reQuest Crossover capacitor upgrade

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TomDac

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[size=+2]reQuest Crossover capacitor upgrade[/size]
Sent in by James Carroll on December 11, 2003
Overview
Based on my previous experience upgrading the crossover capacitors of several other speakers, I decided that it would be a good project to pursue on the Martin Logan Requests I purchased recently. However, the Requests do not have a simple crossover, so I needed to evaluate what could be upgraded. The link below is to a PDF version of the schematic of the Requests.






<CENTER>reQuest Crossover</FONT> (see attachment for Crossover)




</CENTER>

Looking at this setup, the simplest and most cost effective upgrade is a simple capacitor upgrade on the high-pass (stat) circuit. I could examine better resistors and inductors, but given the size and complexity of this crossover, I figured best not to play it too much, plus, it's a pretty darn good speaker as is. Plus, the only practical upgrade, that I figure would have the biggest bang for the buck are the 3 smaller capacitors. Primarily the 10mfd and 15mfd that are directly in the signal path, but while I was at it I figured I'd do the 5mfd cap as well. Several options: Jensen, Arui, Hovland, etc... Decided based on past experience that Auri's are reasonably priced, and offer sound every bit at good as the Hovlands (some might disagree, this is just my experience) and as a nice perk, are physically about half the size of the Hovlands and Jensens. The total price for both speakers ran about $160. The capacitors are available directly from Audience at: www.audience-av.com

The upgrade itself is simple, snip the old capacitors out, and solder the new ones in. Keep in mind, that all stat speakers use a bias voltage supply to raise the voltage on the stators, so you have MUCH higher voltages going on inside there so be very careful. I unplugged the speakers long before opening them up, and made sure they were discharged by trying to play them without power, you'll still hear a little coming from the stat panels, but it is very significantly reduced, barely audible.

Procedure
Lay the speaker on it's side. You can't do this with them standing up as the cords inside aren't long enough to allow you to lay the back panel down unless the speaker is on it's side. Unscrew the back panels and pull them off. They are heavy and take some coaxing to get off. Below is a picture of the panel removed. Notice, this is about as complex a crossover as you'll find (mainly because it's more than just a crossover)







<CENTER>




</CENTER>

Below is a close up of what we'll be removing, the 2 Solen capacitors and one yellow one. Left to right, these are 5mfd, 15mfd, and 10mfd. They are held in place with a little bit of hot glue. You'll probably want to reglue the new caps when you install them. I just used a little ShoeGoo adhesive. So, snip these out one at a time. Follow the schematic carefully, as the Auri caps claim to be polar, and you'll want to put the red lead towards the signal input (+).







<CENTER>




</CENTER>

Here's a shot showing the new capacitors in place. They are each a little bit bigger than the ones they replaced, but not much and fit. Anything bigger and you'd have to get a little creative.







<CENTER>




</CENTER>

Here's a close up. Double check the connections, make sure the solder joints are good, and button it up, repeat on the next speaker







<CENTER>




</CENTER>

Impressions
I have done this upgrade on my older Magnepan MG12's and a pair of 1.6QR's. On both of those the effects were dramatic. So far I've only been listening to the Requests for about an hour so this is initial impressions, and the caps haven't broken in yet. Overall the sound is definitely improved. Not as dramatically as the MG12's were, but due to the complexity of the crossover, I expected this. The sound is more focused, natural, and open. It's been my experience that Solens tend to sound a little harsh, and this upgrade bears that out. The Auri's definitely sound cleaner and more natural. A hint of grain appears to be gone, and each instrument is more focused and detailed. A voice or instrument that previously seemed to cover an area of about 12" in the sound field now seems like it's only 6" wide. More focused and clear. The speakers have definitely disappeared a bit more. There are definitely some subtle details that are comming out that I didn't hear before, particularly at low volumes. The harshness of the treble (not that there was much to begin with) seems gone. The treble is still there, but it's not grainy at all. Overall I highly recommend this upgrade. Granted, your experience may vary, and at $160 it's not cheap, but compared to the price of the speakers it's a bargain.


Editor's Note
James is obviously very comfortable working with electronics. Please be VERY careful if you decide to perform this tweak to your system. Capacitors are very tricky and must be fully discharged before working with them. As he noted in one of the images, the bias voltage circuit is very dangerous as well. BE CAREFUL!
 

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Rothen

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James and rest of ML-world,

I'm owner of an Prodigy and also made very positive experience with upgrading capacitors. I replaced the Solen by Mundorf MCap Supremes.

I'm now considering the option of activating the panel of me Prodigy, therefore I have a question concerning the cross over: The transformer of the Request and also Prodigy have 3 cables coming in - why not 2? I read in my separate thread I opened some days ago that the panel works as "push-pull". But still I'm not quite sure whether I can connect "red" and "brown" when the panel is driven directly by an amp with an active cross over.

Volker
 
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Gerrybisch

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Request & Capacitor Upgrade

After reading this tweak, I ordered a set of "MUNDORF Mcap400" caps for a price of 39 Euros incl shipping. (the "MUNDORF Supreme" will be at 180 Euros"). I replaced the caps following the instructions.
The result was: more details, more room. It has to be said, that the new caps needed some time to be "played in", about 15-20 hours. Within this period there were still improvements to be recognized.
 
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Spike

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Bump... The pictures in this thread have disappeared. Does anyone know how to recover these lost pictures? They are very helpful for such an involved project.

Thanks in advance,
Spike
 

patounet

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YES... I did it on my Prodigy : looking for better capacitors. But which part of the crossover are you talking about ? The worse on these speakers is the bass unit, HP driver and 12dB crossover, this part is not as good as the ESL..., every body agree. Bass crossover is in the tray in front of the speaker and easy to access. Martin Logan uses electrolytic cheap BENNIC capacitors. Only better capacitors in Statement speakers but cheap in Prodigy... But if you try any others, the best one's, the speakers will not sound the same, even with Mundorf that I tried. Better dynamic, tought bass... but too much level, it spoils the ESL, you should have to re -calculate all the crossover values of the original elements. I spent much money and returned to original ERSE capacitors... And after 10 years trying to get better with these speakers, I just ordered new ESL 15A Renaissance, active with ARC... So, these are electrostatic speakers, take them as they are from Martin Logan and do not try to loose your soul... regards to all from France
 

jaffrie

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James and rest of ML-world,

I'm owner of an Prodigy and also made very positive experience with upgrading capacitors. I replaced the Solen by Mundorf MCap Supremes.

I'm now considering the option of activating the panel of me Prodigy, therefore I have a question concerning the cross over: The transformer of the Request and also Prodigy have 3 cables coming in - why not 2? I read in my separate thread I opened some days ago that the panel works as "push-pull". But still I'm not quite sure whether I can connect "red" and "brown" when the panel is driven directly by an amp with an active cross over.

Volker
Hi Volker,
I've totally rebuilt my Odyssey including recoating panels & fully modified & tweaked XO etc.
The trafo was something that I've been researching for sometime which till now could not find any details. There's are very knowlegable gentleman over at Diyaudio who advice that the CT of the ML trafo is used to shape the response of the panel. In short without details it's no go for me to try a better Trafo.

Cheers
 

jaffrie

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YES... I did it on my Prodigy : looking for better capacitors. But which part of the crossover are you talking about ? The worse on these speakers is the bass unit, HP driver and 12dB crossover, this part is not as good as the ESL..., every body agree. Bass crossover is in the tray in front of the speaker and easy to access. Martin Logan uses electrolytic cheap BENNIC capacitors. Only better capacitors in Statement speakers but cheap in Prodigy... But if you try any others, the best one's, the speakers will not sound the same, even with Mundorf that I tried. Better dynamic, tought bass... but too much level, it spoils the ESL, you should have to re -calculate all the crossover values of the original elements. I spent much money and returned to original ERSE capacitors... And after 10 years trying to get better with these speakers, I just ordered new ESL 15A Renaissance, active with ARC... So, these are electrostatic speakers, take them as they are from Martin Logan and do not try to loose your soul... regards to all from France
From my own experiment I can confirm that you can turn old ML speakers to be much better than stock.
Yes when I opened up my Odyssey it was a real let down when considering the price I paid when new.
Anyway what you said about the woofer caps is true, upgrading caps here to say film caps is a no no.
Though XO is at 250hz many may not realize that the woofer section contributes lots to the overall sound & coherence of the speakers. Many tweakers thinks that changing Inductors to heavier gauge or foil type would improve sound but the catch is DCR. In general commercial products XO's are design & simulated with the DCR of the inductors included to achieve their goals, by changing to say thicker gauge inductors or foils, it will definately muck the response curve of the XO due to it's lower DCR.
 

jaffrie

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Sorry the other thing that I forgot, after years of listening ours ears gets used to the sound even when the panels begins to deteriorate so moral of it make sure that panels are in great shape before you start tweaking you'd be in for a huge surprise either with new panels or diy re coating work without touching anything else.
 

R1200CL

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Hi Volker,
I've totally rebuilt my Odyssey including recoating panels & fully modified & tweaked XO etc.
The trafo was something that I've been researching for sometime which till now could not find any details. There's are very knowlegable gentleman over at Diyaudio who advice that the CT of the ML trafo is used to shape the response of the panel. In short without details it's no go for me to try a better Trafo.

Cheers
There are schematic drawings in this tread. Not sure if any help.

 

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