the transistor as a common emitter, which tends to infinity. Ie, the output stage is a voltage controlled current source, and the control voltage is what comes out of the driver secondary winding. But the negative feedback through the bias network will lower the output impedance.

Differ away. I never thought I had the only possible interpretation of a circuit.

But... the thing is an NPN totem pole with a load between one emitter and one collector and the ground of a split supply. The driver secondaries float with the emitters. The top half has the load tied to the emitter of the upper transistor and a fixed upper voltage supply between the ground end of the speaker load and the collector of the transistor. Even given that the base drive winding floats, I think that makes this section an emitter follower.

The bottom section is more problematic. That might well best be seen as a CE stage.

Probably the reason this amp sounds good is that we're both right about half of the output stage and the differences in output impedance from top to bottom make for asymmetrical drive on the speaker.

As for the requirement for tight coupling, I think that may be because the leakage inductance of the transformer is in the output stage's local feedback loop, betwee the bias network and the base. If it needed multifilar winding, I guess it would be about impossible to use a tube driver like I suggested.

Yep, there is no question that the problem with the tight coupling is that the leakage and self capacitance of the driver transformer is added to the forward response of the amplifier. A couple of references early in the search were pretty emphatic about that.

Actually, I think the driver transformer isn't all that hard to rewind. If I ever get a burned out one, I'll give it a go. All you really have to do is to figure out the number of turns on primary and secondary and make up your multifilar wires out of a number of lengths of magnet wire in parallel, then wind away.

I've experimented with sneaking ten turns of fine magnet wire into an existing Beatle driver transformer and measuring the voltage on it while the primaries and open secondaries were driven. That gives me a reasonable grasp of the turns involved. I'd have to look it up, but as I remember the primary was about 300t, the secondaries about 60t each, making for a penta-filar windng. The way to make a new one would be to make up a hank of wire of five sections of smaller magnet wire and two sections of six-sizes-bigger wire for the secondaries, twist that just enough to keep the wires together, then whip on 60t of the bundle. After that it's just phasing and connecting the primary sections all in series. The window usage will be poor for that style of winding, but it gets it to be multifilar and probably the wires would squash into a rectangular windonw.

Probably.

[Steve Conner]

Even given that the base drive winding floats, I think that makes this section an emitter follower.

Well no, I say that it's the very fact that the base drive winding floats, that makes the top section a common-emitter stage just the same as the bottom one, with the same high output impedance.

The floating winding means that an output stage section only has two terminals for current to go in or out. Therefore, it can only have one impedance between those two terminals: it can't matter which end you look from.

Therefore both the top and bottom sections must have the same impedance, which I say is that of a common-emitter amp with some local feedback.

This also implies that a complementary version with NPN and PNP transistors would behave pretty much the same as the original, so we might as well use all NPN.

I also think the leakage inductance in the _local_ feedback loop between collector and base could be what makes the transformer so critical. Or maybe the transistor driver stage in the TV amps leads to a much higher loop gain than a tube driver, what with transistors having so much more gm than tubes. After all, the Fender 300PS has a feedback loop around two transformers, without much in the way of interleaving, and it's stable.

Anyway, you have me fired up enough to try building this hybrid output stage now!

[Slobrain]

Hey Fellas,
cool thread, gets me inspired just reading this stuff

Well I got the Peavey Renown in today from an Ebay auction and boy I had to clean it up, looks like a rat was living in the back. LOL

well it fired up ok and one problem I found was the scorpion speakers had come unglued from the base of the speaker basket so I'm hoping Enzo can help with ideas of how to glue these back.

I plugged in this 26 year old amp into my 2x12 cab with celestions and tweaked it for a while and bam... It sounded like I remember from the mid 80s club days playing heavy rock. It was considered heavy metal then but I guess it grandad rock now.

Any way I was talking to a buddy that had a GK ML250 from 1985 and he was saying how he really thought that amp was so killer sounding but then it blew up
I still remember him playing this amp thru a Marshall 4x12 and thinking how damn good it sounded back in the day. he was playing the song (In my dreams) by Dokken and seem to nail the tone.

Anyone remember the GK ML250, little stereo amp?

Slobrain

[R.G.]

Well no, I say that it's the very fact that the base drive winding floats, that makes the top section a common-emitter stage just the same as the bottom one, with the same high output impedance.

The floating winding means that an output stage section only has two terminals for current to go in or out. Therefore, it can only have one impedance between those two terminals: it can't matter which end you look from.

Therefore both the top and bottom sections must have the same impedance, which I say is that of a common-emitter amp with some local feedback.

This also implies that a complementary version with NPN and PNP transistors would behave pretty much the same as the original, so we might as well use all NPN.

Good point. It's certainly worth looking into.

I think that the originals were all NPN because that's the only cheap, good outputs that they could get. The original is a house-numbered 2N3055. I think that the availability of only NPNs plus familiarity with transformers led to the driver transformer use.

I also think the leakage inductance in the _local_ feedback loop between collector and base could be what makes the transformer so critical. Or maybe the transistor driver stage in the TV amps leads to a much higher loop gain than a tube driver, what with transistors having so much more gm than tubes.

Which local feedback loop is that?

After all, the Fender 300PS has a feedback loop around two transformers, without much in the way of interleaving, and it's stable.

Stability depends on the size of the forward gain as well as the number of poles and phase shift. An equal-TC phase shift oscillator with a gain under 27? , 29? will not oscillate either, even though the amount of phase shift is clearly sufficient. The amount of phase shift limits how much gain you can use, and the amount of gain limits how much phase shift you can have and remain stable.

Anyway, you have me fired up enough to try building this hybrid output stage now!

Good! Give it a go. I'd like to see what you come up with.

If I were not so enveloped in other stuff, I'd like to get out the old Beatle head, disable the feedback loop and measure the output impedance.

Here's a thought. The old TV amps sound much better to my ears than they ought to sound by conventional wisdom. I put this down to the limiter ahead of the power amp. What if it's both the limiter and a high output impedance? The high output impedance would give the amp a looser grip on the speaker just like a pentode stage with little feedback.

There is just so darned much to explore and so little time!!

[rocket]

I think it is funny that the old SS amps from the 60ies and 70ies that earned the bad reputation of SS amps, now are said to be the best sounding ones.

It reminds me to the Fender guitars from the 70ies that a few years ago nobody would even have touched and that now start commanding "vintage" (=exorbitant) prices.

[rocket]

How is the Peavey Dweezil Zappa amp?

[dai h.]

the old Roland Cube 60 seemed pretty good esp. with a good external speaker. Made every gtr. sound the same way, but in a good way. The overdrive on the amp sounded like the Toto record on which Steve Lucather used some solid state amp (least that's what my fog-filled memory recalls).

[Earl Norton]

Worst SS amps:

Anything by Univox, The first SS fender bassman (hard to find today thank God)

[TD_Madden]

I like my (horrors!) Crate PowerBlock through one of my old Gibson GG-100 (circa 1965 or so) 2x10 sealed cabinets (8 ohm).

Can't believe it's SS when gain/tone/volume is set right. Loud as hell too.

[Rob Mercure]

Autotranny output PVs

For a while there Peavey made several SS models that used an autotransformer to couple the output transisitors to the speakers - the Special Solo Series was one - and these SS amps really sounded nice when used with humbuckers in a rock and roll band. Quite a few local musicians loved these thangs in the 1970s - one even traded in his Marshall (with serious "boot" back with the PV) for one of the SSS's.

A few years ago I was given that same amp chassis and cabinet, with speaker, which had been more-or-less "gutted" by some unknown but still had the autotranny. It's in my "get around to it" pile but someday I intend to reconstruct the basic PV circuit.

Rob