NOS John Mayer Sig / Wonderland 100W

[norburybrook]

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

use these values in this layout it's the most recent known good values from the original JM amp. You can see the 120k has been replaced with 220k which made all the difference to my amp.

jmsig-fullLayout.png

M

[Gtsirvou]

Thanks for your quick reply. So it is the reverb mixing resistor that needs switching it seems right? Or I am completely ignorant on how the mixing network works... Just to make it crystal clear for future builders as well, because the two schematics below, have the 68K resistor on different sides (reverb/dry) and I saw yourself and other frequently referring to the 120K one as the dry resistor, which in the layout you posted is NOT on the dry side. I only insist because on this amp it is just two identically configured triodes and the grid inputs swapped could be an easy mistake. Thanks for your time once again.

[dbharris]

Yes, it is the Wet side mixing resistor that is increased. This has the effect of letting more dry signal through.

Look at the second schematic you posted. There is a 1M/68K voltage divider that attenuated the signal earlier in the circuit. Maybe that is what the references yiu saw were about? Then there is also the 68K/xxxK network to combine the reverb and dry signals.

People here used to swap out that first 68K to attenuate less signal. Now they are swapping the xxxK for a 220K in the reverb mixer.

I actually just got some 220K Dralorics in the mail yesterday. I think I will swap that resistor and the 750pf cap this weekend.

-Dan

[Gtsirvou]

Thanks Dan for sharing this information, please let us know how your amp has improved after the changes

[dbharris]

I made these 2 mods today and as I was reviewing this thread a little before I posted, I realized that I had wanted to adjust the dropping string too. Totally forgot about that earlier when I was doing the mods. Maybe tomorrow or next week....

I did not feel that the 120K/0.01u cap vs. the 220K/750pf was a huge difference. You can certainly hear it and feel it, but I can also imagine if you had two identical amps next to each other with only these changes it would come down to people's preference and they would split between both.

As mentioned above, these two mods work in opposite directions of each other, so the overall shift is not huge when doing both simultaneously. Increasing the resistor lowers the reverb in the mix, while decreasing the cap increases the reverb in the mix and also brightens it.

I swapped the 220K first and removed the return cap. Then I hooked up some alligator clips so I could test different caps while playing (there is low voltage on that part of the circuit). I started with the 0.01u cap. This definitely seemed "wrong" with the 220K. You had to really crank the reverb to get it to respond there was almost no reverb at noon. I then tried no cap. This was not for me, the timbre changed drastically and was "tinny" to my ears also like a fender where reverb at 9 o clock is more than enough. Next I tried a 500pf NOS sprague ceramic I got from Jelle (I pulled one that measured about 530pf). This was better, but still a bit bright. I did not have any 750pf caps. So, I clipped in some 220pf caps in parallel to the 530pf. I tried the small yellow vishay (china), the "quarter" sized orange vishay from CZ, and a Cornell Dubilier mica. The vishay caps were pretty similar, hard for me to really tell a difference in this context. The mica was a bit harsher sounding. I went with the smaller vishay just for ease of installing it.

I do think the 220K/750pf combo is "correct" and it definitely cuts a little better. Maybe something like 1000pf or 1500pf would be nice to try too for somebody who wants a darker sounding reverb without killing too much signal.

Interested to hear other people's experiences.

-Dan

[Guy77]

I made these 2 mods today and as I was reviewing this thread a little before I posted, I realized that I had wanted to adjust the dropping string too. Totally forgot about that earlier when I was doing the mods. Maybe tomorrow or next week....

I did not feel that the 120K/0.01u cap vs. the 220K/750pf was a huge difference. You can certainly hear it and feel it, but I can also imagine if you had two identical amps next to each other with only these changes it would come down to people's preference and they would split between both.

As mentioned above, these two mods work in opposite directions of each other, so the overall shift is not huge when doing both simultaneously. Increasing the resistor lowers the reverb in the mix, while decreasing the cap increases the reverb in the mix and also brightens it.

I swapped the 220K first and removed the return cap. Then I hooked up some alligator clips so I could test different caps while playing (there is low voltage on that part of the circuit). I started with the 0.01u cap. This definitely seemed "wrong" with the 220K. You had to really crank the reverb to get it to respond there was almost no reverb at noon. I then tried no cap. This was not for me, the timbre changed drastically and was "tinny" to my ears also like a fender where reverb at 9 o clock is more than enough. Next I tried a 500pf NOS sprague ceramic I got from Jelle (I pulled one that measured about 530pf). This was better, but still a bit bright. I did not have any 750pf caps. So, I clipped in some 220pf caps in parallel to the 530pf. I tried the small yellow vishay (china), the "quarter" sized orange vishay from CZ, and a Cornell Dubilier mica. The vishay caps were pretty similar, hard for me to really tell a difference in this context. The mica was a bit harsher sounding. I went with the smaller vishay just for ease of installing it.

I do think the 220K/750pf combo is "correct" and it definitely cuts a little better. Maybe something like 1000pf or 1500pf would be nice to try too for somebody who wants a darker sounding reverb without killing too much signal.

Interested to hear other people's experiences.

-Dan

Hi Dan, thanks for posting your experiments with the different value mixing resistors and caps.
Another option I have found to increase the signal with these amps, while keeping the mixing resistors at there stock values (120k/68K and a .01uf cap or the 220K/68k
750pf combo) is to change the plate voltages of the V1 tube.

I have increased this from the stock value of about 168v all the way up to 225v and have preferred various higher voltages over the 168v . You may find that you prefer a higher voltage on v1.
I have also placed the 1M/68k dropping string on a switch to change this to different values and really like this modification as well for increasing volume.

Cheers!

Guy

[dbharris]

I made these 2 mods today and as I was reviewing this thread a little before I posted, I realized that I had wanted to adjust the dropping string too. Totally forgot about that earlier when I was doing the mods. Maybe tomorrow or next week....

I did not feel that the 120K/0.01u cap vs. the 220K/750pf was a huge difference. You can certainly hear it and feel it, but I can also imagine if you had two identical amps next to each other with only these changes it would come down to people's preference and they would split between both.

As mentioned above, these two mods work in opposite directions of each other, so the overall shift is not huge when doing both simultaneously. Increasing the resistor lowers the reverb in the mix, while decreasing the cap increases the reverb in the mix and also brightens it.

I swapped the 220K first and removed the return cap. Then I hooked up some alligator clips so I could test different caps while playing (there is low voltage on that part of the circuit). I started with the 0.01u cap. This definitely seemed "wrong" with the 220K. You had to really crank the reverb to get it to respond there was almost no reverb at noon. I then tried no cap. This was not for me, the timbre changed drastically and was "tinny" to my ears also like a fender where reverb at 9 o clock is more than enough. Next I tried a 500pf NOS sprague ceramic I got from Jelle (I pulled one that measured about 530pf). This was better, but still a bit bright. I did not have any 750pf caps. So, I clipped in some 220pf caps in parallel to the 530pf. I tried the small yellow vishay (china), the "quarter" sized orange vishay from CZ, and a Cornell Dubilier mica. The vishay caps were pretty similar, hard for me to really tell a difference in this context. The mica was a bit harsher sounding. I went with the smaller vishay just for ease of installing it.

I do think the 220K/750pf combo is "correct" and it definitely cuts a little better. Maybe something like 1000pf or 1500pf would be nice to try too for somebody who wants a darker sounding reverb without killing too much signal.

Interested to hear other people's experiences.

-Dan

Hi Dan, thanks for posting your experiments with the different value mixing resistors and caps.
Another option I have found to increase the signal with these amps, while keeping the mixing resistors at there stock values (120k/68K and a .01uf cap or the 220K/68k
750pf combo) is to change the plate voltages of the V1 tube.

I have increased this from the stock value of about 168v all the way up to 225v and have preferred various higher voltages over the 168v . You may find that you prefer a higher voltage on v1.
I have also placed the 1M/68k dropping string on a switch to change this to different values and really like this modification as well for increasing volume.

Cheers!

Guy

Hi Guy, thanks for the tips! I know you've built several of these. My voltages now are about half way between the layout and your higher voltage preferences. I'm going to try lowering them to stock soon and if I don't like that I'll try going in the other direction as you suggested.

This amp is just amazing! I am still surprised that I can really crank this up to 70% master volume with a 2x12 and it is enjoyable to play in a small practice room at 100 watts. I never thought I would sell my mesa lone star special, but can't justify the space it takes up. I never play it anymore so I am going to trade it in at guitar center for some pedals and a small pedal board to bring to jam sessions.

I need to start my D'Lator build soon and then I have a 102 on deck afterwards. Hoping to get on the ODS bus before the end of the year.

-Dan

[Guy77]

I made these 2 mods today and as I was reviewing this thread a little before I posted, I realized that I had wanted to adjust the dropping string too. Totally forgot about that earlier when I was doing the mods. Maybe tomorrow or next week....

I did not feel that the 120K/0.01u cap vs. the 220K/750pf was a huge difference. You can certainly hear it and feel it, but I can also imagine if you had two identical amps next to each other with only these changes it would come down to people's preference and they would split between both.

As mentioned above, these two mods work in opposite directions of each other, so the overall shift is not huge when doing both simultaneously. Increasing the resistor lowers the reverb in the mix, while decreasing the cap increases the reverb in the mix and also brightens it.

I swapped the 220K first and removed the return cap. Then I hooked up some alligator clips so I could test different caps while playing (there is low voltage on that part of the circuit). I started with the 0.01u cap. This definitely seemed "wrong" with the 220K. You had to really crank the reverb to get it to respond there was almost no reverb at noon. I then tried no cap. This was not for me, the timbre changed drastically and was "tinny" to my ears also like a fender where reverb at 9 o clock is more than enough. Next I tried a 500pf NOS sprague ceramic I got from Jelle (I pulled one that measured about 530pf). This was better, but still a bit bright. I did not have any 750pf caps. So, I clipped in some 220pf caps in parallel to the 530pf. I tried the small yellow vishay (china), the "quarter" sized orange vishay from CZ, and a Cornell Dubilier mica. The vishay caps were pretty similar, hard for me to really tell a difference in this context. The mica was a bit harsher sounding. I went with the smaller vishay just for ease of installing it.

I do think the 220K/750pf combo is "correct" and it definitely cuts a little better. Maybe something like 1000pf or 1500pf would be nice to try too for somebody who wants a darker sounding reverb without killing too much signal.

Interested to hear other people's experiences.

-Dan

Hi Dan, thanks for posting your experiments with the different value mixing resistors and caps.
Another option I have found to increase the signal with these amps, while keeping the mixing resistors at there stock values (120k/68K and a .01uf cap or the 220K/68k
750pf combo) is to change the plate voltages of the V1 tube.

I have increased this from the stock value of about 168v all the way up to 225v and have preferred various higher voltages over the 168v . You may find that you prefer a higher voltage on v1.
I have also placed the 1M/68k dropping string on a switch to change this to different values and really like this modification as well for increasing volume.

Cheers!

Guy

Hi Guy, thanks for the tips! I know you've built several of these. My voltages now are about half way between the layout and your higher voltage preferences. I'm going to try lowering them to stock soon and if I don't like that I'll try going in the other direction as you suggested.

This amp is just amazing! I am still surprised that I can really crank this up to 70% master volume with a 2x12 and it is enjoyable to play in a small practice room at 100 watts. I never thought I would sell my mesa lone star special, but can't justify the space it takes up. I never play it anymore so I am going to trade it in at guitar center for some pedals and a small pedal board to bring to jam sessions.

I need to start my D'Lator build soon and then I have a 102 on deck afterwards. Hoping to get on the ODS bus before the end of the year.

-Dan

I agree Dan its an amazing sounding amp! You other projects sound great! Let is know how they go.

I am building a variation of the JM with higher value plate resistors and higher voltages on several of the preamp tubes and different dropping resistors before the mixer tube stage and different value cathode bypass resistors on v1. Its actually for a fairly large guitar effects company. I cant say the name for legal reasons but I will report back regarding how the amp sounds when its done!

Cheers

Guy

[amplifiednation]

I’ll do another run of chassis if there is enough interest...these are truly killer!

[dbharris]

Hi Dan, thanks for posting your experiments with the different value mixing resistors and caps.
Another option I have found to increase the signal with these amps, while keeping the mixing resistors at there stock values (120k/68K and a .01uf cap or the 220K/68k
750pf combo) is to change the plate voltages of the V1 tube.

I have increased this from the stock value of about 168v all the way up to 225v and have preferred various higher voltages over the 168v . You may find that you prefer a higher voltage on v1.
I have also placed the 1M/68k dropping string on a switch to change this to different values and really like this modification as well for increasing volume.

Cheers!

Guy

Hi Guy, thanks for the tips! I know you've built several of these. My voltages now are about half way between the layout and your higher voltage preferences. I'm going to try lowering them to stock soon and if I don't like that I'll try going in the other direction as you suggested.

This amp is just amazing! I am still surprised that I can really crank this up to 70% master volume with a 2x12 and it is enjoyable to play in a small practice room at 100 watts. I never thought I would sell my mesa lone star special, but can't justify the space it takes up. I never play it anymore so I am going to trade it in at guitar center for some pedals and a small pedal board to bring to jam sessions.

I need to start my D'Lator build soon and then I have a 102 on deck afterwards. Hoping to get on the ODS bus before the end of the year.

-Dan

I agree Dan its an amazing sounding amp! You other projects sound great! Let is know how they go.

I am building a variation of the JM with higher value plate resistors and higher voltages on several of the preamp tubes and different dropping resistors before the mixer tube stage and different value cathode bypass resistors on v1. Its actually for a fairly large guitar effects company. I cant say the name for legal reasons but I will report back regarding how the amp sounds when its done!

Cheers

Guy

That sounds like a cool amp Guy! Would love to hear it with the high plates and other changes you are making.

Taylor, good to hear from you too, I see you're keeping pretty busy these days!

-Dan

[Gtsirvou]

Not sure if it's OK to hijack another thread like this, but since I already engaged here let me share my build too. It's a JM signature with the EF86 channel of the Matchless C-30 combined, for a friend who couldn't decide.

[dbharris]

Not sure if it's OK to hijack another thread like this, but since I already engaged here let me share my build too. It's a JM signature with the EF86 channel of the Matchless C-30 combined, for a friend who couldn't decide.

Looks great! How does it sound?

Where did you get that amp badge made?

-Dan

[Gtsirvou]

Hey Dan, Thanks.

It sounds really awesome, only slight drawback is that the inactive channel needs to be at full volume for the active one to not be loaded down ( if it's at 0 the mixing resistors attenuate it by 6db and it sounds weak) but that's no big deal.

The logo as well as the faceplates were made by tube-town

[dbharris]

Well years later I decided to pull this chassis and adjust the dropping string. I didn't have a mojo 10K in the proper wattage, so left that one as is.

Now I have 2K2 draloric, 27K piher, and 2K2 draloric. While B+ is still a bit low (I assume PT choice), swapping the 22K for a 27K helped get the rest.of the voltages within about 5% of the layout values.

PXL_20240616_232908367.jpg

Voltages:
Line 121.4
Heaters 6.68
B+1 435
B+2 434
B+3 410
B+4 256
B+5 250

V1: 1-170.3, 3-1.19, 6-166.5, 8-1.25
V2: 1-181.2, 3-1.13, 6-180.0, 8-1.14
V3: 1&6-368.0, 3&8-7.1
V4: 1-179.8, 3-1.14, 6-178.9, 8-1.16
V5: 1-294.7, 3&8-51.5, 6-293.5

Sounds great a bit softer/warmer.

-Dan