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Hi fellows.My power amp is a Rotel RB-1092, a class D behemoth in terms of power and I am looking to replace my king Rex preamp with either an active line stage like First Watt B1 or a no-frills tube preamp.
I only play spotify which combined with Class' D power amp produce a neutral sound leaning to the bright side indeed. Definitely the nature of 320 kb streaming and Class-D combined, may not be forming the ideal initial set of conditions for a very transparent preamp such as a no-gain line stage. For a bit of musicality and muscle a tube line-stage may be preferable. What do you think?
I have listened a nice tube pre with my gear and the result was quite impressive. Although it might have been its high gain that filled and boosted the sound and not its alleged sonic merits.
xtsili
Edits: 09/12/14 09/12/14Follow Ups:
which company makes the king Rex pre-amp?
Kingrex. A company from Taiwan.
http://www.taiwantrade.com.tw/EP/kingrex/
http://www.kingrex.co.uk/
xtsili
Thank You!
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
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
I use a Quicksilver linestage with my Rotel rb-1050 and it sounds good. However, the Quicksilver has too much gain for the amp. Fortunately, my Rotel has volume controls, which enable me to tailor the gain of the preamp to better match the amp. I don't know if your Rotel has volume controls, so you may want to limit your options to those preamps that you can try before you buy.
Yeap this is what I feel what the problem might be with a tube preamp: much of unnecessary gain. Mine doesn't have volume controls, Jriver has though (I use Jriver's engine to stream Spotify). Maybe I could lower Jriver's volume so that compensate for the excessive gain. Jriver uses very robust algorithms to handle digital volume.
xtsili
Edits: 09/14/14
It might work. Good luck.
If you go with a tube preamp:
Rotel's have a coupling cap at the input; tube preamps have them at their outputs.
Going with a tube based preamp will cause a "fight" for the corner Hz as well as really muck up the tone.
I suggest replacing the Rotel's input coupler with a jumper wire.
Cheers,
W
What you are suggesting is getting too technical for my knowledge. Could you elaborate a bit?
xtsili
The simple - Only one coupling cap is needed in-between a preamp and an amp. Tube preamps have a coupling cap. Some (not all) SS amps have them as well.
When this scenario exists the coupling cap in the amp needs to replaced with a jumper wire.
SS > SS and tube > tube works fine. When mixing the two this issue may arise and needs resolution.
You won't notice the gross sonic degradation until the Rotel get some surgery. It's easy to find/fix from the schematic.
Thanks so much. It is much clearer now. To be honest a tube pre I tried once with my amp delivered impressive results. At least this was my impression.
xtsili
I found my 'd' amp, a GCC250 from PSAudio with B&O ICE modules to have a 'funny' top end which my panels didn't completely enjoy. I think there were some upper frequency phase issues, too.
Now, is spotify a 32kb sample rate or higher, like 44.1 or perhaps 48?
A 32kb sample rate implies a max frequency response of 16khz which makes your feed pretty much equivilent to decent FM.
I don't care about up/down/sideways sampling, what is the online feed rate?
Replacing the 'd' integrated with conventional stuff in the form of Parasound A23(s) made quite a difference for the better. With rms power a fraction less but I suspect as much as 1db more headroom or more….
Too much is never enough
Spotify uses 320kbps for streaming that's only I know. Surely it is not the mantra of high-end but the quality is not bad at all.
I decided to go the preamp-change road and keep my amp. Otherwise I have to sell it very cheap and this will be waste of money. The chalenge is to find a good match for the amp and I am sure it exists.
xtsili
Don't get me wrong. My 'small dish' has Sirus / XM feeds which are really good for casual listening or doing housework.
I have 2 sets of file of my better stuff. Set #1 is ALAC and goes to the stereo. Set #2 is converted to MP3 at 160, which I find to be a reasonable compromise between memory used and fidelity.
It is SAMPLE RATE which would appear to set the upper limit of frequency response. Since NONE of my sample rate indicators light, I know that small dish is 32khz. And THAT tells me I'm limited to what would be pretty much FM frequency response, except digital has much better bass.
If you can get over tubes, the Parasound P5 has a built-in DAC which is perfect for those feeds you enjoy. I reserve my DACMagic+ for my Playstation or feed from the confuser.
Too much is never enough
I see what you mean with the sample rate. To be honest what I miss is some muscle alongside with mellowness If you know what I mean. In both fields tubes may offer some improvement. And I tend to believe that streaming quality isn't the problem.
For Spotify reviews please check this. it is quite telling as to its quality :http://www.whathifi.com/spotify/review
xtsili
playing with a software based parametric EQ before changing the preamp.
I did it. But the tube preamp I have tried already surpassed any eq settings in JRiver I used to enhance the sound.
xtsili
How do you stream Spotify? Upgrading your DAC may solve the problem.
The Spotify premium version through optical from Asus Xonar Essence STX to a Rotel Rd-006 DAC.
I wouldn't call it a problem just a situation with room for improvement.
xtsili
Sorry, bad choice of words. A tube preamp will definitely tame the upper end. I use the Rotel RB-1090 which is the previous, non digital version, of your amp. I stream Spotify premium and google play via Sonos to a NAD D1050 Dac to a Vincent SA-T1 tube preamp. The Rotel amp is very non fatiguing with a sweet top end. The tube pre only makes it more so.
Thanks Trouser Trout
Pretty much comparable your gear to mine indeed. Wouldn't you consider the option for a no-gain line stage?
xtsili
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