[doggie]

I have a Single Power Extreme headphone amp that runs 6SN7/5998 tubes. It is ~9 years old. At one point it was discovered that many of these SP amps had some serious shortcuts made in their circuitry. I subsequently followed some suggestions on Head-Fi to replace the transformer and a few other under-spec'ed parts. It has been working great and I really enjoy the sound especially now that I am running my Schiit Yggy DAC through it.

To the point. It is starting to be a little noisy. This noise is inconsistent and present whether music is playing or not. It does not seem to come from one specific channel. It is there when cold or when warmed up. Changing tubes does not help. I also opened up the amp and re-soldered as many joints as I could get to. No joy...

The noise is like a dull, muted "rustling". It is never terribly loud but is still distracting.

Any ideas?

[sfox7076]

What caps are in it?  What Interconnects?  Did it start with the new DAC?

[doggie]

It has persisted between at least two DACs and a couple of pairs of interconnects.

The caps are all stock. I suspect that one of them might be deteriorating. The way it is constructed it will be hard to replace them. SP used a circuit board that pretty much locks the tube sockets in place with the chassis. It would basically be a near rebuild...

[G Georgopoulos]

Sounds like a source problem...

[doggie]

Sounds like a source problem...

Thanks. Noise still there with no source connected.

[G Georgopoulos]

Thanks. Noise still there with no source connected.

ok

to be 100% certain is the h-amp short the h-amps inputs to ground and see if the noise goes away..

[borism]

Doggie, instead of putting more effort/money into this amp I would consider getting a new one. For example, if you don't mind DIY, a Bottlehead amp. I built an inexpensive Crack BH that uses 12au7 and 5998 tubes. With a simple adaptor you can use a 6SN7 instead of the 12au7. However, it does depend on your headphones since the Crack is an OTL design and only drives high impedance HPs. For Sennheisers it's great.
Another plus for the Bottlehead is the ability to customize it (caps etc.).
Good luck!

[doggie]

Doggie, instead of putting more effort/money into this amp I would consider getting a new one. For example, if you don't mind DIY, a Bottlehead amp. I built an inexpensive Crack BH that uses 12au7 and 5998 tubes. With a simple adaptor you can use a 6SN7 instead of the 12au7. However, it does depend on your headphones since the Crack is an OTL design and only drives high impedance HPs. For Sennheisers it's great.
Another plus for the Bottlehead is the ability to customize it (caps etc.).
Good luck!

Good suggestion. Bottlehead is on my short list if this amp really tanks. I use Sennheiser 650's so OTL is perfect. Would also allow me to use my present tubes. I use a 7N7 driver with an adapter currently. My other option is to find a DHT amp and modify it as I do love the DHT sound and have a bunch of 45's and 71a's which would make nice music.

Sort of narrowing down the noise issue to the heater circuit right now with some help from Kevin Gilmore over on Head-Fi. Crossing my fingers for that but would still like to try DHT...

[doggie]

ok

to be 100% certain is the h-amp short the h-amps inputs to ground and see if the noise goes away..

Thanks. Will look for my RCA shorting plugs!

[doggie]

Got it worked out. It was a fried/overworked resistor in the HV supply. Replaced and all is very well...

[JerryM]

Got it worked out. It was a fried/overworked resistor in the HV supply. Replaced and all is very well...

Sweet!