Power transformer wire grouping help

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Re: Power transformer wire grouping help

Post by davemojo »

geoff 1965 wrote:
Sat 03/13/21 10:38 am
add a pic of your mains socket & fuse,first you need to determine the orientation of the mains lugs i.e. which is positive and negative,also if you have a solder lug i would ground the mains socket seperately close to its mounting.
been trying to find any feedback on this stewmac with no success,i don't have the tremolo circuit in either of my amps but i know from watching other builds you have to be very careful with both grounding and lead dress or you will have problems.
As you can see the black and the white are the mains one is positive one is negative. Not sure which one is which.
at this point looks like the black goes to mains switch and the white goes to fuse holder and from there with a jumper to power inlet.

I also ran the yellow from stand-by switch to pin 3 of V6. In addition one more wire a jumper from lug left on mains switch down to the other lug of the power inlet.
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Re: Power transformer wire grouping help

Post by geoff 1965 »

i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 11:36 am
i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
Thank you, I am getting a little lost :-( I didn't realize that the power transform wire were different , I thought they would be all the same color for all power transformer versions.

Now I can do what you said but this will change everything else and will not allow me to continue on my own.

I need to understand the black and the white on my transformer to what stewmac color do match? In order to try to continue using that same schematic.

I noticed that all USA schematic have the power transfer colors do not match the power transformer I bought here at Tonefactory

Is the way you proposed better technically speaking?
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 11:36 am
i would run a wire from the negative mains lug to the tag pointed out on pic,then you wire one of the pilot light leads and the black transformer wire to the same tag. if you move the other tag strip to the cap mounting bolt "see pic" you can use that as your star ground point.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
Ok I understood the way you proposed is actually a different method to achieve the same.

However the white wire on my PT is the 240v which is basically what stewmac has in black/white 120v which basically is not matching or they have the black/red which is the 240V, so in other words the white is the match for the black/white or red/black in stewmac, so based on that I can follow that schematic.

I understand your point, for you it may be very easy for me isn't strugling a lot, so... let's hope I can make something working fine :-)
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Re: Power transformer wire grouping help

Post by geoff 1965 »

the confusion is just different wire colours on the PT, if you wire the negative like shown it will be good.then you can wire the positive lug to the fuse holder lug as shown "in red" then from other fuse lug to the power on/off switch,when you run lengths of ac wire push it into the corner of the chassis tight around then up to the switch.then you can wire the white transformer lead and second pilot light wire to the second switch lug.
the unused blue & orange wires can be cut short and soldered to the isolated tag "see pic" and you can earth the mains with a lug at point shown "green"
this is just helping you with mains/PT wiring and relocating the ground points is good practice,it won't affect the rest of the build but it's up to you to decide.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
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Re: Power transformer wire grouping help

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geoff 1965 wrote:
Sat 03/13/21 12:50 pm
the confusion is just different wire colours on the PT, if you wire the negative like shown it will be good.then you can wire the positive lug to the fuse holder lug as shown "in red" then from other fuse lug to the power on/off switch,when you run lengths of ac wire push it into the corner of the chassis tight around then up to the switch.then you can wire the white transformer lead and second pilot light wire to the second switch lug.
the unused blue & orange wires can be cut short and soldered to the isolated tag "see pic" and you can earth the mains with a lug at point shown "green"
this is just helping you with mains/PT wiring and relocating the ground points is good practice,it won't affect the rest of the build but it's up to you to decide.
0b15481c-0029-4cc4-843c-b8d712923e00.jpg
Yes, I got it now and I understand the first option you offered may go that way, tomorrow I can dedicate some hours and go ahead with the project. I really don't know how to thank for your patient on helping out and clearing out any doubt, again thanks :-)
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Re: Power transformer wire grouping help

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Hey All

I made some progress this is how far I got so far.
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Re: Power transformer wire grouping help

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Hey. Nice to watch the progress. It isn't advisable to solder the pots bodies to ground. It's easy to damage the pots like that. Watch the grounding tips in Josh’s signature. Look at photos of Josh’s builds. Trust me, you'll benefit from this on the end results.
You might wanna look into the determination of the orientation of the caps too,not only the electrolytic caps. There is an outer foil side in every cap. But you need a scope for that ...or d@mn good ears...
This is not a major problem, but it's still better practice.
Don't worry... take it slow and thourough.
Ok, now I'll stop being verbose 😄😉
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Re: Power transformer wire grouping help

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davemojo wrote:
Tue 03/16/21 12:22 pm
Hey All

I made some progress this is how far I got so far.
Unless I'm mistaken, you've connected the grounds on the jacks to the chassis through those pot shells. That's begging for a ground loop. I would clean all that up before continuing. It doesn't benefit the amp for the shells to be connected into the circuit; they'll act as shields just because they're mechanically attached to the chassis.

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Re: Power transformer wire grouping help

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Bieworm wrote:
Tue 03/16/21 2:00 pm
Hey. Nice to watch the progress. It isn't advisable to solder the pots bodies to ground. It's easy to damage the pots like that. Watch the grounding tips in Josh’s signature. Look at photos of Josh’s builds. Trust me, you'll benefit from this on the end results.
You might wanna look into the determination of the orientation of the caps too,not only the electrolytic caps. There is an outer foil side in every cap. But you need a scope for that ...or d@mn good ears...
This is not a major problem, but it's still better practice.
Don't worry... take it slow and thourough.
Ok, now I'll stop being verbose 😄😉
My soldering technique isn't great but I paid some attentions on soldering over the pot.
I agree with all of you since it makes sense ground loop hum, sure but why the orginal 18 watt use similar schematics as soon as i can I will send here a picture of the 74x Amp 18 watts my friend owns one, I also seen other schematics doing the same soldering on pot shell.

Some other schematic don't and discourage this practice
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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

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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

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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

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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

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"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

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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

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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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