AR MST

[ra.ra]

As good as those original Sprague caps often proved to be, you can be reasonably certain that the new Audyn caps you have purchased are superior in construction and performance. Be patient, and take your time with the re-cap and testing.

[TimmyTonga]

It's interesting that the front-facing tweeters dealing with frequencies above 1600 and the side-facing dealing with those above 5000 are both controlled by the switch. Without wishing to move into territories that are more suitable for the mods and tweaks section of the board, I would wonder whether there was an advantage to be had from having the switch control only the 'supertweeters'. 

[TimmyTonga]

.....or perhaps, as 'increase' is actually 'non-attenuation' (at least in an electrical sense), the front-facing tweeters alone. This would mean you have the ability to control the mid-range energy and the hi-range, but in different proportions, as the side-facing tweeter(s) will be constant.

[Alessandro]

Dear All ,

 

As I arrived I had finally announced the new capacitors 10 MF . So I started with replacing old Sprague 6 MF with new Mundorf M Cap Supreme Classic ( Features : Polyprophylene Dielectric strength : 600-1400 VDC Loss angle : tan∂ = 0.0002@1 kHz ; 0.0001@10 kHz Permissible ambient temperature 85 ° C / 185 ° F ). So at the time I made this first step without changing the 4 Tweeter configuration.

Now I will begin to test this first implementation. Already at a low volume the sound has become much more open and clear. Tomorrow morning now I will test my AR MST to more sustained and in any event well suited to these speakers that require a lot of power .

I'll come back to report on topic.

I attach two images from which you evincie the remarkable capacitor size !!!

 

regards

[owlsplace]

On 8/5/2016 at 6:27 PM, ar_pro said:

It gives me hope that there might still be some sealed AR-3a or AR-5 speakers out there, somewhere!

ar-pro your wish is my command -- maybe -- sequential serial numbers with sales receipt from original owner -- 172302927991

Alessandro, nice work so far and not stealing your thread here -- just kibitzing

Roger

[Alessandro]

2 hours ago, owlsplace said:

ar-pro your wish is my command -- maybe -- sequential serial numbers with sales receipt from original owner -- 172302927991

Alessandro, nice work so far and not stealing your thread here -- just kibitzing

Roger

Thank You Roger !

 

Alessandro

[TimmyTonga]

If replacing the Sprague caps with films, is there any need for a series resistor? If so, what kind of value?

[Alessandro]

2 hours ago, TimmyTonga said:

If replacing the Sprague caps with films, is there any need for a series resistor? If so, what kind of value?

Hi Timmy,

It is not necessary is almost irrelevant given the tolerances of the caps. I am also considering to increase the performance of the crossover by the addition of an inductance from 0.82 mH and a zobel circuit mounted directly on woofer exactly as on the AR 6 crossover ... but I will let you know how it will sound, while maintaining the four tweeter configuration

Alessandro

 

[Alessandro]

Hi,

Hello,

I point to the new implementations made my AR MST: in my previous post I replaced the capacitors with 2 new 10 mF high quality and now I have also added two inductances from 0.68 mH around so as to get a crossover frequency to about 2,000 Hz (Look for reference the attached crossover scheme) . Now at last the AR MST have a much better sound and so all musical instruments are at the right distance. I am waiting for the arrival me more capacitors and resistors (24 mF caps and two resistors 10 Ohm) so as to place them directly on the woofer terminals such modified Zobel circuit. This should improve, I think, to correct the issue as a result of the correction of the inductive area in the woofer crossover with tweeter. Unfortunately, at this point, not having available an anechoic chamber and suitable instruments, go forward by trial. Therefore any of your suggestions will be valuable to me. Thanks for your attention.

 

regards

Xover AR_MST.pdf

[Stimpy]

Nice progress.  Plus, adding a low pass on the woofer is a nice experiment.  And with using a first order 6 dB high pass and low pass crossover, you shouldn't have any phase issues.  So, you could keep the tweeters and woofer wired with the same polarity.

 

As to the recap, good job.  I can't argue the use of Mundorf Supreme caps!  I hope I can afford to use them on the UMR, of my AR90s, when I recap?  I hope you like their sound?

 

[Alessandro]

On 15 agosto 2016 at 2:52 AM, Stimpy said:

Nice progress.  Plus, adding a low pass on the woofer is a nice experiment.  And with using a first order 6 dB high pass and low pass crossover, you shouldn't have any phase issues.  So, you could keep the tweeters and woofer wired with the same polarity.

 

As to the recap, good job.  I can't argue the use of Mundorf Supreme caps!  I hope I can afford to use them on the UMR, of my AR90s, when I recap?  I hope you like their sound?

 

Hello Stimpy,

Actually I am very pleased to have entered a filter for the woofer and in fact now AR MST sound very good . I confirm that the woofer and the tweeter are all of the same polarity and everything seems to work well. Next weekend will put zobel circuit on the woofer as on AR 6 and see if there will be further improvements. The caps are very good and I highly recommend them. They have a very good and clear sound on medium and high frequencies .

Alessandro

[Stimpy]

Thanks Alessandro!  I'm glad the hear that the mods have been successful.  Plus, I appreciate the feedback on the replacement capacitors, as I definitely want to try Mundorf Supreme caps in my crossover rebuild.  At least on the UMR, if possible.  Mundorf EVO Oil for the LMR, and ClarityCap ESA caps for the tweeter, and finally a NPE with a Solen bypass on the bass.  Probably around $350 for the caps, all total.  Then maybe a few Mills resistors.  And I want to refinish my 90 cabinets too.  That's it, as I've already refoamed the drivers.

[Alessandro]

16 hours ago, Stimpy said:

Thanks Alessandro!  I'm glad the hear that the mods have been successful.  Plus, I appreciate the feedback on the replacement capacitors, as I definitely want to try Mundorf Supreme caps in my crossover rebuild.  At least on the UMR, if possible.  Mundorf EVO Oil for the LMR, and ClarityCap ESA caps for the tweeter, and finally a NPE with a Solen bypass on the bass.  Probably around $350 for the caps, all total.  Then maybe a few Mills resistors.  And I want to refinish my 90 cabinets too.  That's it, as I've already refoamed the drivers.

Hi Stimpy,

It ' a pleasure for me to give to you some information that may be useful for your fantastic AR Speakers !

Alessandro

[TimmyTonga]

OK, so I have two sets of functioning MSTs from the same year, and plan to up(?)grade one pair to MST 1 incrementally in order to make some kind of judgement as to which is preferable. I think it's too easy for the mind to play tricks when it comes to aural memory, and having a control experiment to hand is the only way round that.

 I have two immediate questions; one conceptual and one pragmatic.

• Alessandro, even though he may not upgrade further to MST 1s (he has not posted for a while), has exchanged the 6uf cap for a 10uf ostensibly in order to move the crossover frequency from 1600 to 2000. What would be the expected advantage of this, at a theoretical level? Or is the rationale tied inextricably to his other mods? (Sorry to talk as if you are not here Alessandro, please respond if you wish!)

• in order to insert the 2uf cap for the side tweeter(s), it seems you need to get to the central connector of the switch, which is covered in hard brown glue. Is there an elegant way to avoid this? I really don't relish the idea of having to get in there and possibly cause some damage.

thththanx as ever

t

[Alessandro]

2 hours ago, TimmyTonga said:

OK, so I have two sets of functioning MSTs from the same year, and plan to up(?)grade one pair to MST 1 incrementally in order to make some kind of judgement as to which is preferable. I think it's too easy for the mind to play tricks when it comes to aural memory, and having a control experiment to hand is the only way round that.

 I have two immediate questions; one conceptual and one pragmatic.

• Alessandro, even though he may not upgrade further to MST 1s (he has not posted for a while), has exchanged the 6uf cap for a 10uf ostensibly in order to move the crossover frequency from 1600 to 2000. What would be the expected advantage of this, at a theoretical level? Or is the rationale tied inextricably to his other mods? (Sorry to talk as if you are not here Alessandro, please respond if you wish!)

• in order to insert the 2uf cap for the side tweeter(s), it seems you need to get to the central connector of the switch, which is covered in hard brown glue. Is there an elegant way to avoid this? I really don't relish the idea of having to get in there and possibly cause some damage.

thththanx as ever

t

Hello Timmy,

How do you know my AR MST are the model to 4 tweeters and as written earlier I was not happy with the sound so I tried everything that was written about and this forum I found many answers and many aid. So I started to make some gradual changes and now that I have come to an end are really satisfied. Now they're playing very well with powerful bass and mids and clear highs. The first step was to replace the capacitor 6 mF with a 10 mF high quality (and expensive), and I had already obtained a marked improvement in performance, and are then passed to the three tweeters version by following the chart instructions ( with the exception of "Decrease" position in which the resistance had to be done in parallel ... I simply adopted as also adopted in the RA 6). In addition to ease banking problems between woofer and tweeter I also added an inductance of 0.82 mH. Finally I removed a Twewter for each speaker (one right and one left and I closed the hole with stopper plywood carefully cut for the purpose.

I now have a pair of AR MST fantastic. I hope to be liked and the rest at your disposal for any clarification. However, the brown glue melts with the heat of a soldering iron. Now I bought a pair of AR 7 I'm trying to restore ... but it will be difficult because the furniture is shabby.

Thank you !

[Alessandro]

2 hours ago, TimmyTonga said:

OK, so I have two sets of functioning MSTs from the same year, and plan to up(?)grade one pair to MST 1 incrementally in order to make some kind of judgement as to which is preferable. I think it's too easy for the mind to play tricks when it comes to aural memory, and having a control experiment to hand is the only way round that.

 I have two immediate questions; one conceptual and one pragmatic.

• Alessandro, even though he may not upgrade further to MST 1s (he has not posted for a while), has exchanged the 6uf cap for a 10uf ostensibly in order to move the crossover frequency from 1600 to 2000. What would be the expected advantage of this, at a theoretical level? Or is the rationale tied inextricably to his other mods? (Sorry to talk as if you are not here Alessandro, please respond if you wish!)

• in order to insert the 2uf cap for the side tweeter(s), it seems you need to get to the central connector of the switch, which is covered in hard brown glue. Is there an elegant way to avoid this? I really don't relish the idea of having to get in there and possibly cause some damage.

thththanx as ever

t

Hello Timmy,

This is the end xOver schematic.

Regardas

Alessandro Catalano

 

[TimmyTonga]

Thanks Alessandro, that photo really helps.

regards/Tim

[ra.ra]

Interesting thread, and very nice crossover components - - I've never seen a 10uF cap with such ample dimensions. So, in comparison to the two schematics attached here, is it correct to state that the only differences in Alessandro's final schematic are:

a.) top schematic: addition of woofer coil

b.) bottom schematic: addition of woofer coil and removal of one side tweeter

Alessandro, how did you decide to add this coil and then assign its value (0.82 mh), and did you ever experiment with your earlier notion with the Zobel circuit? 

[Alessandro]

Hello ra.ra.

 

Thank you for asking. In fact when they arrived the two 10 mF caps I was surprised by the size, which is why I was forced to position them as you can see in the pictures otherwise the woofer could not be positioned correctly. However this kind of caps are really recommend, have a high-speed response.

 

Therefore the choice of including an 0.82 mH inductance I used a computer for passive crossover filters in order to obtain a lower cut at a frequency of 1,600 Hz to 6 db per octave while the frontal Tweeter couple have a cut to a frequency of about 1.900 Hz up to 5,000 and finally the single tweeter side operates by the frequency of 5,000 Hz always at 6db per octave. Although apparently seems to be a gap between the 1600Hz and 1900 did I just get a slight decline as I used cuts only 6dB per octave. As regards the application of Zobel filter did not give me satisfactory results as such filter from considerable advantages in the presence of crosses at the same frequency. In fact also acoustically I obtained a response bending at low frequencies (between 70/80 Hz and 400 Hz).

Finally accurate that actually exist on the diagram of my AR-MST and that of AR-MST / 1 on the "decrease" position, in fact I've kept a 3 ohm resistor instead of 6 ohms and not in parallel to the main line .

 

I hope to have a clear statement of how elaborate and in any case I can not help but thank You All for the valuable tips that have allowed me to have now a pair of AR-MST of which are extremely happy as well as my pair of fantastic AR-6 (European version). Now I'm working on the restoration of an AR-7 pair ... but this is a new challenge!

 

Regards 

 

Alessandro