Hum problem with jfet Aleph 3 (babbelfish)

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Running all ground connections to the psu always caused some hum, when I tried it.
Babo San, you forgot the last 4 words;) I didnt mean always, always:D
you and your ppl OK?
Yes, thanks a lot mate. Hope you and yours are too. Especially that sweet little girl of yours:) How come I never had such a cute thing? I "only" have 4 boys:D BTW looking at their girlfriends, I cant complain:clown:

Steen:)
 
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Babowana said:



Old farts like to tell that the star ground can be located at any place as long as the concept and principle of grounding is clearly understood and applied. There is no simple belief that the star ground is to be on PSU or on PCB or on a dot in the inner space of the enclosed chassis :D

Ask Papa if he is also an old fart :bigeyes:


don't be so religious and philosophic regarding star gnds and old farts ;

you are in danger that only I understand you .....hehe.....just because I'm always proponent of star gnd and old fart ,too..........
ps.but don't tell that to Papa,you'll ruin my chances that he ever adopt me :devilr:

just think of it - Papa as Step Father, give you assignment to make inventory of his warehouse...............:att'n: :devilr:


epilog..............."ZM......lost in action"
 
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Babowana said:



Four? :bigeyes: Oh my . . .

I am already a poor father only with two boys.
I am zzelus Zen Mood or Choky (no matter whichever is the right name . . . :D)

When I build my Babbelfish, I will show you where my star ground is ;)

bad boys.......ruining so nice topic and making playground of it :D
btw I know why steen is so good in making things....now when boyz don' need him ( in all stages of puberty) ,he have so much things to do,but have no their permission......so he make amps ........

similar will catch me in few years,I have no doubts ;)

anyway ...I know where my good star ground always are...... right in a middle of my zen :clown:
 
Thanks for all your posts - old farts! ;)

I have been twisting and turning this problem of mine and I'm beginning to think that my toroids are to blame. Either they are not powerful enough or there is some mismatch with the 2x10 parallel secondaries.
I use two donuts - one for each rail. Each secondary is 17V and 1.5A.

Is it correct that this corresponds to 10x17x1.5=255VA?
Is that simply too low - even for one channel?
I have another two of these - would it be worth it to try to run the amp with 2x20 parallel secondaries?

Perhaps I should just shell out the big money and buy a single decent toroid 2x18V 625VA?
 
Update

One of the things I did to fix my amp was to change the pnp's, but now I just checked the gain in the parts I pulled out and one of the two pnp's is dead....
Could it be so simple?
How could it have died - a <-5V drop on vbe?
It could be interesting to check if the current pair has a dead device somewhere.
 
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cviller said:
.............

Is it correct that this corresponds to 10x17x1.5=255VA?
Is that simply too low - even for one channel?
I have another two of these - would it be worth it to try to run the amp with 2x20 parallel secondaries?

Perhaps I should just shell out the big money and buy a single decent toroid 2x18V 625VA?


you have enough VA, don't try with 20 secs in parallel ;

just in case-buy few sixpacks,as I told before :devilr: , go to steen's, and try with other donut
 
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Re: Update

cviller said:
One of the things I did to fix my amp was to change the pnp's, but now I just checked the gain in the parts I pulled out and one of the two pnp's is dead....
Could it be so simple?
How could it have died - a <-5V drop on vbe?
It could be interesting to check if the current pair has a dead device somewhere.


does that solve hum problem?
if yes- good.........if not,there is still donut solution ;

reason for died pnp?

remember -that's not a toob.................hehe

transistors don't need reason to go poof ,mostly :devilr:

JJ, of course .......
 
It is so much nicer to have made something that actually works! :D

The only problem now is that the amp is so detailed and unforgiving. I can hardly hear streamed radio anymore, because the digital artifacts from compression are so cleanly reproduced. :(

I'm considering designing a sound-stage reduction module for my preamp so I can make the amp compatible with low end sources... Perhaps a cheap opamp stage with huge amount of feedback and <0.0001 THD could smear the whole thing out to blurry image required for digitally compressed music to sound nice.

I'm not kidding! I will have to make something like this, because the amp is also connected to my home brewed hdd recorder, but for this purpose I think an adjustable notch filter would be more appropriate because some of the channels I record from have annoying noise on certain frequencies.
 
glad to hear it is problem solved!

It was a dead BC556 that was causing all the problems?

I assume the hum was in both channels.
Curious that it was able to inject hum into both channels, but not too farfetched.

I am going to change the input to my Mini-aleph to j-fets -- maybe I will be asking for help soon!

JJ
 
Arghhh its back

The hum was not completely gone with the fix previously mentioned, but it tolerable. Now I have mounted the whole thing in a box and tried to use make a better starground, but the hum is just getting worse! :bawling:

The transformers have started humming too. I tried to switch the primary, but that didn't help.

I have taken some pictures of how the whole thing is mounted:

http://viller.org/audio/2007jan_jfish/hum2/

Blue is either gnd or neutral, black is either +21V or live. Brown is +21V. The red and white is speaker connections and I have both XLR and RCA inputs.
 
It looks like you are running the 220V AC to the psu board? The AC must ONLY connect directly to the trafo's primary (both AC leads!) Hard to tell from a pic though.
The DC supply leads are running closer to the trafo's than needed. Try and pull them towards the back of the chassis and run them parallel with the amp boards. Looks like they touch the trafo's, and thats not good:)
And I am not really fond of you grounding scheme.

Steen:)
 
Hi Steen, thanks for looking at my pictures.

It looks like you are running the 220V AC to the psu board? The AC must ONLY connect directly to the trafo's primary (both AC leads!) Hard to tell from a pic though.

Both neutral and live are soldered to the psu board and then to the mains on trafo. But it has been wired like this all along.

The DC supply leads are running closer to the trafo's than needed. Try and pull them towards the back of the chassis and run them parallel with the amp boards. Looks like they touch the trafo's, and thats not good

They did actually touch slightly, but moving them away didn't help.

And I am not really fond of you grounding scheme.

What exactly do you think is wrong with the scheme?
 
What exactly do you think is wrong with the scheme?
I will work out a drawing.
Both neutral and live are soldered to the psu board and then to the mains on trafo.
I dont like the AC running so close to the DC. It should be easy to connect the AC directly to the trafo. It might have worked at some point, but those things interfers with each other.

Steen(still looking at the pic's):)
 
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