It is very easy to fit a leach amp in the DH200/220 chassis. I don't know how much better it would sound then a DH200.
My leach amp is in a new version of the dh-200 chassis. All I had to really do is make some metal brackets to adapt the 3-hole mounting to the 4 hole mounting that the leach amp boards use. The boards are only $25 for two from Dr. Leach. Of course, the sound quality probably can't even compare to the design that Mr. Pass has...
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Brian
My leach amp is in a new version of the dh-200 chassis. All I had to really do is make some metal brackets to adapt the 3-hole mounting to the 4 hole mounting that the leach amp boards use. The boards are only $25 for two from Dr. Leach. Of course, the sound quality probably can't even compare to the design that Mr. Pass has...
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Brian
Attachments
picture of the beautiful non-functional hafler channel:
more on my website...
http://brian.darg.net/dh200rebuild/
--
Brian
more on my website...
http://brian.darg.net/dh200rebuild/
--
Brian
Attachments
mlloyd1,
I was referring to them bridged only. Personally I didn't think they ran all that hot when run as stereo but they ran a lot warmer bridged. As for the sound...back then it was what I could afford and while they were not the best on the block they did an all right job compared to a lot else that I had access to (although bridged, as I recall, they sounded totally different and not very good). Other than my A-40's!
However, I am definitely interested in NP's ideas on turning these amps into smaller class A amps!
rt
I was referring to them bridged only. Personally I didn't think they ran all that hot when run as stereo but they ran a lot warmer bridged. As for the sound...back then it was what I could afford and while they were not the best on the block they did an all right job compared to a lot else that I had access to (although bridged, as I recall, they sounded totally different and not very good). Other than my A-40's!
However, I am definitely interested in NP's ideas on turning these amps into smaller class A amps!
rt
Need some advice and help here...my DH200 is giving some annoying crackling sound(left channel only) when cold. However after powering it up, for about 20mins, the crackling disappears. Though, there is still some very faint sporadic crackling when its warm.
I tried using a hairdryer to warm up the components after opening the cover. It worked. But it's still crackling when cold.
I disconnected the inputs and turned the volume to zero...didn't help. Looks like the amp likes to be warmed up...anyone knows why? Any hints would be very much appreciated.
I tried using a hairdryer to warm up the components after opening the cover. It worked. But it's still crackling when cold.
I disconnected the inputs and turned the volume to zero...didn't help. Looks like the amp likes to be warmed up...anyone knows why? Any hints would be very much appreciated.
There are many possibilities.
--Loose mechanical connections (the main power supply electrolytics use screw lugs, check those)
--Bad solder joint
--Impending component failure
--Dirty bias pots not making good contact
Comments about Haflers tending towards reliability problems have to be seen in context. Conservatively speaking, the Hafler folks sold approximately one googleplex of these amps. They were actually--statistically speaking--very, very reliable amps. They were able to take an absurd amount of punishment without complaint. It's not that you see so many that have problems...it's that you see so few. They live on happily in PA systems, subwoofer applications, and even as primary amps, doing their job day in and day out without complaint.
I've got a DH-500 (the pro version, whatever they called it) with an intermittant dropout in the right channel. I'd like to trace the problem and fix it directly, but every time I touch the thing the channel wakes up. Probably a cold solder joint. What I need to do is reflow every solder joint, but that's a nuisance and I never seem to get around to it. Oh well. I traded some bass gear I wasn't using for it, so it's not like it cost me much. I'll get there one of these days.
Grey
--Loose mechanical connections (the main power supply electrolytics use screw lugs, check those)
--Bad solder joint
--Impending component failure
--Dirty bias pots not making good contact
Comments about Haflers tending towards reliability problems have to be seen in context. Conservatively speaking, the Hafler folks sold approximately one googleplex of these amps. They were actually--statistically speaking--very, very reliable amps. They were able to take an absurd amount of punishment without complaint. It's not that you see so many that have problems...it's that you see so few. They live on happily in PA systems, subwoofer applications, and even as primary amps, doing their job day in and day out without complaint.
I've got a DH-500 (the pro version, whatever they called it) with an intermittant dropout in the right channel. I'd like to trace the problem and fix it directly, but every time I touch the thing the channel wakes up. Probably a cold solder joint. What I need to do is reflow every solder joint, but that's a nuisance and I never seem to get around to it. Oh well. I traded some bass gear I wasn't using for it, so it's not like it cost me much. I'll get there one of these days.
Grey
Incidentally, the classic mod for a 200 was to replace all the caps in the circuit with film caps. It got to be such a popular idea that they put it into production and called it the 220; otherwise, changes between the two models were minimal.
It doesn't hurt to add a couple of beefy electrolytics to the power supply. If memory serves, there was only one 10000 uF cap per rail. If you do this, watch out for the power switch giving up the ghost. That was the one fault these amps had; it just wasn't able to take the turn-on surge and would eventually freeze in the on position. (Later production models did upgrade the switch, but they still failed--just not as quickly.) I used to make good side money selling the amps, then offering to add an external box with some beastly caps and a P&B delay relay and resistor to take care of the surge.
A bit dark sounding and lacking detail by today's standards, but for the money a damned fine amplifier. Highly recommended for subs.
I've got a one-channel-dead 200 in the morgue. (Domestic transformer, hence single primary.) I'd like to locate another DOA and do a monoblock project. Got the beginnings of an idea; might make a good write-up. Probably ought to cruise the pawn shops and see what I can find.
Unless someone's using one for a doorstop and wants to get it out from underfoot...
Grey
It doesn't hurt to add a couple of beefy electrolytics to the power supply. If memory serves, there was only one 10000 uF cap per rail. If you do this, watch out for the power switch giving up the ghost. That was the one fault these amps had; it just wasn't able to take the turn-on surge and would eventually freeze in the on position. (Later production models did upgrade the switch, but they still failed--just not as quickly.) I used to make good side money selling the amps, then offering to add an external box with some beastly caps and a P&B delay relay and resistor to take care of the surge.
A bit dark sounding and lacking detail by today's standards, but for the money a damned fine amplifier. Highly recommended for subs.
I've got a one-channel-dead 200 in the morgue. (Domestic transformer, hence single primary.) I'd like to locate another DOA and do a monoblock project. Got the beginnings of an idea; might make a good write-up. Probably ought to cruise the pawn shops and see what I can find.
Unless someone's using one for a doorstop and wants to get it out from underfoot...
Grey
I guess likewise, it's not easy tracing dry joints. Will look out out for loose connections as a start. Thanks!
Yes, I do agree that the DH200 is a hardy piece of amp that will survive harsh punishments. Mine had been trouble free for 15 years until recently. It's crazy by today's standards. Who will produce an amp that can outlast the life of the company?
Vincent
Yes, I do agree that the DH200 is a hardy piece of amp that will survive harsh punishments. Mine had been trouble free for 15 years until recently. It's crazy by today's standards. Who will produce an amp that can outlast the life of the company?
Vincent
I didn't want to start a new thread, as there seem to be some knowledgeable people checking in on this one, and my question is about a DH-200 acting strangely. My situation is different though...
My DH-200 had a dead channel when I bought it. I replaced a fuse and now it seems to work fine once everything is hooked up, however, in the process of hooking it up I noticed some oddities.
1.) If the amp is on, speakers connected, but nothing is connected to the inputs, there is an audible white noise hiss. When the cables from the preamp are connected, hiss disappears.
2.) If the amp is on while the speakers are being connected, as soon as the + speaker wire touches the + terminal on the amp, there's a big thump and the woofer moves enough to make me nervous...
Are these typical problems indicative of common aging-related component failures? That's what I'm hoping...any advice appreciated.
My DH-200 had a dead channel when I bought it. I replaced a fuse and now it seems to work fine once everything is hooked up, however, in the process of hooking it up I noticed some oddities.
1.) If the amp is on, speakers connected, but nothing is connected to the inputs, there is an audible white noise hiss. When the cables from the preamp are connected, hiss disappears.
2.) If the amp is on while the speakers are being connected, as soon as the + speaker wire touches the + terminal on the amp, there's a big thump and the woofer moves enough to make me nervous...
Are these typical problems indicative of common aging-related component failures? That's what I'm hoping...any advice appreciated.
You've got more problems than a blown fuse.
You'll need to go over it with a fine-toothed comb to see what else is going on. There shouldn't be any significant DC offset at the output (the thump).
Nor should the amp make much noise. A little, yes, if your ear is right against the tweeter or if you're using horns. But enough to hear across the room...no.
Good luck.
Grey
You'll need to go over it with a fine-toothed comb to see what else is going on. There shouldn't be any significant DC offset at the output (the thump).
Nor should the amp make much noise. A little, yes, if your ear is right against the tweeter or if you're using horns. But enough to hear across the room...no.
Good luck.
Grey
I did according to your suggestions. Funny, but the 2.2 Ohms resistor is on the right channel only. It's OK but I found the problem to be due to one of the 100 Ohms resistor at the input side of the left channel. The end caps of the carbon film resistor are getting loose. Any suggestions on which kind of resistor I should upgrade to? Many thanks!
Happy 2003!
Happy 2003!
Vincent said:
If you haven't yet, I suggest you get The Audio Amateur's article on modifying a DH200. They change all resistors onto metal films, as well as caps and a bit more.
For just a resistor change, my suggestion is to go for metal films all over, using generic types for all parts except those on the feedback, where you should pick a Caddock or better.
Carlos
"heres another one for you why not throw out the hafler pcb and install the pass A40 pcb beef up the current source jfet "
If you leave out the current source jfet and cascode the Vas you will now have a Musical Concepts P3A.
Of course if you remove a couple of transistors from the Hafler boards, change the outputs to MJ15003/04, and put in the correct voltage transformer, you will now have a KRELL KSA-50
How about a conversion kit for turning tired DH200/220 into KSA-50s?
If you leave out the current source jfet and cascode the Vas you will now have a Musical Concepts P3A.
Of course if you remove a couple of transistors from the Hafler boards, change the outputs to MJ15003/04, and put in the correct voltage transformer, you will now have a KRELL KSA-50
How about a conversion kit for turning tired DH200/220 into KSA-50s?
hmmm hafler morphing into krell that is tempting too
it would take more effort thou
actually i beleive randolph vikan built a pass a40 with
2sj49-23k175 with success.
since these outputs are allready present in the hafler it would be an easy mod .
you would need to build up the pass pcb with higher Vce devices
I use 2n5401-2n5551 and use a supertex jfet for the current source. and of course and by all means reduce the bias(not anywhere near enough sink in the hafler chassis to run class a.
having assembled pass a40s and owning\repairing haflers
I can say it would be a vast improvment!
is it just me or do some other naim (oops i mean name) brand
amplifiers bear a striking resemblance to the pass a40
it would take more effort thou
actually i beleive randolph vikan built a pass a40 with
2sj49-23k175 with success.
since these outputs are allready present in the hafler it would be an easy mod .
you would need to build up the pass pcb with higher Vce devices
I use 2n5401-2n5551 and use a supertex jfet for the current source. and of course and by all means reduce the bias(not anywhere near enough sink in the hafler chassis to run class a.
having assembled pass a40s and owning\repairing haflers
I can say it would be a vast improvment!
is it just me or do some other naim (oops i mean name) brand
amplifiers bear a striking resemblance to the pass a40
Interesting thread, especially the notion of turning this chassis into a quasi-Aleph or quasi-Krell.
A year ago, I rebuilt my venerable DH-220. Salient changes:
a. Musical Concepts PA-3B driver boards
b. Dual-secondary toroidal power transformer from Plitron via Musical Concepts
c. Separate IXYS FRED rectifier bridges for L and R channels
d. 48000uF power supply filtration per channel
e. "Step-start" relay+resistor to limit PS charging inrush current
f. New input jax, output binding posts, audio & PS wiring
I took pix of the mod process, especially the mounting of the FRED bridges, transformer, and big electrolytics, with the idea of eventually turning it all into some form of step-by-step guide. If there's significant interest in this from the communty, I'll write this up & post after the Holidays.
Howzit sound? Overall, improved clarity in mids and highs, equal to or just a hair ahead of my Odyssey Stratos Extremes. But a couple steps behind the Odysseys on low-end punch & impact. Even with speakers having efficiencies in the mid-90s.
I expect it to soldier on for another 20 years as the dining room system's amp.
Karl
A year ago, I rebuilt my venerable DH-220. Salient changes:
a. Musical Concepts PA-3B driver boards
b. Dual-secondary toroidal power transformer from Plitron via Musical Concepts
c. Separate IXYS FRED rectifier bridges for L and R channels
d. 48000uF power supply filtration per channel
e. "Step-start" relay+resistor to limit PS charging inrush current
f. New input jax, output binding posts, audio & PS wiring
I took pix of the mod process, especially the mounting of the FRED bridges, transformer, and big electrolytics, with the idea of eventually turning it all into some form of step-by-step guide. If there's significant interest in this from the communty, I'll write this up & post after the Holidays.
Howzit sound? Overall, improved clarity in mids and highs, equal to or just a hair ahead of my Odyssey Stratos Extremes. But a couple steps behind the Odysseys on low-end punch & impact. Even with speakers having efficiencies in the mid-90s.
I expect it to soldier on for another 20 years as the dining room system's amp.
Karl
djk said:"heres another one for you why not throw out the hafler pcb and install the pass A40 pcb beef up the current source jfet "
If you leave out the current source jfet and cascode the Vas you will now have a Musical Concepts P3A.
The pA3A is the intellectual property of musical concepts so i would rather leave that one be.
but i do have experiance with the pass a40 and it would be a simple swap and give a second amp I could live with .
still waiting to see nelson pass circuit for hafler hack
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