By popular demand, and because....

[daz]

.....you bastages keep hounding me for a schematic. So after that thread on configuring the output of one stage to the next i spend a large part of the day tweaking endlessly trying to find the magic. I found what isn't magic so far is the best and it turns out the key part of it was a part that was there in the first place. A 470k grid stopper. After dozens of configurations with resistor values and putting treble peakers in places when a resistor darkened the tone to much and everything else imaginable, it finally came down to that one resistor. With anything less in that position i got tone that sounded like the amp was about to start blocking. Sometimes a good tone but you could feel what seemed like too much compression and a tiny tiny amount of fizz in the attack and it didn't sound quite right. No matter how much gain i threw away and how i did it, that was never quite eliminated, or if it did it also eliminated anything close to great tone. Another key was the .001uf treble bleed on the gain pot. Smaller values just didn't sound right but as soon as i tried the .001 it just felt right and every time i tired a smaller one it wasn't good. Somehow that cap and the 470k grid stopper together shape things just right and remove the feeling of impending blocking distortion. Oh, and the .0047 coupler was another change because i just wanted to drop some gain in the low end to clean the would strings up and make them more percussive and it seemed to do that and make the overall balance better.

So once i hit on what sounded best so far i sat down and spent a long period finishing the schematic which started as one from my old el34 version i asked endless questions about here a couple years back, and i just changed everything to reflect this amp. There may be mistakes and things i missed but this is basically it. Critique it if you wish, but i warn you my amps always have circuit design aspects that are not conventional due to the fact I'm not tech and mostly go by ear and the little i know. But regardless of that i like the tone a lot right now and not sure if i will keep F'ing with it, but i'm sure you guys will probably point out stupid details i should change. And out of curiosity i'll probably fall victim to your suggestions and try some of em. Dammit.

[SoulFetish]

That one's okay, but.... could you redraw it using a San-serif font this time?

.... a little color wouldn't hurt. In fact, it'd be FABULOUS!

[nickb]

A picture says a thousand words . The serif font gives it a vintage style too

[Leo_Gnardo]

A picture says a thousand words . The serif font gives it a vintage style too

I'm with nickb. Schemo looks terrific at first blink. Don't shoot the serifs.

[J M Fahey]

Schematics by definition are black on white.
And .gif or .png , because that´s the sharpest format which lets you read small text if enlarged, while .jpg is blurry *by definition* because an algorithm unfocuses and blurs edges to better mix colours and hide pixelation.
No big deal on holiday or party pictures, a mess on schematics or PCB designs.

Besides that , I have a personal gripe against coloured schematics because 98% of them are blurry screen captures (by people who can´t actually "print" the schematic), often fuzzy white /yellow/blue lines on a black or grey background, or those dreaded brown and green on white Eagle schematic colour choices.
And as said before, use of colur automatically saves as .jpg unless oredred to use .gif or.png which almost nobody does.

As of the serif font, it´s as good as any other and looks good

[daz]

Wow, here i am thinking i'd get a ton of critique on my circuit design and instead i get critique on the drawing?! Where have you guys been ? Do you not notice that it's probably clearer than 90% of schematics out there? And color? When was the last time i saw a color schematic....lets see....how about......NEVER !

Now i'm assuming this may just all tongue in cheek but if not i'm a bit shocked. I'm not a draftsman or such, i just wanted to post a readable schematic after constant jabs about not doing so and i think it's as clear and readable as anything i've seen. Hell, half the marshall and fender schematics out there are so blurry you can't even see the component values. Man, you guys are a tough crowd !

[Dave H]

Schematic is very clear and readable and I don't see any mistakes. A few more voltage readings would be nice and btw the 6V6 symbol has no cathode

[SoulFetish]

Well the jury's in. Tradition wins. No color it is.
(But I hold strong on my san- serif opinion. This isn't a "wanted" poster. But thats a damn fine joke, Leo. Damn fine)


VIVA LA HELVETICA!!!

[SoulFetish]

Wow, here i am thinking i'd get a ton of critique on my circuit design and instead i get critique on the drawing?! Where have you guys been ? Do you not notice that it's probably clearer than 90% of schematics out there? And color? When was the last time i saw a color schematic....lets see....how about......NEVER !

Now i'm assuming this may just all tongue in cheek but if not i'm a bit shocked. I'm not a draftsman or such, i just wanted to post a readable schematic after constant jabs about not doing so and i think it's as clear and readable as anything i've seen. Hell, half the marshall and fender schematics out there are so blurry you can't even see the component values. Man, you guys are a tough crowd !

Of course I'm joking about the color and the font. It's perfectly fine. It was just good 'ole fun to see that you finally posted a schematic, and bust your balls about it. Now everyone's busting mine

[daz]

Schematic is very clear and readable and I don't see any mistakes. A few more voltage readings would be nice and btw the 6V6 symbol has no cathode

Well, like i said it was a different schematic i just updated, but it shows pin 8 and thats all that matters.

[Dave H]

Yeah, it's a good schematic. I was only pulling your leg.

[daz]

Yeah, it's a good schematic. I was only pulling your leg.

Well, don't. I've gota bum hip and that hurts like a mofo.

[Malcolm Irving]

After two cathode-bypassed gain stages, I think blocking would indeed normally be an issue at the V2A stage.

The partial cathode-bypassing of stages V1A and V1B, and the low value coupling cap (0.0047uF) to V2A, all give some bass cut (I think - without doing any calculations) which is good when blocking might be an issue later in the circuit.

With the large 470k grid stopper on V2A, combined with the 220k to make up the grid leak, you get a good balance between the charging and discharging time constants for the 0.0047uF coupling cap – again a good measure against blocking.

If we take the output impedance of the V1B stage as (say) 40k, the charging time constant when the grid is conducting is approx.
( 40k + 100k + 470k||220k ) x 0.0047 e-6 = 1.36mS

And for discharging (when the grid is not conducting):
( 40k + 100K + 220k ) x 0.0047 e-6 = 1.69mS

It’s a nice design, in my opinion.

[daz]

After two cathode-bypassed gain stages, I think blocking would indeed normally be an issue at the V2A stage.

The partial cathode-bypassing of stages V1A and V1B, and the low value coupling cap (0.0047uF) to V2A, all give some bass cut (I think - without doing any calculations) which is good when blocking might be an issue later in the circuit.

With the large 470k grid stopper on V2A, combined with the 220k to make up the grid leak, you get a good balance between the charging and discharging time constants for the 0.0047uF coupling cap – again a good measure against blocking.

If we take the output impedance of the V1B stage as (say) 40k, the charging time constant when the grid is conducting is approx.
( 40k + 100k + 470k||220k ) x 0.0047 e-6 = 1.36mS

And for discharging (when the grid is not conducting):
( 40k + 100K + 220k ) x 0.0047 e-6 = 1.69mS

It’s a nice design, in my opinion.

Wow, thanks ! Because i go strictly by ear and don't understand much of what you described. I just try use what i DO know as far as tonal results that certain components do in particular spots to try to visualize what is needed to change a given aspect to what i want. Much of it doesn't work but after stupid amounts of trial and error i usually find it.

[nickb]

Wow, thanks ! Because i go strictly by ear and don't understand much of what you described. I just try use what i DO know as far as tonal results that certain components do in particular spots to try to visualize what is needed to change a given aspect to what i want. Much of it doesn't work but after stupid amounts of trial and error i usually find it.

Gulp! Art and science finally agree! I never thought I'd see the day. Daz, you are one special dude.