Want Pre500 tone? Here's how to get it!

[JCDenton6]

I think I'm going to switch out the presence pots to 25k while I'm inside the amp.
I was thinking of going with audio taper pots instead of linear taper pots...

I know they sound like going from 1,2,7,10 abruptly and so on. :lol:
I know the audio pots have more of a natural taper to them, like a steady increase of 1-10.

Audio and Linear taper pots have the same total resistance but differ in which position of rotation the pot will reach the 50% value.
Any reason to stick with linear?

 

[Anonymous]

I think I'm going to switch out the presence pots to 25k while I'm inside the amp.
I was thinking of going with audio taper pots instead of linear taper pots...

I know they sound like going from 1,2,7,10 abruptly and so on. :lol:
I know the audio pots have more of a natural taper to them, like a steady increase of 1-10.

Audio and Linear taper pots have the same total resistance but differ in which position of rotation the pot will reach the 50% value.
Any reason to stick with linear?

I actually thought the presence control was set up in such a way that a linear pot would let you hear a smooth taper. I could be wrong though; I haven't tried an audio pot there.

 

[JCDenton6]

I actually thought the presence control was set up in such a way that a linear pot would let you hear a smooth taper. I could be wrong though; I haven't tried an audio pot there.

Hmm, now you got me thinking about this... time to do some digging :?

 

[clutch71]

On to the mod!

1. Change the gain pots to 1MA. Make sure you swap the cap that jumps the two lugs to the new pot.

2. Swap this capacitor to one valued at .005uF, with a voltage rating of at least 450. (0.0047uF Orange Drop is perfect)

This should do it! Of course, changing the Red presence control to a 26k linear would be closer still, but the stock 100k gets you the same sound (just has more presence past 9:00).

Can we assume that these values were changed between revisions?

 

[domct203]

On to the mod!

1. Change the gain pots to 1MA. Make sure you swap the cap that jumps the two lugs to the new pot.

Can we assume that these values were changed between revisions?

+1. This post http://www.grailtone.com/forum/viewtopic.php?f=24&t=47732 has Marcus at Mesa saying they were all 250K gain pots, not 1M (see the last couple of posts).

If it sounds good though it really doesn't matter, does it?

Dom

 

[Anonymous]

+1. This post http://www.grailtone.com/forum/viewtopic.php?f=24&t=47732 has Marcus at Mesa saying they were all 250K gain pots, not 1M (see the last couple of posts).

Huh. Not quite sure where that information comes from. I know from reliable sources that the earlier revisions (C and D) did have a 1M pot.

On to the mod!

1. Change the gain pots to 1MA. Make sure you swap the cap that jumps the two lugs to the new pot.

2. Swap this capacitor to one valued at .005uF, with a voltage rating of at least 450. (0.0047uF Orange Drop is perfect)

This should do it! Of course, changing the Red presence control to a 26k linear would be closer still, but the stock 100k gets you the same sound (just has more presence past 9:00).

Can we assume that these values were changed between revisions?

From earlier to later revisions, these are the differences that I believe really count. There are other differences - series effects loop, attached power cord, different transformers, etc. - but those will be less obvious and more subjective. Rev. G has 250k gain pots, the cap value for that position is .01uF, and the presence control is 100k.

 

[ChrisRocksUSA]

pardon my n00bliness, but what is the advantage of all that gain?

how is it 'more usable' if it's got the max amount of gain a reg recto has at 11 o clock? Everything past that is just overdoing it, and you have less ability to dial in a really sweet spot b/c there is so much more gain per knob rotation.

seems like a waste to me.

 

[Anonymous]

pardon my n00bliness, but what is the advantage of all that gain?

how is it 'more usable' if it's got the max amount of gain a reg recto has at 11 o clock? Everything past that is just overdoing it, and you have less ability to dial in a really sweet spot b/c there is so much more gain per knob rotation.

seems like a waste to me.

It's a different type of gain. Similar to the way people use OD pedals with the gain low in front of their Rectifiers because they want a more immediate response. When the gain is at 11:00, it has as much gain as a normal Rectifier, but it's so much tighter that adding additional gain isn't over the top flub, but harmonically rich saturation. In this case, pushing the gain knob past 11:00 wouldn't be overdoing it, and even when the gain is at 3:00, it's still just a little bit tighter than a normal Rectifier.

This clip that I did has the gain at about 1:30.

 

[Third Age Amps]

The gain pot is a voltage divider. As you turn the gain up, you are lowering how much of the signal is getting shunted to ground and increasing how much gets passed on to the rest of the preamp.

7 o'clock or off, takes the signal straight to ground so it goes no further. As you increase the gain you split how much of the signal is being grounded versus being passed on to the rest of the preamp. At full volume, a 1M pot is passing much more voltage that a 250k pot is. So you ARE getting more gain at lower settings because instead of having to dime the gain with the 250k, you can set it at 1-2 o'clock to get the same amount of gain out of the 1M.

You can get even more saturation out of it by engaging the loop, diming the Channel Master and using the Loop Active Master as the volume control. It gets a little tricky but you can get some really interesting tones out of it.

 

[Anonymous]

You can get even more saturation out of it by engaging the loop, diming the Channel Master and using the Loop Active Master as the volume control. It gets a little tricky but you can get some really interesting tones out of it.

Interesting! I'm going to have to try that.....

 

[JCDenton6]

Based on TheMagicEight's last clip, this makes me think that most of what Mesa did when revising the recto is play around with that specific capacitor value and the gain/presence pot values, because that is the pre 500 tone to a T.
When comparing the various boards of each revision, they look identical except for this small change (addition of another resistor and position change from sideways to upwards on the PCB and the resistor next to the LDR) which happened with revision E (circled in yellow)

Revision C


Revision D


Here is where the addition of the third resistor and the positioning (from sideways to upwards) change took place.

Revision E


Revision F


Revision G


This addition of this third resistor and change of positioning (from sideways to upwards and the addition of the resistor next to the LDR) happened with Revision E.

 

[Anonymous]

Based on TheMagicEight's last clip, this makes me think that most of what Mesa did when revising the recto is play around with that specific capacitor value and the gain/presence pot values, because that is the pre 500 tone to a T.
When comparing the various boards of each revision, they look identical except for this small change (addition of another resistor and position change from sideways to upwards on the PCB) which happened with revision E (circled in yellow)

Very interesting! I'm curious if that actually affects tone or if it has to do with another type of circuit (such as switching). I also notice the absence of a resistor to the left of the LDR near those two 0.047uF caps (to the bottom right of the circled cluster of resistors). Do you know what they're for?

 

[JCDenton6]

lol, I forgot about that change as well, haven't been to sleep in 2 days. :lol: :lol: Fixed and updated my pics above.
I'm not certain but I think it was there to help with the slight tonesuck of the LDR , but I'm still deciphering the schematics with my friend.

Hoping we can fully crack the case on the "pre 500" tone but I think what you did was "it"

 

[JCDenton6]

Today's the day... got the parts and will swap them out... :mrgreen:

 

[Anonymous]

Today's the day... got the parts and will swap them out... :mrgreen:

Awesome!!! I've been waiting for someone else to try this!

 

[JCDenton6]

Got the parts in but the shaft is a little short on the pots (they are 1 meg audio pots). I'm going to have to call mesa for the correct pots.
I hear a difference... sort of. I'm sure I soldered correctly but I'm not getting the drastic change in tone you did.
Hmm...

I have more usable gain and it's tighter but I'm not getting that same type of growl that you did :?
It sounds almost the same but with more gain... :|
I'm pretty sure it's the gain pots though...

 

[Anonymous]

Got the parts in but the shaft is a little short on the pots (they are 1 meg audio pots). I'm going to have to call mesa for the correct pots.
I hear a difference... sort of. I'm sure I soldered correctly but I'm not getting the drastic change in tone you did.
Hmm...

I have more usable gain and it's tighter but I'm not getting that same type of growl that you did :?
It sounds almost the same but with more gain... :|
I'm pretty sure it's the gain pots though...

Hmm...and silly question, but you swapped the cap as well?

 

[JCDenton6]

Yep, and got the caps on both pots. Maybe my ears are fatigued (I got back from band practice a little while before going to work on the amp)
Maybe I burned out the caps on the pots? I'll go over the amp a little more tonight.

I'll post a clip tomorrow as well.

 

[JCDenton6]

OK my ears were definitely fatigued... the amp kills! :mrgreen:
It's a monster now... :twisted: Clips incoming later today!

 

[YellowJacket]

OK my ears were definitely fatigued... the amp kills! :mrgreen:
It's a monster now... :twisted: Clips incoming later today!

We're waiting! The idea of only modding one channel to the pre-500 tone is an interesting one. I wonder if it would retain the good clean tone and the wicked crunch?