My first build Jim 5watt V2.0

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JMPGuitars
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Re: Need ideas for my first build

Post by JMPGuitars »

If you like the sound with R11 and R15 jumpered, you should instead remove R12 and R16. Then replace the R11 and R15 jumpers with 10K resistors.

EDIT: I wasn't awake yet when I wrote that, and was focused on the voltage divider, not the tube.

Thanks,
Josh
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Re: Need ideas for my first build

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JMPGuitars wrote:
Tue 03/15/22 6:12 am
If you like the sound with R11 and R15 jumpered, you should instead remove R12 and R16. Then replace the R11 and R15 jumpers with 10K resistors.

Thanks,
Josh
That sounds interesting, will it tighten up the distortion but also keep the amount of distortion I have right now ?
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Re: Need ideas for my first build

Post by Tomten »

you should instead remove R12 and R16
You mean just remove, and not jumper R12 and R16 ?
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Re: Need ideas for my first build

Post by JMPGuitars »

The 10Ks will help block unwanted noise, and shouldn't have any noticeable change to your volume/gain level.

Without hearing your distortion, I wouldn't know what to change. Though if I were going to guess at something, I might lower the value of C2.

Another thought, and again, without hearing your distortion, is that those voltage dividers might have been there for a reason. Maybe dropping less voltage would increase gain without being crazy.

Thanks,
Josh
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Re: Need ideas for my first build

Post by Tomten »

Without hearing your distortion, I wouldn't know what to change. Though if I were going to guess at something, I might lower the value of C2.
The C2 is now 10uF, what value would you suggest and what will it possible to do the distortion ? :D
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Re: Need ideas for my first build

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I have 3.3uF 50 volts.. would that work ?
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Re: Need ideas for my first build

Post by 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.. :D
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Re: Need ideas for my first build

Post by zaphod_phil »

Do we have a schematic for this amp somewhere?
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Re: Need ideas for my first build

Post by Tomten »

zaphod_phil wrote:
Tue 03/15/22 12:50 pm
Do we have a schematic for this amp somewhere?
Yeah... right here

https://www.tube-town.net/cms/userfiles ... op_pcb.pdf
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Re: Need ideas for my first build

Post by Tomten »

Schematics also here...
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Re: Need ideas for my first build

Post by TriodeLuvr »

Tomten wrote:
Tue 03/15/22 8:49 am
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.. :D
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
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Re: Need ideas for my first build

Post by 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
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Re: Need ideas for my first build

Post by Tomten »

TriodeLuvr wrote:
Wed 03/16/22 12:17 pm
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 ?
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Re: Need ideas for my first build

Post by 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..
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Re: Need ideas for my first build

Post by 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
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Re: Need ideas for my first build

Post by Tomten »

TriodeLuvr wrote:
Wed 03/16/22 9:17 pm
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.
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Re: Need ideas for my first build

Post by 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.. ?
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Re: Need ideas for my first build

Post by JMPGuitars »

C16 is backwards in your schematic. If you're using a polarized cap, negative goes to ground there.
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Re: Need ideas for my first build

Post by Tomten »

JMPGuitars wrote:
Thu 03/17/22 7:49 am
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.. :D
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Re: Need ideas for my first build

Post by TriodeLuvr »

Tomten wrote:
Thu 03/17/22 8:03 am
JMPGuitars wrote:
Thu 03/17/22 7:49 am
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.. :D
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
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