S.E.X with C4S too hot?

[boulos]

Hello,

I feel that my amp (SEX 2.1) is running a lot hotter with the C4S than before I installed it. Granted, I didn't measure this before and after, but I never noticed earlier that the headphone jack is so hot when I took it out. Then I touched the aluminum chassis and it seemed really hot. The tubes are relatively cool, but I think the transformer is running hotter than before. Is this expected?

Another issue is that the background hum with the C4S is higher than without it. The amp was almost dead quiet before I installed it. I'm starting to regret having installed the upgrade, and I can't go back since the nose pliers damaged one of the resistors I took out to install the C4S.

Thoughts?

Thanks
Boulos

[Paul Birkeland]

The C4S load has higher power supply isolation than the 150K plate load resistors, but it also provides higher gain (which will make the noisefloor more apparent with the volume control at the same position, but there will be more signal there).

The temperature should remain unchanged, if you have concerns about the operation of the amplifier, you can measure the DC voltage on either side of the 680 Ohm resistors in the power supply (the ones not connected to the tube sockets) and that will tell us the current draw of each half of the amplifier.

-PB

[boulos]

Thanks PB!  That explains why it sounds louder with my speakers (the noise floor is only apparent on my headphones, which are 32ohm).

I'll check the resistances across 7,10 and 17,20 and report back. I may not get a chance until the weekend.

Boulos

[Doc B.]

Wiring the output transformers for 4 ohms can lower the noise floor into headphones.

[boulos]

Would that work better with the Orcas?  I have them attached to the amp as the speakers and listen mostly to them (only occasionally to the headphones).
Thanks!

[Doc B.]

8 ohms is theoretically optimal, but 4 will sound fine and maybe cut the headphone noise floor in half. You could try it and see if the lower headphone noise floor outweighs any change in the sound of the Orcas. If the Orcas are running with a sub the change should be very small. If they are running full range the bass might get a little tighter but also a little lighter.

[boulos]

Hi PB,  The voltages are 19.9 (terminals 6,10) and 19.7 (terminals 16,20) across the 680 ohm resistors. Are these around what they should be?

Hi Doc, The Orcas are running full range. I think I will wait and see if the hum still bothers after I've spent more time with the upgrade and how the speakers sound before making the 4ohm change. I'll report back then on the change.

Thanks
Boulos

[Paul Birkeland]

Yeah, the current that your amp is drawing is within spec.

-PB

[boulos]

Great.  That alleviates my concern about the heat.  Thanks!!

[boulos]

One more observation. When listening to the speakers, the amp does not get that hot.  Does this have to do with the fact that my headphones are low impedance (32ohm)? I can barely raise the volume beyond 35min (it starts at 30min).  Would higher impedance headphones draw less current and be more appropriate?  Can I instead add a resistor (e.g. the 680 ohm I took out) right before the headphone jack (or is this totally stupid)?
Thanks
Boulos

[Paul Birkeland]

You took out 680 Ohm resistors?

The amp should run slightly warmer with speakers hooked up.

[boulos]

Sorry, no I didn't. I took out the 150kOhm resistors. I tested the 680ohm resistors as you suggested, but of course confused the two in my post

[Paul Birkeland]

Oh, whew, good to know.