Recommended Preamp for pairing an Adcom 555II Amp and Theil CS 3.5 speakers


My Bryston 0.5B preamp was inadvertently put down over the holidays by an incident now known as 'The Sippy Cup Mystery'.  Regardless of the cause, I need a new preamp for my system.  I am driving a pair of Thiel CS 3.5  (with the electronic bass equalizer) speakers with an Adcom GFA-555II amp.  The majority of the eclectic music (classical, 80s, folk, funk) being played on the system is streamed from iTunes through my Audioengine B1 DAC.  I have read a number of posts with various recommendations for the GFA-555II or the Thiel CS 3.5s but not for their paring.  Short of winning the lottery this week, cost is a factor. Any suggestions or directions would be very much appreciated.
iowanna33
Hello iowanna33

PLease join us over on the Thiel Owners thread since you own CS 3.5 speakers. Several of the guys also own this model as well.  If you enjoy the Adcom 555 II amp, I would certainly consider an Adcom pre to match.
At one time, I owned the 565 pre-amp / 555 power amp, then 5400 power amp combo on B&W 805 speakers.

Happy Listening!
CJ PV10 is a great match.  Thiels sound best with a tube pre in the chain. The CJ is warm and full bodied, just what the Adcom and Thiel need.  
+1 pops!  As I read your OP ?, the first thing to come to mind would be a vintage cj preamp.  What a nice system that would give you!
You might want to be mindful of the Adcom’s low input sensitivity and input impedance numbers. The impedance might be a bit low for some tube pres output impedances and the high sensitivity could make the volume control on some tube pres (like some c-j’s) have rather restrictive range.
The new Schiit Audio Vacuum tube preamp is a great buy for under $1000
You might want to be mindful of the Adcom’s low input sensitivity and input impedance numbers.

The Adcom GFA-555 II Spec sheet states an input impedance of 100Kohms, which should be fine with almost any preamp.

http://www.kenrockwell.com/audio/adcom/gfa-555-ii.htm#spex


The CJ PV-10A output impedance is measured by Stereophile at 690 ohms.
https://www.stereophile.com/content/conrad-johnson-pv10-preamplifier-measurements
No problem at all.

Good reco Jerry (pops)!

Cheers,
John
Brown Audio in North Texas is reported to make a fine tube-pre for about a grand.
Thanks John, and I am sure the OP appreciates your research.  I always said you almost know as much as me...  :-0

I used Stereophile's specs:

https://www.stereophile.com/content/adcom-gfa-555-power-amplifier-specifications

but, I suspect John's might be more correct.

If the 3.5's eq is used between pre and amp, it would probably also offer some "buffering" in this regard as well.

iowanna33
  Recommended Preamp for pairing an Adcom 555II Amp and Theil CS 3.5 speakers


Your lucky you don't have the 3.6 as they are a pig to drive to get the best out of, these 3.5's are a different beast and quite easy for your Adcom 555 mkII

https://www.stereophile.com/images/archivesart/189CS35FIG1.jpg

Stereophile's John Atkinson:.
" Jim Thiel has used some form of conjugate load system in his crossover designs to give such flat curves with frequency. (This is where elements are added to the crossover to compensate for phase and impedance changes to result in a simple resistive load.) I would suggest, therefore, the Thiel CS3.5 should be easy to drive, even given its 4-ohm rating."


Cheers George
I have had the older 555 paired with the 750 preamp for many years in my vinyl only system. I recently bought a full-tube preamp for another system and used it with the 555 for a few days and it really rounded out the rough edges, especially when played at higher volumes. There's another thread where someone is asking for tube preamp recommendations and should give you some good ideas. Lots of options out there, new or used.
I would search out a tube pre. As mentioned above, being mindful of gain and output impedance.
Thanks John, and I am sure the OP appreciates your research. I always said you almost know as much as me... :-0

That is the highest compliment I've ever heard!! Thank you Jerry!
You've known for years that my life's dream is to aspire to your level!!

Cheers,
John
I have used the GFA 555 with the GFP 565 and while the pair is very good sounding (and the 565 has a great phono section if your into vinyl). But, I will say that when I installed the Modwright SWL 9.0 SE ($1000 used) it really showed me how beautiful sounding the Adcom 555 can be. A tubed pre amp is what I highly recommend. Manley labs shrimp?? possibly. Doge 8 Clarity, Dehavilland Ultraverve III, these are all tube based and around your price range and are very special indeed. Also, all of these will have very low output impedance to drive the Adcom no problem.


Matt M
iowanna33
Recommended Preamp for pairing an Adcom 555II Amp and Theil CS 3.5 speakers

Your Audio Engine B1 has
Analog Output: 2V Max.
Analog Output Impedance: 57 Ohms.

And your Adcom 555II as was pointed out has:
100kohm input impdance
only needs 1.75v in for full 200w output

As you can see the 2v from your B1 is more than enough to run the 555 to full output, so you don’t need an active preamp with gain that you don't need.
Also the output impedance of the B1 is 57ohms and this is a great match for a passive preamp, which will aslo match prefectly with the 555’s 100kohm input impedance.

Get one of these and save a fortune, you’ll have the most transparent/dynamic sound and save a fortune on not needing a fancy/expensive preamp that will colour the sound in comparison.

$49 http://www.schiit.com/products/sys passive only

$349 http://www.schiit.com/products/saga if you want to switch from passive to tube output as well .

$699 http://www.schiit.com/products/freya if to want to switch from passive to solid state or tube output.

In all three I think with your setup the passive will win out, so for $49 go the first one.

Cheers George

While george is right about the specs on paper, the actual outcome is a different story. I have tried the $49 Schiit Sys between my CD player and 555 and the sound quality was completely lifeless and flat as compared with my Adcom preamp and nowhere near the sound quality when I experimented with the tube preamp in there. The volume control on the Sys is also marginal at best. But it's definitely worth the $49 price when used as an input selector.

What's the budget?

@kalali  You beat me to it!  I was going to respond to George much as you did above that my anecdotal understanding of passive units is that the PRAT as the Brits like to call it, is diminished.  I'm not making a categorical statement here, just that anecdotally over many years reading lots of audiophiles' experiences, that the drive is diminished by passive gear.
Post removed 
I have tried the $49 Schiit Sys between my CD player and 555 and the sound quality was completely lifeless and flat as compared with my Adcom preamp and nowhere near the sound quality when I experimented with the tube preamp in there. The volume control on the Sys is also marginal at best. But it's definitely worth the $49 price when used as an input selector.

iowanna33  This all depends if you want the source to be transparent or you want to colour the sound, which a tube pre will do.

If you want to have it all, get the Freya and you have passive, solid state, and tube that you can change on the fly while listening, all with little or no gain, which in your case you don't need. Many here and on other forums that have bought it prefer the passive mode after they've lived with it for a while.
  
And in it you have the best volume control with the Freya which is 128 position switched relay volume control, better than any rotary volume pot, and it's all remote controlled, 3 x inputs, 2 x outputs all RCA or XLR. 
http://www.schiit.com/products/freya only $699 and you can send it back if not happy, win, win. 

Cheers George  
iowanna33 Here is a 6 page discussion on the sound of the Freya and do a bit of tube rolling in Australia.

https://www.stereo.net.au/forums/topic/116843-schiit-new-preamp-freya/

Cheers George
I have a pair of 555 Mk2's driving a pair of Kef 107's and I use a Cary SLP03 with them. I replaced an Adcom GTP760 with the Cary and there's just no going back. You can find this pre amp for around $1000.
hifiman5
that the drive

Please explain to all here, what the difference is of the "drive" to the poweramp in electronic terms, whether it’s driven from a preamp output or from the sources output. when voltage output is sufficient enough for the poweramp to be clipped and impedance is a match is fine.

Nelson Pass:
"Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."



Cheers George

 When considering a pre that will be used with Thiel 3.5's I would suggest that one consider those pres that either have an extra analog tape loop and/or preferably have most of their design parameters based around single ended output, unless one either has two Thiel 3.5 eq's modified to mono balanced operation or one can find a better stereo balanced eq with at least 12 dB of boost (and good luck with that). Otherwise the extra money and effort spent on balanced operation will be for naught.

I am new here. I hope someone can help me out. I am looking for a 500+ watt amp to drive my power hungry Gallo 3.5's. Budget is "UP TO" US$3000. Most people don't ship to Canada. I found one, from a store, in Europe. I couldn't finish the transaction because of language barrier. The guy told me to wire him the money. I thought eBay/Amazon all advise "NOT TO". Then I found a pair of adcom 555 II in my city. 
Questions
1. My first pick is the one from Europe. Is it safe? (US$1600)
2. Demo the pair of adcom in my space (US$700)
3, buy new emotiva XPA-DR2 US$1800 or a pair of XPA-DR1's US$2500
Any input is much appreciated. Thank you in advance.
DonRua
Canada