Some help with schematic please

[runaway!]

Seriously trying to understand tube amps here, made this schematic based off of the information I've been reading - and by referencing other designs.

That being said, I have no way of validating this design without building it or asking for help ...

So, if anyone could review the schematic - I would be very grateful. I'm not exactly certain if the channel switching is viable, which was lifted from an Engl Fireball. Engl apparently puts errors in their schematics, and I'm not sure if the intentional errors are simply tone influencing values or the wiring too.

Please be brutal (but not insulting), a proper critique if very valuable.

As far as goals, I am trying to achieve a reasonable amount of distortion and frequency balance. I may put an additional switch in a later stage, because I'm thinking the clean channel won't be very clean...

Thanks for anyone who can help!

[Wilder Amplification]

Seriously trying to understand tube amps here, made this schematic based off of the information I've been reading - and by referencing other designs.

That being said, I have no way of validating this design without building it or asking for help ...

So, if anyone could review the schematic - I would be very grateful. I'm not exactly certain if the channel switching is viable, which was lifted from an Engl Fireball. Engl apparently puts errors in their schematics, and I'm not sure if the intentional errors are simply tone influencing values or the wiring too.

Please be brutal (but not insulting), a proper critique if very valuable.

As far as goals, I am trying to achieve a reasonable amount of distortion and frequency balance. I may put an additional switch in a later stage, because I'm thinking the clean channel won't be very clean...

Thanks for anyone who can help!

Looks like a simple 4 stager with a cathode follower buffered tone stack and a cathodyne phase inverter.

I'd drop the 4.7uF cathode caps down to something more like a 2.2uF or lower. The 4.7uFs give a lower corner frequency of about 41Hz, which seems a bit low of a frequency to be adding gain to...especially on the early stages.

Also, 1 or more of those gain pots could be eliminated with a simple voltage divider arrangement at the output of each stage.

The channel switching arrangement also appears to be legit as well, grounding the output of stage 3 while taking the signal straight from stage 2 to the last gain stage/cathode follower arrangement.

[madkatb]

I realise you haven't shown any of the power supply schematic but you shouldn't really run all those tubes off a single node (B+++ or whatever it is). Two at a time with their own power supply filter caps or you could end up with oscillation.

[runaway!]

Looks like a simple 4 stager with a cathode follower buffered tone stack and a cathodyne phase inverter.

The fact this schematic speaks the language to you is comforting to me, I was afraid of "WTF are you doing?", lol

I'd drop the 4.7uF cathode caps down to something more like a 2.2uF or lower. The 4.7uFs give a lower corner frequency of about 41Hz, which seems a bit low of a frequency to be adding gain to...especially on the early stages.

Noted, there must be something I am just not getting on this subject yet - seen lots of amps with 20uF plus caps. Not entirely sure what the differences are.

Also, 1 or more of those gain pots could be eliminated with a simple voltage divider arrangement at the output of each stage.

Is there a benefit of using this? I figured such a simple amp needs more controls - thus the extra pots...

The channel switching arrangement also appears to be legit as well, grounding the output of stage 3 while taking the signal straight from stage 2 to the last gain stage/cathode follower arrangement.

That's a relief to hear! Thanks for your help

[runaway!]

I realise you haven't shown any of the power supply schematic but you shouldn't really run all those tubes off a single node (B+++ or whatever it is). Two at a time with their own power supply filter caps or you could end up with oscillation.

Thanks for the heads up, the PS was my next step to study and design. I'll keep this detail at the front.

[DIY_Guy]

Noted, there must be something I am just not getting on this subject yet - seen lots of amps with 20uF plus caps. Not entirely sure what the differences are.

Some amps do, but there is usually a balance of frequency shaping so to speak, elsewhere in the preamp. It all depends on what you are going for in the voicing. Read a few books that explain preamps to learn all about the subject.(Merlin)

[DIY_Guy]

Is there a benefit of using this? I figured such a simple amp needs more controls - thus the extra pots...

You could control the gain between stages like that, but do you really want to? Seems kind of excessive. Sometimes going simple is the better way(hence why almost all amps use a single gain control, and set the rest of the stages)

I'd say using trim pots in those positions would be a better option, you could tweak them to what you like and then just leave them, and have your main gain pot out front.

All in my opinion of course.

[Wilder Amplification]

A little history on guitar amps and how they came about...the first ones were circuits that Fender copied straight out of an RCA tube manual. They weren't intended originally to be "guitar amps".

The reason for such a high value originally was to decouple every frequency in the audible spectrum (some even go so low you might as well diode bias the stage and decouple everything from DC to light). This gives the amp a somewhat "flat" response.

However...we humans don't hear flat. Moreover, guitar frequencies start at around 80Hz. Most guitar speakers are voiced in the 75Hz-5kHz or so range.

As such, we amp modders have used the cathode bypass caps as a way to voice the stages in a range that's better suited to guitar frequencies.

When you have your early stages providing maximum gain at everything almost down to DC, you tend to get low end distortion. This is why lots of us use low values on the early stages...to shelve bass and provide the gain boost at stuff much higher in frequency that can make better use of being overdriven. If you ever play amps that have a loose/flubby low end, lots of times you'll find it's due to using high value cathode bypass caps in the early stages without any surrounding circuitry to provide a low end rolloff before it hits the next stage. As such your lows end up getting distorted along with the mids and highs. By dropping the cathode bypass cap values at the early stages, the lows stay tight/controlled while everything else above it gets overdriven. Without the low end distortion, you get the tighter lows and much more definition in the mids/highs without the definition getting drowned out by distorted sub-bass frequencies that are of no use to a guitar.

Now in a clean circuit, high bypass cap values will give you a broader/more "open" tone than lower ones will. But if you're a country guy or a "white boy 80s rocker blues" guy (like me ), lower values will give you more of the punchy/tight "spank" in the lows.

[runaway!]

Excellent info, thanks for the advice. Especially Wilder's thorough explanation. I will certainly change those cap values, and determine what values I need for the voltage dividers.

Whats the best way to add a low pass filter of sorts? I would like to add one for a very slight cut - my ears sting when I crank an amp with a ton of highs. I'm wondering if unfiltered highs can also contribute to "fizzy" or insect like distortion.