NOS John Mayer Sig / Wonderland 100W

[mojotom]

On my amp I removed the 10n cap, run an AT7 with 25u cathode cap and a feedback network around the AT like a SSS.

[Bombacaototal]

I think Two Rock added the cap to (i) address the reverb hum, which happens due to the classic tone PT and small headshell, and placement of the tank.

The value of the cap used will have very little effect at 50-60 Hz, so reducing hum is not likely to be a factor. I can agree that a poorly positioned reverb tank can create a hum problem, but why do you think the Classic Tone PT is worse than others?

Hi Martin, in my case that was a fix for the Hum (or at least to decrease it substantially) so I have to disagree.. although I prefer the sound without and have since removed the cap and decided to live with a bit of hum...and Two Rock uses (at least historically) several different cap values, not just one.....id say any laydown PT including classic tone, as the stand up one seems the be the only option to prevent the hum . specially if you are running EU voltages

[martin manning]

in my case that was a fix for the Hum (or at least to decrease it substantially) so I have to disagree..

Seems odd as the recover amp gain isn't affected at those frequencies.

[mojotom]

I think Two Rock added the cap to (i) address the reverb hum, which happens due to the classic tone PT and small headshell, and placement of the tank.

The value of the cap used will have very little effect at 50-60 Hz, so reducing hum is not likely to be a factor. I can agree that a poorly positioned reverb tank can create a hum problem, but why do you think the Classic Tone PT is worse than others?

Hi Martin, in my case that was a fix for the Hum (or at least to decrease it substantially) so I have to disagree.. although I prefer the sound without and have since removed the cap and decided to live with a bit of hum...and Two Rock uses (at least historically) several different cap values, not just one.....id say any laydown PT including classic tone, as the stand up one seems the be the only option to prevent the hum . specially if you are running EU voltages

Working with EU voltage on a tight chassis.
I prefer to isolate RCA Jacks and tried various ground points (did help on reverb hum). You got to pay attention to the reverb transformer ground too, try to send it to the ground of the HT supply.
I did use 22k/22u on that node and wired to the screen supply, not the PI like Two Rock did (if I remember correctly).
No hum on mine, but the tank is on the ground, not bolted I side a cab.

[Bombacaototal]

The value of the cap used will have very little effect at 50-60 Hz, so reducing hum is not likely to be a factor. I can agree that a poorly positioned reverb tank can create a hum problem, but why do you think the Classic Tone PT is worse than others?

Hi Martin, in my case that was a fix for the Hum (or at least to decrease it substantially) so I have to disagree.. although I prefer the sound without and have since removed the cap and decided to live with a bit of hum...and Two Rock uses (at least historically) several different cap values, not just one.....id say any laydown PT including classic tone, as the stand up one seems the be the only option to prevent the hum . specially if you are running EU voltages

Working with EU voltage on a tight chassis.
I prefer to isolate RCA Jacks and tried various ground points (did help on reverb hum). You got to pay attention to the reverb transformer ground too, try to send it to the ground of the HT supply.
I did use 22k/22u on that node and wired to the screen supply, not the PI like Two Rock did (if I remember correctly).
No hum on mine, but the tank is on the ground, not bolted I side a cab.

On my case and also Two Rock the hum is caused by the PT electromagnetic field, and not from grounding. A quick test of removing the pan from the head will reveal the PT as the source. Having the tank outside the head like you did is a way to fix this

[dbharris]

I built mine with Classictone iron and grounded per Taylor's layout. All caps are the proper values but some of my resistors are are little off, closest I could get with the dralorics Jelle had. I did use isolated rca jacks. I believe I ran the ground on those back to the preamp star.

I have no reverb hum or noise otherwise. This is by far my quietest amp including Marshall 18w variant I built, modded Fender champ 600, mesa LSS, and Egnater tweaker 15. My house has original wiring from the 1940s and is usually really noisy.

I like that the reverb is a little dark or modern sounding. More like a studio reverb than blackface fender.

-Dan

[jfs322]

I think Two Rock added the cap to (i) address the reverb hum, which happens due to the classic tone PT and small headshell, and placement of the tank. (II) reduce the amount of reverb for a better dry/wet ratio given they use the 1M resistor on the dry path which really reduces gain (III) as mentioned above to make the reverb darker

I've spoken to Two-Rock explicitly about why that cap was added, and not once was PT/reverb hum mentioned. I was told it was simply to darken the reverb signal a little bit.

Also, a note to the larger group: the JM Sigs reverb return cap value is 750pf, so I'm not sure where the 10nf value is coming from, so that may be a mistake in the Wonderland schematic and may explain why people are not liking it with a 10nf cap there...

[neskor]

I've spoken to Two-Rock explicitly about why that cap was added, and not once was PT/reverb hum mentioned. I was told it was simply to darken the reverb signal a little bit.

Also, a note to the larger group: the JM Sigs reverb return cap value is 750pf, so I'm not sure where the 10nf value is coming from, so that may be a mistake in the Wonderland schematic and may explain why people are not liking it with a 10nf cap there...

that 750pF make more sense

[martin manning]

I wonder if in the amp the schematic was drawn from the 10n might have been a 1n?

[jfs322]

I wonder if in the amp the schematic was drawn from the 10n might have been a 1n?

Below is the gutshot of the actual amp that the Wonderland schematic/layout were drawn from. It is not one of the actual 25 limited edition amps, but rather a post-production version built for a customer in 2009. You can see the small cap on the reverb return pot. It's a 750pf 1kv ceramic. The Wonderland layout (and schematic) both say 10nf, which is an error. Ryan's updated layout (here: https://ampgarage.com/forum/download/fi ... &mode=view) has the more accurate values, but his has that cap listed as 75pf, which I believe he simply forgot to add the zero to reflect the cap's actual value of 750pf.

[dbharris]

Thanks for the info! I saw Ryan's layout had 75p but I went with Taylor's value there. Next time I crack her open I'll adjust that cap too. I don't think I have a 750p, but I'm sure I have a 500p and 250p. Of course my mouser order just shipped on Friday

-Dan

[neskor]

I see different values for this resistor in the mixer circuit
108K,120K,220K..
what is the original value?

[jfs322]

I see different values for this resistor in the mixer circuit
108K,120K,220K..
what is the original value?

Go with the values in Ryan’s updated layout (which I posted above, and re-posting here: https://ampgarage.com/forum/download/fi ... &mode=view). His updated layout was created after being inside an actual JM Sig amp and cross-referencing with gutshots of multiple other JM Sig and post-production amps, including mine. His layout should be considered the most accurate authority we have thus far.

[norburybrook]

well after all these years of me thinking the 68k-1meg divider was the issue regarding loss of gain it was in fact the mixer in the resistor circuit. the original AN layout shows a 120k there, I swapped with Ryan's latest version of 220k and boom...it's how I always thought the amp should be level/gain wise , I've no need for the variable gain pot on the back now the amp is lovely and loud.....


thank you guys for finally getting to the bottom of this. I would urge everyone who's built a wonderland in the past to modify their amps ASAP ,especially if you're @50w

I changed the cap on the reverb too and added 300R to the bass pot resistor to bring it in line with the new measurements. 1.82k

really great


M

[Gtsirvou]

Hello everybody,

I also built an amp based on the JM, and it too seems to have somewhat anemic gain. The solution of swapping the mixing resistor to 220K seems like the first thing to try, but looking on all the discussion in this and another thread by Marcus i get some conflicting information. You are mentioning changing the DRY resistor to 220k from 120K, but all the schematics and layouts posted actually have the WET resistor at 120K/220K (tied to the plate of the triode with reverb RETURN at its grid) and the DRY one at 68K. Only the preliminary schematic by Aaron has 68 K on the WET side. Is this perhaps just a mistake on preparing the layout or schematic, since the two triodes are just next to each other? Thanks for your time