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Thread: Upgrading old amps?

  1. #1
    Senior Member maxwedge's Avatar
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    Upgrading old amps?

    Is it worth it?

    I'm so attached to my my poor old Hafler P500's but I just picked up a QSC PL340 to run my 18's and the QSC is so much better sonically than the Hafler. Of course the QSC has a lot more power, but running them at lower levels the it still has a much nicer bass response than the P500.

    I've put some IXYS HyperFred bridge rectifier's in the P500's and maybe I should replace the power supply caps but that's all I could do that would be somewhat cheap. Driver board replacing gets expensive!

    I put the P500's at the bottom to anchor the rack down!
    Really got to get rid of that particle board!

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by maxwedge View Post
    Is it worth it?
    In my opinion, yes - but pay attention to the Class of the amps you are deploying, and what your application is. A/B are best, sonically, to me, particularly in the home, but we use others in SR due to their efficiency.

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    Senior Member maxwedge's Avatar
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    Quote Originally Posted by boputnam View Post
    In my opinion, yes - but pay attention to the Class of the amps you are deploying, and what your application is. A/B are best, sonically, to me, particularly in the home, but we use others in SR due to their efficiency.
    I'm thinking the same.
    I bought the QSC because I have a minor ambition to rent out my gear out and play soundman and that amp is really light compared to the Haflers. I know a few bands I could maybe tag with and lugging 50 lbs amps around can be a pain.

    Plan of attack will be beef up the power supply's 1st then maybe some driver boards but the only place I've seen offering driver boards for diy is Musical Concepts and they run 400-500 a pair for theses Haflers, but I hear they sound good though.

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    Quote Originally Posted by maxwedge View Post
    .
    Plan of attack will be beef up the power supply's 1st then maybe some driver boards but the only place I've seen offering driver boards for diy is Musical Concepts and they run 400-500 a pair for theses Haflers, but I hear they sound good though.
    The Musical Concepts upgrade parts are really intended for home audio, not Pro. I think it would be a waste of money. If you had a broken amp, John probably has a few older (PA-3) boards in a box somewhere that could get it working, but short of that.....

    Now, if you wanted to turn one of those Haflers into a great home audio piece, fully rebuilt with his parts, they sound amazing.

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    Senior Member maxwedge's Avatar
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    Quote Originally Posted by rusty jefferson View Post
    The Musical Concepts upgrade parts are really intended for home audio, not Pro. I think it would be a waste of money. If you had a broken amp, John probably has a few older (PA-3) boards in a box somewhere that could get it working, but short of that.....

    Now, if you wanted to turn one of those Haflers into a great home audio piece, fully rebuilt with his parts, they sound amazing.
    Their not broken at all and I routinely set the bias and dc offset. They still kick hard.
    I don't really think that I plan to move these out of the house much and I like to work with electronics, so I think I'll work on improving them.

    John (Musical Concepts) really has some nice looking parts for these amps and I'm really itching to try out some of his power supply boards for 4-pole caps. They look really slick!

    Thanks for the replys

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    The QSC amps are great, I have many!

    I have a Hafler DH200 for my home stereo, same basic amp as yours only less power. I believe the front end of the amp uses the same board, no I take that back I believe it's the same board as the DH220 power amp. You may want to think about replacing the electrolytic caps on the boards. I just did that to my DH200 a month ago and it made a huge improvement! There were four electrolytic caps on each board. I ordered them from Mouser Electronics, total parts and shipping were about $15. I had notice the left channel starting to sound thin, the main problem was the input coupling cap on that channel that was a 10 uf actually measured about 100pf.
    I just took a quick look the DH500 schematic and there are six electrolytic caps on the each board.

    Replacing those caps would be worth it first before spending big dollars on main supply caps.

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    Senior Member maxwedge's Avatar
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    Quote Originally Posted by Mike Caldwell View Post
    The QSC amps are great, I have many!

    I have a Hafler DH200 for my home stereo, same basic amp as yours only less power. I believe the front end of the amp uses the same board, no I take that back I believe it's the same board as the DH220 power amp. You may want to think about replacing the electrolytic caps on the boards. I just did that to my DH200 a month ago and it made a huge improvement! There were four electrolytic caps on each board. I ordered them from Mouser Electronics, total parts and shipping were about $15. I had notice the left channel starting to sound thin, the main problem was the input coupling cap on that channel that was a 10 uf actually measured about 100pf.
    I just too a quick look the DH500 and there are six electrolytic caps on the each board.

    Replacing those caps would be worth it first before spending big dollars on main supply caps.
    The later DH200's had the same board too, mine does. Yes, I have more Haflers LOL.

    Good idea replacing all the electrolytic's and I've considered it before.
    I think that's the plan because I just put a chunk down for a pair of Truextent Diaphragm's..

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    For $20 bucks or so it would well worth it. The electrolytic caps in a 30 year old give or take amps that run warm by design and maybe were not the best quality caps to start with, changing them out is big improvement for little money.

    Where do you run the bias at on you DH500 amps. I settled on 270ma on the DH200.

    Here the link to Hafler for the DH500 schematic.
    http://hafler.com/techsupport/pdf/DH-500_amp_man.pdf

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    Senior Member maxwedge's Avatar
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    I set to bias at 330ma but could and go little higher but I try and keep the fans running at slow speed. The bias is less on the 200's and 220's. 275ma bias is spec for the 220 and I guess it's the same for the 200 but it's funny that this spec isn't given in all of the manuals. I think I got the 330ma spec for mine from Musical Concepts.

    I was wrong about the DH200, it uses a different driver board.

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    The DH200 boards do not have the DC offset adjustment, the DH220/500 does. There maybe a few other tweaks going on as well.

    For what it worth got and built my DH200 as a kit in the early 80's right after they came out. For a while I used to run bullet tweeters in a tri-amp system.

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    Senior Member maxwedge's Avatar
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    Gonna order all the electrolytic caps for the driver boards and balance boards today for the P500s. Might as well do all the small electrolytics while I'm in there! Going to wait on the power supply caps until I decide to go hi-tech or not.

    Looks like I will have a project for nest weekend!

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    Mouser electronics will have what you need. Two of the five electrolytic caps on the driver board are non polar, the 470uf 6.3 volt feedback loop cap and the 1uf 25 volt input cap.

    Let us know how the project goes.

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    Senior Member maxwedge's Avatar
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    Stupid me!

    I ordered caps to do 4 of my older haflers but went off of my original manual that includes the schematic and parts list for the P500. Well it's incorrect! I should have taken it apart 1st and I know better, lol!

    I got the driver boards done for one P500 today but had to reorder caps for the control/input boards. None of the caps I replaced today were out of spec but it looked like one of the 100uf/100v has been leaking.

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    Senior Member maxwedge's Avatar
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    One done

    After 4 orders that cost me about $30 in shipping, I finally got everything I needed! I either ordered wrong, forgot something or didn't pay attention to temperature spec. Oh well......

    I got one of my P500's done today and didn't F it up. I actually said "wow" to myself so I guess I did ok. I think I'd need to do some more testing with speakers using passive crossovers and switch between the amps to tell if there really is an improvement. None of the capacitors I replaced were out of spec (I have a meter).

    Setting Bias and dc Off Set


    Next Picture shows the IXYS Rectifier
    (between the pws caps and relay)

  15. #15
    Senior Member maxwedge's Avatar
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    PWR Supply Capacitors

    Need new ones? I just got 3 quads of these for my Hafler 220's. Great deal on 100v 10kuf caps. I need to buy some new power supply's now, to run those amps in dual mono!
    http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT

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