My first build Jim 5watt V2.0

[Tomten]

I have 3.3uF 50 volts.. would that work ?

[Tomten]

My report is that taking away the R12 and R16 will make the amp dead quiet, not a tone coming out from it, so I put those back and put in a 2,2uF on C2 and i did keep the 10K on R11 and R15. I think I hear some difference in the sound.

My plan is to take away the 10k on R11 and R15 and go back to jumpers to see what difference it makes with the 2,2uF on C2...

It would be awesome with a little smoother distortion though..

[zaphod_phil]

Do we have a schematic for this amp somewhere?

[Tomten]

Do we have a schematic for this amp somewhere?

Yeah... right here

https://www.tube-town.net/cms/userfiles ... op_pcb.pdf

[Tomten]

Schematics also here...

[TriodeLuvr]

My report is that taking away the R12 and R16 will make the amp dead quiet, not a tone coming out from it, so I put those back and put in a 2,2uF on C2 and i did keep the 10K on R11 and R15. I think I hear some difference in the sound.

My plan is to take away the 10k on R11 and R15 and go back to jumpers to see what difference it makes with the 2,2uF on C2...

It would be awesome with a little smoother distortion though..

You can't remove R12 or R16; those provide the ground reference for the grids of the tubes they're attached to. C2 is not the solution either. The issue you're experiencing is a lack of front end gain. I don't know why they designed the amp like this. There's plenty of gain available overall, it's just in the wrong place. There's no simple way to increase the gain ahead of the tone controls. Even jumpering R6 won't do much, because it's driving an extremely high impedance (much higher than the 1M grid resistor would imply). This amp really needs another gain stage between V1A and V1B, and V2A or V2B could be used there. Not too difficult from an electronics standpoint, but it would require some rewiring around the PCB.

Jack

[TriodeLuvr]

Here's what I have in mind. I think this can be accomplished with minor rewiring, but not sure how well the PCB will lend itself to this. Not shown below - R11 should be jumpered.

Jim Mod.jpg

[Tomten]

Here's what I have in mind. I think this can be accomplished with minor rewiring, but not sure how well the PCB will lend itself to this. Not shown below - R11 should be jumpered.

Jim Mod.jpg

This looks interesting, would this give me more gain and maybe a little tighter gain ?

[Tomten]

Its the first time ever using some sort of software for schematics and PCB, but I just wanted to see if I can get this right as Jack showed with the picture, is this something that it would look like to be a correct schematic of your thoughts ? Keep in mind that I have never done this before so there may be wrong items for some components etc..

[TriodeLuvr]

Yes, that's it. I would just make the following additional changes (parts designators same as in your V2 schematic):

Install a jumper in place of R6 (220K). Replace R15 (470K) with the 220K removed at R6. Change R13 (6.8K) to 1.5K and bypass it with a 10uF capacitor (just like the first stage).

These changes will allow you to compress the front end using the Volume control, but still control overall gain with the Master.

Jack

[Tomten]

Yes, that's it. I would just make the following additional changes (parts designators same as in your V2 schematic):

Install a jumper in place of R6 (220K). Replace R15 (470K) with the 220K removed at R6. Change R13 (6.8K) to 1.5K and bypass it with a 10uF capacitor (just like the first stage).

These changes will allow you to compress the front end using the Volume control, but still control overall gain with the Master.

Jack

This is getting better and better, i made those changes in my schematic just to see what it would look like with all the changes, i will try those things today on the original PCB and i will get back with a report.

[Tomten]

When I put in a 1.5k on R13 and bypass it with a 10uF the amp is not working properly, almost no sound coming out of it, if I put in the 6,8k it works but the distortion sounds not very good if I go past 1 o clock on the Volume knob..it sounds ok before I go past 1 o clock, maybe similar to full blast before all these mods.

How do I fix this so its working as you was thinking Jack ? These mods makes sense to me so I think it needs some minor adjustments.. ?

[JMPGuitars]

C16 is backwards in your schematic. If you're using a polarized cap, negative goes to ground there.

[Tomten]

C16 is backwards in your schematic. If you're using a polarized cap, negative goes to ground there.

Yeah.. i noticed that before i started the project, in the amp its polarity is ok..

[TriodeLuvr]

C16 is backwards in your schematic. If you're using a polarized cap, negative goes to ground there.

Yeah.. i noticed that before i started the project, in the amp its polarity is ok..

Check the connections and wiring carefully at V2A. It's just a standard amplifying stage. Check the voltages on the tube with the 1.5K and 10uF installed. They should be essentially the same as the first stage.

Jack

[Tomten]

Check the connections and wiring carefully at V2A. It's just a standard amplifying stage.

Jack

Yeah I've double checked and re-soldered all those connections, as soon as I hook up that 10uF/63 Volts capacitor its not working properly.. it sounds normal if the Volume is at 8 o clock in the morning, then I just touch it a little and its all super distorted and there is almost no sound comming from the cabinet at all, so I just turn the amp of and to be honest, I can't understand why that capacitor is making this problem...

[Tomten]

But its not only the capacitor causing a problem, as I said earlier also I can't have the Volume (Gain) more than 1 o clock, or else the distortion starting to sound very very bad.. like there is 300% to much gain or something..

[zaphod_phil]

I can't have the Volume (Gain) more than 1 o clock, or else the distortion starting to sound very very bad.. like there is 300% to much gain or something..

It sounds like your amplifier is probably suffering from blocking distortion,a well-known problem:
https://guitar.com/features/opinion-ana ... uitar-amp/
https://hiwatt.org/2_mod.html
So I recommend using a 470k value for the grid stopper R15, instead of 220k and likewise inserting a 470k grid stopper on V2a. I also recommend changing cathode resistor R13 to 620 ohms, to bias that stage warmer, for a thicker and less fizzy overdrive sound
Also to balance the overall frequency response for guitar,
I suggest changing C2 and c16 to 1uF, with C10 and C12 = 10nf or 22nF (you decide which sounds best to you )

This circuit looks like the preamp from something "Single-ended Plexi-like", complete with a "half-PI", but where oh where is the power amp?

[Tomten]

It feels like I just want to put back the original components and just build another one, another model of amp but the same wattage and better schematic, I mean an amp that is designed alot better than this Jim amp. I would ditch the PCB and use a Point to Point board instead so it will be alot more simple to mod and change components. Would this amp schematic make more sens then the Jim ??

[JMPGuitars]

Take a look in our downloads section for some well-tested options.