Diminished SDA with new preamp/amp combo

[trubluluc]

Hi guys-

I got the new amp / preamp (Bryston 4B-ST, BP-25)
set up with the 1.2's and I'm getting no SDA effect, though the sound is clean and clear and very enjoyable.
A very strong center stage pressence.

I switched back to my yamaha RXZ1 receiver and the SDA is back.
But I find the overall sound less enjoyable,
I can't really describe it other than it's more fatiqueing to my ears, less velvety.

Any ideas as to how can I get the SDA effect to work on the Bryston set up?

-Luc

[Tour2ma]

Ima thinking the Bryston is not common ground...

Do you have a VOM to check it?

[F1nut]

The 4B ST is a pure dual mono design, you need a AI-1 interconnect cable for it to work with the SDA's.

[trubluluc]

Tour-
I have to plead ignorance here,
what is a VOM.....variable ohm meter?

Jesse-
Is there a way to adapt a standard pin/blade IC ?
Or anyway to make the 4B-ST common ground?

-Luc

[Tour2ma]

VOM = Volt - Ohm Meter.... but since Jesse just confirmed my thoughts on the non-common ground, forget it, you don't need one.

But you're in luck since you have a pin-blade model SDA you can make an AI-1 SDA interconnect.

See reeltrouble's thread over in Electronics for past and I can e-mail you the schematic.

EDIT: Here's a link to rt's thread...
http://clubpolk.polkaudio.com/forum/...2&goto=newpost

[F1nut]

Adding to Tour's good info, you can not make the Bryston a common ground amp, so you'll have to make the cable. I'd suggest making a entirely new cable instead of hacking up your original.

EDIT: Actually, I just remembered that you can't use the original cable because it only has one wire that runs from end to end and you will need two wires with the AI-1.

[trubluluc]

Looks like a job to make the cable.

I still can't believe POLK doesn't make the IC cable available,
even if it was a prepaid special order.
It would just be good customer service,
like they do by providing drivers and tweeters for 15 year old speakers.
But if I can't find one, I guess I'll have to build one.

Does anyone have a picture of what the original polk version looked like?

Tour, yes, please email me the drawing.

-Luc

[madmax]

Shouldn't a pure dual mono amp design work without the special cable? I realize the grounds are not tied together but they are not pulled to different potentials either. I know some amps are actually "bridged" to make each mono side but they are the exception. Just questioning.

Another issue I have found is that as you upgrade components the SDA sound appears to diminish. With some of my older less audiophile components the SDA swirls around, throws sounds everywhere and sounds awesome, but less lifelike. With every upgrade the sound becomes more normal.

madmax

[trubluluc]

...here MadMax.

What do you guys think?

I'll email Bryston, hopefully they are familiar with the SDA situation, and ask them if that's the case.

-Luc

[madmax]

Be sure you do before you play it anymore. If they do not understand the "SDA" question you can ask in a different way. The real question is "Can I connect the two grounds together without damaging the amp".
madmax

[trubluluc]

I'm back to using my receiver which,
after listening to it for a couple days now,
sounds pretty good.

Thanks man!

-Luc

[F1nut]

FWIW, I hooked up a pair of 7B-ST's, used the AI-1 and had no problems with the sound, infact it sounded pretty damn good.

[trubluluc]

Holy Crap! I didn't know you were running dual 7ST's
So I guess it would be worth it to build the freaking AI-1 cable huh?

Thanks man,

-Luc

Originally posted by F1nut
FWIW, I hooked up a pair of 7B-ST's, used the AI-1 and had no problems with the sound, infact it sounded pretty damn good.

[F1nut]

Nah Luc, I brought them home for a demo before I ended up buying the Musical Fidelity (dual mono) Tri-Vista. You should still build the AI-1.

[trubluluc]

....So I'm *#!* around with the rig,
as usual.
I decide to hook up the preamp to the receiver, just to see, I mean if the problem was the amp, then this should work right.
Wrong! SDA was gone!
Now I'm stumped.
I go back to all receiver and bingo SDA is back.
I'm thinking the mono/stereo switch on the preamp is bad or something.
I use the receiver as preamp to the amp and SDA is back.
So it's definitely not the amp.
There are two sets of outputs on the preamp, I figure what the hell, I'll try the other set, VOILA! SDA IS BACK.
I'll have to email Bryston, (I'm sure they're tired of hearing from me)
and find out if there is a difference in the out's, or if one set is just not working right.

Bottom line...... SDA IS BACK ! and F'n A it sounds good!
Just a minute let me hold the keyboard up to the speakers so you can hear.:D

-Luc

[madmax]

CAN YOU TURN IT DOWN!!!

Thanks,
madmax

[Kenneth Swauger]

Hello,
In all likelihood one of the sets of outputs is reversed in polarity from the other. This is done when the pre-amp is connected to an inverting power amplifier. In other words some amplifiers, because of their circuit topology, invert the output signal with respect to the incoming signal. So, the pre-amp has a second set of outputs that have reversed polarity. This has to do with what is known as "absolute" polarity. This begins at the recording microphone and ends at the motion of the speaker's cone or diaphragm. For ideal playback the complete audio chain, from beginning to end, should be the same polarity. This is why some audiophile recordings sound better if the positive/negative speaker wires are reversed on both speakers. Next time you feel like experimenting, try reversing the positive/negative wires on your front speakers and see if the image shifts forward or backward (SDA owners will also notice a change in the SDA content).
Ken

[trubluluc]

Funny that you should mention polarity, because this preamp has a polarity switch on it, so maybe that's it.

Thanks,

-Luc