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Old 21st July 2003, 04:56 PM   #11
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I rather suspect that you may have scored a pair of doorstops or bookends...
Well at least they are pretty....

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Old 21st July 2003, 05:24 PM   #12
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You might also want to know whether they are suitable for choke-input use as well; eg whether they can stand some DC without loosing too much inductance and buzzing.
What makes a choke buzz? My new amp buzzes, and I'm not sure which piece of iron in there is doing it. I haven't really bothered with fixing it because I can't hear it over the music, but it would be nice if it could be fixed.

I'm also wondering if I should bother about the hum. I can only hear it late at night with no music playing, and I'd need 3 new transformers to convert all my heaters to DC, I think. My RS DMM says 2mV, my scope is uncalibrated so I don't trust what it says.
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Old 21st July 2003, 07:26 PM   #13
cdeveza is offline cdeveza  United States
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This choke looks like a filament choke, low inductance/high current, what do you think?

Alex Deveza
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Old 21st July 2003, 07:41 PM   #14
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Hi,

Quote:
What makes a choke buzz?
Crud from the mains is one source, badly implemented ground another amongst a dozen.

Oh, and if your mains xformers are toroids you can say hello to a lot of that aggrevating buzzing too.

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I haven't really bothered with fixing it because I can't hear it over the music, but it would be nice if it could be fixed.
That would bother me no end...your noisefloor becomes too high for comfort and it make soundstage depth colapse.

Does it happen with the input of the amp shorted?

Cheers,
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Old 21st July 2003, 08:25 PM   #15
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That would bother me no end...your noisefloor becomes too high for comfort and it make soundstage depth colapse.
I'm just starting to get over being dazzled by how much better this amp is than what I had before So I'll start fixing/changing things on it soon. I tried the caps from B+ to cathode using clip leads, and while they didn't lower the noise floor, the sound did improve. I also need to reduce the filament voltage on my 6SL7s a little (it's about 7.1V, IIRC), and change a few other things.

Quote:
Crud from the mains is one source, badly implemented ground another amongst a dozen.
Well, it could certainly be the second. Any specific grounding issues that I should look at? And how would I test for mains noise? I have a small cap across the transformer primary. Also, I don't know if it's the choke that's buzzing or the power trasformer or the filament transformers.

Quote:
Oh, and if your mains xformers are toroids you can say hello to a lot of that aggrevating buzzing too.
No toroids.

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Does it happen with the input of the amp shorted?
Haven't tried that yet. I'll try it tonight.
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Old 21st July 2003, 08:32 PM   #16
dhaen is offline dhaen  Europe
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Quote:
Originally posted by Saurav


What makes a choke buzz? ..snip..
Apart from loose windings and laminations, it can be caused by using the wrong choke for an application.

Chokes used in choke-input filters should be 'specially designed. They have some DC across them. Ordinary chokes buzz in this application.

Cheers,
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Old 21st July 2003, 08:45 PM   #17
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This is what the design called for (though I've modified the PSU from the original design):

Quote:
193G 10H, 150ma, 102 ohms, 800VDC. EACH $42.
This is what I used:

Quote:
193J 10H, 200ma, 82 ohms, 800VDC. EACH $40.
Increased current handling and lower DCR for a lower price, made sense to me. These are Hammond chokes, the prices are from the Angela website. Here's my PSU:

Click the image to open in full size.
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Old 21st July 2003, 09:43 PM   #18
dhaen is offline dhaen  Europe
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Choke spec:
http://www.hammondmfg.com/193.htm
Doesn't say it'll work on choke input. But your circuit has a small but reasonable first cap. I wouldn't expect a problem.

Cheers,
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Old 21st July 2003, 09:52 PM   #19
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Thanks. I could try temporarily increasing the cap to see if the buzzing goes away, but that will upset all the voltages. And I'd rather not use resistors to adjust the voltages - they'd have to be rated for pretty high power, and it seems to me that the more series resistance I have, the more the PS output will sag during high current transients.

Just making sure I understand this - in a choke input filter, the choke sees much higher current surges, because the first cap that's charging up comes after it. In a cap input filter, the current surges through the choke are smaller. Thus, even if the choke's current rating (200mA - that's DC, right?) fits the circuit, it might not work with a choke input filter. Is that correct?

Also, the 800VDC rating - voltage between what and what? The drop across the choke itself is fairly small. Is it the voltage between the windings and the enclosure (which may be grounded to teh chassis)?
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Old 22nd July 2003, 12:50 AM   #20
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Quote:
Originally posted by Saurav
Here's my PSU:
What's the point of the 3uF cap? It only makes for bad regulation, effectively increasing the critical inductance value.

Dave: do you have a mic or vernier to measure the wires coming out the bottom?

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