2. amps-preamps
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first tube rolling: expert advice needed - take 2

Annoyingly my first thread that went under this header has disappeared. Apologies to everyone who had contributed and put a lot of thinking into this.

Here is the plot again: I had bought a second hand Unison Research Unico SE hybrid integrated amp with two Electro Harmonix 12AU7A in the pre-amp section. Very fine in musical terms, the amp caused an unacceptable (in my solid-state biassed opinion) amount of hiss and slight traces of hum coming from the speakers in silent parts. I had assumed this was caused by (perhaps defective) tubes. Not knowing where or what substitutes to start searching for, I have had the benefit of Audiogoner's advice and finally acquired a pair of NOS tubes at Machmat in the Netherlands, namely:
Tesla ECC802S unused NOS (virtually the same as Telefunken's ECC802S, I have been told, picture: see my "Guests" system).

Here is the good news: Am I glad I tried this! I am getting a cleaner and more saturated sound, as if creases had been ironed out; bass appears more finely detailed (tried this with different speakers with reproducible results)
And here is the bad news: The hiss is still there, perhaps even more disturbing than before because the music is better. Guess I'll have to have the amp inspected and probed (hope I haven't been "had"). Anyway, if it doesn't work out with this machine, I'll be looking at a full valve integrated from Unison (I do like this sound).

One tip I gladly pass on (not just to the Europeans): Mattijs de Vries of Machmat sure is someone to rely on!
http://www.machmat.com/index.htm

Finally one question to the experts: Is there something like a burn-in procedure I should observe or time I must allow for with unused NOS?

Thanks in advance and regards
Karel
karelfd

Showing 3 responses by karelfd

karelfd OP
476 posts
 
Hi Mechans, good to hear from you again. With regard to the hiss I hear, it's not the phenomenon you describe I'm afraid. I can actually hear it from a few meters away, definitely too much if you ask me.
Interestingly, you mention Jadis. I first heared my Well Tempered table with Jadis gear and was mightily impressed. Eventually, things would take another turn and, in honesty, I am perfectly satisfied with the Tidal amps in my main system. For the second system Jadis seems indeed too expensive (I have seen one or the other used but even then it's a lot of $$ and I'm becoming wary of some offers after what I'm experiencing with my Unison), but I'm seriously considering an all tubes alternative.
As to my deleted thread, apart from opinions on one or the other dealer, I only saw people of the same conviction exchanging thoughts. To me this thread held a lot of information and introduced me to a fascinating new field. Too bad it had to go.
karelfd OP
476 posts
 
I guess the question on the Unico was actually addressed to me. I have been swapping cables, experimenting with isolation bases and moving the unit to different places in the apartment but never succeeded to get rid of the noise. Hooking up different speakers however made a huge difference. With Lua Con Fuoco Mk3 (4 Ohm impedance, SPL rated around 89db) the hiss reached the annoying level I described. With Chario Constellation Cygnus (4 Ohm, SPL 87db) the level was at a point that I could probably live with: audible in 1m, ear at the height of the drivers; to me that is, a friend told me he barely noticed anything in the ambient of a living room at daytime. I had been intending sending the Unison to the distributor for examination whether there was a defect after all, but I didn't get that far since the guy I mentioned bought the amp and the speakers from me.

Meanwhile, I got myself a Unison S2K tube integrated rated at 2x15W (an enormous difference in terms of output from the hybrid Unico SE with its 2x130W) that I'm driving the Lua with, and guess what: dead silent. I have also hooked up a couple of Zu Druid Mk4 (rated at 101db), again: silence. The S2K sports 2 ECC802S (I use NOS Tesla with EAT Cool Dampers) and 2 KT88 (presently the original Sovtek - with my fingers itching to try EAT KT88 Diamond Valves, ridiculously expensive but reportedly as good as NOS Genalex).

I'm not stating that the problem with the Unico was reducible to speaker sensitivity (there may be other tech specs that complete the picture) and I cannot be sure whether there wasn't an inherent defect on top of it (the lottery with buying used gear). But in my case the speakers made all the difference.
karelfd OP
476 posts
 
Hi everyone. Thanks for your input! Unfortunately, I can't put some of your advice to the test as I sold the amp meanwhile (see my posting of 04.04 above).
Still, very grateful for any further thoughts you may have (I now own a fully tubed integrated :^) fortunately without problems).
Slates, your observation is quite worrying! However, I don't think my tubes were bad since I'm using the very same ECC802S Teslas in my new Unison S2K - without hiss - that I had tried in my Unison Unico - with hiss. The guy I brought them from claims they were thoroughly tested.
Then again, since the Unico is part of my friend's system now, perhaps, just for the sake of it, I can convince him to experiment a bit (although he's happy with its performance, I must add).
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