Jeff Rowland

Good luck, I hope that you'll be very pleased with your decision!

Fabulous.... Do keep us posted Richard!

Guido

06-02-15: Ricred1
Onhwy61,
I have a clearly defined vision. I want better separation between instruments and better front to back placement of instruments.How to get there(what's my weakest link) and how much it's going to cost is the question? It may be time to investigate replacing my Aerial 7Ts!

06-12-15: Ricred1
Thanks for the advice and good conversation...decision has
been made to purchase another 525 and use them bridged. I
will provide some feedback within several weeks.

Ricred1, I've been following this thread & noting the exchange between you & the other members. Some members like Bill_k & Zd542 have tried to give you good advice but I suppose you were not listening. I'm not sure that adding a preamp would have solved your issue (of lack of instr sep & soundstage depth) but IMO its a heck of a lot better than a decision to use 2 525s in bridged mode.

Do you understand how bridged mode works?? I'm inclined to say "no" but I'm making an assumption (maybe a big one). I don't see any conversation here re. bridged mode & your decision seems sudden & I'm not sure what it is based on? In bridged mode, the 2 channels of the amplifier drive the speaker in a differential mode - one output of one amp drives the plus terminal of the speaker & the output of the 2nd amp drives the minus terminal of the speaker. So, the output current is doubled (since each amp is working independently to drive the same speaker). The doubling of current can also be viewed in another way - to the amp, the speaker impedance is halved. This is the key part - in bridged mode, the amp now sees a 4-ohm speaker that was nomimally 8-ohms. All of a sudden in bridged mode, the amp is outputting 2X the current. Can the 525 amp handle this in bridged mode?
If you read the specs, it says 950W at 8-Ohms. It does not specify what is the minimum load impedance that the speaker is allowed to go such that the amp remains in spec.

http://jeffrowlandgroup.com/us/amplifiers-model-525-stereo-amplifier.html

If you look at bridged mode specs from amp manuf, in general, you will notice that the speaker impedance is 2X for the output power in bridged mode. For example:
300W/ch, 8 ohms
600W/ch, 4 ohms
1200W/ch, 2 ohms
600W/ch, 8 ohms, bridge-tied load (or BTL) mode <----
in bridged mode, you don't get the 600W/ch at 4 ohms (that was specified in non-bridged mode); you get the 600W/ch at 8-ohms. That's because the output current capability has doubled in bridged mode.

What is the minimum speaker load for the 525 in bridged mode?
if you look at the Aerial 7T spec, it clearly says that the impedance dips to 3-ohms.
http://www.stereophile.com/content/aerial-acoustics-model-7t-loudspeaker-specifications

and you can see that here in the impedance + phase plots - Fig1
http://www.stereophile.com/content/aerial-acoustics-model-7t-loudspeaker-measurements

Make sure that the 525 can handle 3-ohms minimum in bridged mode without frying the output stage of the amp. Rowland has not spec'd it on his webpage; a call to Rowland is in order to confirm this.

Also, sonically, you are providing brute force to the Aerial 7T in bridged mode (assuming that it will work, as questioned above). I have never seen any amp or any system provide more nuances (instr sep, soundstage depth - the attributes you are looking for) when it is brute forced. In fact, search these archives, people have expressed their dismay at worsening of the sonics in bridged mode. In fact, those in the know, will never resort to running an amp in bridged mode unless it's for PA (public address)work when using, say, a Crown amp where SQ does not matter much at all.

Rowland gave you good advice. Note that they did not advise you to run the 525 in bridged mode. They knew & know that bridged mode is not a preferred mode for audiophile listening purposes.

Soundstage depth might not be the domain of class-D amplifiers as yet - I could be wrong here. They have acquired many other nice attributes as class-D has matured but soundstage depth might not be one of them. In my experience soundstage depth is a function of linearity & in this department the SET wins hands down. Single output tube doing push & pull, directly heated tube, there is no matching of push & pull transistors or tubes & you get the best front-back layering.
Solid-state does not do front-back layering as well as a SET & again in my experience, the class-A solid-states do a better job of front-back layering than any other solid-state topology.

I think you are going to be sorely disappointed at the outcome. My 2 cents for whatever they are worth. Thanks.

Bombaywalla,

I take all advice with a grain of salt. Ultimately my ears
and wallet determines what I purchase.

I called Jeff Rowland several times and talked to them
regarding bridging the 525 to drive Aerial 7Ts. Per my
conversation with them, the 525 wouldn't have any problems.
I will follow-up on Monday to confirm bridged 525s can
drive the Aerial 7ts. They recommended the 625 mk2 as the
best option, but as already stated the 625 is out of my
price range.

I respect your opinion, but to insult my intelligence by
assuming I don't understand how bridged amplifiers work is
a little too much...I'm capable of reading..JR clearly
shows how the 525s are connected when bridged. Furthermore,
your assumption is I haven't compared bridged 525s to a
single 525. To my ears bridged 525s have more bass impact,
an ease to the music, and yes a more open soundstage. No it
wasn't with my speakers, but I should have the opportunity
to listen to bridged 525s in my system.

I don't know your experience with Jeff Rowland Class D
amplifiers, but if the recording allows, the 525 presents a
very good soundstage and separation, but just like many on
Audiogon, I want to go to the next level.

Finally, I enjoy Audiogon and post questions to provide
food for thought. That being said, I submit anyone that
purchases components simply on the advice of others is a
fool.

Bombaywalla,

Yes you are correct, M525 would not be more inherently nuanced in bridged mode than in standard stereo mode. However, if in bridged mode each chassis is on a lower duty cycle for the Ariel speaker, it is quite possible that the end effect will be... One of enhanced nuance. I already know from eyewitness reports that M525 delivers markedly greater authority in bridged mode than in stereo mode.

From all reports I have heard, M525 do not degrade their performance in any way in bridged mode... That is why Rowland has decided to place an easy to flip selector switch in back of amp.

Rowland specs are extremely conservative and simply do not tell the whole story.... Yes, Rowland has applied M525 bridged to large lower impedance speakers with great results... Sorry I do not remember which ones.

This is not a tribunal... Richard need not justify his audiophilic cravings in front of us *grins!*

I for one am looking forward to hearing Richard's findings... I am following threads to learn more than anything else... Damm the specks... All steam ahead Richard! *Grins!*

FG.