JCM-800/2204 Build

[Reeltarded]

The volume cut is what that last resistor or a 25kL pot is all about.

Yeah, .0022 over the signal leg of the 470k/470k voltage divider on the way to the third stage.

[john l]

The volume cut is what that last resistor or a 25kL pot is all about.

Yeah, .0022 over the signal leg of the 470k/470k voltage divider on the way to the third stage.

Crap, I need to learn to speak tech. Pic?

[Reeltarded]

Here is a layout from Steve Miller's layout place. The second tube has a green grid wire going to it from the two 470k resistors. The signal side (on right) has a 470p peaker over it. Sub a .0022uF (just like the first stage coupler to the left of that) instead of the 470p.

It will seem to lose bass and get real flat mids. It isn't losing bass, it's gaining mids in a pretty wide band there.

[Mark]

That could be real good mod in the Caswell style amps, the one I heard was quite bright, I have heard of people ditching the 470pF peaking caps but the amp gets muddy fast and loses something.

[john l]

Here is a layout from Steve Miller's layout place. The second tube has a green grid wire going to it from the two 470k resistors. The signal side (on right) has a 470p peaker over it. Sub a .0022uF (just like the first stage coupler to the left of that) instead of the 470p.

It will seem to lose bass and get real flat mids. It isn't losing bass, it's gaining mids in a pretty wide band there.

Oh okay I did understand you then. Ive heard that whatever you do to one of the treble peakers that you should do to the other or else things get can get weird. Do you do the same thing to the one off the board on the input? Would clipping a .002 right over the 470 give a somewhat good representation?

Also did I understand your original post right where you like a bypassed 2.7k/.68uf cathode combo on v1a-v2a? Would you recommend this without diode clipping?

[john l]

Wow .002 across 470k is killer. I just ran right over the 470pf and it sounded great. Is there a reason you prefer that peaker to the one on the input to gain pot Miles? The one on the input also sounds good but this was at house volumes. Id love to incoperate this but as I said earlier Im trying not to mess with my board which is why I ask.

What did you mean by 56k CF in your little list? What resistor is that and what does altering to 56k do?

[Reeltarded]

Sorry was out sleeping then out sitting with a friend today. Excellent on the peaker as you found it good paralleled with the 470p.

Too much of a good thing can be too much. If your amp sounds like it isn't spitting fire through gritted teeth you might try a 1000p over the first stage signal divider. It gets bright. You might want to play it at some higher volumes to test if a little is enough.

The identical stages do focus that sound but all of these things working together makes you have to add some lowend later down the line for balance unless you really like the very midrange forward thing.

You are working on an otherwise stock 2204 circuit?

[john l]

Sorry was out sleeping then out sitting with a friend today. Excellent on the peaker as you found it good paralleled with the 470p.

Too much of a good thing can be too much. If your amp sounds like it isn't spitting fire through gritted teeth you might try a 1000p over the first stage signal divider. It gets bright. You might want to play it at some higher volumes to test if a little is enough.

The identical stages do focus that sound but all of these things working together makes you have to add some lowend later down the line for balance unless you really like the very midrange forward thing.

You are working on an otherwise stock 2204 circuit?

Heres where im at

[IMG:800:600]http://img.photobucket.com/albums/v299/Johnspics/20130721_203744_zps5b2a99ac.jpg[/img]

Yeah between bypassing V2/a with 1uf, the variable slope and now the .002 for the peaker Im super mid heavy. I can see why having a resonance pot would be nice. I might just skip the pot just stick a .002uf in there and see how that fares since Ive I don't have many holes for switches. I pulled thee preamp pot and stuck a push pull in there and yanked a speaker out and added the 50k push pull there too ha ha.

So back to my question. Why that peaker and not on the input? It seemed like the effect was more pronounced there.

What about the 56k CF thing you mentioned? I assume its altering something in the cathode follower to that value.

EDIT
And yes with the exception of a 6550 to EL34 Conversion and a full recap Im working on a very stock but curiously dark sounding 1980 2104 stuck in a repro headshell

[Reeltarded]

Ahh totally spaced on the CF.

The 56k vs 100k is MUCH more compression there. Let's stay away from that for now though. I don't want to bake your V2 tube.

Fixed resonance doesn't require a switch. Do you have a .0047u cap around? Just to see if you like that you solder the cap in series with the NFB wire off the presence circuit. Purple wire. Put the cap right on the output tap and fix the purple wire to it. You need to moderate your bass settings, but if you like the thump you can put that same cap paralled over a 470k resistor in the same configuration and try again. If still not balanced dink with the resistor value up or down until it suits you.

I prefer the larger peaking there because generally it works better to add highs very early, mids later, and bass at the end of the circuit. Not always true but a good rule to play with for a dirty amp.

Nice rig there buddy! What do you want it to sound like?

[john l]

Ahh totally spaced on the CF.

The 56k vs 100k is MUCH more compression there. Let's stay away from that for now though. I don't want to bake your V2 tube.

Fixed resonance doesn't require a switch. Do you have a .0047u cap around? Just to see if you like that you solder the cap in series with the NFB wire off the presence circuit. Purple wire. Put the cap right on the output tap and fix the purple wire to it. You need to moderate your bass settings, but if you like the thump you can put that same cap paralled over a 470k resistor in the same configuration and try again. If still not balanced dink with the resistor value up or down until it suits you.

I prefer the larger peaking there because generally it works better to add highs very early, mids later, and bass at the end of the circuit. Not always true but a good rule to play with for a dirty amp.

Nice rig there buddy! What do you want it to sound like?

Thanks man! And thanks very much for all the help too, I have a lot of holes in my game so its nice to have a little guidance here. Ive added the just the cap in series with the NFB wire but never in parallel with a resistor. What would the difference be between using a resistor vs a smaller cap to tailor be?
I wouldn't mind some more high end, where would you look to for that sort of thing?

To be honest I don't really know what I want it to sound like because I don't really know whats possible yet ya know. Im enjoying the hell out of learning though. Im very intrigued by the compression mod, sounds like its pretty hard on the tube though. Whats that all about?

What do you like for filtering.

Sorry for broadsiding you with question miles

[Reeltarded]

The resistor value takes the place of a pot at a given setting. (How much) The cap selects the eq point. (Where) Simple RC circuit.

If I were you I would assemble a new board and remove the original then you are only an hour or so from getting it back to stock and no hacking up the PC board. So much easier to swap in stuff on a turret board. I would hate to kill your baby.

[john l]

No worries, Im not going to hack anything up. I have an 800 kit coming this week so this ones just going to have slight tweeks to make it work a little better for what I do. How hard is the 56k CF on V2?

[Reeltarded]

Pretty rough on startup. When you hit the power the grid goes to HT potential but the cathode is at ground. Takes 45 seconds or so to get out of trouble.

Aha.. here ya go. Scopes of it so you can see the effect plus a way to save the tube.

http://www.freewebs.com/valvewizard1/dccf.htm

NEVER use modern Tung-Sol in that V2 position. I say it alot.

[john l]

Heres where I get to make a fool of myself and show how little I understand of schematics

So I grab a 1N4007 and a 47k resistor in series and then (cathode heading to V2)connect it from the the grid of V1b to the cathode of V2a? Then I can safely do the 56k CF?

[Reeltarded]

Resistor off pin 7 diode off pin 8 and tie them together. Be mindful of which way the diode is oriented. Yep. Banded end to pin 8.

I think. I can't get that link up for some reason.

Oh I see. This is all on V2 socket. Merlin gives individual triodes their own V because everything isn't a dual triode or a Marshall I guess. I remember that.