bypass caps on AR LST

[roundhome]

I have new solen caps for my lst except the 2500uf will a .56uf solen work as a bypasss cap on this 2500uf cap? or do i need it?

Thank you

[dynaco_dan]

Hi there;

Anything I have ever read about bypass caps is, that every little bit helps.

Certainly not a waste of your time if you are already prepared with one and have the time and are already inside the cabinet.

[rrcrain]

I've read several extremely contradictory opinions concerning bypass capacitors. One strong opinion against was from a company marketing very high end capacitors and gave a reasonaly sound explanation why bypass caps aren't a good thing and another opinion in favor of bypass caps was from a vendor marketing nothing but bypass caps.

Therefor, my official opinion is this. Try it, if you think it works, go with it. If you discover it's a waste of time and money, don't.

Either way, do share your opinion of your experience.

[dynaco_dan]

Hi again;

A site with a personnal capacitor review of a few dozen various caps was listed here recently.

The article was of great interest to me, if not un-biased.

It is a shame sources and prices were not mentioned, for availablity only, not for evaluation differences.

It was suggested that a small cap be used as a bypass in some cases.

Obviously, if something sounds real bad, no bypass will bring out a whole new tweeter or mid driver sound.

In the case of the mentioned AR-LST big caps, if they are gone, they are gone and would need replacing of course.

[rrcrain]

Here's a link for those interested in the effects bypass caps have in a circuit. This paper is on bypass caps in general rather than specifically in audio circuits but I believe the math is applicable none the less.

http://www.ultracad.com/articles/esrbcap.pdf

A lot of math, heavy reading and graphs involved; this is not exactly an easy read.

[roundhome]

ok small ? on caps it been a long time for basic electronis but if you take two 300uf caps conect the negs you would get a 150uf bipolar cap is this correctr?

[rrcrain]

Your exactly right. Two 300 uf caps connected in parallel result in a 150uf, if you consider only the capacitance. Apparently, other variables change that our basic electronics never introduced us to.

[Carlspeak]

My electronics manuals indicate parallel connections of caps give an additive result (i.e. two 300 uF caps in parallel will result in 600 uF). This is for non-polar electrolytics. Not sure about polar models though.

It's all about the music

Carl

Carl's Custom Loudspeakers

[rrcrain]

ARRG...

I was thinking resistors....

The article I left the link for brings into play other variables other than simple capacitance, Q and ESR for starters. It's not what I consider an easy read.

[dynaco_dan]

>Your exactly right. Two 300 uf caps connected in parallel

>result in a 150uf, if you consider only the capacitance.

>Apparently, other variables change that our basic electronics

>never introduced us to.

Hi there;

Carl is correct, add the two capacitances together if in parallel.

The voltage capacity is the lesser voltage, unless they are the same.

[rrcrain]

I had to REALLY stop and think for a bit, and started thinking I had made a good goof rebuilding the crossovers in my own speakers.

Resistors in parallel reduce the combined resistive value, and capacitors in parallel are additive in value.

I know this, and have know it for several decades. I just haven't had to deal with it for a long time.

[onplane]

roundsound,

I find this entire discussion somewhat confusing. The article quoted has to do with by-pass caps in regulated power supplies. The article doesn't state, but the implication this is for digital boards with 100's of by-pass caps adjacent to IC’s.

As digital processing keeps going faster and faster (i.e. higher and higher in frequency) the strain on the power supplies also increases and designers need to be careful of self-resonance of the entire system or … bits and bytes will be “flipped” unintentionally.

That huge cap bank in your LST’s are NOT part of any power supply. Their entire mission is to counteract the inductance of that autotransformer. You don’t need any by-pass caps to do that.

According to the drawing I saw, the LST’s require a single 5000 mfd non-polar cap. Frankly, I don’t know if such an animal exists. AR solved the problem by putting 4 polarized caps in a series/parallel configuration.

Now, before anyone gets upset with my “heresy”, please remember we are in the “tweaks and mods” forum.

Roundsound, I can’t believe the combination of that autotransformer and cap bank is doing anything, but detracting from the sonic potential of the LST. Now, the autotransformer very cleverly provides you with 6 options for balancing the drivers.

Bi-amping, however, could provide you with an unlimited number of balancing options. Let me clarify, with bi-amping you would have not just 6 options but a truly unlimited number of options to balance the woofer with the mid driver. This still would lever the issue of the tweeters relative to the mid drivers. In the 3a’s we need everything we can get out of the tweeters. Indeed, in the LST positions 1, 2 and 3 are exactly that … flat out - everything we can get out of the tweeters!

In any event, if you wish to attenuate the mids relative to the tweeters, there are a number of low cost solutions. My personal favorite is Roy’s L-Pad solution as it’s very inexpensive ($5.00 l-pad + $1.00 25 ohm 10 watt resistor), it mimics the pots used in the AR-3a’s and there is essentially no compromise on power dissipation.

Roundsound, I know it’s heresy, but if I had LST’s, I’d eliminate that autotransformer AND cap bank. Add two new terminals (for the woofer) and add a low power amp (possibly a tube amp) to drive the mids and tweeters. In this case NOT only do you gain flexibility, but that transformer and cap bank absolutely must be degrading the resulting sound.

Regards,

Jerry

[roundhome]

>roundsound,

>

>I find this entire discussion somewhat confusing. The article

>quoted has to do with by-pass caps in regulated power

>supplies. The article doesn't state, but the implication this

>is for digital boards with 100's of by-pass caps adjacent to

>IC’s.

>

>As digital processing keeps going faster and faster (i.e.

>higher and higher in frequency) the strain on the power

>supplies also increases and designers need to be careful of

>self-resonance of the entire system or … bits and bytes

>will be “flipped” unintentionally.

>

>That huge cap bank in your LST’s are NOT part of any power

>supply. Their entire mission is to counteract the inductance

>of that autotransformer. You don’t need any by-pass caps to

>do that.

>

>According to the drawing I saw, the LST’s require a single

>5000 mfd non-polar cap. Frankly, I don’t know if such

>an animal exists. AR solved the problem by putting 4

>polarized caps in a series/parallel configuration.

>

>Now, before anyone gets upset with my “heresy”, please

>remember we are in the “tweaks and mods” forum.

>

>Roundsound, I can’t believe the combination of that

>autotransformer and cap bank is doing anything, but detracting

>from the sonic potential of the LST. Now, the

>autotransformer very cleverly provides you with 6 options for

>balancing the drivers.

>

>Bi-amping, however, could provide you with an unlimited

>number of balancing options. Let me clarify, with

>bi-amping you would have not just 6 options but a truly

>unlimited number of options to balance the woofer with the mid

>driver. This still would lever the issue of the tweeters

>relative to the mid drivers. In the 3a’s we need everything

>we can get out of the tweeters. Indeed, in the LST positions

>1, 2 and 3 are exactly that … flat out - everything we can

>get out of the tweeters!

>

>In any event, if you wish to attenuate the mids relative to

>the tweeters, there are a number of low cost solutions. My

>personal favorite is Roy’s L-Pad solution as it’s very

>inexpensive ($5.00 l-pad + $1.00 25 ohm 10 watt resistor), it

>mimics the pots used in the AR-3a’s and there is essentially

>no compromise on power dissipation.

>

>Roundsound, I know it’s heresy, but if I had LST’s, I’d

>eliminate that autotransformer AND cap bank. Add two new

>terminals (for the woofer) and add a low power amp (possibly a

>tube amp) to drive the mids and tweeters. In this case NOT

>only do you gain flexibility, but that transformer and cap

>bank absolutely must be degrading the resulting sound.

>

>Regards,

>Jerry

>

At present i'm not happy with the restored LST sound I had them tri amped with electronic crossovers and mono blocks these same drives sang like the music should sound once put in the LST crossover i'm not happy with the sound I'm going to give the solen caps some time to break in but don't think this will still sound the same as when they were tri amped they were 250 watt units.

Jim

ps I have four more LST's to restore two don't have crossovers was going to use AR11 crossover but think I will set them up tri amped and do an AB of the two sets

[onplane]

>

>At present i'm not happy with the restored LST sound I had

>them tri amped with electronic crossovers and mono blocks

>these same drives sang like the music should sound once put in

>the LST crossover i'm not happy with the sound I'm going to

>give the solen caps some time to break in but don't think this

>will still sound the same as when they were tri amped they

>were 250 watt units.

>Jim

>

>ps I have four more LST's to restore two don't have crossovers

>was going to use AR11 crossover but think I will set them up

>tri amped and do an AB of the two sets

Jim, my sense is that LST xover will never be able to sound like your tri-amp with electronic crossovers. A simpler xover like the AR11 might be closer.

There is a half and half solution. That is, electronic low pass xover for the woofer and electronic high pass for the mids/tweeters. Then you'd leave the passive high pass for the tweeters (this is just a single cap) and then a passive low pass for the mids. This will reduce the passive componets by a factor of 2 and require only two amps. (Total passive components = 2 caps + 1 coil + 1 rheostat)

Jim, I've never tried this, but I've read where others claim you get 80% of the benefits of tri-amping.

Regards,

Jerry

[Wally]

Regardless of whether you believe that bypass caps make a difference,

by my calculations a.56 mfd cap -3db point would be 71+khz at 4 ohms system impedance.

Your dogs and cats might hear the difference but I suspect they won't care....... LOL (somebody check my math....)

This means that a .56 mfd will make no audible difference. This is at 4 ohms... the nominal impedance of the LST. In actual fact the 2500 mfd cap precedes the autotransformer which may present a lower impedance than that...... for sure the LST goes below 4 ohms in parts of the audio spectrum and below 2 depending on the position of the front switch.

If you believe that a bypass cap makes a difference, use a 10 ufd or so film cap so you at least cover the tweeter range of frequencies......

[Diamonds&Rust]

I have new solen caps for my lst except the 2500uf will a .56uf solen work as a bypasss cap on this 2500uf cap? or do i need it?

Thank you

Absolutely nothing we (my listening buddy and I) tried as a "by-pass" sounded worth a flip and we went from "Harmony" North Creek caps to about 470uF of NPEs to whatever polys those were we had laying around. It's not about ESR. I'm not sure it's about capacitance.

I'd really like to know. I plan on knowing what the effect is, if not what the reason for the effect is, very soon now... waiting on some equipment and some capacitors.

You can get rid of the problem with the 2500uF cap by replacing it with a new one. Been there, done that, three times: Solution - replace the 2500uF cap.

ALL of the signal passes through that capacitor. That capacitor is bad. Replace it.

If you rip out the transformer, I suspect you will be sorry. The crossover was designed and the speaker was "finalized" with that transformer in there.

[dynaco_dan]

Absolutely nothing we (my listening buddy and I) tried as a "by-pass" sounded worth a flip and we went from "Harmony" North Creek caps to about 470uF of NPEs to whatever polys those were we had laying around. It's not about ESR. I'm not sure it's about capacitance.

I'd really like to know. I plan on knowing what the effect is, if not what the reason for the effect is, very soon now... waiting on some equipment and some capacitors.

You can get rid of the problem with the 2500uF cap by replacing it with a new one. Been there, done that, three times: Solution - replace the 2500uF cap.

ALL of the signal passes through that capacitor. That capacitor is bad. Replace it.

If you rip out the transformer, I suspect you will be sorry. The crossover was designed and the speaker was "finalized" with that transformer in there.

Hi there;

"You can get rid of the problem with the 2500uF cap by replacing it with a new one. Been there, done that, three times: Solution - replace the 2500uF cap"

Any suggestions for brand or models of the replacement 2500 uf cap(s)?

Vern

[Carlspeak]

Hi there;

"You can get rid of the problem with the 2500uF cap by replacing it with a new one. Been there, done that, three times: Solution - replace the 2500uF cap"

Any suggestions for brand or models of the replacement 2500 uf cap(s)?

Vern

Sprague Compulytic NPE caps are no longer available. You can still get Sprague 2500 uF caps, but they are not bi-polar.

I ended up getting (2) 1000 uF and (1) 500 Benic NPE's from Madisound and wired them together in a parallel bundle.

[dynaco_dan]

Sprague Compulytic NPE caps are no longer available. You can still get Sprague 2500 uF caps, but they are not bi-polar.

I ended up getting (2) 1000 uF and (1) 500 Benic NPE's from Madisound and wired them together in a parallel bundle.

Hi Carl;

Thank you for the suggestions and a possible source.

Vern

[dynaco_dan]

Hi Carl;

Thank you for the suggestions and a possible source.

Vern

Hi again;

Not that this is exactly the same situation but I thought that it may be helpful here.

W Marshall Leach Jr used, or rather added, at a later date, 0.1 uf polyester caps in parallel, to improve his amplifier's high frequency grounding.

I just went to the Dahlquist forum and PeteB has added a link to AVA about The DQ-10 xover.

They have modified a crossover bypass using 620 pf silver mica caps.

Vern

[Carlspeak]

He Vern.

Bypassing is done a lot these days. There is also much debate about its pros and cons on the net.

North Creek audio systems promoted bypassing alot back in the days when they were retailing parts. Perhaps they were simply trying to sell caps?

Peter Snell also used pF caps to bypass many of his NPE cap bundles in his early Snell speakers. They were ceramic disc types that were glued to the bottom of the bundle and aided in the gluing of the whole cap bundle to the xover board.

[kkantor]

"Peter Snell also used pF caps to bypass many of his NPE cap bundles in his early Snell speakers. They were ceramic disc types that were glued to the bottom of the bundle and aided in the gluing of the whole cap bundle to the xover board."

Hmmmm, is that really true? I've personally never heard of PS using anything less than 0.1uF, which would be 100,000pF.

-k

www.kenkantor.com

[Carlspeak]

Hmmmm, is that really true? I've personally never heard of PS using anything less than 0.1uF, which would be 100,000pF.

-k

www.kenkantor.com

Yes Ken, it was really true at least for ser. #'s 1511 and 1512. Those were the Model A's I upgraded the crossovers on. I searched around today for a picture I had of one of those pF caps I took off from the bottom of a cap bundle but could not find 'the smoking gun'. Sorry, I don't remember the exact value of that cap but am sure is was considerably less than 100,000pF.

Maybe someone else who has worked on PS's early models will stumble across this discouse and add some insignts.

[kkantor]

Yes Ken, it was really true at least for ser. #'s 1511 and 1512. Those were the Model A's I upgraded the crossovers on. I searched around today for a picture I had of one of those pF caps I took off from the bottom of a cap bundle but could not find 'the smoking gun'. Sorry, I don't remember the exact value of that cap but am sure is was considerably less than 100,000pF.

Maybe someone else who has worked on PS's early models will stumble across this discouse and add some insignts.

OK, so here's a scan of 12 capacitors that happened to be in my nearby parts bin. All are nominally 100,000pF, (=0.1uF). Not at all a comprehensive survey of what's available, still, this value cap is usually pretty small.

-k

www.kenkantor.com

ww.ztamplifiers.com

[roundhome]

Hello all thank you for all the information My goal is to have all 8 LST speakers restored put into a stacked quad system. the only road blocks have been the 2500uf caps and the fact that I don't have crossovers for two of them I have picked up two 10pi crossovers that can be modded to fit just with different db slops but with some test equipment could find a place were they match a setting on the originals.

AR has in the past on some of the LST speakers used two 5000uf polar caps to come up with the 2500uf this would be possible to do again there are plenty of these caps around.

like they came up with 5000uf non polar in the early LST using four 5000uf polar caps in them. as we have found out this was quit hard on some amps .so they dropped it to 2500uf. using two 5000uf polar them came up with 2500uf polar caps they then used in the 10 pi and the AR 9.

It would solve a lot of problems for some one to just take two 5000uf polar caps pos to pos and test them on the negs to confirm they come out to 2500uf and we could all get our speakers up and running if they are LST or 10pi or AR9.

Thank you all again for the helps so far.

Jim