What Makes a Sunn a Sunn

[Fred Cook]

  It's been too quiet at this site!

Calling all gearheads and techno boffins.

Classic Sunns (late '60's), especially Sunn guitar amps, don't sound like others. Why?
-- Tube choice?
-- Tone control frequencies?
-- Big transformers?
All of the above?
Inquiring minds want to know!  

[Greg Z]

All of the things you mentioned, plus the fact that they are pretty much carbon copys of the dynaco mkIII and mk-VI hi-fi amps and use the 6an8a pentode triode PI-driver circuit which gives them  big headroom and the classic Sunn grind. Check the schematics on the Dynacos.

[Fred Cook]

Greg,

For us liberal arts types what can't read schematics ...

What does the 6an8 driver do that, say, Fender does not?

(My obsesseion with the Contour control is already noted.)

[Rocketboy]

What Greg Z said; I would like to add that the classic Sunn sound, because the amps use so few stages, is very close to what your instrument actually sounds like.  Very little coloration, very Hi-Fi.
Rocketboy

[Fred Cook]

RocketBoy,

The lack of stages and the hifi sound (and design history) are most interesting. On my Lone Star Strat' it translates to a very different sound in each switch position. Not a bad thing at all!

[Anonymous]

I wouldn't call it the lack of stages.  That would imply the Sunn amps have too few stages.  Such is not the case.  As you most likely know, every additional stage of amplification  detracts from the sonic purity of the source signal.  The Sunn 100S and 200S (and I believe the rest of the line of that period) used two preamp stages prior to the 6AN8A driver/phase inverter.  The second stage is non-bypassed, which puts negative feedback on that stage.  It also lowers the gain in that stage, and increases the audio fidelity in the whole preamp.  If you refer to the schematic diagram of the 100S, you will note the negative feedback loop goes no further upstream than the driver portion of the 6AN8A cathode.  These amps are very hi-fi.

You may have put your finger on why these amps were not more popular.  Back then most folks were using old worn out flat-wound strings, and many were playing instruments that would not pass tonal muster today.  The audio fidelity of the Sunn amps in such cases would only emphasise the poor sound of an inferior instrument, or a poorly/indifferently maintained instrument.

Given a good audio source, fewer stages is better.

Yours for a better tomorrow,
Ricardo Rocketboy

[Anonymous]

I wouldn't call it the lack of stages.  That would imply the Sunn amps have too few stages.  Such is not the case.  As you most likely know, every additional stage of amplification  detracts from the sonic purity of the source signal.  The Sunn 100S and 200S (and I believe the rest of the line of that period) used two preamp stages prior to the 6AN8A driver/phase inverter.  The second stage is non-bypassed, which puts negative feedback on that stage.  It also lowers the gain in that stage, and increases the audio fidelity in the whole preamp.  If you refer to the schematic diagram of the 100S, you will note the negative feedback loop goes no further upstream than the driver portion of the 6AN8A cathode.  These amps are very hi-fi.

You may have put your finger on why these amps were not more popular.  Back then most folks were using old worn out flat-wound strings, and many were playing instruments that would not pass tonal muster today.  The audio fidelity of the Sunn amps in such cases would only emphasise the poor sound of an inferior instrument, or a poorly/indifferently maintained instrument.

Given a good audio source, fewer stages is better.

Yours for a better tomorrow,
Ricardo Rocketboy