My 2019 Update Thread - My final system I think.

[AJSki2fly]

Front end swaps...you mean everything from the Preamp backwards Adrian?
Suspect its the Pre, as even with nothing connected Im still getting the hiss on all inputs, RCA and XLR.

Thats why I was thinking attenuators, reduce the gain between Pre and power.
Never had to tackle this before an interesting problem!

Why not try a simple passive pre like a Tisbury foe £130, I had one and it was great. As long as you have .5 to 1v feeds you should be fine with an amp like that I used mine with a Meridian 557 and a pair of 308 mono blocks

[Gazjam]

Thanks Adrian,
Sure its gain will maybe eliminate the hiss, but loath though to discard my current Preamp it brings a helluva lot to the table.
So keeping my Pre, may change out the input valves as an option?

[AJSki2fly]

Hi Gary, Personally I have mixed views on pre-amps, in my experience if you can loose it and manage with the pure signal to the power stage then you get closer to reality. It’s a difficult one.

[Gazjam]

I'll sound "sanity check" again a direct connection from my Dac to power amp tomorrow, given I have a completely different power amp.
Didn't make sense when I had the 300B SET, see what happens with a Beefy solid state.

Makes sense to try.

[Gazjam]

Ok,
In this mornings fun I swapped out the Premp and connected the Dac direct to power amp.
Slightly less hiss, but sound quality dropped away, sounded flatter and more like a recording of a song rather than people playing instruments in the room.
So back in went the Pre.

Funny thing...
I’ve kept the Rotel amp powered on since I first hooked it up, either my brains getting used to it or there’s less hiss from the amp with some hours on it now.
If it hadn’t been switched on since January this might make sense?

Maybe the amps stabilising a bit after being off for 3 months...
Anyway, whatever the reason I’m happy to say I don’t really notice the hiss anymore.

Cool.

[Firebottle]

That's excellent Gaz.

With regard to being above your pay grade that's crap. If you can wire in balanced mains you can attach a couple of resistors in an amp.
I am making the assumption that there is a silk screen on the PCB showing the component references.

What position is your volume control at, to judge the level of system gain?

[Gazjam]

The service manuals online Alan, which is handy!
https://www.vintageshifi.com/reperto...ice-Manual.pdf

Balance volume between setting on the amp with digital volume setting on the Dac.
Pre at 53
Dac between 20 and 40 depending on music.

[Gazjam]

Took a different tack looking at the slight hiss I'm still getting with the Rotel power amp?
My Preamp has a valve driven input stage, and there's quite a lot of adjustability built in with it - so had a look at that.

You can swap out valves so the sound is tweakable, can be set to use either 12V 12AU7 tubes or 6/7 volt tubes.
Additionally you can set the bias current to be 4 or 5ma, so a few different permutations to try and see if it has an effect on the hiss.

From the Manual:


If I was running less efficient speakers it wouldn't be an issue, but at 95dB...
Ordered some different input valves coming today, see how I get on.

[Opti-cal]

If I was running less efficient speakers it wouldn't be an issue, but at 95dB...
Ordered some different input valves coming today, see how I get on.

I'm in the same boat Gaz . . . except my speakers are over 100db! I've actually managed to all but eliminate the hiss using certain tubes . . . but not the ones I want of course.

The ones I want to run are new(ish) so may quieten down a little I'm hoping. The preamp is also very high gain for the power amp anyway. I tried -10db attenuators but it murdered the sound. A sound which I'm very happy with bar the hiss between tracks.

I'm considering putting a higher value resistor in the output path too.

Always a compromise somewhere I feel . . . some adjustable gain and volume in our preamps would be darn useful right now.

[Gazjam]

Hey Chris,
Yup, more times than not there's always a trade off...

Have a set of Tungstram ECC-82's which when ran at 5ma sound amazingly transparent and dynamic, literally perfect.
Apart from increased hiss.
Knock the bias current back to 4ma, hiss drops a lot...but so does the "magic".

Some brand new valves to roll in, my other ones are NOS and have a fair amount of time on them, so will see what happens.

The JJ 12AU7 pair are thought very highly with other guys with the same pre-amp, so fingers crossed.
Glad to hear your experience of Attenuators, that was maybe a road I was going to go down.
The higher value resistor is a good shout from Alan, in the queue if different valves don't sort it.

TBH unless I put the ECC-82s in at 5ma, all other combo's are liveable, but want that magic without the hiss - if possible!