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A Home Theater Opinion/suggestion RFC (re:LST)


Guest LaboratoryStandard Xsducer

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Guest LaboratoryStandard Xsducer

Greetings from a newcomer reading the entire AR forum:

My darling daughter, Jess, and her life partner Brad gifted us with an Onkyo TX-SR606 AVR.

http://www.onkyousa.com/model.cfm?m=TX-SR6...eceiver&p=s

AND a http://panasonic.net/avc/blu-ray/dmp-bd35_55/ for optical discs

for the TV, we have a 16:9 CRT from Sony the 34xbr970

As you may know these are in the 'bang-for-the-buck' range of Hi-Fi. The big minus for me is in the power supply/complex impedance driving range of the AVR. The thing has crowbarred off a few times for me already. I mean I'm grateful, but the european model _CAN_ be made to drive 4 Ohm loads. >:-(

So I have many issues to deal with. The Center channel speaker is one. Being very low on discretionary outcome, another (and mint, not like my barely restored) LST is out of contention, LOL.

Can you recommend for audition a much more modest unit?

I may end up, in any case, with one of these.

http://www.vanns.com/shop/servlet/item/det...kef-iq2c-walnut

http://www.vanns.com/shop/servlet/item/det...46/klipsch-sc-5

simply because of the really, REALLY good price.

The KEF, is a co-axial driver and aesthetically pleasing cabinet.

The Klipsch, being a better engineering match as an acoustic suspension/dome tweeter system with little spent on aesthetics.

Both can be considered horn like but the difference in LF driver loading may throw my choice.

If forced to choose, what do you think?

The AVR can BI-AMP in 5.1 mode. This presents a possible solution in the amp/speaker issue.

I have the LST diagram and with a little talented work on my part, I may be able to cut the system in half so one amp drives the LFs and the other drives MF/HF drivers. While not a classic restoration of ARs fantastic technology, something I cannot afford, it would go a ways to easing the burden on the AMPS, wouldn't you say?

I look forward to hearing from you if you have a moment to reply. Thanks. :-)

David

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It is interesting that the dynamic power is listed into 4 and 3 ohm loads which suggests

that it at least does not current limit into low impedances. This suggests that heat might

be the issue; is there free air flow around the unit, or is it in a cabinet?

You might try a 1 ohm 25W resistor in series with each system to see if it shuts down.

I can help you with bi-amping as I worked out the details some time ago but have not

come across a pair to try it out.

Have you done any work on your LST's do you know what value input cap is there and

is there a resistor across it? An auto-transformer was used in this design, BTW.

What part of the country do you live in, perhaps I could help you.

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Guest LaboratoryStandard Xsducer
Is there no way you can exchange this receiver? One model up in the Onkyo range, the 706 is 4 ohm stable.

You are correct in your phraseology. There is no way and no, it did not 'fall off the truck'.

I guess I should have mentioned that pertinent fact in my post, so I apologise and very much appreciate your reply.

Would that my issue could be solved that way.

Could I sell 606?; yes but not for enough that I could grab a 706 without putting my LST's or maybe a kidney on eBay. ;-)

I have some reason to believe that bi-amping (in the least destructive manner to the LSTs) would allow the 606 to distribute the complex load more evenly. Heck, at this point I am not even using the surround amps yet. I imagine when I get all the amps working the 606 will keep the house a bit warmer and if I don't push it in an Audessy Equalized- multichannel mode too hard, there won't be many crowbars. I will also explore the option of stereo only, or for real old fashioned fun, move the stuff in the room around so I can have the genuine Bell Labs Standard for stereophonic sound. LSTs 30 feet apart with a center in between. You know, kind of like two Klipschorns with a Heresy center. I wonder what Mr. Vilchur thought of that set-up?

Thanks for the reply.

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Guest LaboratoryStandard Xsducer
It is interesting that the dynamic power is listed into 4 and 3 ohm loads which suggests

that it at least does not current limit into low impedances. This suggests that heat might

be the issue; is there free air flow around the unit, or is it in a cabinet?

You might try a 1 ohm 25W resistor in series with each system to see if it shuts down.

I can help you with bi-amping as I worked out the details some time ago but have not

come across a pair to try it out.

Have you done any work on your LST's do you know what value input cap is there and

is there a resistor across it? An auto-transformer was used in this design, BTW.

What part of the country do you live in, perhaps I could help you.

Thank you for your interest, and I have made significant modifications to the enclosure where the 606 resides to reflect the space requirements from the manual. I can't make the sides wider (there is open space there) but there is now plenty of room for thermal draft. Perhaps I should fan it as others on the dedicated thread in the AVS forums have done, few of which are driving as challenging an impedance as I.

I reside in the Lehigh Valley area of the Keystone state. I see you hail from the Nutmeg State.

I have taken the LF drivers out for Millersound resurrounding. Bill has my highest recommendation.

Have I exhaustively disassembled the LSTs? No, but you could say that I have field stripped them. I have also built my own speakers at a time shortly after the LSTs were introduced. They were Sherwood Ravinias with drivers and Xovers hand picked by one of Sherwood's engineers. A large 3 way sealed enclosure system with a tweeter very much like the LST midrange and a sealed 6 inch paper cone for midrange and 12 inch LF.

I will have to expose the Xover of the LST to determine my approach and will photograph all in detail.

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Well, if money is tight, why purchase a center channel speaker? I'd wait until you have the LST's bi-amped and see whether it's necessary.

As I recall, David, the LST has a circuit board that will require modifications, if you were to bi-amp with two independent amps. When using a quad or a multi-channel amp, it becomes much easier as you no longer have to touch the circuit board.

The idea would be to set the Onkyo to 4 channel output and then select Stereo ALL. This puts the same signal on the surround amps as on the front amps. You would then have the front amp drive the mids/tweeters and the surround amp power the woofers.

Next, you would completely by-pass the transformer and the huge cap bank. These things create problem loads and without them your Onkyo should have no problems at reasonable volume levels.

The separate amps (front & surround) provide a methology to balance the mids and woofers. What is lacking is a way to control the tweeters. The best way to control the tweeters would be to insert a variable resistor in the mid driver circuit. That is, you need a way to "pad the mids". Once you do that, you'll have far more control over LST voicing than you get with the 6 position switch.

Send me a PM once you get the woofers back and I'll send you a diagram showing how you would wire the speakers with the very least modifications (so that you could easily return to stock form).

Regards,

Jerry

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You're welcome, yes I believe that some low speed fans would help if you're certain that it is a thermal problem.

Interesting project, will enjoy reading your updates.

I commented on how to eliminate the auto-transformer and input cap, which

would allow bi, or tri-amping. Then it was confirmed when a member here

posted this letter from Roy Allison:

http://www.classicspeakerpages.net/IP.Boar...amp;#entry72334

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Guest LaboratoryStandard Xsducer
Well, if money is tight, why purchase a center channel speaker? I'd wait until you have the LST's bi-amped and see whether it's necessary.

As I recall, David, the LST has a circuit board that will require modifications, if you were to bi-amp with two independent amps. When using a quad or a multi-channel amp, it becomes much easier as you no longer have to touch the circuit board.

The idea would be to set the Onkyo to 4 channel output and then select Stereo ALL. This puts the same signal on the surround amps as on the front amps. You would then have the front amp drive the mids/tweeters and the surround amp power the woofers.

Next, you would completely by-pass the transformer and the huge cap bank. These things create problem loads and without them your Onkyo should have no problems at reasonable volume levels.

The separate amps (front & surround) provide a methology to balance the mids and woofers. What is lacking is a way to control the tweeters. The best way to control the tweeters would be to insert a variable resistor in the mid driver circuit. That is, you need a way to "pad the mids". Once you do that, you'll have far more control over LST voicing than you get with the 6 position switch.

Send me a PM once you get the woofers back and I'll send you a diagram showing how you would wire the speakers with the very least modifications (so that you could easily return to stock form).

Regards,

Jerry

Hi Jerry,

Thanks for replying and I should've mentioned at first that _my_ name is David. :-) Hello again.

The nature of the primary listening material specifies a center channel. I am just the sysadmin (husband). The CEO almost exclusively requires this type material.

I think I know where you are coming from and I very much see what you mean about 'why spend if you don't have to spend'. I'm using a borrowed Klipsch computer 5.1 in-a-box center speaker. I have heard different specific %'s but the concensus is that a majority of what you hear in this material is from the center signal. Even without it the LSTs sound great great but with my less than ideal A/V feng shui, the center fills a hole better that the TV's speakers ever could.

The Onkyo 606 AVR BI-AMPs this way:

Start of quote

The FRONT L/R and SURR BACK L/R terminal posts

can be used with front speakers and surround back

speakers respectively, or bi-amped to provide separate

tweeter and woofer feeds for front speakers, providing

improved bass and treble performance.

• When bi-amping is used, the AV receiver is able to

drive up to 5.1 speakers in the main room.

For bi-amping, the FRONT L/R terminal posts connect

to the front speakers’ tweeter terminals. And the

SURR BACK L/R terminal posts connect to the front

speakers’ woofer terminals.

• Once you’ve completed the bi-amping connections

shown below and turned on the AV receiver, you must

set the Speaker Type setting to Bi-Amp to enable biamping

(see page 42).

[i have included this irrelevant bit below for context]

Important:

• When making the bi-amping connections, be sure

to remove the jumper bars that link the speakers’

tweeter (high) and woofer (low) terminals.

• Bi-amping can only be used with speakers that support

bi-amping. Refer to your speaker manual.

end quote

This is where my work comes in. What to cut, where to cut and where to place the extra set of connectors with as little damage as possible. I read PeteB's thread suggestion. Would this apply to the LST?

Thanks!

David

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This image is the LST crossover schematic marked up by Roy Allison. The changes however

are fairly extensive if you compare it to the original LST schematic and the contour switch is

removed. You could use LPADs as in the 3a, switched attenuators, or fixed resistor based

series-shunt pads set to your preferred settings:

http://www.classicspeakerpages.net/IP.Boar...ost&id=3185

I've also had thoughts of keeping the autotransformer for the mid-tweeter array, with the

woofer wired as in the above diagram which would allow bi-amping and remove the cap

and transformer from the woofer circuit.

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You are correct in your phraseology. There is no way and no, it did not 'fall off the truck'.

I guess I should have mentioned that pertinent fact in my post, so I apologise and very much appreciate your reply.

Would that my issue could be solved that way.

In this situation I would probably opt for an impedance matching autoformer between the speakers and the amp. Russound has several models that come in black box form and built into remote volume or speaker selector controls. Autoformers do introduce some degradation in performance, but the receiver and center channel speaker you're trying to work with are not high end performers and high end performance is generally wasted on home theater sound anyway. Given the lack of durability of modern electronics, you'll likely be replacing that receiver in 5 years or less; I wouldn't open up and modify a 30+-year-old classic speaker to try to make it compatible with it.

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Hi Jerry,

• For bi-amping, the FRONT L/R terminal posts connect

to the front speakers’ tweeter terminals. And the

SURR BACK L/R terminal posts connect to the front

speakers’ woofer terminals.

This is where my work comes in. What to cut, where to cut and where to place the extra set of connectors with as little damage as possible. I read PeteB's thread suggestion. Would this apply to the LST?

Thanks!

David

David, the boldfont above from Onkyo is exactly the same as I was suggesting. This will require the least cutting/chopping of your LST's.

The only problem area is the mid-drivers. They need to be padded or they will over power the tweeters. The LST xover has some padding already, but it's simply not enough once you eliminate the transformer. Further, you'll want some ability to control the amount of padding, so either an AR-3 type pot or a variable resistor.

Pete, you mentioned keeping the autotransformer for the mid/tweeters. Boy, I would think there are two problems with that:

1. the autotransformer and cap bank are a "bad load" for powerhouse amp and what we have here is modest power amps

2. life just becomes too complicated as the balance between woofer and mids will be controlled by the volume levels in the front and surround amps. This leaves the switch just controlling the balance between the mid and tweeter. Frankly, I think there are simplier ways to do this.

Gene, is suggesting that you use a transformer to bring the impedance of the LST's UP so that's it will be more compatible with the Onkyo. Now, that will work, but remember you already have a transformer INSIDE the LST's. When you put two transformers PLUS that huge cap bank together, anything can happen. That is, the entire system may oscilate. I mean, we are really into an unknown area with the only certainity that audio quality will degrade.

Hope this helps ...

Regards,

Jerry

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Pete, you mentioned keeping the autotransformer for the mid/tweeters. Boy, I would think there are two problems with that:

1. the autotransformer and cap bank are a "bad load" for powerhouse amp and what we have here is modest power amps

2. life just becomes too complicated as the balance between woofer and mids will be controlled by the volume levels in the front and surround amps. This leaves the switch just controlling the balance between the mid and tweeter. Frankly, I think there are simplier ways to do this.

Gene, is suggesting that you use a transformer to bring the impedance of the LST's UP so that's it will be more compatible with the Onkyo. Now, that will work, but remember you already have a transformer INSIDE the LST's. When you put two transformers PLUS that huge cap bank together, anything can happen. That is, the entire system may oscilate. I mean, we are really into an unknown area with the only certainity that audio quality will degrade.

Hope this helps ...

Regards,

Jerry

Jerry, I don't see the logic in your point that what I suggest would be a "bad load".

I could use complex conjugate load matching if I thought it was a problem, however

I don't expect any issues. The input impedance is easy to measure.

I would not do it this way (normally) but the auto-transformer is there and would

need to be replaced with pots, or whatever if it was removed.

The external transformer is a real bad idea, good high power transformers are

expensive and heavy. Better to outboard a high current amp at that point.

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The external transformer is a real bad idea, good high power transformers are

expensive and heavy.

The OP's receiver is rated 90W, 20-20k, 2 channels driven.

With all channels going for surround or biamp use, he'll be

lucky if he can get 50WPC before it clips or the circuit

protector kicks in. 40 real, classic era WPC is more likely.

He'd be throwing his money away on anything with a rating

higher than 50W RMS.

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