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In Reply to: RE: Rotel RB-1092 and tube preamp posted by xtsili@grnet.gr on September 12, 2014 at 01:18:44
Your Rotel 1092 only has 11kohms input impedance, no tube preamp will like driving into this kind of load.
You need a solid state preamp that is say below 100ohms output impedance, there maybe the odd tube one that is but they are very thin on the ground and are usually hybrids.
Cheers George
Follow Ups:
If one goes by the 10x "rule of thumb",
a preamp with an Zout of 1K would work.
Granted 11K is not ideal.
0.02 :-)
Yes I know georgehifi how unusual the 11kohm input impedance is and hard to match with a tube pre. But as I mentioned in earlier postings, I tried a good tube pre and the results were astonishing in first place - no extended listening though.
xtsili
You yourself provide a clue.
Were the levels MATCHED between the original and test preamps? If not, the Louder of the 2 will most assuredly be preferred.
And as for the 11k input impedance? That is a nominal number. It could perhaps drop to 5k or 6k at one frequency extreme or the other, or BOTH ends.
Perhaps one of the SS offerings which could be as low as 100 ohms would be more, appropriate.
If I had the loot, I'd try the W4S STP-SE which acts as a passive than adds a little gain at a certian point. I don't know if this is a good electrical match, or not.
Too much is never enough
No the levels were not matched and yes the loudest one was preferred - at least this is what I suspect in terms of physoacoustics!Yeah I know that 11k are nominal and can become much less than that, which is a pain in the neck for preamps
Yes indeed, I was considering W4S STP-SE precisely for its capability to combine passive and active behavior according to gain demands. However purchasing electronics that have to be shipped overseas and going through the hassle of customs etc it is not my thing :-)
xtsili
Edits: 10/21/14 10/21/14
Would you guys consider a tube buffer to to do the job? Keeping my current preamp + adding a buffer? Or it is really too many of components in between the signal path?
xtsili
It's one resistor at the input of each channel.
Than
xtsili
Thanks wheezer. Did you manage to find the schematics?
xtsili
Not for the 1092.
There's a service manual for the RB-1090-2,3.
It indicates an input Z of 33K and nowhere lists 11K.
It states the input impedance as 11.1kohm here on the Rotel spec site.
As for raising the input Z just by changing the resistor, this is fine if the input transistors are fet. If they are bi-polar then there could be trouble with dc offset.
http://www.rotel.com/NA/products/ProductDetails.htm?Id=5&Tab=2&Pic=1
Cheers George
The owners manuals I found indicated 11K1.
No SM to be found.
These have no FETS, just BJTs.
I've not experienced any offset issues with the many I've modded (33K input Z) when sweeping on the oscope or DC at the outputs.
No oscillation either.
Your lucky then if it has bi-polars, that the dc offset did not raise (as it would of with the rca input open circuit) to beyond the ability of the the dc servos (if it has them) to pull it back down again.
Cheers George
Edits: 09/18/14
Guys I am loosing you...Forgive my ignorance..
xtsili
I have used it with gear having Zout 500ohm resulting to significantly lowering the output of Rotel.
xtsili
resulting to significantly lowering the output
That's probably due to lower gain of that particular source.
0 gain actually. Just an active volume controller
http://www.6moons.com/audioreviews/spl/volume2.html
xtsili
Interesting pre.
Have you performed the calibration for gain?
What do you mean? I ve got issues anyway because the SPL has XLR in/outs while my Rotel RCAs - not really a proper match even with the right adapters.Besides, this damned thing was lowering the output by -6db.
So all in all although it was really slim and fit and been conceived for one purpose only, to control the volume, it didn't quite work out in my case.
xtsili
Edits: 09/20/14
The owner's manual had a "calibration" section.
Consider doing some mods to the volume pot.
....Series and or shunting them.
That will kill a lot of the gain and provide sonic improvement.
Are you talking Wheezer about the SPL or what?
xtsili
If the SPL is in that section, I didn't read it.
I just saw a section on "calibration".
...If you're happy with the system, look into the volume pot mods.
Oops - me bad
Wheezer Hi.
I managed to find the schematics of Rotel Rb-1092
http://elektrotanya.com/rotel_rb-1092_sm_no-sch.pdf/download.html
Could you tell if there is a coupling cap at the input?
Many thanks!!
xtsili
I couldn't open or download the SM.
Can you download it? If so, PM and send it to me.
There absolutely is a input coupler in that amp.
Cheers,
W
Ok wheezer, I am trying to figure out how to attache the .pdf
xtsili
There you go!
xtsili
Were you able to send it?
Yes I did few seconds after you gave me your email! Have you checked in the spam folder?
xtsili
Please post here after sending it again.
Thanks,
W
I did send it again
xtsili
Got it.
Will get back to you later.
Super!
xtsili
Did you receive my response?
Yes and I replied thanking you etc ! (never received it?)
I was also saying that I pursued to get a customized preamp, made by a local company.
xtsili
Ignore...
xtsili
I am talking about this model
http://spl.info/en/products/monitor-controllers/volume2/description.html
xtsili
By the way, today I auditioned the following pres with my amp:Project RS-BOX (hybrid from Austria)
Densen B-200 (SS from Denmark)
Copland CTA 350 (tubes form Denmark)
Primare PRE32 (SS from Sweden)and the Oscar goes to Primare: transparent, solid, holographic sound.
xtsili
Edits: 09/20/14
I like Primare as well. In particular, I would like to hear the new CD player CD32.
I think the auditions were made with this new Primiare CD player. Very natural sound indeed. No digitalitis at all!
xtsili
I am actively seeking a dealer/retailer that has one for demo. The CD32 features the new Sanyo drive/transport- I am anxious to hear it!
Come over to Athens Greece then! :-)
xtsili
Primare doesn't show specs on their website.
Yes they do. All the way down to the bottom of the page, you'll see the specification button (barely seen to be honest :-))
http://www.primare.net/product.asp?ProductID=53&d=2
xtsili
Yes the RB-1092 has a 11kohm. I have had bad experiences combining the rotel with various preamps. In several trials it could be barely heard!It is a nice amp that can deliver the goods given that I can find the right mate for preampring.
xtsili
Edits: 09/18/14
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