Would a power conditioner help with audible hiss from Luxman C1010?

[Warm_tunes]

Recently had my Luxman C1010 and M2000 recapped and everything sounds great, but one thing bothering me is that there's a pretty audible hiss coming from the speakers now and I'm not sure what's causing it. I've got the Luxmans and a Mac Mini plugged into the same surge protector. Also have a Denon AVR/Xbox/ATV/UHD player plugged in on the opposite wall (also into their own surge protector).

There's no hiss when just the M2000 is powered on. It's only when I turn on the C1010, and the hiss is not volume dependent. It's not really audible when listening to music, but with no music playing, I can hear the high frequency hiss from across the room. Also, have unplugged all inputs from the C1010 and switched amp cables and still hear the hiss.

My house is about 90 years old, so who knows how old the wiring is (circuit box is about 25 years old), but I'm wondering if spending a few hundred bucks on something like a Furman condition would help, or is this more likely something going on with the electrolytics of the C1010?

 

[nj pheonix]

I'd be inclined to think its in the 1010. I don't think a power conditioner will solve your problem.

 

[mbz]

What caps were used in the preamp? I would expect low noise/leakage caps in the audio path. This is common knowledge, however
if general caps were used then an increase in noise is expected. Another source of noise is known/problematic transistors however
expect this to be years before the C1010, will check sm.

 

[restorer-john]

It's the residual noise of the preamplifier.

I would guess you have your power amp level controls at maximum. Turn them down to 50% and use the range of the volume pot of the preamplifier. Hiss will be much less obvious.

 

[Warm_tunes]

What caps were used in the preamp? I would expect low noise/leakage caps in the audio path. This is common knowledge, however
if general caps were used then an increase in noise is expected. Another source of noise is known/problematic transistors however
expect this to be years before the C1010, will check sm.

I am not an electronics expert but I understand they were replaced with 300 MHz transistors with high Hfe and low noise. Replaced the tantalums as well as 60+ transistors.

 

[restorer-john]

I'd like to know what exactly was replaced in the preamplifier.

 

[mbz]

Appears to be a thorough job. The tantalums and other audio path caps should have been replaced with Nichicon UKL or film caps.
Other "audio" electrolytic caps will raise the noise floor

 

[Warm_tunes]

It's the residual noise of the preamplifier.

I would guess you have your power amp level controls at maximum. Turn them down to 50% and use the range of the volume pot of the preamplifier. Hiss will be much less obvious.

Attenuators on the M2000 were set at 0 dB... noise is eliminated around -17 dB and reduced to tolerable levels at around -10 dB. Is that noise floor normal for this preamp?

 

[restorer-john]

You likely also have efficient speakers? >90dB.

Combine wide open power amp level controls on a sensitive amplifier (800mV sensitivity for full power), efficient speakers and the residual noise from a preamplifier and you get easily heard hiss. I believe this scenario is the most likely and not a fault.

I haven't got the schematic for the preamplifier, but it is also possible that when it is 'off' it may essentially short its output (relay NC contacts) which would silence the front end of the power amp.

The front end of the power amp has an unusual twin transistor impedance matching emitter follower/buffer before the usual differential pair. It employs the notoriously noisy (in their old age) 2SC1345s made by Hitachi. I would inspect the amp to see whether they have been replaced. They are on the level pot PCB. They are in the the distinctive 'tombstone' package variation of TO-92. If their legs are black from oxidation, they are likely bad or about to go bad.

 

[Warm_tunes]

You likely also have efficient speakers? >90dB.

Ha, yes... Heresy IIIs.

Combine wide open power amp level controls on a sensitive amplifier (800mV sensitivity for full power), efficient speakers and the residual noise from a preamplifier and you get easily heard hiss. I believe this scenario is the most likely and not a fault.

I haven't got the schematic for the preamplifier, but it is also possible that when it is 'off' it may essentially short its output (relay NC contacts) which would silence the front end of the power amp.

The front end of the power amp has an unusual twin transistor impedance matching emitter follower/buffer before the usual differential pair. It employs the notoriously noisy (in their old age) 2SC1345s made by Hitachi. I would inspect the amp to see whether they have been replaced. They are on the level pot PCB.

I haven't opened it up since I got it back from being recapped (shipped it about 1500 miles to have this done), but I was told (and I trust the guy who did the recap) all caps were replaced as well as the transistors. I'm positive he would have replaced Hitachis. I think the original output transistors were rated at 160W max, and he replaced with 400W max transistors, if that makes sense?

It's sounding pretty good right now with the M2000 attenuators cut down about 50% and a slight bump up on the C1010 attenuator knob, so it's likely your advice in post #4 has done the trick!

 

[restorer-john]

That's great.

The other factor is many preamplifiers exhibit better S/N and reduction in residual noise the further the volume pot is advanced. Some become completely silent at maximum volume, others get noisier. It depends on the topology.

It seems you just had the 'perfect storm' combination for audible hiss, especially with Heresy speakers on the end!