Power transformer wire grouping help

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davemojo
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Re: Power transformer wire grouping help

Post by davemojo »

Hey All
I am here to accept all corrections, as you all know, i am new and never done anything like that. I can definitely play some nice guitar riffs but my thing is Fender Rhodes and Organ B3 style therefore using such Amp can enhance the sound I am looking for especially because it will be dirty and distorted and that is my goal since I have to play some Classic but nasty rock hehehehe

Now getting back to the build

There are at least 2 schematics soldering over the volume pots. I agree with you this can cause hum or ground looping can end to hum, but we have also another amp, build by another musician that followed a project such the one on photo and there is no hum or issues, so what is it really that is going to determine hum issues?

I also agree that soldering on top of the pot shell can damage it.

Could anyone help on advising how I shall change that since it may imply quiet few changes now

My schematic guide is from stewmac but the mojotone are the same no difference, I believe tubedepot is also the same, so can we say that those companies are commercial and just dropping there a low quality build schematic?
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Re: Power transformer wire grouping help

Post by Bieworm »

davemojo wrote:
Wed 03/17/21 3:37 am
Hey All
I am here to accept all corrections, as you all know, i am new and never done anything like that. I can definitely play some nice guitar riffs but my thing is Fender Rhodes and Organ B3 style therefore using such Amp can enhance the sound I am looking for especially because it will be dirty and distorted and that is my goal since I have to play some Classic but nasty rock hehehehe

Now getting back to the build

There are at least 2 schematics soldering over the volume pots. I agree with you this can cause hum or ground looping can end to hum, but we have also another amp, build by another musician that followed a project such the one on photo and there is no hum or issues, so what is it really that is going to determine hum issues?

I also agree that soldering on top of the pot shell can damage it.

Could anyone help on advising how I shall change that since it may imply quiet few changes now

My schematic guide is from stewmac but the mojotone are the same no difference, I believe tubedepot is also the same, so can we say that those companies are commercial and just dropping there a low quality build schematic?
look at this:
modern classic layout grounding.pdf
Sorry Josh, I don't want to compromise your drawing.. just adding some highlights for clarification
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Re: Power transformer wire grouping help

Post by davemojo »

Would be possible to fully built my next amp using carbon film resistors opposite to composite?
I heard a less chance of noise and if on my layout is using .5 w composite can i use 1 w film, would that work fine?
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Re: Power transformer wire grouping help

Post by JMPGuitars »

davemojo wrote:
Wed 03/17/21 9:54 am
Would be possible to fully built my next amp using carbon film resistors opposite to composite?
I heard a less chance of noise and if on my layout is using .5 w composite can i use 1 w film, would that work fine?
Yes. Though your 1M input resistor should always be metal film. I used to build with all carbon film, but now I build with all metal film CMF series resistors.
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Re: Power transformer wire grouping help

Post by TriodeLuvr »

davemojo wrote:
Wed 03/17/21 3:37 am

There are at least 2 schematics soldering over the volume pots. I agree with you this can cause hum or ground looping can end to hum, but we have also another amp, build by another musician that followed a project such the one on photo and there is no hum or issues, so what is it really that is going to determine hum issues?
Soldering to the back of the pots and then using the pots to support a ground bus in this way is simply bad practice. It invites grounding problems. However, sometimes a designer who doesn't know better gets lucky, and his poor technique works satisfactorily with the particular layout he creates.

You have two choices: Wire it the way the pictorial shows and hope you also get lucky, or use a method that's more certain to work well. If you believe the original layout is repeatable in terms of performing well and that other builders have not experienced any issues, you might want to continue forward as-is. It's a judgement call.

Could anyone help on advising how I shall change that since it may imply quiet few changes now

My schematic guide is from stewmac but the mojotone are the same no difference, I believe tubedepot is also the same, so can we say that those companies are commercial and just dropping there a low quality build schematic?
If you decide to change it, you will need to remove all connections that are wired to the ground bus. You would need to instead connect all those points to a common terminal on the board, then run a wire from that terminal back to the ground at the supply capacitor. The capacitor on the Tone control can be wired directly to the Intensity pot, then a ground wire run from the two lugs of the Intensity pot to the common ground on the board.

Again, if you believe the existing design is repeatable and has proven to be trouble-free for other builders, you could continue to follow the existing layout. I don't have any personal experience with this build.

Jack
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Re: Power transformer wire grouping help

Post by Bieworm »

"If" you solder to the pots directly there is something important to consider. The pot should be dialed to zero or to max. It's important the wiper is free from overheating because the carbon might be damaged and ruin your brand new pot.
Its just better practice not to solder to the pot housing. I've seen people solder a ground buss at the pots, but with legs to the grounding lugs of the pots, so the buss is like 1/2" in offset from the pots
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Re: Power transformer wire grouping help

Post by JMPGuitars »

TriodeLuvr wrote:
Wed 03/17/21 12:53 pm
If you decide to change it, you will need to remove all connections that are wired to the ground bus. You would need to instead connect all those points to a common terminal on the board, then run a wire from that terminal back to the ground at the supply capacitor. The capacitor on the Tone control can be wired directly to the Intensity pot, then a ground wire run from the two lugs of the Intensity pot to the common ground on the board.
The pots should be connected to a separate preamp ground, not to the power amp star ground with the filter caps. See the thread in my signature for more details.

Thanks,
Josh
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Re: Power transformer wire grouping help

Post by davemojo »

Bieworm wrote:
Wed 03/17/21 1:20 pm
"If" you solder to the pots directly there is something important to consider. The pot should be dialed to zero or to max. It's important the wiper is free from overheating because the carbon might be damaged and ruin your brand new pot.
Its just better practice not to solder to the pot housing. I've seen people solder a ground buss at the pots, but with legs to the grounding lugs of the pots, so the buss is like 1/2" in offset from the pots
I have set the pot volume to zero, it was written on the instructions.
I don't believe to have overheat the pot, hopefully.
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Re: Power transformer wire grouping help

Post by TriodeLuvr »

JMPGuitars wrote:
Wed 03/17/21 2:42 pm
TriodeLuvr wrote:
Wed 03/17/21 12:53 pm
If you decide to change it, you will need to remove all connections that are wired to the ground bus. You would need to instead connect all those points to a common terminal on the board, then run a wire from that terminal back to the ground at the supply capacitor. The capacitor on the Tone control can be wired directly to the Intensity pot, then a ground wire run from the two lugs of the Intensity pot to the common ground on the board.
The pots should be connected to a separate preamp ground, not to the power amp star ground with the filter caps. See the thread in my signature for more details.

Thanks,
Josh
Good catch! I said: "...then run a wire from that terminal back to the ground at the supply capacitor." I meant to say "the supply capacitor for the preamp." Had it in mind, but forgot to write it down. Thanks!
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Re: Power transformer wire grouping help

Post by davemojo »

So the Amp is going to be completed this week I got stuck on couple on capacitors and one resistor but I will get them tomorrow and took few day off since I have to record some music at our rehearsal place, nothing big just some hobby stuff.

I begun to play guitar in parallel to my organ play so I am exited to try to Amp assuming that all is going to work right off I am done with the build.

Unsure if I showed here the Combo cabinet photos, it is now completed, the next one will be perfect while doing it I realized a few mistakes on working with Tolex but you know this is my first one so... some imperfections are expected I bet :roll:
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