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Old 6th June 2009, 01:03 PM   #11
mcgaag is offline mcgaag  Netherlands
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He Erik,

Thats it, i put in the wrong value. 220 instead of 220k. I have to go now so i am going to change is tonight.

Thank a lot, i will let you know how it turns out.

Regards,
Rob
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Old 6th June 2009, 03:31 PM   #12
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Hi Rob

Glad you found it out that fast! I am almost sure that once you change that resistor you will have music: I hope you have some in stock, so you can still listen to the amp this weekend!

Erik
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Old 6th June 2009, 05:42 PM   #13
mcgaag is offline mcgaag  Netherlands
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Yep, there is music now! Thanks Erik pointing me in the right direction. Learned a lot building this amp.

Now the next challenge. Remove a nasty hum.

I will post a picture of my 1st diy tube amp!

Thanks for thoughts everyone.

Regards,
Rob
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Old 6th June 2009, 07:22 PM   #14
mcgaag is offline mcgaag  Netherlands
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It sounds nice except for that nasty hum. If i remove the tubes the hum is gone. Does this mean the tubes are broken?
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Old 6th June 2009, 08:09 PM   #15
mcgaag is offline mcgaag  Netherlands
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After reading some stuff i don't think its hum but buzz i hear...
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Old 6th June 2009, 08:15 PM   #16
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Quote:
Originally posted by mcgaag
It sounds nice except for that nasty hum. If i remove the tubes the hum is gone. Does this mean the tubes are broken?
Not necessarily...

try elevating the heaters to +40-50 volts with refrence to chassis, Use simple two-resistor pot.divider from +b to chassis, and de-couple with summit like a 0.22uF cap....

That should remove the heater-bourne hum often found in gain-stages like that shown...
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Old 6th June 2009, 08:43 PM   #17
mcgaag is offline mcgaag  Netherlands
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I don't think the buzz comes from the heaters. If i remove the heater power when the amp is buzzing the buzz is still there.

By the way, i did not rectify the heater power so it is AC.
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Old 6th June 2009, 09:23 PM   #18
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Quote:
Originally posted by mcgaag
I don't think the buzz comes from the heaters. If i remove the heater power when the amp is buzzing the buzz is still there.

By the way, i did not rectify the heater power so it is AC.

I have spent many happy hours trying to fix hum problems.

Running heater wires near inputs is bad.
Good decoupling is vital or the hum on the rails will modulate the audio signal.
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Old 6th June 2009, 11:03 PM   #19
chrish is offline chrish  Australia
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Read this star grounding.

Wiring these things is an art. Once you learn the tricks, as discussed in the link above, you will most likely produce hum-free amps.

Chris
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Old 6th June 2009, 11:07 PM   #20
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Quote:
Originally posted by mcgaag
I don't think the buzz comes from the heaters. If i remove the heater power when the amp is buzzing the buzz is still there.

By the way, i did not rectify the heater power so it is AC.

Is it a buzz or mains hum ?

I had a problem with my pre amp with diode switching spikes.
I cured it with 100nF across the decoupling capacitors.
This sounded like a buzz rather than hum despite it being mains frequency.
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