Humming pultec / HT voltage

[Samuel Groner]

Both time domain (pultec_hum_td.pdf) and spectrum (pultec_hum_fft.pdf) look very strange. The only time I've seen something similar the issue was caused by a bad solder joint which made a connection wire act as an antenna. I'm pretty sure that this is neither power transformer induced hum nor ripple or unhappy grounding.

It is clearly caused by rectifier switching though; what does this cyan-violet wire pair across the entire cap collection do? Might this go to a relay PSU?

Samuel

 

[dagoose]

[quote author="Samuel Groner"]Both time domain (pultec_hum_td.pdf) and spectrum (pultec_hum_fft.pdf) look very strange. The only time I've seen something similar the issue was caused by a bad solder joint which made a connection wire act as an antenna. I'm pretty sure that this is neither power transformer induced hum nor ripple or unhappy grounding.

It is clearly caused by rectifier switching though; what does this cyan-violet wire pair across the entire cap collection do? Might this go to a relay PSU?

Samuel[/quote]

OK, that looks the about the same as i looked at it, not like a regular hum indeed.
I'm also thinking about the rectifiers right now, i'm using these rectifiers http://docs-europe.electrocomponents.com/webdocs/00af/0900766b800afbf3.pdf andf then the W08G version, should be ok i think? I think i'll try to hook up some 1n4002's as a rectifier in the 6.3v section to test.

 

[Samuel Groner]

Try to hook up some 1n4002s as a rectifier in the 6.3 V section to test.

That's very likely just waisting time. If it's not a bad solder joint (or something similar) than it's more about the routing of the wire from the transformer to the breadboarded PSU. What happens if you move that wire?

Samuel

 

[dagoose]

[quote author="Samuel Groner"]

Try to hook up some 1n4002s as a rectifier in the 6.3 V section to test.

That's very likely just waisting time. If it's not a bad solder joint (or something similar) than it's more about the routing of the wire from the transformer to the breadboarded PSU. What happens if you move that wire?

Samuel[/quote]

I tried the rectifier and it didn't work indeed but it was worth a try. :sad:

The breadboarded PSU cable is not the answer either, i just build that section yesterday to drive the leds and 12v relais and i had the problem before i build that in.
It doesn't matter at all if i move any cables and stuff, no changes at all so it's not caused by any induction between cables and transformers.
I also did some testing with moving grounding and extra grounding to the case etc but also no result.

Dammit.... i'm seriously thinking of removing the tube stage and head to a humfree solid state stage wich i'm sure of will work, the EQ stage works like a charm!

 

[dagoose]

[quote author="CJ"]oh, now you add the input irron to make me look like a punk, ok, be that way.
:razz:
:grin:

:wink:

:?
:roll:
:shock:

:sad:

:evil:
:twisted:
:green:

Wow, I just did a scientology tone chart with the moticons,
tom cruz, eat your heart out you gay mutha f....

hey now....chill it.

OK, I will bring you back up...

That angry girl loked like she was gettin a nut!

:green: :green: :green: :green:[/quote]

your'e nuts.. :green:

 

[Samuel Groner]

As I said it looks like a bad solder joint might be the solution.

Samuel

 

[dagoose]

[quote author="Samuel Groner"]As I said it looks like a bad solder joint might be the solution.

Samuel[/quote]

No... checked, checked triple checked and soldered about every part in both boards in and out did rewire everything so i think i must have gotten around the bad solder then. :sad:
I'm allmost 100% sure it is coming from the 6.3v heater, i was googling last night on heaters and stuff and all i read was bad voltage with ripple causing hum. But actually most diagrams i found where withAC instead of DC with a hum reduction adjustment section.
I'm going to google some more and maybe try to add a 1000uf elco after the lm317 to try, now it's only 10uf while the elco before the regulator is 4700uf.

 

[dagoose]

OK, did some stuff again and with a little result, makes me happy allready But far away from a clean machine.
I redid all PSU wiring, i paralleled the psu sections of the board through board one, now both boards have seperate twisted think wires going to the trafo directly which did something, now the hum is the same in both channels, before i had a diffrent humming coming from both channels and it;s a bit lower now.
I also redid some grounding again which brought it down a little as well.
Also tried some extra caps at different places without result.
The heaters take about 1 amp of current (AC) when i remove the fuses and put the meter in between.

Right now i'm thinking of the LM317's i'm using (they are running quite hot), they are LM317T, is there any difference between them? maybe current or something like that? did a search but i just found they are 1.5 amp each.

This what the hum looks ans sounds like right now:

http://www.dagoosemusic.nl/temp/hum.pdf
http://www.dagoosemusic.nl/temp/hum2.pdf
http://www.dagoosemusic.nl/temp/humtest3.pdf

If did not drive the EQ that hard so the hum s more noticable, if i crank the sound up it's still there a lot but less then before (not much)

 

[Samuel Groner]

Maybe try to add a 1000 uF elco after the LM317.

Try whatever you want but I can tell you that this is highly unlikely to have any effect.

Have you tried shorting the input of the unit and entirely bypassing the EQ section (as suggested by other contributors) to see if this changes anything? Locating the problem helps much more than randomised swapping and adding parts.

I'm almost 100% sure it is coming from the 6.3 V heater.

Why guessing--I'm sure you have a voltmeter at hand which reads AC; if the AC signal reads below a few mV all is fine.

I can't help advising you to get a scope. The time you've spent debugging this EQ would have easily bought you a suitable second-hand unit and will save hours if not days for later builds.

Samuel

 

[dagoose]

[quote author="Samuel Groner"]

Maybe try to add a 1000 uF elco after the LM317.

Try whatever you want but I can tell you that this is highly unlikely to have any effect.

Have you tried shorting the input of the unit and entirely bypassing the EQ section (as suggested by other contributors) to see if this changes anything? Locating the problem helps much more than randomised swapping and adding parts.

I'm almost 100% sure it is coming from the 6.3 V heater.

Why guessing--I'm sure you have a voltmeter at hand which reads AC; if the AC signal reads below a few mV all is fine.

I can't help advising you to get a scope. The time you've spent debugging this EQ would have easily bought you a suitable second-hand unit and will save hours if not days for later builds.

Samuel[/quote]

Yep, i'm seriously thinking of getting a secondhand scope for these kind of things.
Also bridged the IO of the board (one the first things i did) and that's why i no 100% sure it's coming from the tubestage.
I'm also sure about the 6.3v because when i remove the fuse and so the 6.3v drops the hum is instantly gone.
But to bad i still didn't find the real reason.. I will try with the AC meter to see if i have some AC voltage instead of just DC.

 

[Samuel Groner]

When I remove the fuse and so the 6.3 V drops the hum is instantly gone.

I'm not familiar with the design--you mean the fuse of the heater? Or the mains fuse which cuts all supply lines?

Samuel

 

[dagoose]

[quote author="Samuel Groner"]

When I remove the fuse and so the 6.3 V drops the hum is instantly gone.

I'm not familiar with the design--you mean the fuse of the heater? Or the mains fuse which cuts all supply lines?

Samuel[/quote]
It's the fuse of the heater, so just the 6,3v supply is cut wit the fuse, 250v continues.

 

[Samuel Groner]

Why didn't you say that before (or did I missed that one)? At least now we have good info which we can use. :grin:

So what happens if you just power one channel, e.g. by removing a tube?

Samuel

 

[dagoose]

[quote author="Samuel Groner"]Why didn't you say that before (or did I missed that one)? At least now we have good info which we can use. :grin:

So what happens if you just power one channel, e.g. by removing a tube?

Samuel[/quote]
I did, in one of the first posts :green: But ok... now i did it again
When i just one channel (remove the tube) the hum in the working channel even seems to get louder. that's one of the weird things actually.. :?

Like i mentioned before, could it be the LM317T i'm using? what is the difference between a LM317T and other versions? the current or something else?
Maybe it could also be the resistors, i have standard resistors and i measure 6.3v so it should be ok but meybe i need 0.5watt resistors? just some thinking..

 

[ioaudio]

no, the lm317t is ok.

look at the layout description http://www.gyraf.dk/gy_pd/pultec/gy_pd.pdf
i never build that pcb, but it seems you connected the transformers different.

 

[dagoose]

[quote author="ioaudio"]no, the lm317t is ok.

look at the layout description http://www.gyraf.dk/gy_pd/pultec/gy_pd.pdf
i never build that pcb, but it seems you connected the transformers different.[/quote]

I know what you mean with the connections, but that's not it, i connected everything in the same way.
The only difference is the wire that goes from one trafo to the other, that one goes directly to my trafos instead of to the boards first.
Right now i'm driving the input of the EQ real loud and the noise level came down to about 60db so quite acceptable but still not good enough for me tough.
I know (i hope) it can be a bit better then that.. still have to fix that soon so i can finally finish the project and fill up my rack with it and start with a new project

 

[Samuel Groner]

You might quickly check the heater line by just running it into your AD audio converter. 6.3 V is low enough to not cause any damage though you might want to include a 1k series resistor and perhaps a ~100 uF just to be sure.

Samuel

 

[ioaudio]

[quote author="dagoose"]
I know what you mean with the connections, but that's not it, i connected everything in the same way.
[/quote]

so thats the reason why only the heater voltage turns off when you take out the fuse.

[quote author="dagoose"]The only difference is the wire that goes from one trafo to the other, that one goes directly to my trafos instead of to the boards first.[/quote]
you mean both wires parallel connected to board and secon transformer?

 

[dagoose]

[quote author="ioaudio"][quote author="dagoose"]
I know what you mean with the connections, but that's not it, i connected everything in the same way.
[/quote]

so thats the reason why only the heater voltage turns off when you take out the fuse.


[quote author="dagoose"]The only difference is the wire that goes from one trafo to the other, that one goes directly to my trafos instead of to the boards first.[/quote]
you mean both wires parallel connected to board and secon transformer?[/quote]

Yep, just the 6.3v goes down that way, 250v stay's up and running.

The trafo's themself to get 250v are connected directly on the second sec windings so now the 6.3v has a seperate output on the trafo for both channels.
I tried the original setting in the beginning but then it even got worse, tried about every possibilty with the trafo's, reverse, seperated, parallel and that didn't matter so it's not the trafo's causing it (or the current must be too high but i don't think it could be too high)

When i google on humming 6.3v heaters i allways come up on sites where they use AC instead of DC for the heaters with a humming adjustment circuit but i think DC should be better anyhow. I just think the DC is not very clean in my case, but what is the reason?


To samuel: you mean run the 6.3v voltage into an analog input (could also be a mixer then) to check if that gives a flat clean signal? Couldd be worth trying..

 

[Samuel Groner]

You mean run the 6.3 V voltage into an analog input (could also be a mixer then) to check if that gives a flat clean signal?

Yes--if you have it digital you can check the waveform as well, similar to a scope but with much limited bandwidth (which should probably not be much of a problem for this case).

I'm not familiar with the design but I think there is some confusion about the fuse. Is there one or more fuse? And before or after the transformer? On the first page you said that when you remove power the hum's gone (which is not much of a surprise). Later one you said that when you remove the fuse for the heater the hum is gone (which is something entirely different as it seems to narrow the problem to the heater).

Samuel