#102 Build started

[vibratoking]

Why do you think it's the value of the filter caps? FYI, many Dstyle amps have successfully been built with 100uF and even less without the distortion problems that you describe.

[ToneMerc]

Why do you think it's the value of the filter caps? FYI, many Dstyle amps have successfully been built with 100uF and even less without the distortion problems that you describe.

Exactly, there are 120+watt Musicman style power Dumbles with only 50uF on the mains.

TM

[Ang3lus]

it's speculation, cause it's a value I hadn't seen in any "official" layout, i just grabbed it from the layout i used and I reckon it's too low, it comes out at
110uf~.

I can only guess that's the problem since I chopsticked every solder joint and moved around every wire i have in the amp with no change to the tone, so i'm guessing it's not oscillation.

I plugged into the return jack (fx loop) so i can hear only the poweramp, and it is distorting, so I guessed it's ghost notes, which can be caused by a low valued choke (though i'm using 4H 90ma as in the schem) or underfiltered supply, which is the only culprit I came at so far.

if anyone has any other ideas, i'd love some input.

I checked also between all the gnd points in the amp, and i get 0.004ohms-0.008ohms between all of them, so i'm guessing grounding is now fine (I got 1.1-2.2 ohm before i sorted grounding according to the layout)

Could it also be power tubes ? they are matched and brand new (JJs), maybe 2 hours of play on them.

bad filter caps ? (I planned on changing the rubys to F&T anyways)

all things i could think of.

[ToneMerc]

I've built maybe six 100 watt D amps with only 110uf and two MM 120+ watt ones with only 50uF and none have the same issues as yours. My 183 clone only has 110uf and no apparent issues with power amp distorting on the MM style supply with only 50uF.

I don't really hear ghost notes, but it's hard for me to throw darts at a problem when I cant physically hear it or inspect it myself.

TM

[Ang3lus]

it's not subharmonic or overtones, it's like a distorted note riding on top of the clean one, I'll try paralleling 100uf with the 220uf already there and hopefully the problem will be gone.

on the other amps i built, i have 220uf of filtering, though they are very high gain.

i do live in a country with 230v/60hz, so filtering might need to be different ?

[ToneMerc]

I would be breaking out the O'scope and signal generator.

TM

[Ang3lus]

don't have those :[

i do live in a country with 230v/60hz, so filtering might need to be different ?

[Structo]

Are you sure your main filter is that high?

If you run two 220uF caps in series, the total is 110uF.

On my 100w D amp I am running two 320uF for a total of 160uF.

For example, #183 ODS has two 330uF caps in series for a total of 165uF.

Usually the result of heavier filtering will be a tighter feel to the amp.

If you want to reduce the boomy bass, try 5uF cathodes and .05uF couplers on the PI output.

[Structo]

don't have those :[

i do live in a country with 230v/60hz, so filtering might need to be different ?

yes but the B+ should be similar to what we have since it's just the primary that has to change for the higher wall voltage.

[aflynt]

Hmm... I put the 220uFs on the layout because that's what I used in the amp that I built using it and because they're easy to source. I've got 220uFs wired up the same way for the primary filtering in my other build too. They are both squeaky clean on the clean channel. Is this distortion riding on top of the clean a new phenomenon with this amp? Does it do it through other speakers?

-Aaron

[Ang3lus]

Yes, it's new, started only after i sortd out the grounding, could be shared grounds that are doing it?

I have the 0v bias, pt shield, pwr board gnd, pt Ct and heater Ct on the same gnd lug, maybe I need to seperate the CT taps?

Tony, triple checked the schem for the slo and uberschall, both have 220uf for mains filtering, I actually don't notice any stiffness in those amps, maybe due to lower filtering on the other parts ? Got 10-16uf there

Aflynt, your layout is great!!! Thanks a ton for the hard work

And thanks everyone for chiming in

[aflynt]

Yes, it's new, started only after i sortd out the grounding, could be shared grounds that are doing it?

I have the 0v bias, pt shield, pwr board gnd, pt Ct and heater Ct on the same gnd lug, maybe I need to seperate the CT taps?

Tony, triple checked the schem for the slo and uberschall, both have 220uf for mains filtering, I actually don't notice any stiffness in those amps, maybe due to lower filtering on the other parts ? Got 10-16uf there

Aflynt, your layout is great!!! Thanks a ton for the hard work

And thanks everyone for chiming in

Have you ruled out your speakers, power tubes and phase inverter tube? If so, then maybe you fried a resistor or cap in the power section somewhere.

-Aaron

[Ang3lus]

speakers yes and pre tubes yes, power tubes not yet, didn't have the time yet, maybe tomorrow, they are brand new though, will suck if they are already giving me problems, also i purchased the burned in option.

all resistors read ok, and i get the appropriate voltages on all b+ nodes, is that enough to rule out a bad cap ? also visually they appear to be ok.

I forgot to mention i raised the b+ to 475v~, so maybe that's why i need extra filtering ? (assuming everything else is fine)

[ToneMerc]

I forgot to mention i raised the b+ to 475v~, so maybe that's why i need extra filtering ? (assuming everything else is fine)

Not sure why you are still hung up on the filtering and again, 700V plate Dumbles with only 50uF of filtering.

How about some detailed pics.

TM

[Ang3lus]

well... i'll try a matched set of power tubes tomorrow and if it's the tubes i will send them back and buy some winged c's this time.

Will post some tomorrow once i get to my amp (it's at my parents house).