roberto wrote: ↑Wed Aug 05, 2020 1:42 pm
Thanks for the detailed explanation Scumback! It is clear now.
By personal experience, the data shown is more a copy-paste rather than something else (same power at the same THD for two very different schematics is not so easy to be obtained).
Also, whilst I can agree with the low THD wattage, the THD at full wattage seems quite optimistic to me.
With such high B+ (around 500 Vdc) and Raa 3.4 kOhm, it is safer for most of the modern EL34s to lower B+ or raise Raa.
My former amp tech said he measured a 67 Marshall 100w at 130w clean, and 220w cranked, no pedals.
Plate voltage was in the high 500V range, though, back when tubes could handle that type of punishment. These days it's more like 480-510 max.
In regard to the question about how many gain stages it takes for a power amp signal to reach an entirely square wave my own personal “I’m just a guitar player” understanding is: it depends on a multitude of factors that can’t be directly attributed to a singular gain stage or even the whole of the amplifier’s preamp and power amp design themselves. Like previously mentioned, if you were to feed the input of an amplifier an already highly amplified and compressed fuzz tone generated from a pedal circuit, it would be much easier for that preamp to theoretically reach a square wave (or at least a very close to square wave signal because of the phase shifts and frequency-specific gain from cascading gain stage to gain stage) before it enters the power amp to be further amplified. Granted, these same circumstances could occur when you are using high-gain amps without pedals as well. As little as 2 gain stages could generate said results with no problem if the preamp is designed (albeit poorly; I know from experience I might add) to do as such.
In regard to the Soldano SLO 100 circuit, there are actually five gain stages present in the dirty channel before it arrives at the phase inverter, not four. The two gain stages before both of the cathode followers (the first one driving the effects loop Send, the second one driving the effects loop Return) both add some additional gain and clipping. Mike probably used these circuits because for their ability to drive the cables and devices placed in the effects loop more efficiently. The cathode follower EQ in the Return stage is a distinctly unique Soldano design choice as well. When stacking this many gain stages amplifying basically the same frequency range in a serial configuration like this, a square or (square-ish) wave in the preamp is a relatively easy result to achieve. Conversely, adding extra serial gain stages in the preamp will not add more power to the power amp. That extra preamp gain is simply a more amplified signal (and perhaps clipped) signal being injected into the power amp. The two aforementioned gain stages in the SLO 100 (the Effects Loop’s Send and Return CF’s) both impart their own tube diode clipping when they are wound up with higher signal levels as well.
Some preamp tube circuits may alter the power amp so it behaves differently before clipping like an ultra-linear driver that replicates ultra-linear output transformer taps in the case of the Fender Super Twin or some variations of the now-legendary SSS. Or in the case of a Hiwatt using a single triode as a voltage buffer for a phase inverter reference voltage. For the most part those circuits don’t add actual audio gain to the preamp signal like a typical gain stage does. Rather, I tend to look at some of these preamp tube based circuits as power amp circuits designed to make the power amp more efficient under certain operating conditions. The amps you mentioned do not utilize any fancy power amp related preamp tube circuits besides their typical long tailed pair phase inverters (if my knowledge serves me right; which is always suspect as hell anyway to be fair).
A lot of why gain staging can be puzzling is that most preamp stages don’t amplify uniformly from stage to stage nor do they amplify the same frequencies from stage to stage. The order of the gain stages, the tubes used, the power supply design, the component values used and the actual electronic design itself (and many, many other things) have drastic effects on the sonic characteristics of the entire amplifier, not just the preamp. For a quick example, if you were to take a simple Fender “blackface” preamp-a relatively simple two stage preamp-and simply reverse the order that the gain stages cascade, you would notice drastic differences in the operation of the controls and their relationships to each other. And that’s just switching the gain stage/signal chain order by putting the EQ after the input stage instead of original Fender specs where the input stage includes the EQ. With this kind of sensitivity being stated, you could conceivably have four back to back serial gain stages with relatively small amounts of gain generated at each stage without it sounding very gain-y at all. In the end, it’s all about the design and the designer’s desired performance.
And of course, in regard to speaker failures (which is your wheelhouse, definitely not mine) in the SLO I would reckon to think that running that amp dime’d with any speaker rated below 100 watts would be somewhat troublesome. Because of the nature of the power amp’s efficiency (the output transformer Soldano uses are particularly efficient) coupled with a preamp that has the ability to generate what is real close to a square wave in certain settings particularly with an outboard distortion or fuzz device, I could see this be a recurring problem with one single 100w 12”. Perhaps a 150w speaker would hold up, but I think even that might not be enough headroom if the end user is slamming the already dime’d preamp with a fuzz like a dummy. Of course, the majority of users wouldn’t use the amp like this because it sounds like absolute garbage, but some doomers gonna doom I suppose. And if they are playing anything tuned lower than Eb at those settings with a single twelve inch speaker, they’re probably entering a world of coil burnin’ pain, as well as minimizing the potential for an ideal dynamic range from their powerful boooo-tique amp. As Martin stated, it probably would be a wise idea to double your speaker’s wattage rating if you are running a 100 watt amplifier in this manner…if that is even possible.
The problem it seems is that many users think that just because there are knobs that turn all the way from left to right, that those knobs SHOULD be turned from left to right with absolutely no consequences for their gear. Obviously, anyone who has spent any amount of time playing a Soldano SLO 100 knows that they sound their best when the preamp gain is backed off while the Power Amp Volume is wound up to drive the power amp more.
"Genius manifests itself. You got a hammer. You either build a Cathedral or you build a shithouse." - Carl Schroeder
Obviously, anyone who has spent any amount of time playing a Soldano SLO 100 knows that they sound their best when the preamp gain is backed off while the Power Amp Volume is wound up to drive the power amp more.
Obviously, anyone who has spent any amount of time playing a Soldano SLO 100 knows that they sound their best when the preamp gain is backed off while the Power Amp Volume is wound up to drive the power amp more.
NO ! But is what you like .
That's fair. Usually with that much gain being generated in the preamp, turning the Power Amp Volume up narrows the dynamic range if the Preamp gain is too goosed; it's a cool sound, but it is not as dynamic as the SLO power amp can be if the preamp signal is backed off and the power is doing the heavy lifting.
Scumback Speakers wrote: ↑Fri Sep 11, 2020 1:14 am
I never really bonded with the SLO Soldano amp tone for my style of playing.
They are fickle at lower volumes and you really have to play them loud to get them to do what I think Mike intended in his design. I think there are better amps out there these days that do similar things as the wound up SLO trip but are more flexible at different volumes. Not an amp I'd knock someone over to play, but at this point I suppose it's a "New Classic" design.
"Genius manifests itself. You got a hammer. You either build a Cathedral or you build a shithouse." - Carl Schroeder
Travis_HY wrote: ↑Fri Sep 11, 2020 3:18 am
That's fair. Usually with that much gain being generated in the preamp, turning the Power Amp Volume up narrows the dynamic range if the Preamp gain is too goosed; it's a cool sound, but it is not as dynamic as the SLO power amp can be if the preamp signal is backed off and the power is doing the heavy lifting.
I personally like the SLO with very low gain settings on overdrive channel. Has that feeling that you cannot find in other amps.
High gain settings can be done better nowadays, and I never liked clean and crunch tones with that much of feedback on the poweramp.
The tone IMO improves if you add a NFB pot in series with the fixed 39k resistor.
Scumback Speakers wrote: ↑Fri Sep 11, 2020 1:14 am
I never really bonded with the SLO Soldano amp tone for my style of playing.
I agree that stock is quite hard to play, but if you have a close friend or a customer close to you with some passion for DIY, do some trials on a modded clone.
It is a very good platform to get a very wide palette of sounds.
