Really strange hum issue! (Please help)

ForthMonkey · Feb 8, 2016

I finished my Poorman's Pultec.It's working good but there is hum!And it's louder than signal!I did everything about grounding.Now i want to make list about what happening!

1.When i plug in it to AC,directly getting hum and really low level signal like crosstalk!But power switch is off!I checked everything and there is no leakage.How is it possible?Even there is no electricity on board!But if i connect LM317's heatsing to chassis,i can reduce all hum and signal.What?!

2.When i open power switch,sometimes signal coming slowly like fade in without hum and sometimes again coming slowly with hum.But after 10 seconds,hum comes back!

Here is my schema...I need your helps!

Thanks.

ruffrecords · Feb 8, 2016

Where do you connect your power supply 0V to the chassis?

Cheers

Ian

ForthMonkey · Feb 9, 2016

ruffrecords said:
Where do you connect your power supply 0V to the chassis?

Cheers

Ian

Thanks for reply,Ian.

PSU's 0V and audio ground is same in my design as you can see.Should i connect groum to chassis?

Deepdark · Feb 9, 2016

ForthMonkey said:
ruffrecords said:

Where do you connect your power supply 0V to the chassis?

Cheers

Ian

Click to expand...

Yup. Straight on the nearest bolt around iec inlet

Thanks for reply,Ian.

PSU's 0V and audio ground is same in my design as you can see.Should i connect groum to chassis?

ForthMonkey · Feb 9, 2016

Deepdark said:
ForthMonkey said:

ruffrecords said:

Where do you connect your power supply 0V to the chassis?

Cheers

Ian

Click to expand...

Yup. Straight on the nearest bolt around iec inlet

Thanks for reply,Ian.

PSU's 0V and audio ground is same in my design as you can see.Should i connect groum to chassis?

Click to expand...

iec inlet already connected to chassis.Should i connect board's ground to chassis?

Deepdark · Feb 9, 2016

yes, same place as the iec

ruffrecords · Feb 9, 2016

You should read my Grounding 101 document. It is under the DIY tab of my web site in the Power folder:

http://www.customtubeconsoles.com/diy

Cheers

Ian

ForthMonkey · Feb 9, 2016

ruffrecords said:
You should read my Grounding 101 document. It is under the DIY tab of my web site in the Power folder:

http://www.customtubeconsoles.com/diy

Cheers

Ian

I read and did what you told in documents.And now i got rid of "strange" hum.No hum when power switch off.Thanks!

Now only have "simple" hum issue when gear working.But i believe,it's about power supply caps.Are they too small for power supply? Cause i changed C12 and C6 to 1000uf and hum gone little bit.I guess C4,C5,C6,C9,C10,C12 must be bigger.4700uf or higher is ok?

Deepdark · Feb 9, 2016

ForthMonkey said:
ruffrecords said:

You should read my Grounding 101 document. It is under the DIY tab of my web site in the Power folder:

http://www.customtubeconsoles.com/diy

Cheers

Careful tube selection can help quiet a bit. Did you used a toroid? If so, try rotating it. If you use big EI, is it outside or inside the case? If inside, try puting it inside a steel box.

Ian

Click to expand...

I read and did what you told in documents.And now i got rid of "strange" hum.No hum when power switch off.Thanks!

Now only have "simple" hum issue when gear working.But i believe,it's about power supply caps.Are they too small for power supply? Cause i changed C12 and C6 to 1000uf and hum gone little bit.I guess C4,C5,C6,C9,C10,C12 must be bigger.4700uf or higher is ok?

ForthMonkey · Feb 9, 2016

Deepdark said:
ForthMonkey said:

ruffrecords said:

You should read my Grounding 101 document. It is under the DIY tab of my web site in the Power folder:

http://www.customtubeconsoles.com/diy

Cheers

Careful tube selection can help quiet a bit. Did you used a toroid? If so, try rotating it. If you use big EI, is it outside or inside the case? If inside, try puting it inside a steel box.

Ian

Click to expand...

I read and did what you told in documents.And now i got rid of "strange" hum.No hum when power switch off.Thanks!

Now only have "simple" hum issue when gear working.But i believe,it's about power supply caps.Are they too small for power supply? Cause i changed C12 and C6 to 1000uf and hum gone little bit.I guess C4,C5,C6,C9,C10,C12 must be bigger.4700uf or higher is ok?

Click to expand...

I'm using solid-stade power supply.And trafo is not toroid.

I did everything about grounding.But still have hum.As i said,it looks like psu issue.Need bigger caps,i guess.

ForthMonkey · Feb 9, 2016

And maybe i can add capacitor somewhere close to transistors.As decoupling caps?

Transistors are really close to each other.maybe it could work to get rid of hum.I'll try...But first i will change PSU caps.

ruffrecords · Feb 10, 2016

ForthMonkey said:
I read and did what you told in documents.And now i got rid of "strange" hum.No hum when power switch off.Thanks!

Now only have "simple" hum issue when gear working.But i believe,it's about power supply caps.Are they too small for power supply? Cause i changed C12 and C6 to 1000uf and hum gone little bit.I guess C4,C5,C6,C9,C10,C12 must be bigger.4700uf or higher is ok?

I think your caps are large enough. Have you used input and output transformers or is the EQ unbalanced? Does the hum level change if you short the input?

Cheers

Ian

ForthMonkey · Feb 10, 2016

ruffrecords said:
ForthMonkey said:

I read and did what you told in documents.And now i got rid of "strange" hum.No hum when power switch off.Thanks!

Now only have "simple" hum issue when gear working.But i believe,it's about power supply caps.Are they too small for power supply? Cause i changed C12 and C6 to 1000uf and hum gone little bit.I guess C4,C5,C6,C9,C10,C12 must be bigger.4700uf or higher is ok?

Click to expand...

I think your caps are large enough. Have you used input and output transformers or is the EQ unbalanced? Does the hum level change if you short the input?

Cheers

Ian

I just tried to shorting input and hum still coming.

Still can't find problem...

ForthMonkey · Feb 10, 2016

Now i changed one of LM317 and sound changed.No hum but low and distorted signal.Then i soldered again,i got normal signal level and again hum.What?

By the way i have no idea why but my soundcard burnt...I measured Pultec's output,there is no voltage.Cause i thought it gave voltage to soundcard input but it didn't.

Deepdark · Feb 10, 2016

ForthMonkey said:
Now i changed one of LM317 and sound changed.No hum but low and distorted signal.Then i soldered again,i got normal signal level and again hum.What?

By the way i have no idea why but my soundcard burnt...I measured Pultec's output,there is no voltage.Cause i thought it gave voltage to soundcard input but it didn't.

You burnt your soundcard

Are you sure you didn't connected B+ to ground ;D

ForthMonkey · Feb 10, 2016

Deepdark said:
ForthMonkey said:

Now i changed one of LM317 and sound changed.No hum but low and distorted signal.Then i soldered again,i got normal signal level and again hum.What?

By the way i have no idea why but my soundcard burnt...I measured Pultec's output,there is no voltage.Cause i thought it gave voltage to soundcard input but it didn't.

Click to expand...

You burnt your soundcard

Are you sure you didn't connected B+ to ground ;D

Yeah,burnt!But how did i do it,i have no idea!Cause i was listening drum sample when i test Pultec.And Pultec's out was going to directly soundcard input.I was trying to eq.Then suddenly no sound!Anyway...It was cheap model.Time to buy new one.

But for now i can't work on Pultec.Cause no way to hear what happens.I weill go on when i get new one.Actually i will buy two soundcard.One cheap Behringer to use equipment tests.And another one for recording and mixing.

I have to fix that hum!

Deepdark · Feb 10, 2016

Hope it's not the Pultec that burnt your soundcard. But maybe cheap soundcard tend to burnt easily when they get old, I don't know

ForthMonkey · Feb 10, 2016

Bought new and cheap soundcard.I hope,i will go on fixing humming issue about 3-4 days.

Show must go on!

Deepdark · Feb 10, 2016

AC or DC heater? Elevated or not?

ForthMonkey · Feb 10, 2016

Deepdark said:
AC or DC heater? Elevated or not?

No tube circuit.Gain stage is solid state.You can see circuit at first post.I guess,i have problem about regulators.

Really strange hum issue! (Please help)

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