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Mon Jun 27, 2016, 02:40 PM

 

I need a better headphone amp

I have one that literally has tubes, but there is quite a bit of hum. Maybe the tubes aren't affixed properly?

There is a LOT of hum. I'm great with car stereos but headphone hi-fi is not my wheelhouse.

This is what I have:

https://www.amazon.com/Little-puffer-Preamp-Preamplifier-amplifier/dp/B00OY1PR9K/ref=pd_lpo_23_tr_img_2?ie=UTF8&psc=1&refRID=MT094E3AXW58WMCBNVRN

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Reply I need a better headphone amp (Original post)
Aerows Jun 2016 OP
mahatmakanejeeves Jun 2016 #1
Aerows Jun 2016 #2
Aerows Jun 2016 #3
mahatmakanejeeves Jun 2016 #5
Aerows Jun 2016 #8
Aerows Jun 2016 #10
Aerows Jun 2016 #4
Aerows Jun 2016 #6
Aerows Jun 2016 #7
Aerows Jun 2016 #9
mahatmakanejeeves Jun 2016 #11
Aerows Jun 2016 #12

Response to Aerows (Original post)

Mon Jun 27, 2016, 02:54 PM

1. Tube-anything is generally pricier than solid state-anything.

At least for hi-fi equipment. Old boat anchors, not so much.

Which tube headphone amp do you have? Is the schematic available on the internet?

Usually, defects in the tubes that do the signal processing do not cause hum. Hum, if it's pretty loud, originates in the power supply. Without further knowledge of what's going on, I'd immediately head for the filter capacitor in your power supply, assuming your amp has a linear power supply.

Vacuum tube hi fi equipment is about as easy a thing to fix as there is.

Please show us the schematic. Thanks.

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Response to mahatmakanejeeves (Reply #1)

Mon Jun 27, 2016, 03:39 PM

2. I'll pull the schematic up and post it

 

but I think you are on target with the power supply. I'm going to switch to an isolated one - you've probably diagnosed it already!

I didn't think about that.

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Response to mahatmakanejeeves (Reply #1)

Mon Jun 27, 2016, 03:49 PM

3. Schematics

 

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Response to Aerows (Reply #3)

Mon Jun 27, 2016, 04:13 PM

5. Do you have a voltmeter?

The voltages involved are pretty low. I didn't even know you could run a tube amp on 12 volts B+.

Tube hi fi equipment can be sort of scary to work on. A Dynaco Stereo 70 has 400 volts B+ and enough current to be lethal. Also you can get burned if your hand brushes up against an output tube. This headphone amp looks less hazardous to work on.

Anyway, can you read any AC voltage on the heater supplies? It looks as if maybe you have an external 12-volt power supply for this. There should be no AC there. It should be all DC.

Have you tried running this off a car or motorcycle battery? You should get no hum from that. If it works okay an a motor vehicle battery, then you have a power supply problem.

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Response to mahatmakanejeeves (Reply #5)

Mon Jun 27, 2016, 04:26 PM

8. I messed around making a CMOY

 

This is strictly a headphone amp - nothing dangerous.

I've done dangerous audio, and this is so low amp, the worst you get is a small zap, and in my case, crap sound.

Don't worry - this isn't going to drive the big guns. This is for tiny little headphones.

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Response to mahatmakanejeeves (Reply #5)

Mon Jun 27, 2016, 05:04 PM

10. Of all the things I have

 

a voltmeter is not one of them, sadly.

I really need to invest in one, though.

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Response to Aerows (Original post)

Mon Jun 27, 2016, 03:52 PM

4. My configuration is an ASUS DGX

 

to the amp, and my go to headphones are Sennheisers. The Oxygen chipset it superior to anything, imho.

I'm not going to leap into the divide of Grado vs. Sennheiser, just let it rest that I've had both and love Sennheiser sound.

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Response to Aerows (Original post)

Mon Jun 27, 2016, 04:18 PM

6. Tubes in question

 

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Response to Aerows (Reply #6)

Mon Jun 27, 2016, 04:20 PM

7. And yes, I'm aware I need a manicure

 

Last edited Mon Jun 27, 2016, 05:02 PM - Edit history (1)

I've been busy.

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Response to Aerows (Original post)

Mon Jun 27, 2016, 05:00 PM

9. Isolated the power supply

 

but it still has that hum.

Maybe I need a different power supply?

The hum is pronounced, less when I isolated it, but still noticeable.

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Response to Aerows (Reply #9)

Mon Jun 27, 2016, 05:14 PM

11. Bad ground.

You have a high-impedance input. The manufacturer specifies 100k, but 20k is probably more like it. The manufacturer also says it has a 100k output impedance, which wouldn't work too well for a headphone amp.

Anyway, it's like a guitar amp with a cord that's not plugged into the guitar. The amp is picking up the hum. Try pressing on parts of the solder traces with some non-conducting device - a piece of plastic. Not a jeweler's screwdriver. See if you can find someplace where you press that makes the hum goes away. Then you'll have to solder that bad part back to what it's supposed to be attached to.

That's a bad description, I know.

Chinese devices are not, IMHO, known for the integrity of their hardware. Specs are okay, but the hardware gives out easily. If a tube socket has deteriorated, there could be a bad connection there causing the hum.

PS: take off the ring before working on electrical stuff. Even 12 volts. Especially 12 volts, if a car battery is involved. I can dig up an OSHA report to show why.

Even an el cheapo voltmeter - the free one from Harbor Freight Tools - will work. With a voltmeter, you could see where the hum (AC voltage) was. An oscilloscope would work too.

I'm about to log off for the day.

Best wishes.

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Response to mahatmakanejeeves (Reply #11)

Mon Jun 27, 2016, 07:53 PM

12. In other words, it sucks.

 

Yep, that is the conclusion I came to, as well!

Thanks for your help, though - I appreciate it.

I shop at Harbor Freight too! I get the big old catalog, it's wonderful!

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