SDA SRS Bridged vs. Biwire + Amp Suggestions Anyone?

jtconnell · December 2004

Okay - definitely need some help here. I have one Luxman M-117 amplifier from the 80s. It pushes 200W per/8 and can also be bridged. My idea was to purchase a second M-117. I have a pair of original 1986 vintage SDA SRS and a pair of 1989 vintage SDA SRS 1.2TL. I understand that using bridged amps on the originals is a no-no but can be done on the 1.2 series provided that a wire connects the both amp chassis together. I've read the recent posts about the guy with the Macs but I haven't gotten my head completely around it so I figured I'd start a new post addressing my specific issues.

So my question is if it is better to use the two amps and bi amp the system at 200W for the highs and lows OR is is better to bridge the amps and biwire or does it not mean squat? If the bridged solution was truly better, my thought was to eventually pick up two more and then I'd basically have two bridged amps driving each 1.2TL. Perhaps everyone's advice will be to stay away from that but I thought I'd ask before I spend any more money. I think I'm just going to leave the original SDA SRS as is for now.

As an aside, if the forum consensus is that the Luxman amps just don't do the job, then what will? Finally, I've read several posts on the dynamat and putting it in the baskets to reduce "ringing". Maybe I'm getting tin-eared, but I must confess that I'm missing 1) what the ringing is, 2) what causes it, 3) how to install the dynamat and 4) where to get it.

Any assistance would be appreciated as always.

dorokusai · December 2004

The basket ringing is for freaks, like most of us, and is not audible. I would do it just to do it, because I'm bored and it's a cheap "tweak".

Luxman is a perfectly fine amplifier.

As long as you have the AI-1 interface cable, you can do whatever the heck you want as far as amplifier configuration.

What's the McIntosh reference you're talking about?

I would just bridge two amps mono, and leave it at that. Easier, cost effective, simple.

4 amps, for your 2CH? Don't waste the money, you should be more than happy at that point, anything more is just self-indulgence IMO....but it would look very nice.

Dennis Gardner · December 2004

With a pair, you can try both worlds. Biamp or bridged. You can't do it without 2 117s so I would get another to see what you like better. 4 bridged/biamped is overkill.

My first experience with the SRS was on Luxman 117s. It was a truly sweet setup.:)

reeltrouble1 · December 2004

After building the AI-1 and bridging my NAD amps with SDA-1C's I was very satisfied, the NAD run very cool at the 6ohm resistance.

As you are aware some amps can simply be connected with a wire, check with the manufacture if you are not sure if they can be run mono this way.

RT1

F1nut · December 2004

Ringing happens when the sound waves hit the stamped steel basket. You can get some idea of what it would sound like by flicking the basket with your finger, nail first. Is it audible while the speakers are playing? Maybe, maybe not, but since it's a cheap and easy tweak why not do it. You cut the Dynamat to fit the spokes and press it on. Do the PR baskets too. A good place to get Extreme Dynamat is www.thezeb.com Get the door kit and you'll have plenty left over for doing the covers on your amps, cdp, etc.

PolkFreak · December 2004

Hi, I see you mentioned that the amp you were going to run was 200 watts per channel @ 8 ohms. Your speakers are 4 ohm and should be run at that. You will not realise the full potential of your SUPER speakers trying to run them at 8 ohm. You don't want to risk damaging your AMPs or speakers running them at the improper resistance. Those are sweet speakers! I wouldn't like to see them blow on ya.:) To be honest I've never had the pleasure of bridging a couple of nice amps before. I am unaware from a technical standpoint exactly how to do it or what it does to the resistance. Would bridging them drop the ohm rate from 8 to 4?
Anyone can can turn the light on for me in this matter. If it does drop the ohm load to 4, I have just wasted my time going on about nothing

I just have a big feeling that it is possible. Forgive my ignorance in advance.

jtconnell · December 2004

This was the original thread I was reading about bi-wiring and bi-amping:

http://clubpolk.polkaudio.com/forum/showthread.php?s=&threadid=23710

Secondly, I don't think the amp cares about the load per se just as long as it's rated for the lowest resistance being driven. My impression was that the SDA SRS 1.2TLs are 8 ohm and the originals are in the 5-6 ohm range. With respect to bridging the amps, I believe you're almost doubling the wattage at similar resistance. I'm not sure what happens to the amp's overall stability at lower resistances here. My reason for asking bridging versus biwire versus biamp is really aimed at improving dynamic range and making sure I have adequate power reserves for demanding musical transitions. Theoretically a, biwired, bridged amp would have the most available power on a per speaker basis as opposed to two amps splitting the high/low frequencies but I'm not sure how frequency effects the amplifier. My guess is that the one doing the bass would be working pretty hard while its high freqency counterpart would be resting comfortably. For this reason, I tend to still think the bridged/bi-wired approach may work best but I'm not stuck on this opinion at all. I was looking at the Monster M series cable and I'm trying to avoid buying more wire that is necessary. If I can get by with a bi-wire set, great. If not, then I'll eventually wind up with two pair which tends to get pricey. Anybody got thoughts on wire?

As an aside to this point, I have heard that as some speakers are played, the resistance changes which then causes the amplifier to "conform" to the speaker's resistance curve which can cause an audible change over the frequency range, i.e. the response curve is no longer flat and you loose dynamic range. As a result, people tend to think their amp is under powered when really its the speaker that's stirring the drink. Any thoughts here - my impression has always been that Polks resistance changes with volume but I can't say I notice any changes.

Finally, my understanding was you only needed the AI-1 on the original SDA SRS and/or if you knew your amplifiers were not of the common ground variety. I guess I'll need more help on that one.

BlueMDPicker · December 2004

Originally posted by jtconnell
This was the original thread I was reading about bi-wiring and bi-amping:

http://clubpolk.polkaudio.com/forum/showthread.php?s=&threadid=23710

Hi jt,

What speaker wire are you currently using? How are they terminated on the speaker ends?

My SDA SRSs truly benefited from bi-wiring (bass definition and mid/high separation.) And, more specifically, with spade terminations at the speaker. I had been running 6 awg Esoteric Reference single wire with banana terminations. When I got the bi-wire cables, I used bananas for a short period. But, due to the weight of the cables (PS Audio xStream Statement), I noticed some bending of the terminations. I switched to spades to relieve that issue and the change in overall dynamics of the SRSs was instantly noticable. I attribute the marked difference to a.) increased contact area with the binding posts of the spades over the bananas, and b.) cleaner contact (the binding post banana jacks probably have 20+ years of unseen spooge

)

Your Luxman should be providing approx. 375-400 wpc into the 4 ohm load of the SRSs (about the same as my PS Audio 200 Delta) and is quite probably a high current amp. That amount of headroom sure is adequate here. I guess more power never hurts, but I'm wondering if you'd get more pleasure from your pesos with the addition of a better source component (like a tubed CDP, SACD player, etc) and a good set of bi-wire cables?

Mike

jtconnell · December 2004

In a word - crap. I'm using original Monster Cable with the "push pin" ends. Better than lamp cord but certainly not audiophile by any means. This is exactly why I'm in the market for better cables and just want to get the answer to my biamp/biwire dilemma before I go shopping since cables aren't exactly cheap.

F1nut · December 2004

SDA SRS = 4 ohm nominal
SDA SRS 1.2TL = 6 ohm nominal

The AI-1 will not work with the SDA SRS and the only way to run non-common ground or mono block amps with the SRS is if you can tie the negative outputs on the amps together. However, not all amps will allow you to do that. Using bridged amps is not an option with the SRS.

Most amps when bridged are only rated to drive 8 ohm loads, but will probably be ok if used with the 1.2TL's.

JT, there are much better choices than Monster.

dorokusai · December 2004

Originally posted by F1nut
SDA SRS = 4 ohm nominal
SDA SRS 1.2TL = 6 ohm nominal

The AI-1 will not work with the SDA SRS and the only way to run non-common ground or mono block amps with the SRS is if you can tie the negative outputs on the amps together. However, not all amps will allow you to do that. Using bridged amps is not an option with the SRS.

Most amps when bridged are only rated to drive 8 ohm loads, but will probably be ok if used with the 1.2TL's.

JT, there are much better choices than Monster.

Ah that's what he's talking about....gotchya.

BlueMDPicker · December 2004

Originally posted by jtconnell
In a word - crap. I'm using original Monster Cable with the "push pin" ends. Better than lamp cord but certainly not audiophile by any means. This is exactly why I'm in the market for better cables and just want to get the answer to my biamp/biwire dilemma before I go shopping since cables aren't exactly cheap.

Someone on the Flea Market forum had a set of Signal Cable double run wires recently for $99... ah, here it is. They have the BFA bananas as well, so looks like a nice price. Might be a fairly economical way to move up the wiring food chain to see if cables (although not b-wire) make a noticable difference?

Here's another good value ($75) at Audio Advisior: PS Audio 2 meter Prelude - MSRP $300

PolkFreak · December 2004

JT, the resistance changes along with the freqency response. For example, as the bass gets lower the resistance gets lower. The resistance is higher in the higher freqency range. The resistance is always changing as the speaker operates. F1-Nut filled in the thought I was missing and overlooking. That those bridged amps resistance gets higher when bridged which makes sense. Its like connecting two speakers together lope the negitive then have the positive to each speaker.

PolkFreak · December 2004

ERR, was trying to say the resistance of the two speakers would go up like the bridged amps.

twochannel · December 2004

I started out using one Adcom GFA-555 with my SDA-SRS's. Believe me when I say that the amp became very warm. The 4 ohm nominal rating is what it says, nominal. These speakers drop very low in impedance when played. My second configuration was two 555's biwired, one for the high end and one for the low end. My final set-up for the last twelve years has been GFA-565 mono blocks, a GFP-555 preamp, Audioquest interconnects, and a Nakamichi OMS-7A CD player. SDA's always needed alot of channel seperation to hear the full effects of their design. These components achieve that. I have not changed anything since. I would highly recommend finding these items on E-bay.

jtconnell · January 2005

Well, I'm now the proud owner of two Luxman M-117 amplifiers. The note in the owner's manual reads as follows:

"Caution: The "BTL" - lead (or any other speaker terminal) must never be connected in common with any other speaker common lead or grounded to any other equipment or point whatever!"

Pretty clear cut on the bridging aspect - stay away!

With respect to speaker wire, all of the research I've done leads me to conclude that it's more snake oil than anything else and a solid pair of 10 gauge appliance cord from Lowe's or Home Depot will work just as well as some $1000+ esoteric product. A couple of 10-4 cables and I should have a solid biamped set.

F1nut · January 2005

Originally posted by jtconnell
With respect to speaker wire, all of the research I've done leads me to conclude that it's more snake oil than anything else

The problem with your conclusion and the basic flaw with your research is that you haven't tried any "esoteric" speaker wire, so how would you know???

jtconnell · January 2005

The problem with your conclusion and the basic flaw with your research is that you haven't tried any "esoteric" speaker wire, so how would you know???

This depends on whether or not you believe a good listening experience is mainly a product of science or psychology. I tend to prefer the science route because sound reproduction is a function of applied physics as opposed to "beauty" which is a function of the human psyche.

As such, I can quite correctly draw a conclusion based on objective data regarding the performance of certain cables in much the same way that I can tell you with certainty that a Porche 911 will beat a Chevrolet Cavalier from 0-60 all other things being equal and my not having driven either vehicle. That having been said, I can't tell you which car is better looking outside of my own opinion of course.

Belief is a powerful thing and I'm not trying to criticize anyone's decision to go with any type of wire/equipment/etc. whatsoever. If you believe something's better , then for you it is and that's great but that doesn't necessarily mean it's an objective fact. Having said that, I've long been a fervert believer in the marketing literature put out by various companies on the virtures of their cables just like I continue to hope I'm only one new golf club away from curing my slice forever. I'm just getting to the point where I have to honestly say I can't tell the difference.

Given the fact that human hearing really starts to degrade once people hit their mid-thirties while their income reaches its full potential once they're 50, I'm really starting to wonder what all the fuss is about anyway.

F1nut · January 2005

Nope, you're looking at it all wrong. Science has got shine-ola to do with quality sound. Using data one can see the specs for SS gear are far better on paper than tube gear, but the fact is tube gear sounds more musical and is therefore better at sound reproduction as anyone who has heard tube gear will tell you.

It's just another case of hearing is believing.

SDA SRS Bridged vs. Biwire + Amp Suggestions Anyone?

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