Is PS Ripple Integral to an Amp's Tone?

[Leo_Gnardo]

Where does a choke fit, or not fit, in all this? The 5F6A has a choke, but the best sounding 30W amp I have built was a 4-6V6 with a 3K resistor where the choke would be, and a 60uF reservoir cap to two 5Y3s in parallel.

Probably plenty of compression as G2 voltage falls when you're hitting the power amp hard. If you had a choke instead of 3K resistor, G2 voltage would be higher and not so saggy, still a good amp - more Fender-like - but obviously less compression when you're asking it to turn out max power.

"A well filtered screen grid supply is essential to good amp tone" so I've heard it said.

[roberto]

I agree on the transitory effect on the screens as part of the sound more than the ripple, if we are talking about PP amps.

A simple trial is scaling the RC keeping the ripple constant.

[gingertube]

Be aware that this discussion relates to fixed biased push pull output stage.

In my HiFi Amp design I include a common unbypassed cathode resistor of approx 15% of the value of what you would use as a cathode bias resistor for each tube (individual). The rest of the required bias is applied by fixed bias. Why? The object was to supress some 3rd and other odd order harmonic distortion by commonmode feedback (the old Bell Labs Harmonic Equalizer scheme). It actually did that to some degree but the surprising thing which showed up in spectrum anayser plots was an almost complete elimination of the the sidebands from intermodulation with residual power supply ripple.

So I would expect the discussion above to NOT apply when using a common unbypassed cathode bias resistor.

Cheers,
Ian

[trobbins]

There is a natural preference for anything but a zero distortion, stable tone from a signal source. The preference is certainly there for the addition of modulated sidebands, whether they be from ripple, or even very noticeable vibrato.

Similar situation occurs with electronic organs - the use of highly stable frequency generators is often perceived as being improved if some random variation of the frequency is added. Perhaps the perception is in the mind of those who often listen to pipe organs where there is natural randomness to the fundamental frequency being generated.

[roberto]

In my HiFi Amp design I include a common unbypassed cathode resistor of approx 15% of the value of what you would use as a cathode bias resistor for each tube (individual).

I've read something similar here: http://www.tubecad.com/2005/March/02/Wh ... %20Use.pdf

[Roe]

There were dual recto Marshall SLs?? Got a pict anyone?

I was under the impression those never made it past prototype. If they exist they'd be crazy rare.

there are plenty of dual rectifier mid 1967 100w marshalls around,

cf. http://folk.ntnu.no/roef/JTM100
http://www.amparchives.com/album/Marsha ... es/14.html

http://www.amparchives.com/album/Marsha ... 32993.html[/url]

[rp]

there are plenty of dual rectifier mid 1967 100w marshalls around,

Great images, that was as good as being a teenager and getting the Barbi Benton Playboy issue.

Unfortunately, now I want to build one.

[roberto]

One Barbi Benton?
Please build two, one for me too.

[teemuk]

My two cents, and take this as my opinion.

I'm familiar with the ripple modulation scheme, and I also know that Pritchard solid-state amps, for instance, have implemented modelling of that ripple modulation. (He calls it "fat"). So there are certainly people who feel it is an important ingredient in amp tone.

Personally, I disagree.

I have experimented with "artificial" voltage sag in solid-state amps. Basically that's about modulating clipping thresholds like B+ sag would do. To such scheme it is also easy to implement a 60/120 Hz voltage source for "ripple modulation" during extreme sag.

The unfortunate thing, however, was that I simply couldn't hear it doing anything in an A/B test against an identical system sans ripple modulation. Even when the modulation was ridiculously apparent in a visual image of the audio track. No, it just isn't that distinctive to hear.

Additionally, how realistic it is to expect that you drive an amp with signal having crest factor and envelope similar to a sine wave? Yes, such input signal most definitely reveals voltage sagging in all its glory, but -in practice- with real life input signals amplitude peaks tend to be quick transients and the average signal amplitude remains much below them. Such input signals simply won't push the amp into extreme, sustained sagging, which is exactly what is needed for ripple modulation to manifest itself. Yes, there might be brief pulses of sagging. Ripple modulation requires that the state sustains for several cycles.

Not gonna happen with typical input signals. Not gonna happen.

So, personally I can't really hear ripple modulation even if it's evident visually in oscilloscope screen, and I haven't generally experienced guitar amps to be driven to a state where voltage sag is both so extreme and sustained that ripple modulation could take place in full effect.

Usually when you need THAT much clipping and distortion rest assured it is generated in the preamp stages where noth sag and ripple modulation are rare occurences. Why, because you have class-A biased low current draw stages so not much dynamic in current draw characteristics, let alone not much current draw. Even "meh" filtering capacitance tends to be proper to AC bypass the supply rail. Yep, it effectively means "ripple" gets AC bypassed too.

[John_P_WI]

I can't really hear ripple modulation even if it's evident visually in oscilloscope screen, and I haven't generally experienced guitar amps to be driven to a state where voltage sag is both so extreme and sustained that ripple modulation could take place in full effect.

Well said, furthermore, how many of us have an environment that we can actually push an amp to its' "full roar" sag limits? I expect very few besides the working professionals.

[Roe]

there are plenty of dual rectifier mid 1967 100w marshalls around,

Great images, that was as good as being a teenager and getting the Barbi Benton Playboy issue.

Unfortunately, now I want to build one.

They are fun to build but it can be difficult to get the ghosting minimized

[trobbins]

The unfortunate thing, however, was that I simply couldn't hear it doing anything in an A/B test against an identical system sans ripple modulation. Even when the modulation was ridiculously apparent in a visual image of the audio track. No, it just isn't that distinctive to hear.

Teemuk, when you refer to a 'sans ripple' configuration, do you mean you had an amp with just a simple power supply and the nominal ripple that would be expected from such an amp, to which you then added even more ripple? Or did you start with an amp that had a power supply with a regulator that eliminated ripple, and to which you then added ridiculous ripple levels back in to?

[teemuk]

Not an amp. A circuit emulating one.

Basically modulated references for two clipping diodes. Generated by extracting envelope of rectified and filtered signal from a steady DC reference level. If "ripple" is required you simply mix a ripple component to the DC component.

Result is the same: Signal clips to dynamically varying threshold instead of a fixed one. With plenty of artifical "sag" the effect of ripple component is higher, when signals aren't clipping the ripple in the treshold naturally has no impact. So, more "sag" and clipping, more ripple modulation, less "sag" and clipping, less ripple modulation.

[LOUDthud]

I built a solid state amp where I can hear the 120Hz modulation. It's a simple single rail design with a cap coupled speaker. If I play a high E on the 12th fret of the high E string at full overdrive, it just sounds like a 120Hz hum underneath the note. I haven't found a tube amp that does it as clearly. At best, I can hear some intermodulation products when I try the same test on a tube amp.

[trobbins]

Teemuk, was your modulation technique generating tremolo or (phase shifted) vibrato modulation of the signal?