18 Watt Trem TMB: Gain Pot bleeding through

[rexindigo]

hi, after some years without building anything, i tried it again....and again i failed....
build an18 Watt Tremolo TMB and it works, but:
- at first the gain pot did not do anything, only the Master Volume worked
- i replaced it and now there is sound when its all turned down- but it gets louder and overdriven when i turn it up
- Somehow with the gain pot all closed there is still a fair amount of guitar coming through
any ideas what i did wrong? double checked the all the solder joints etc. but i cant find the solution,
any help is appreciated thank you in advance
cheers Rex

[JMPGuitars]

That's not an easy build, but you're not describing a problem. Look at the schematic. There's a resistor between the gain pot and ground. That means the gain pot always has a minimum resistance, which also means the gain pot will never fully mute the guitar.

Do you have any actual issues with the build? If so, post photos and your voltages.

Thanks,
Josh

[rexindigo]

Thank You Josh, for pointing me at the obvious! Other than the "problem" with the gain pot, i am very happy with the amp! Sounds phantastic! The tremolo is very nice!
Now that my "problem" is "by design", i will keep this as is. Thank You again! Cheers Rex

[Bieworm]

Nice! Another one who can enjoy this amp
The first design didn’t even have a gain pot, just a 470k/470k voltage divider.
Due to the fact I didn’t have a 250k pot at hand when we were testing the prototype, I put in a 500k pot there. I like it more, even though the sweep on the higher value pot isn’t ideal like the 250k, because it adds some shimmer and a little more OD to the circuit. Maybe try it too and let us know if you’re experiencing it too?
What speaker do you use? Mine is an old 70’s G12H30 75Hz 16 Ohm… just perfect for “the one” amp!

[JMPGuitars]

Nice! Another one who can enjoy this amp
The first design didn’t even have a gain pot, just a 470k/470k voltage divider.
Due to the fact I didn’t have a 250k pot at hand when we were testing the prototype, I put in a 500k pot there. I like it more, even though the sweep on the higher value pot isn’t ideal like the 250k, because it adds some shimmer and a little more OD to the circuit. Maybe try it too and let us know if you’re experiencing it too?
What speaker do you use? Mine is an old 70’s G12H30 75Hz 16 Ohm… just perfect for “the one” amp!

Bieworm, I'm curious what the maximum resistance value is that you use on that prototype.

The sweep is better on the 250k pot, but the main reason I didn't design it with a higher value pot was the signal was too hot in the upper range, and lead to noise issues. ~300K total on that side of the voltage divider gave us the ideal maximum signal level. The 47K to make up the difference (while using a 250k pot) was because I didn't want the gain pot muting the signal at any point.

If somebody wanted to experiment with a slightly hotter signal, they could use a higher value pot, and measure the maximum resistance level that still sounded good to them. Then either use a different pot value, or use a 250k pot and increase the resistor to ground's value.

[Bieworm]

Nice! Another one who can enjoy this amp
The first design didn’t even have a gain pot, just a 470k/470k voltage divider.
Due to the fact I didn’t have a 250k pot at hand when we were testing the prototype, I put in a 500k pot there. I like it more, even though the sweep on the higher value pot isn’t ideal like the 250k, because it adds some shimmer and a little more OD to the circuit. Maybe try it too and let us know if you’re experiencing it too?
What speaker do you use? Mine is an old 70’s G12H30 75Hz 16 Ohm… just perfect for “the one” amp!

Bieworm, I'm curious what the maximum resistance value is that you use on that prototype.

The sweep is better on the 250k pot, but the main reason I didn't design it with a higher value pot was the signal was too hot in the upper range, and lead to noise issues. ~300K total on that side of the voltage divider gave us the ideal maximum signal level. The 47K to make up the difference (while using a 250k pot) was because I didn't want the gain pot muting the signal at any point.

If somebody wanted to experiment with a slightly hotter signal, they could use a higher value pot, and measure the maximum resistance level that still sounded good to them. Then either use a different pot value, or use a 250k pot and increase the resistor to ground's value.

I will have to open her up for that measurement, but I dial it to about 70 or 80%. Another VERY important side note is the cab. I realise that the top controlled big combo gives the tone a balance that feels just right. It’s a big amp for a 1x12, but it delivers in oozing amounts

[rexindigo]

Hi, everyone, to be honest, i have meanwhile tinkered around with the value of the resistor going to ground and in the moment it is a 8.2k i had lying around, i know this changes the voltage divider, but i just tried and like it so far. Is there a Chance to go without any resistor to ground at all? That would probably make the Volume more tweakable.The reason for my tinkering is, the amp is still incredibly loud.. unplayable at my home. Also changed the Volumen to 1M, so the 500k that was there, is free... maybe i'll check this out as the Gain Pot?

[rexindigo]

Forgot: speaker i use (because of the small combo enclosure i had)
is a Celestion G10T-75 CE. I had this for some years in my Musicman RD50, but went back to the original electrovoice with the gigantic magnet.....

[JMPGuitars]

Hi, everyone, to be honest, i have meanwhile tinkered around with the value of the resistor going to ground and in the moment it is a 8.2k i had lying around, i know this changes the voltage divider, but i just tried and like it so far. Is there a Chance to go without any resistor to ground at all? That would probably make the Volume more tweakable.The reason for my tinkering is, the amp is still incredibly loud.. unplayable at my home. Also changed the Volumen to 1M, so the 500k that was there, is free... maybe i'll check this out as the Gain Pot?

500K will increase the signal level and make it higher gain.
8.2k is fine, by having a lower value, you're simply lowering your maximum gain level. Omitting the resistor would lower the maximum gain slightly more. However, remember that we're talking about a gain knob that's primary function is to control the amount of overdrive. Overall volume is the main volume control that controls the power amp level.

If your overall volume level is the issue, you need an attenuator. Take a look at the Break Wind Attenuator in the downloads section.

[rexindigo]

Just changed the gain pot to 500k and got rid of the resistor to ground and i like it. Now i have the small very portable amp, that i can take everywhere. And it has a beautiful tremolo.

Have a fx loop kit from tubetown that i wanted to install for reverb and delay. (https://www.tube-town.net/ttstore/kit-s ... nd150.html) But there is simply no space in the tiny chassis i used for the build.... .

And i cant figure out how to get the light in the power switch to work. But this are all minor issues.

[JMPGuitars]

Look at the other versions of the Tremolo TMB and you'll see a passive FX loop that should fit fine.

[Bieworm]

Josh is right. The FX loop is very small and easy. I have one in the prototype and it works flawlessly.
The 18 watt is no bedroom amp though. It is loud pretty quick on the dial. Luckily the preamp OD on the Tremolo TMB is so nice that you don’t hunger for power tube saturation

About the power switch light.. is it a switch with 4 poles and a neon inside? In that case you will need a 180k resistor and the L and N wired to it in a specific way

[rexindigo]

Thank You for pointing to the fxloop of the 36watt. i will try this.
The Powerswitch has 3 lugs, i have attached a picture.
i have wired the hot to 1 and 2 goes to the circuit, i thought 3 should go to ground, but that does not give any light...

[Bieworm]

Remove the ground connection from lug 3!!!
I think you need this. But first try it without the green jumper wire. The light might be internally connected. Some switches do, some don't.
One thing you need to know about these kind of switches that the + is L and the - is N, not ground! I have struggled with this too and it's hard to find wiring diagrams that you can clearly relate to the application in an amp

Neon Rocker Switch.png

You can also go the non EU conform route and do this:
(in other words, jumper a wire from N to lug 3)

Neon Rocker Switch non EU conform.png

[rexindigo]

Thank You Bieworm, this pointed me to the right direction, its actually two switches but as i only showed You the back side You could not see this. i have one wired for the AC and the other for standby. the standby does not have to light up (i dont know if it will work at all, because both are for AC). But of Course if the Powerswitch is for AC i have to connect 1 to L, 2 goes to the transformer and 3 will go to N.
So when switched on, the Lamp (AC) is switched in parallel to the whole circuit and lights up. i will try this.
but first the passive fx loop, found all the parts, holes are drilled...
ill keep You informed

[rexindigo]

Did the light thing first, worked exactly like your second drawing, Bieworm, Thank You for that

[Bieworm]

Here’s a quick demo of the possibilities with my Ironside and just the guitar volume pot. Like I said the Ironside is the Tremolo TMB with a 500k gain pot, and a 330p treble cap
https://youtu.be/JQlVP8fGekg?feature=shared

[rexindigo]

Thats very cool, sounds great! ive added the loop, but now everything is very noisy, i think i have to go with shielded wires. no more tinkering today....

[rexindigo]

Noise was a faulty tube, changed the preamp tubes to lower gain , now its dead quiet and clean, just love it!! With the telecaster only slight breakup, with the SG humbucker light crunch, perfect! Will check it out in rehearsal on tuesday.

[rexindigo]

Here is a clip of the amp, 1978 Fender Telecaster, 60ties Sennheiser 421 into mackie mix 12 fx and scarlett 4x4 2end gen into Sonar, ligth reverb added in the DAW ;_)