(Vintage) Hafler XL-600 Musical Concepts Modifications - AVS Forum
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post #1 of 11 Old 12-29-2012, 05:54 PM - Thread Starter
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Good day to all

First of all, I would like to wish to all members a Happy, Prosperous, Peaceful and Healthy New Year.

Very recently, I acquired a Hafler XL-600 from ebay (it is still in its way to my home). This is the third XL-600 I am getting hands on. I had bought two others back in the early nineties. I modified/upgraded the first with the - then - PA-1 modification kit of Musical Concepts. Later, I was so stupid to sell it. However I kept the second, which I upgraded with the newer PA-3B kit, plus the replacement of its original transformer with a pair of TP-500 ones. Till today, I have not regret it.

I purchased one more XL-600, after having decided to drive my Infinity RS Kappa9 speakers ( a really good speaker but a difficult load) with two amplifiers in a bi-amp vertical mode (one stereo amplifier for each speaker). This should have been done in the past, of course, when I had the first (and sold) XL-600, but now it is too late for tears.

Therefore, at this time, I am going to have a modified/upgraded XL-600 and one more unmodified, as originally made. Intending to use both of them for the bi-amplification of the Infinities, I am in a dilemma which one to be used for the low frequencies and which for the middle and high ones. The upgraded and modified amplifier has some certain advantages over the non-modified one. It performs much better in the frequency range (it has an extended range at both ends of it) and it uses the dual toroidal transformers, which - theoretically - adds in the total power handling vs the non modified one.

Given these two main advantages, I am not sure if I have to use it for the middle and high frequencies, where the critical part of music exists, and have the non modified one for the low frequencies
or
use the non modified one for the middle and high frequnecies and let the modified to handle the more power demanding low frequencies.

There is of course one more option: Spend the money and modify the new amplifier. But I am not sure if this would be a wasting of money or not (we are living in hard times, as you understand), in case that such a modification adds very little or nothing to a bi-amplification, if I have to choose one or the other option of driving.

The minimum amount that I have to spend for a PA-4 modification is $250, which does not include the TP-500 twin transformers and the shipping expenses to Greece. Then, there are more PA-4 versions with cost rising gradually up to more than $2k, depending of course how far one wants to go.

I would appreciate your opinion on this matter.

Happy New Year.
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post #2 of 11 Old 12-30-2012, 04:17 AM
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Originally Posted by Panayotis Melas View Post

Good day to all

First of all, I would like to wish to all members a Happy, Prosperous, Peaceful and Healthy New Year.

Very recently, I acquired a Hafler XL-600 from ebay (it is still in its way to my home). This is the third XL-600 I am getting hands on. I had bought two others back in the early nineties. I modified/upgraded the first with the - then - PA-3 modification kit of Musical Concepts. Later, I was so stupid to sell it. However I kept the second, which I upgraded with the newer PA-3B kit, plus the replacement of its original transformer with a pair of TP-500 ones. Till today, I have not regret it.

I purchased one more XL-600, after having decided to drive my Infinity RS Kappa9 speakers ( a really good speaker but a difficult load) with two amplifiers in a bi-amp vertical mode (one stereo amplifier for each speaker). This should have been done in the past, of course, when I had the first (and sold) XL-600, but now it is too late for tears.

Therefore, at this time, I am going to have a modified/upgraded XL-600 and one more unmodified, as originally made. Intending to use both of them for the bi-amplification of the Infinities, I am in a dilemma which one to be used for the low frequencies and which for the middle and high ones. The upgraded and modified amplifier has some certain advantages over the non-modified one. It performs much better in the frequency range (it has an extended range at both ends of it) and it uses the dual toroidal transformers, which - theoretically - adds in the total power handling vs the non modified one.

Given these two main advantages, I am not sure if I have to use it for the middle and high frequencies, where the critical part of music exists, and have the non modified one for the low frequencies or use the non modified one for the middle and high frequencies and let the modified to handle the more power demanding low frequencies.

There is of course one more option: Spend the money and modify the new amplifier. But I am not sure if this would be a wasting of money or not (we are living in hard times, as you understand), in case that such a modification adds very little or nothing to a bi-amplification, if I have to choose one or the other option of driving.

The minimum amount that I have to spend for a PA-4 modification is $250, which does not include the TP-500 twin transformers and the shipping expenses to Greece. Then, there are more PA-4 versions with cost rising gradually up to more than $2k, depending of course how far one wants to go.

My biggest concern with used equipment is that it first and foremost, perform at last as well as it did when it was new. Amplifier components particularly electrolytic capacitors are likely to degrade over the years. Hafler provided a fairly complete set of technical specifications with the owner's manual which can be downloaded from here:

http://www.hafler.com/techsupport/pdf/XL-600_amp_man.pdf

Any well-equipment competent audio service facility should be able to perform these tests and advise you of any potentially audible degradation.

Secondly, my biggest concern about any modification would be that it actually improve the audible performance of the piece of gear.

I've reviewed the Musical Design modifications as described here:

http://www.musicaldesign.com/Haf_pwrmods.html

I find no reason, based on the sketchy information provided there, to believe that they will necessarily improve the sonic performance of the Hafler XL 600, partially because the amp itself seems to be a fine performer as originally shipped. For example, they make any number of claims, but the claims themselves are given in poetic terms not technical terms. They provide no improved measurements to back their claims up.
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post #3 of 11 Old 12-30-2012, 08:09 AM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

(1) My biggest concern with used equipment is that it first and foremost, perform at last as well as it did when it was new. Amplifier components particularly electrolytic capacitors are likely to degrade over the years. Hafler provided a fairly complete set of technical specifications with the owner's manual which can be downloaded from here:
http://www.hafler.com/techsupport/pdf/XL-600_amp_man.pdf
Any well-equipment competent audio service facility should be able to perform these tests and advise you of any potentially audible degradation.
(2) Secondly, my biggest concern about any modification would be that it actually improve the audible performance of the piece of gear.
I've reviewed the Musical Design modifications as described here:
http://www.musicaldesign.com/Haf_pwrmods.html
I find no reason, based on the sketchy information provided there, to believe that they will necessarily improve the sonic performance of the Hafler XL 600, partially because the amp itself seems to be a fine performer as originally shipped. For example, they make any number of claims, but the claims themselves are given in poetic terms not technical terms. They provide no improved measurements to back their claims up.

Thank you very much, Arnold, for your post.

(1) I fully agree with your comments. The information I got from the ebay seller is that the amplifier is lightly used in a home studio environment, its condition is very good (with some light scratches) and that it performs very well. This, of course, needs to be proved in action. But let's make the assumption that it is basically true. After all, as you state, I can find a reliable audio lab, where I can perform the tests described in the manual (thanks for the PDF file, I already have it). If the tests are OK, I am set to use it. If not, then the case becomes a little complicated and perhaps the modification - which incorporates new and fresh parts, including capacitors - may be the only solution.

You are basically right about the capacitors and their degradation during time. Am I wrong or not, that this is particularly true if these (the capacitors) remain inoperative for a very long time? I've learned that, if the device is in use, the capacitors last much longer. Is this correct or not?

(2) My memory does not serve me well with the first PA-1 modification, so I can't remember today if there was a really significant sound improvement, compared with the original XL-600. However, my expererience with especially the PA-3B modification (including the replacement of the original transformer with the TP-500 pair) is very positive, as compared with the original amplifier sound. Perhaps, the credit goes more to the transformers and less to the modification kit, but it exists.

You wrote that you have reviewed the Musical Concepts modifications.
Any link?

Thank you so much. Happy New Year.
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post #4 of 11 Old 12-30-2012, 09:05 AM - Thread Starter
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In order to add some juice to my previous post, here is a Musical Concepts modified XL-600 user's opinion and report in Audiokarma.com, back in November, 2007:

http://www.audiokarma.org/forums/showthread.php?t=135984&page=2

The guy there says that after the modification, he had his XL-600 tested in a independent lab in L.A. and it sounded "very lliquid" " very clear", "midrange was very pronounced (a perfect match to his speakers)", "very natural". "Like a high powered tube amp". The link gives more details, both, technical and observed.

Well, I am not new in this hobby and I know that many of us want to have their equipment recognised as "the Best", even if they know that this is not true. Therefore, many of us (perhaps even myself, occasionally) would like to feel that our choices are correct and valid. However, an independent lab can always be a more trustworthy source than ourselves.

My wishes again for the coming New Year.
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post #5 of 11 Old 12-30-2012, 11:16 AM
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Installing TRT Dynamicaps as the input coupling caps on an amplifier can dramatically improve the sound quality. You might want to try that.

I have done this on a couple of amplifiers and the result was really amazing.

I also put them into the output coupling of an old Audio Research LS2B preamp, and that made a big difference. Audio Research uses these caps for the output coupling of their LS-27 and Reference preamps now. I assume they also use them on their power amplifiers.

You can get them from parts connexion. Expensive, but excellent.
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post #6 of 11 Old 12-30-2012, 11:23 AM
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^How much time passed between your "before" and your "after" listening tests?

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post #7 of 11 Old 12-30-2012, 11:26 AM
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Not very long. The difference was quite audible.

Audio Research would not be spending the money on these caps if they did not make a big difference; they are quite expensive.
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post #8 of 11 Old 12-30-2012, 11:31 AM
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Originally Posted by commsysman View Post

Not very long. The difference was quite audible.
Audio Research would not be spending the money on these caps if they did not make a big difference; they are quite expensive.

I think you meant to say "Audio Research would not be spending the money on these caps if they weren't able to market their product as 'high-end' and then charge exorbitantly for it."

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post #9 of 11 Old 12-30-2012, 01:33 PM
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Originally Posted by Panayotis Melas View Post

In order to add some juice to my previous post, here is a Musical Concepts modified XL-600 user's opinion and report in Audiokarma.com, back in November, 2007:

http://www.audiokarma.org/forums/showthread.php?t=135984&page=2

The guy there says that after the modification, he had his XL-600 tested in a independent lab in L.A. and it sounded "very lliquid" " very clear", "midrange was very pronounced (a perfect match to his speakers)", "very natural". "Like a high powered tube amp". The link gives more details, both, technical and observed.

Well, I am not new in this hobby and I know that many of us want to have their equipment recognised as "the Best", even if they know that this is not true. Therefore, many of us (perhaps even myself, occasionally) would like to feel that our choices are correct and valid. However, an independent lab can always be a more trustworthy source than ourselves.

To me the key to understanding (or not understanding) the above thread is contained in post 17 linked by http://www.audiokarma.org/forums/showpost.php?p=1482957&postcount=17

It contains some interesting performance measurement that were taken after a large number of modifications. Here's the problem - they are meaningless because there are no comparable measurements from "before mods".

Here's you challenge - find someone who is gutsy enough to provide relevant measurements from before and after the modifications. Without both sets of numbers, you have no idea whether the mods help or hurt.
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post #10 of 11 Old 12-30-2012, 01:39 PM
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Originally Posted by commsysman View Post

Not very long. The difference was quite audible.

I think that congratulating yourself like this does not say a lot. You like yourself, and think you are some kind of a technical genius. So does my friend's 9 year old son!

Where are the measurements or unbiased listening tests showing:

(1) We need to see measurements showing that the original parts were good, and had not become defective rendering their replacement just an example of some very unremarkable equipment maintenance?

I have it on good authority that replacing flat tires makes cars handle and ride better. If all you did is replace some obviously defective parts how extraordinary can your story be?

(2) We need some measurements showing that there was any kind of non-imaginary change in performance.

Absent both, it is just another bedtime story...
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post #11 of 11 Old 12-30-2012, 02:52 PM - Thread Starter
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Originally Posted by arnyk View Post

To me the key to understanding (or not understanding) the above thread is contained in post 17 linked by http://www.audiokarma.org/forums/showpost.php?p=1482957&postcount=17
It contains some interesting performance measurement that were taken after a large number of modifications. Here's the problem - they are meaningless because there are no comparable measurements from "before mods".
Here's you challenge - find someone who is gutsy enough to provide relevant measurements from before and after the modifications. Without both sets of numbers, you have no idea whether the mods help or hurt.

Thanks again, Arny, for your comments. I believe that in my case, this can easily be done (at least easier than some other case, with only one amplifier on hands). As soon as I receive the recently acquired XL-600, I will be able to grab both amps and take them to an independent lab (I know one here), where we can perform various tests and check-outs, enough to find out if there is a difference between the modified and the unmodified one, although the modification is certainly older than the one available now at MC.

However, there is also an interesting point in this story. It is called "money", or - I should say - "value per dollar". To my opinion, this factor should always be present at choices. And it seems NOT to exist in the MC modifications. Here is how another guy, who spent his hardly earned dollars on this, expresses his doupts. Again from Audiokarma.com:

http://www.audiokarma.org/forums/showthread.php?p=5958538#post5958538

Reading this post carefully, I believe he is basically right. However, as I said before, many of us think that our choices are always correct and if someone says that we are wrong, we don't want to admit it, even if it is obvious and proven. Anyway, it is not correct for me to open a discussion here about matters discussed in another forum. It would be moral and correct that I participate to that discussion - which I intend to do anyway.

Have a good day
(My wishes for the coming new year are always valid).
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