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Old 4th January 2010, 04:51 PM   #1
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Default Noise in a valve headphone amp kit

I recently purchased the Oatley Valve Headphone amp kit: Oatley Electronics

I was able to put it together with no issues, and the sound quality is great... Only if you use a 9v battery and 300ohm headphones (Sennheiser HD-600's).

If I try to use a 9v unregulated power supply, I get a terrible hum I am assuming from a ground loop. So I hooked up to a 9v battery instead, and that fixed that problem.

However I still get clicking in the output if I move it towards my computer.

It also picks up an induced 60hz hum when placed near mains wiring.

Right now I have it in a plastic project box that has a metal lid. Would a full metal enclosure help a bit with this problem?
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Old 4th January 2010, 05:21 PM   #2
Brit01 is offline Brit01  United Kingdom
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The 9V battery will give a nice smooth B+ supply to the tubes.

What is the unregulated power supply you tried? If its one of those nasty 9V charger type supplies then yes it will be the worst kind of power supply you can use. It does not rectifier the AC properly.

In any valve project the B+ supply is the most important aspect of design.
Smooth and free of noise/ripple is what we aim for.

Quote:
However I still get clicking in the output if I move it towards my computer.

It also picks up an induced 60hz hum when placed near mains wiring.
Also valves are sensitive and need to be shielded and kept away from other electrical devices as you have found out.
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Old 4th January 2010, 05:49 PM   #3
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Quote:
Originally Posted by Brit01 View Post
The 9V battery will give a nice smooth B+ supply to the tubes.

What is the unregulated power supply you tried? If its one of those nasty 9V charger type supplies then yes it will be the worst kind of power supply you can use. It does not rectifier the AC properly.

In any valve project the B+ supply is the most important aspect of design.
Smooth and free of noise/ripple is what we aim for.



Also valves are sensitive and need to be shielded and kept away from other electrical devices as you have found out.
Thanks for the info. I have an O-scope, I dont know why I didnt think to measure the output of the 9v AC adaptor (yes its a cheap junky supply).

The kit has a regulator IC on it, but I think it only regulates filament voltage for the tubes, it does not regulate B+ at all.

So would getting one of those Hammond aluminum project cases work well with the shielding for the tube?
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Old 4th January 2010, 07:01 PM   #4
Brit01 is offline Brit01  United Kingdom
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Quote:
(yes its a cheap junky supply)
yikes!!!
yep never use one of those for your valves.
Batteries are a great source of smooth DC, otherwise to rectify the mains and get a good 9V out is a little complicated.
You'd need to design a rectified power supply using a power transformer.
Search on the threads for ideas, but IMHO it won't be worth it as these little pentodes don't require much current (12mA in total is nothing).

Use a rechargeable 9V battery.

Also a metal casing can sometimes pick up more noise I heard.
Maybe plastic would be better.

Just be careful about the signal cables and always use shielded cables.
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Old 4th January 2010, 07:18 PM   #5
Stixx is offline Stixx  Germany
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Quote:
otherwise to rectify the mains and get a good 9V out is a little complicated.
What is so complicated about it..? Basically it's the same as an HV psu, only at a (much) smaller scale. Get a small print transformer 115:9V, a rectifier bridge or some better rectifiers to your taste, smoothing caps, R's or L's and so on...
Do use PSUDII to simulate what you want.
Or just build a small regulated psu using a 78xx or LM317 IC (search the net about them...)

Hope this helps...

PS. For real good results read the threads about the Simplistic Shunt regs by Salas and Ikoflexer. Very recommended!
(in Power Supplies)

Last edited by Stixx; 4th January 2010 at 07:20 PM.
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Old 4th January 2010, 07:49 PM   #6
Brit01 is offline Brit01  United Kingdom
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Quote:
What is so complicated about it..? Basically it's the same as an HV psu, only at a (much) smaller scale. Get a small print transformer 115:9V, a rectifier bridge or some better rectifiers to your taste, smoothing caps, R's or L's and so on...
okay well not so difficult. but I know you Stixx could do that blindfolded.

Depends on our friends skill level here.

Any reason for not wanting to use batteries?
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Old 4th January 2010, 09:06 PM   #7
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Default Good write-up on this amp

Not sure if you have seen this Web page. Should note also that there is a very long thread about this amp on the AIY Audio Forum for this same site.

Raytheon JAN6418 Valve (Tube) Preamplifier / Headphone Amp Kit
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