Hard question

[rodrigo_echeverri]

guys,

Who can go to page 6 of this the 20/20 manual:

http://www.mesaboogie.com/manuals/20-20%20Manual.pdf

and explain to me what the deal is with the tubes in the preamp section?... is there something I can do to those tubes to change the tone, say, make it brighter?... any thoughts about this?...

Please teach the ignorant ... [img]images/icons/smile.gif[/img]

[ May 12, 2003, 11:25 PM: Message edited by: rodrigo_echeverri ]

[rstites]

Re: Hard question

It's really not a preamp section. Every class A/B amp has a phase inverter. What happens is that the positive portion of the signal is amplified by one EL84 (in this case) and the negative by the other EL84. The phase inverter uses one 12AX7 for each side of the power amp.

For a stand alone power amp, there has to be an input buffer to make sure that you don't have extreme signal loss if driving the input with something like an effects loop. That's what each half of the last 12AX7 is doing here. Ideally, it won't affect the tone at all. It just acts as an impedance match to any solid state output stages. (A stand alone preamp will have the same thing on the output, which is one reason why separate preamps and power amps never sound exactly like the head version of an amp.)

Anyhow, none of these are going to have a big impact on the tone of the amp. I think if you want things brighter, you need to either use the presence controls or boost the highs in the preamp or EQ sections of your rig.

Edit for dumb proofreading typos...

[ May 13, 2003, 01:31 AM: Message edited by: rstites ]

[YetAnotherOne]

Re: Hard question

You could sell me that 20/20 and buy a Marshall. That'd brighten your sound right up. [img]images/icons/grin.gif[/img]

[rodrigo_echeverri]

Re: Hard question

YAO: you got e-mail...

hahaha... you wish!... [img]images/icons/smile.gif[/img]

[ May 13, 2003, 01:00 AM: Message edited by: rodrigo_echeverri ]

[petedz]

Re: Hard question

R.E., does it have that "deep" mod where a couple of caps are clipped off the board? I've never heard what that does, but I'm curious.

[jem777az]

Re: Hard question

Rodrigo you find that the 20/20 isn't bright enough? IMO its too bright to begin with. When I had mine I had to do the "deep mod" just to take off some of the high end and mids, it was just way too much. Especially with the EL-84's being naturally brighter than 6L6's or EL34's.

The deep mod basically evens out the eq curve on the 20/20. Mesa's poweramps inherently have a boost in the highs and high mids, so by clipping these two caps it takes out some of these frequencies.

[rodrigo_echeverri]

Re: Hard question

guys... actually, the question only came to my head from reading the manual but not out of the sound of the power amp... I was just curious how you can do this.

I dont have my own 20/20 here yet but from what I remember trying it in the store, it did sound less bassy than the 50/50... I think I prefer the sounds of EL84s...

I like that Ross pointed out exactly what each of those tubes does and what it means... I think that is useful to know.

Did you read Pete's article yet?...

[ May 13, 2003, 12:42 PM: Message edited by: rodrigo_echeverri ]

[OnlineStageGear]

Re: Hard question

If the 20/20 isn't bright enough for you, you definately don't want to do the Mod to it.

Is it new or used ? Perhaps it is due for some new Tubes.

Matt