3 channel recto sound to 2 channel sound recto mod idea.

[GNZ]

I was looking the 3 channel rectifier schematics, and I realized why theoretically it sound diferent than a 2 channel rectifier.
the gain pot of channel 2 and 3 it is 250k that should be sound a lot more scoop then 1M pot, I did try this in others amps and it is a very big diference wehn you swamp gain pot values.
I think its a very easy mod that someone have to try to make a 3 channel sound a lot more like a 2 channel, I cant do it because I dont have a 3 channel recto.

best regards.

 

[fluff191]

Man if all it took to get a 3 Channel to sound like a 2 Channel is changing out a gain pot, everyone would have changed it out by now.

 

[YellowJacket]

Maybe he's the one guy who actually read a schematic!! LOL!

I wonder if there are any Rev C and / or Rev D schematics out there. It would be interesting to see what mods 'could' be done to make a 3 channel sound more like an early dual. The problem, of course, is tracking down the old output transformers from the Mark III amps. It seems like a prohibitively expensive quest, if you ask me. Better to send the amps off to John! (FJA)

 

[GNZ]

Man if all it took to get a 3 Channel to sound like a 2 Channel is changing out a gain pot, everyone would have changed it out by now.

It is very interesting in the history of mankind there are many examples like this. paradigms are so strong in the minds of people. in fact not surprise me if someone did the mod, and found no further improvement because the mod is "way too easy" for his mind.
think objectively sometimes is very difficult, and perhaps the only reason why nobody has done before, simply because it is way too easy!

I'm pretty sure that the change will bring the sound of a 3-channel so much close to a 2-channel than any other thing in that schematic. and if still does not sound 100% like a 2 channel, find what value you can change to mate 2 channel schematic specs, like 100ohm resistor on the catodes. and if still does not sound 200% like a 2 channel, enjoy it, change 250k to 1M pot will bring better fat midrange gain response to your sound.

GNZ.

 

[GNZ]

100ohms resistor in the catode between 1uf and ground maybe are there emulating the resistance of the LDR that in the 2 channels are.

Regards.

 

[YellowJacket]

It is very interesting in the history of mankind there are many examples like this. paradigms are so strong in the minds of people. in fact not surprise me if someone did the mod, and found no further improvement because the mod is "way too easy" for his mind.
think objectively sometimes is very difficult, and perhaps the only reason why nobody has done before, simply because it is way too easy!

It helps being able to read a schematic, doesn't it? I'm envious, I would LOVE to be able to mod things like you do!

I'd check the model of output transformer being used in the different designs. That can affect tone too.

 

[domct203]

Very interesting.......

I'm curious what values the ch 3 & 4 gain pots are in the Roadster. Everyone says the Roadster is closer to the 2-ch sound.

Dom

 

[msi]

There was more going on in the switch from the two channel amps to the three. Switching from using LDR's to Relays for one thing. Even when off LDR's leak some signal into the disabled channel. Even when on, they still have a little resistance. Relays exhibit none of these traits. Everyplace where a LDR was present in the two channel amp would have to be replaced with two resistors in the three channel amp to get a closer approximation (one for the off resistance, one for the on resistance). Then you'd have to switch between those two resistors depending on which mode the amp was in, and which channel you were using.

Mesa took this into account by adding the 100 ohm resistors at the cathodes of the gain stages to maintain the on resistance of the LDR's that they removed. But to do that for every place an LDR was located is stupid. Also part layout and component choice can affect the sound of the amp as well.

If changing the value of one pot was going to make that big a change then it would have been done by Mesa, patented, and made a bullet point in advertising. The biggest change you'd notice in reality is the taper of the volume control would be changed. It would either get really loud really quick, or do nothing until the very end of the rotation.

The two and three channel amps sound similar enough that most people could never tell the difference between them. And the guitarists that notice the difference can easily find one at a reasonable price. They are not rare amps. Maybe uncommon, but not rare. I have three and none of them cost more than 1000 dollars.

 

[GNZ]

There was more going on in the switch from the two channel amps to the three. Switching from using LDR's to Relays for one thing. Even when off LDR's leak some signal into the disabled channel. Even when on, they still have a little resistance. Relays exhibit none of these traits. Everyplace where a LDR was present in the two channel amp would have to be replaced with two resistors in the three channel amp to get a closer approximation (one for the off resistance, one for the on resistance). Then you'd have to switch between those two resistors depending on which mode the amp was in, and which channel you were using.

Mesa took this into account by adding the 100 ohm resistors at the cathodes of the gain stages to maintain the on resistance of the LDR's that they removed. But to do that for every place an LDR was located is stupid. Also part layout and component choice can affect the sound of the amp as well.

that it not all right, for example if you have an LDR that has 100ohm of resistence wehn it is on, next in series to a 470k resistence (like just after the gain pot in a 2channel recto) you have a 470,1k ohm in total, and every resistance have a 1% of variation at least, so, in that case it realy dont make any diference.
but, in the catode the LDR is betwen ground an a catode, so it makes a litle diference, and thats why you are seen that resistense just there, no in other place of the 3 channel circuit, so LDR`s are not the 2channel sound factor.

If changing the value of one pot was going to make that big a change then it would have been done by Mesa, patented, and made a bullet point in advertising.

The two and three channel amps sound similar enough...

yes the two amps sound similar, so there is no big change. but a lot of people think that 2channel sound better, and change the gain pot will do a diference for sure, maybe just that diference.
I think they thought that change 1M to 250K pot was an improvement for the new model, a litle more scoop and heavyer tone ever for a dual recto, and they always will sale a new model like a better one, but no always new its better.

The biggest change you'd notice in reality is the taper of the volume control would be changed. It would either get really loud really quick, or do nothing until the very end of the rotation.

that is totaly wrong, the gain pot not only works as a variable resistence, it is also the grid resistor of the stage:

Spoiler

"Capacitor Ci is the input coupling capacitor. It is used to isolate the grid circuit from the DC voltage at the output of the previous circuit. This capacitor, in conjunction with the grid resistor, controls the frequency response of the stage.
Rg is the grid resistor, which is used to provide a reference voltage for the grid circuit (ground in this case). It is usually a high value, such as 1Megohm. This resistor controls the input impedance of the stage". from http://www.aikenamps.com

the gain pot works like a conjuntion of two resistances, one variable, other static to ground (grid resistor). the static part is use as a grid resistor, the variable in conjuntion with the static control the gain.
if you measure with your tester the pot leg 1 and 3, no mather how much you move the knob, you will always get the total amount of resistance that the pot are, if you measure leg 2 and 3 or 2 and one, you will read the change resistance wehn you move the knob.

so if you change the gain pot from 250k to 1M (a lot more amount of resistence that 100ohms LDR), you are also change the grid resistor and the low midrange response of the stage.

Regards.

GNZ.

 

[msi]

Very well put. But you ignored another part of what I said. The LDR's also bleed through. And can have a very wide range of resistances. The amount the LDR's light up will be affected by the bold/spongy setting. In spongy they will be darker which means they will attenuate more signal in the on channel.

And also like I said before even if it makes a change, your average person will probably not hear it. Might it affect how the amp feels? I doubt it will very much.

Finally, what we are doing here is equivalent of an internet nerd fight arguing over things we have no power to prove or disprove and is ultimately pointless. This discussion can go on with, "yes it will/no it wont" until someone gets upset and knocks their chess pieces over and runs away to their mommy. So I'm content to say I've established my argument that there is more required to get closer to the two channels sound than that pot, and that changing the pot is not worth the effort. I don't think we can be convinced to see the others point of view.

 

[GNZ]

Very well put. But you ignored another part of what I said. The LDR's also bleed through. And can have a very wide range of resistances. The amount the LDR's light up will be affected by the bold/spongy setting. In spongy they will be darker which means they will attenuate more signal in the on channel.

And also like I said before even if it makes a change, your average person will probably not hear it. Might it affect how the amp feels? I doubt it will very much.

Finally, what we are doing here is equivalent of an internet nerd fight arguing over things we have no power to prove or disprove and is ultimately pointless. This discussion can go on with, "yes it will/no it wont" until someone gets upset and knocks their chess pieces over and runs away to their mommy. So I'm content to say I've established my argument that there is more required to get closer to the two channels sound than that pot, and that changing the pot is not worth the effort. I don't think we can be convinced to see the others point of view.

Not to convince you, for the people that are reading this post and deserve good quality information, yes the LDR`s bleed trough in some special or extreme conditions, but in the 2 channel arquitecture there is no one that will bleed, or work not so acurate then a relay because no one are in a stress condition. iff they impact the signal it will be with some insignificant resistance, 100ohms to 190ohms, and even in spongy setings if they go far to 1Kohm, they will not impact the sound in a way that you can feel or hear.

Changing the pot will be very noticiable and audible change, im sure because i did in others amps, I did hear the change plus in theory it has to be a big change in the frequency response of the stage (did I left no conclusive information about it?)

this is not pointless for a lot of people that are searching for information to find his tone, and I`m not content if some one gets bad information and confused ideas, internet are plenty of that, thats why i have to tell you that you are wrong, nothing personal or ego nerd fight.

output transformer can be other important pre 500 2channel sound factor.

i will do some clips of my tremoverb with 250k pot and 1M pot comparition soon.

regards

 

[TREC]

If the 2 channel rectos are so much better than the current 3 channel versions why dont Mesa try to re create the original tone that "everyone' seem to prefer? Or is it an issue of those parts that made them so special no longer available? you would think as time goes on this should get better not backwards. Its seems that not may people have much good to say about the 3 chanel rectos (stock at least). I have never heard a 2 channel in person but they do seem to sound awesome?



Dunno just my 2 cents

 

[GNZ]

So, I open my tremoverb to change the pot value and finaly do a comparision and clips, but ironicaly, my 2 channel dual rectifier tremoverb has 250K pots!!!!



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waht this mean??? every recto has 250k??? or just the new ones??? do the 2channel rectos pre 500 has 1M pot???
there is my recto serie



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well, it`s the perfect situation for me to tell you if change 250k to 1M make a diference, or not, and how, so i did:



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And my veredict is...

1M pot dont change the tone like you are moving any well of the eq, it changes the feel and tone from the gain, make it a litle more fat, chunkier and adding a more crunch to the mid range, it make a more tight low end too. it is not a night and day change, its like your rectifier just awake more angrier, and horny... :evil:
i like a lot the change, thats way i put new pots and new and better caps as you can see in the picture, and i will make some clips, but to make 1M to 250K i just will run a 330k resistance in paralell to the pot.

regards!

 

[mightywarlock]

i have both.

a 3ch. (which is for sale by the way, feel free to buy it from me cheap to do your experiments on) and a very very old recto.

there has to be more to it than just a pot.

There is something to the entire tone that is different on any modern Recto I have ever tried that is not on the old ones.

There is some kind of halo of distortion surrounding the tone that is not there on the old one. It's the reason I have sold every recto i have owned except for the ancient one.

it's "tone" is clean. very clean, and yet, all not that different.

I always offer but no one ever takes me up, if anyone wants to actually examine my 2ch. rev. c to compare it to the 3ch. and you are in the L.A. area, just let me know.

It's more than just pots. it's also transformer as well.
has to be more than that too in my opinion.

 

[GNZ]

I always offer but no one ever takes me up, if anyone wants to actually examine my 2ch. rev. c to compare it to the 3ch. and you are in the L.A. area, just let me know.

I would love to do that, but I`m in Chile, south america.

It's more than just pots. it's also transformer as well.
has to be more than that too in my opinion.

I never said that are just the pots.

 

[TREC]

Sounds interesting, look forward to hearing the clips you do.

So, I open my tremoverb to change the pot value and finaly do a comparision and clips, but ironicaly, my 2 channel dual rectifier tremoverb has 250K pots!!!!



Uploaded with ImageShack.us

waht this mean??? every recto has 250k??? or just the new ones??? do the 2channel rectos pre 500 has 1M pot???
there is my recto serie



Uploaded with ImageShack.us

well, it`s the perfect situation for me to tell you if change 250k to 1M make a diference, or not, and how, so i did:



Uploaded with ImageShack.us

And my veredict is...

1M pot dont change the tone like you are moving any well of the eq, it changes the feel and tone from the gain, make it a litle more fat, chunkier and adding a more crunch to the mid range, it make a more tight low end too. it is not a night and day change, its like your rectifier just awake more angrier, and horny... :evil:
i like a lot the change, thats way i put new pots and new and better caps as you can see in the picture, and i will make some clips, but to make 1M to 250K i just will run a 330k resistance in paralell to the pot.

regards!

 

[GNZ]

ok, i think that I Fail!

I put a switch and a 330k resistence across the 1M pot, and I did record, but, almost was not any diference, the only diference was that wehn the pot was "virtually" 250K the sound was little more tight in a low mid range, barely i did hear when i was palm muting chunka chunka chunka in a A string
now I doubt that I did hear a diference before, but also maybe puting a resistance across the pot dont make it true 250Kpot. finally i think i have to do a clip swapping the whole pot, but if you ask me right now, 1M to 250k its not a big change and even i dont know if it is a good change.

And by reading the other post about a pre 500 recto gain pot, maybe there is no one rectifier that has 1M pot and it is just a schematic bluff!!!

best regards.
GNZ.

 

[GNZ]

so, finally i have conclutions that satisfy me thoughs.

first, i could not do clips to show waht I did experiment, because it 1M to 250K change in a way that you can barely record with my cheap preamp, but sure you can feel. but i have a better theory background to explain you waht happend.

I was not deaf, waht I did describe like a angrier horny rectifier was true, that´s because 1M pot give you more gain! and take some hig end, so thats why I did feel the rectifier more crunchier in the mid range. and was no so much gain boost and highs loss so thats why i cant record it. also, to put a 330K resistor across the pot don´t make it true 250K pot.

I was expecting a more radical tone change, but it does not happend because the pot was acting WITH the grid resistor thats is before (2m2) so the tone change can´t be a lot. if you try this in a jcm800 like amp you will hear a lot more tone change, because the gain pot it is the grid resistor.

I did back to 250K because it is more clear, less gain and less noise, 1M gives more gain but more noise too, and a litle more low mid range, and wehn you crank the amp it becomes muddy, it was fine at low volumes, i like it a lot, but 250K its a better choice for a overall performance.

i did a drawing



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as you can see, the pot acts like one static resistance (green number 2) and two variable resistances (green number 1 and 3)
-resistance 1, works with 2m2 and 1M drains less signall to the ground than 250K, i think that only drain some low mid range, thats why wehn i put a 330K across the 1M only hear a low mid range change.
-resistance 1 dont take so much gain, it takes highs, that why there is a cap preventing this acros that resistance.
-and resistance 3 take signal to the ground and that have direct impact to the gain.

I enjoy so much doing this, I did simplify the theory as much i can to explain you how did this work and I hope you understand this and maybe some would like to try with 500K gain pot or 1M.

and about 3 channel to 2 channel sound, i dont think that there is a rectifier with 1M pot by reading others posts about gain pots, because my 2 channel recto its original with 250K even wehn the schematics says 1M, and because 1M its not the way to get a better sound rectifier IMO.

best regards!

 

[jamme61]

and about 3 channel to 2 channel sound, i dont think that there is a rectifier with 1M pot by reading others posts about gain pots, because my 2 channel recto its original with 250K even wehn the schematics says 1M, and because 1M its not the way to get a better sound rectifier IMO.

best regards!

My TOV has 250K pots too, not 1 meg.

 

[twothemax]

i had both 2 and 3 ch mesa drs. there is no difference. its all hype as far as i am concerned. i said it before if the 2ch were really any better mesa would still be making them. i know some will disagree but thats my thoughts. i have no problem making my 3ch sound like my 2 ch. but the 2 ch cant make some of the tones the 3ch can.
the 3 ch eq is by far the most trickiest to handle though.
rock on 3ch owners!!!!! 8)