Bi-amplification or Bridged mode for SDA SRS

zagloba

Hello,

This is my first thread after reading a massive amount of useful information from this forum. It has been very appreciated.

I have owned Polk since 1990 starting with the SDA CRS+ as monitors for recording purposes. I now have 3 sets and several years ago finally got a pair of SDS SRS's. They were not the 1.2T model as I believed but paid $2,000 plus shipping to Northeastern CA. They are in near mint condition and are stunning in their abilities.

I am interested in converting still to 1.2T specs but realize the lack of availability of components. I will follow other threads for this information. I seek to buy a good pair of the 1.2T's instead when I can locate them. I would enjoy comparing the differences.

This initial thread however is to ask if anyone is familiar with the difference in using several amps(McIntosh MC300's) in a bridged mode(600 watts) or in bi-amping. I can certainly try it myself but am ignorant in the amps groundings. I am assuming common ground and I can call McIntosh. I have read about a transformer in the inter-connects but have no knowledge.

I have tried using several different amps(Carver TFM-45 with my MC300) in a Bi-amplified configuration and was not impressed.

I know they were different amps but I have not received the second MC300 yet and have several more hours to bid on one.
I do know that both amps either driving the low or high network did not seem to have the punch of a single 300 watt per channel Mcintosh. So I am considering another like McIntosh in a bridged mode.

Forgive the long message but I also learned through this very valuable forum why one speaker's tweeters cut out at only about 250 watts. The polyswitch! I will call Polk tomorrow and order these and may even try to bypass this evening.

Thanks for any information supplied and for all I have learned so far from you folks.

John Capik

Tour2ma

Welcome, John.

I'm sure you the object of your Polk aspirations to which are referring are the 1.2 tl's.

Many true monoblocks (stand alone, single channel amps) can be used with SDA's and the simple wire SDA interconnect by physically wiring the two amps' negative terminals together. If you own any mono-blocks, consult your manufacturer before trying this.

Running SDA's on bridged amps is an issue, be they McIntosh or Carver or whatever. A pair of bridged stereo amps have no ground in common and there are none I know of that you can create a common ground. I believe the AI-1 interconnect (with the transformer in it) will allow most any bridged pairs to be used.

Take it easy on your tweeters intil the new polyswitches arrive...

zagloba

Thank you for the reply. I did bid and win the other MC300 and am anxious to play with a bi-amped vs. bridged configuration. I will attempt to contact Polk tomorrow regarding the interconnect with transformer as well as the polyswitch.

I do have the SDA SRS model. I confirmed this by looking at the drivers. All SL2000 tweeters and all 6503 mid/bass drivers. So I am also assuming I have the 2000A crossover but have not taken it out and looked yet. I will anyway in relation to the tweeters and the polyswitch.

I have read past related threads and saw a "Ken" referenced many times. Is he still a contact at Polk and if not, do you have the name of someone I could call at Polk?

Thanks!

F1nut

You can not use bridged, mono blocks or non-common ground amps with the SDA SRS's, period. Yes, Ken is the "man."

zagloba

Maybe my planning was poor(looking at your tag) in purchasing this second wonderful Mcintosh amp without knowing some things. I can still run in bi-amp mode but what I have heard leads me to pursue a "way" to accomplish a bridged mode. Maybe the bi-amp solution will satify me but I doubt it will for long.

I will speak with Ken and thank you for confirming he is still there.

I know much but am ignorant of just as much. I can only assume what I want and am about to do here.

I finally joined this forum because of the passion I sensed with some of the members. I have such a passion for music and listening to it. Creating it is a separate topic.

For a time, I thought I was alone in this world expressing ideas and needs regarding these speakers and SDA technology. I realize now I am not alone in my appreciation of Polk and especially SDA technology.

I have many more questions and input but will wait for more replies before submitting any new threads.

Thanks!

F1nut

Don't put anything into that 'tag"......it just appears after posting way too many times on this forum. On the up side, having two Mac's around isn't a bad idea at all.

Actually, if you use a pair of true mono blocks and link the negatives together as Tour stated then that will work with the SRS's.

Tour2ma

Thanks, Jesse... I wasn't being very clear. With the AI-1 comment I was thinking 1.2 tl's (future) not SRS's (present)...

There are some mono-blocks whose speaker ground terminals can be connected making them usable with the blade-blade SDA's, e.g., the SRS's.

z,
Not sure you can have too many Mc's in the house. Try vertical and horizontal bi-amp configurations.

F1nut

You were perfectly clear to me Bruce.

Tour2ma

Well, there goes my air of mystery.....

OK, how's this for a question (John, if you don't ask more we will.:D )

Is the reason Polk went to the pin-blade IC to prevent attempts to use the AI-1 with the older SDA's?

F1nut

No, it has to do with the method of creating a ground.

BlueMDPicker

Hello John, and welcome to the forum!

Here's a thread (really, more of a tech article), from 2001, by DarqueKnight (who has probably spent more time inside the SDA's than anyone here) regarding the SDA SRS and SDA SRS 1.2 crossovers:

Improvements to the SDA SRS

I very recently bi-wired my SDA SRS's with PS Audio Statement (shotgun config) cables. I recommend it highly. I replaced the SL2000 Silver Domes with SL2000T tweeters as well (something I'd previously done with my SDA 2B's.) The latter upgrade is well worth the price and even more highly recommended. I hope to one day undertake crossover component upgrades - thanks to DarqueKnight's excellently detailed posting.

Mike

zagloba

Thanks, for the reference. I saw this detail and was impressed. You saved me the time of scrolling and searching to find it and begin again.

The modified crossover looked scary to me. I can manipulate and control a soldering iron and yet? It is inside and out of view so I don't care. And yet.

I appreciate the dedication to the "sound" that was realized.

If I could find the components, I would try this!

Confused, probably interrupted and ultimatley cheering the improved sound.

I did not have the luxury of time to contact Polk or McIntosh today, but will take the time tomorrow.

I need to receive the polyswitch(for both SDA SRS's) before the second Mcintosh arrives(600 watts per channel,bridged). If not, I will bypass them and hope I do not need to seek new sl2000's.

If they do blow, I need a set of 1.2T's. I will rebuild the SRS's and chalk it up to fate and a need to discover.

I am still not clear on the grounding issue with bridged yet individual amps. Does anyone know the influence that the inter-connect has on the two disparate channels in relation to a common ground? How does it work? Either through a central power supply or one/two amplifiers being supplied power within a single unit?

Also, My SDA SRS's have a pin/blade connection for inter-connect.
At one time I believed I had the 1.2 model but as I indicated in an initial thread, all mid/bass drivers are 6503 and I believed that indicated SDA SRS. I know there is a 1.2 and 1.2T version and 3 different crossovers. A, B and C in the 2000 series. I have not looked inside at the crossover yet to determine 2000A but assume this is what I have got.

I know no more than this now but am bent for continual aural improvements and certainly information.

Thank you for any additional information

John

F1nut

First, there is no 1.2T, it's a 1.2 or a 1.2TL.

If you have a pin/blade cable they have to be 1.2's. Maybe someone replaced the mid drivers with the wrong ones. Please look at your crossover before doing anything else. You can not use bridged amps with the SRS's, period. You can't use bridged amps with the 1.2's without a isolation transformer. If you hook up bridged amps to what you have now, it's not a matter of if they blow because they will without question. DO NOT TRY IT!!!

EDIT: I just realized you have all SL2000 tweeters and all 6503's, so you can't have 1.2's and you shouldn't have a pin/blade cable either.......something isn't right here.

zagloba

Forgive the 1.2 vs. 1.2T or TL. I understand that.

I trust the fact that you are saying either way, no bridged amplification without the transformer. I understand that also.

Again, I am attempting to understand the reasoning for the transformer. I am attempting to understand interaction of the crossover via the interconnect.

I should look at a schematic to answer my questions, but do not have one.

I did try this antic with a McIntosh and a Carver(both bridged). I got bored and just risked it. Nothing was blown, and I had no transformer? That is why I believed 2 Mc's would work.

I however head advice and will be less reckless with the second Mcintosh.

I still no not understand the crossover network in relation to bridged amplification. And the beginning of this thread.

John

Tour2ma

John,
It's really this simple...

SDA creates a common ground between the two channels of a stereo amp or the two amps if twin mono's or twin bridged amps are employed.

If the amp or amps cannot tolerate having a ground in common, it's creation appears as a dead short across them and the fireworks begin.

In the AI-1 SDA interconnect the isolation transformer does just what it's name implies, it isolates the two channels. In lieu of passing the signal directly from the right stereo drivers to the right SDA driver (in the left speaker cabinet, and vice-versa for the left channel), the signal only goes as far as the transformer, where a "new" signal is generated and completes the journey.

Above you said you bridged your current McIntosh and a Carver M-1.5t (not tl... ). Please explain how you bridged the Carver. I ask this:
1.) to see if you actually did it, and if you did,
2.) because I want to know how to...

Lastly, I too am at a loss to explain your pin-blade connections and SRS driver complement... We do know that Polk line changes were not always the cleanest. Many change overs were more of a morph than a distinct change. However, this is the first I can remember reading about what you are describing. Pulling the crossover as Jesse suggested is the best plan to follow.

zagloba

Thank you everyone,

I am sending some pictures. 6 of them. Reduced resolution for transmittal. This will show Carver and McIntosh instructions that I followed. Also the speakers and crossover pulled.
(I know the setup is not ideal related to instruments etc).

I believe I need to send them(the Pictures) one at a time and so I will.

I had these two amps connected this way with the inter-connect and was more impressed with the sound than with a bi-amp configuration.

Also, when I pulled out the crossover, I could not identify the "polyswitch". Tweeters still cut out between 250 and 300 watts with any combination of amps.

I got into Mcintosh several years ago and never believed they were just that good. What I have experienced is my McIntosh gear is that good and now I know what all the fuss was about.

Compared to Carver(TFM Series of 42,45 and 55) the McIntosh sounds more complete and full. Without effort and incredible detail and separation. The carver sound seems to exagerate the low end with some emphasis in the higher bass area(300 to 400 cps) that I do not like. I have measureed these things but have my own ears as the last critique.

Anyway, take a look at the photos. I missed another day to contact Polk. PST vs. EST and I missed it.

Does anyone have a contact number for Ken and is he in Baltimore?

Thanks,

John

zagloba

Carver Pic # 2

zagloba

Speaker Pic1

zagloba

Speaker Pic # 2

zagloba

Speaker Pic # 3

zagloba

Speaker Pic # 4

zagloba

McIntosh instructions

F1nut

Your crossover is from the SDA SRS and the polyswitch is the little blue device near the top center of the 1st xover pic. You first said you bridged a m1.5t and now you're saying it was a TFM42/45???
Anyway, things should have gone up in smoke if you did that. The fact that they didn't says something, what I'm not sure, but it can't be good.

Can you post a pic of the interconnect cable socket on the back?

Ken can be reached at 1-800-377-7655

Tour2ma

John,
Thanks for all the photos. Somehow I got it in my head you were bridging the M-1.5t, not the TFM 45. The 45 is a differrent critter.

Nice looking room, but it looks like those SRS's are suffocating a bit, especially the left channel. Nice piano...

Here's a pic of the replacement poly's POLK CS mailed me...

EDIT: The part numbers looks to be XD-135 917J and XD-135 992B. Since they were sent as a pair, I assume they are identical despite the different part numbers.

zagloba

Forgive me. I feel like a doe head here. You were correct. The interconnect is twin blade and no pin. I play with SDA CRS+ stuff so much and believed in a pin/blade in error. Thanks! I believe I do have the SDA SRS and not 1.2 or 1.2tl?

Still, the bridged mode provoked no flames as in my previous information and the submitted pictures. I am still on a quest to play with a bridged mode. When the Mac ran in either low or high end, it peaked the same way with no real increase in volume or clarity. I wondered where all that energy(watts) were going. Especially on the high end where so much less is needed.

I get the transformer stuf but do not know how it sees the signal.

I am assuming it is transparant and if so, I simple need to get this configuration.

John

F1nut

Ah, it was Tour that mentioned the M1.5T, sorry.

I still can't understand how running bridged amps didn't blow something

Tour2ma

And your poly/ thermistor is the blue disc hiding above the Mexican capacitor...

Here's a cropped zoom off of your photo...

F1nut

Originally posted by F1nut
Your crossover is from the SDA SRS and the polyswitch is the little blue device near the top center of the 1st xover pic.

zagloba

Those little tiny things have been driving me crazy for over a year of my life.

I thank you gentlmen! I will call CS @ Polk and get them quick. I am still tempted to bypass tonight.

My Mcintosh has elabarate protection and I do not believe I can blow the tweeters with a 300 wpc amp. Althought the specs on this amp indicate headroom of 600 wpc but a very insight-filled way is incorporated by them to reduce output related to a degree of thd.

I believe the amp down-shifts after about 2% thd thereby protecting itself and the speakers. This is done in 1/1000 sec increments and therfore very fast and perceieved sound does not change.

John

Tour2ma

Damn... all of a sudden it got real crowded posting here...

I see Jesse also pointed out the blue circuit element...

Jesse,
Obviously the Carver/ Mc combo bridged tolerated the common ground. Why? BTHOM...

John,
All transformers induce a current. That's all that is happening in the AI-1's.

F1nut

LOL...sure is.

BTHOM.........ED Z! This is something we need to find out.