somewhat related ...
but closer to borbely's servo 50, especially with the JFET front-end.
i think borbely does the compensation a little different and his designs don't include the Hafler variable cap for optimizing the null.
but closer to borbely's servo 50, especially with the JFET front-end.
i think borbely does the compensation a little different and his designs don't include the Hafler variable cap for optimizing the null.
an easy way to see is to modify one side of your XL600 and then you can take one of two paths:
choice 1: do the Hafler distortion null test on each half and see what happens. pick the approach that results in the "best" null. i personally suspect/expect it will be the stock unit.
or choice 2: just listen to each side and pick the side you like best. easy peasy
good luck!
choice 1: do the Hafler distortion null test on each half and see what happens. pick the approach that results in the "best" null. i personally suspect/expect it will be the stock unit.
or choice 2: just listen to each side and pick the side you like best. easy peasy
good luck!
my last point:
i think the Hafler XL designs have great bones and don't see a lot of value in gutting them for completely new circuitry; the XL series with the JFET front end is pretty good.
if you just HAVE to mess with it, look instead at the Bob Cordell thread on this site somewhere for improvements he made to older (i.e. pre-XL series) Hafler amps and see what you can snarf up from that.
just a warning that somewhere on this site is some comments by someone who had a very nice XL-280, got the urge and modified it, then after evaluation, thought the unit was made worse by the changes, but had thrown out his old parts (!!) so couldn't go back to stock.
take that as a word to the wise ....
i think the Hafler XL designs have great bones and don't see a lot of value in gutting them for completely new circuitry; the XL series with the JFET front end is pretty good.
if you just HAVE to mess with it, look instead at the Bob Cordell thread on this site somewhere for improvements he made to older (i.e. pre-XL series) Hafler amps and see what you can snarf up from that.
just a warning that somewhere on this site is some comments by someone who had a very nice XL-280, got the urge and modified it, then after evaluation, thought the unit was made worse by the changes, but had thrown out his old parts (!!) so couldn't go back to stock.
take that as a word to the wise ....
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XL600 responds very well to any TLC (needs it)
Quite frankly, I was disappointed after purchase of my XL-600, in stock form. I have many Hafler amps, all 11 are modified, I currently own 3 DH500s, in various builds, doing direct comparisons to various circuit implementations, working to establish a clear hierarchy of changes and benefits of each.
I can speak directly to this... I have extensive experience with stock and modified XL-600/XL280s. The biggest "problems" is that there are no DC off-set adjustments on the stock PC40 driver boards... and the front end FETs are not available, a very big deal. I would check the DC offset before connecting to .any. speakers, that you care about. To me, the stock PC40 are 'useless', bordering dangerous.
The single (all be it) fairly big power (~600 va) transformer, like the DH500 is it's Achilles heal, has proven to be a very big limitation, image 2. They are *not big enough*, for such big amps, constrict the sound. The next is WIMPY / very small gauge stock wiring, in-line fuses and protection relay adds to that (a whole other topic and thread) For note: the 4 P/S filter caps, make for easy dual power transformers and dual bridge rectifiers... The aluminum ground buss (image 2), leaves little to be desired, need to be changed.
The Musical Concepts PAxxx driver boards, pretty much transform the amp, a "bigger" / dual P/S renders the benefits further. I have been on the fence about selling my Magnepan MG3.5Rs ~ until hearing a reworked XL600 power them... never heard my Maggies sound like this in prior 10 years of owning them.
I always wanted to put Cardas hardware on my amp, but hierarchically, the budget, was better served with (went towards) dual HEX-FREDS, toroids, the list goes on. In the 3 / 4th iteration... this was done while the entire chassis pan was bare... Still trying to reason my wiring in image 3...
Lastly, testing both 500/600 chassis with these massive CLC supplies [blows my mind] the amp(s) keep responding to every single 'improvement' that I have made. After testing, I am "converting" these amps module back to stockish, inside of the box builds.
I cannot say enough great things about the Musical Concepts PAxxx driver boards. That said I will eventually try one of Bob Cordells amp design... but for now (for that matter, the past 40 years) MC offerings are a known quantity. I have compared them to "big name" SS and vacuum tube designs, they are truly remarkable. *Rowland, Levinson and Spectral - (TC) ARC, (OTL) Futterman and Atma-Sphere = all lofty comparisons.
**I am not suggesting any / or all of these $$$ changes are of interest or practical... I simply relating direct experiences, while am in a test phase, in building "my own" amps from scratch, using the "Hafler power modules" / heatsink and out puts, to test power supply implementations.
Quite frankly, I was disappointed after purchase of my XL-600, in stock form. I have many Hafler amps, all 11 are modified, I currently own 3 DH500s, in various builds, doing direct comparisons to various circuit implementations, working to establish a clear hierarchy of changes and benefits of each.
I can speak directly to this... I have extensive experience with stock and modified XL-600/XL280s. The biggest "problems" is that there are no DC off-set adjustments on the stock PC40 driver boards... and the front end FETs are not available, a very big deal. I would check the DC offset before connecting to .any. speakers, that you care about. To me, the stock PC40 are 'useless', bordering dangerous.
The single (all be it) fairly big power (~600 va) transformer, like the DH500 is it's Achilles heal, has proven to be a very big limitation, image 2. They are *not big enough*, for such big amps, constrict the sound. The next is WIMPY / very small gauge stock wiring, in-line fuses and protection relay adds to that (a whole other topic and thread) For note: the 4 P/S filter caps, make for easy dual power transformers and dual bridge rectifiers... The aluminum ground buss (image 2), leaves little to be desired, need to be changed.
The Musical Concepts PAxxx driver boards, pretty much transform the amp, a "bigger" / dual P/S renders the benefits further. I have been on the fence about selling my Magnepan MG3.5Rs ~ until hearing a reworked XL600 power them... never heard my Maggies sound like this in prior 10 years of owning them.
I always wanted to put Cardas hardware on my amp, but hierarchically, the budget, was better served with (went towards) dual HEX-FREDS, toroids, the list goes on. In the 3 / 4th iteration... this was done while the entire chassis pan was bare... Still trying to reason my wiring in image 3...
Lastly, testing both 500/600 chassis with these massive CLC supplies [blows my mind] the amp(s) keep responding to every single 'improvement' that I have made. After testing, I am "converting" these amps module back to stockish, inside of the box builds.
I cannot say enough great things about the Musical Concepts PAxxx driver boards. That said I will eventually try one of Bob Cordells amp design... but for now (for that matter, the past 40 years) MC offerings are a known quantity. I have compared them to "big name" SS and vacuum tube designs, they are truly remarkable. *Rowland, Levinson and Spectral - (TC) ARC, (OTL) Futterman and Atma-Sphere = all lofty comparisons.
**I am not suggesting any / or all of these $$$ changes are of interest or practical... I simply relating direct experiences, while am in a test phase, in building "my own" amps from scratch, using the "Hafler power modules" / heatsink and out puts, to test power supply implementations.
Attachments
options for the XL600
Personally, I would consider eliminating the stock boards, using such ~abysmal parts~
built to a price point, to pass spec., sounds soft and wooly, unrefined.
It is a part of why many discount those *old Hafler amps*
In terms of hierarchy... most meaningful improvement for the dollar.
(#1) pre-built MC PA6 driver cards (no muss - no fuss) only 300.00
(#2) 2 toroids with HEX-FRED rectifiers ~300.00. Depending on speakers,
may 'be required', it was in my case, with Maggies in mind.
(#3) cleaning up the wiring, limiting proximity of AC to signal, etc.
*I could ..never.. really discern valid differences with the null circuit,
*great on paper thing*, questionable, in the real world... marketing,
is s strange thing, not always based in practical applications.
**I could ..readily hear the differences.., with improved 'proper' PS
implementation even on my Spica TC60s, ...with a 6 in woofer...
I just had to be careful driving them... watching the peaks...
Personally, I would consider eliminating the stock boards, using such ~abysmal parts~
built to a price point, to pass spec., sounds soft and wooly, unrefined.
It is a part of why many discount those *old Hafler amps*
In terms of hierarchy... most meaningful improvement for the dollar.
(#1) pre-built MC PA6 driver cards (no muss - no fuss) only 300.00
(#2) 2 toroids with HEX-FRED rectifiers ~300.00. Depending on speakers,
may 'be required', it was in my case, with Maggies in mind.
(#3) cleaning up the wiring, limiting proximity of AC to signal, etc.
*I could ..never.. really discern valid differences with the null circuit,
*great on paper thing*, questionable, in the real world... marketing,
is s strange thing, not always based in practical applications.
**I could ..readily hear the differences.., with improved 'proper' PS
implementation even on my Spica TC60s, ...with a 6 in woofer...
I just had to be careful driving them... watching the peaks...
What do you make of the Hafler pro 5000 ? Is the Pro 5000 very close to a XL-600 ?
interesting opinions.
any of you with halfer XL-280 or XL-600 driver boards laying around, I'd be glad to take those "abysmal" 2SK163 and 2SJ44 JFETs off your hands ...