Mesa boogie 3 channel dual rectifier tone mod

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Spencerleehorton

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Joined
May 12, 2012
Messages
4,035
Location
Felixstowe, Suffolk, UK
Hi all,
Have had my dual rec for quite a few years now and have never really been happy with it.
I have seen there is a tone mod which replaces the caps to Mallory 150M.
Does anyone have any experience with this?
 
Personally I think much of this kind of thing is arm-chair expert nonesense from solder happy tinkerers. Shot-gun changes are a waste of good drinking time at the pub.

I base that on my own simple tests. Around 2010 I built a test box to listen for myself. The only place that I found a cap type (the same measured values to 5%) which made any noticeable difference was on the first  coupling cap off the first preamp stage. That was on a AC30 type circuit, not a Mesa. In that case I found that one of the really old mica caps sounded slightly less harsh than the modern ones. That is all.

I do still have one unfounded tenet: I try to avoid metallised caps, like the 150M if possible. I like using old production that test good for DC blockage.

Testing for caps for leaking DC in old amps is worthwhile.
 
Spencerleehorton said:
Hi all,
Have had my dual rec for quite a few years now and have never really been happy with it.
I have seen there is a tone mod which replaces the caps to Mallory 150M.
Does anyone have any experience with this?

If your not happy with the amp, changing the parts for ones of the same value is not going to make it much better. Instead you should focus on revoicing the preamp to fit your personal taste.
 
I hate every rectifier I have tried. they sound fizzy and they have too much low end. I don´t think changing the caps will solve that.
I have heard that there is one revision that sound better (perfect?).

I have reach great tones with a tubescreamer in front of it. gain at zero, volume at 12 or more and tone to taste.  without the tubescreamer it is useless to me. the speaker and mic also help a lot with the tone.
 
12afael said:
I hate every rectifier I have tried. they sound fizzy and they have too much low end. I don´t think changing the caps will solve that.
I have heard that there is one revision that sound better (perfect?).

I have reach great tones with a tubescreamer in front of it. gain at zero, volume at 12 or more and tone to taste.  without the tubescreamer it is useless to me. the speaker and mic also help a lot with the tone.

I have a single rectifier that sounds pretty magical. I don't know why, because every other rectifier amp I have played sounds pretty terrible and I have owned a few of them. Speakers like vintage 30s really help control the unbearable bass. Seriously the bass knob on that amp is the easiest way to ruin your tone lol
 
On investigating this further a few people offer a re voicing of the tone circuit:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F301982698046

There is also :

http://www.voodooamps.com/home/default.aspx

I have read that these mods tame the muffled low end, boost the mids, stop the fizz and get a better gain.

I run my amp with basically no bass, mid up full and presence and treble about half way.
Ch2 on vintage and ch3 on modern but ch1 just doesn’t sound great, I’ve also modded the FX loop to series.
I have celestion cream backs in the 2 x 12.
 
There is also a small mod you can do to the effects loop in which you can add a small two pole switch ,it bypasses the buffers and gives a slightly cleaner path in bypass mode. Nearly all amps with extra high gain available such as boogies lack something when compared to a less busy circuit. Another thing about the dual rect is theres lots of options and I had a few customers who found it difficult to pick and stick to a particular setup ,sometimes less choice is better. Id also second the opinion that simple changes in component types and not values wont bring about much change in tone . Fine tooth comb the mods already done by people on this model ,then once youve found the ones that go in the direction you want ,incrementally add the various components one at a time until you get to where you want to be . Its also not the easiest board to work on due to the hard wired nature of the pots, switches and jacks, could be a safer and easier bet when replacing caps to leave some mm's of the original component legs rather than desoldering/resoldering  directly to  the board.
 
I would try to get in to details of revisions and see what it change but it is not easy without official schematics.
the tubescreamer work well because it cut a lot of bass, around 800 hz if I remember correctly.
 
This is what they have said:

The kit contains 8 caps and 2 pots. It limits the low end in the first two stages, increases the signal going through the GAIN pots and shunts the fizz at the VOLUME controls.

Any ideas?
 
What specifically don't you like about the amp? What would you want it to sound like?

There can be a few ways to get there,  these can be a pain to work on though.

 
Spencerleehorton said:
As per my last post, I want to reduce bass, clean up the mids and stop the fizzy top end, also getting better gain would be nice.

Start by reducing the bass then. There are a few ways to do it, small cathode bypass capacitors and/or smaller coupling capacitors. Then try to isolate the other issues. Find the stages that are distorting in an unpleasant way, or adding high harmonics that you dont like, and then you can tweak the circuit values. You dont need to buy a mod kit to do this, need to just start experimenting, as these mods are interactive with each other.

This isnt meant to be a negative post either, just start expieremenint with new values, and see what you like/dont like. :)
 
These are just some thoughts

Some high gain amps use smaller coupling caps after gain stage 1 and sometimes  2. So instead of. 022u there is. 01u. .0047u or even. 0022u. These lower value will thin out the sound of a particular channel.

A 33k resistor in the tone stack will give more mids than 47k .

After the phase inverter  there are coupling caps,  .022 is more typical for Marshall amps,  this will reduce bass for the entire amp.  There is also a cap  connecting the two plates of the phase inverter,  raising this will decrease treble on the entire amp.  Some amps use a bigger cap in series with a pot for a "cut" control.
 
Shelling out £70 on a a few caps and pots I thought was a bit bad considering I probably have all those types of caps anyways!!!

What you have suggested is absolutely perfect.

Stage 1 would be to mod the amp and adjust the bass

Stage 2 more mids

Stage 3 tame fizz

Stage 4 look at gain structure

Here is the schematic

http://diy-fever.com/wordpress/wp-content/uploads/2009/12/dual_rectifier.pdf

Need to find phase inverter coupling caps and change for 0.022uf to reduce bass?
 
On page 7 is that the 47k which needs to be changed in the tone stack?

Think I’ll need a bit of help isolating what is what with this!!
But if this helps everyone and sorts out my problem I’m more than happy to do it!!!!
 
Another question is are you trying to change the clean channel, the distorted channels,  or both? Is everything too bassy and fizzy,  or just the distorted channels?

For post phase inverter caps generally,
Fender use  .1u
Marshall  .022u
Soldano and Mesa  .047u

The caps change the overall low end and response of the power amp section,  Best for clean might not be the same as best for distortion.

Also try to compare schematics for a variety of amps to get a feel for various differences.

 
Spencerleehorton said:
On page 7 is that the 47k which needs to be changed in the tone stack?

Think I’ll need a bit of help isolating what is what with this!!
But if this helps everyone and sorts out my problem I’m more than happy to do it!!!!
That 47k is what is usually referred to as the slope resistor and that is your google search word.
Season to taste.
 
Really i would like to go more Marshall sound, could someone explain where the 47k i need to change to 33k is please?

I used to have a 100watt Plexi, i think i was 1969 and i had Mullards in it and took it to Pete Cornish, he loved it and rated it at 190watts!!! it cracked the wall in my studio when i turned it up full and had the fuzz face on!!!!!
I don't need anything that loud now but i loved the tone i used to get and to be able to get somewhere close would be great.

for me i think the whole amp is too bassy as each channel i have the bass nearly off, the mids up pretty much full.

Ah i see now, after a google search i did find the right area!!!
 

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Those are the ones, but they work as part of the chosen EQ intention together with the other component values. Maybe you need to google the slope resistor in the Mesa context.

Geheimtip: If I was in your shoes, before starting with chopping and changing, I would get hold of a good condition Burman Pro in England and sell the Mesa. That will get you the brachial sound without having to reinforce your foundations or walls. They were a secret weapon of many studios in the UK around the end of the 70's and early 80's.
 

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