How’s this part to use as a hold down clip for the above rectifier?
532-MAXCLIP07G
Some builders would be intersested in the transformers, mfg, part number, cost, VA rating, secondary voltages/ configurations
Unfortunately mine was still performing like a Dodge Dart, even with Hemi GTX money put into it
What mods were done?
532-MAXCLIP07G
Some builders would be intersested in the transformers, mfg, part number, cost, VA rating, secondary voltages/ configurations
Unfortunately mine was still performing like a Dodge Dart, even with Hemi GTX money put into it
What mods were done?
Last edited:
Hafler DH200 mono project
I figured that I would post a few more images of (DH200 based) amps.
I like my P230 mono amps SO MUCH, that I am going to cannibalize a few 200 chassis, that I built / rebuilt and will use them as a proof of concept with some new parts. *more on that later.
I post a picture of all 4 amps, (sadly, as proof, of current ownership and use) to support my comments, strong feelings and direct experience about the fundamental limits of using the stock boards. I have completely rebuilt many of the PC19 boards and used in a variety of chassis cores to eliminate variables that could otherwise influence my observations, when compared the the Musical Concepts PA4 board that I use to reference all work and as my ongoing reference (along with newer PA7 and OTL tube amps). These rebuilt stock boards are [disappointingly] veiled, lacking in transparency and dynamics ~ get in the way ~ of the musical experience... simply said. No negative bias, or overt supposition involved.
The 2 amps on the left are (completed, as shown in previous post) 220 based amps and the (2) 200 based amps on the right are completed projects that are the basis which serves to support my conclusions, as stated. I struggle to 'gut' them, they have served their purpose... sit unused and idle... sadly so. I can build them into something better...
The MM200 in the lower right (image 4) has everything that I could possibly try, the multiple (4) Wima were larger film bypasses, that would not fit any place but the fuse blocks, connected to ground at one end, but across the B+ and B- rails going to the board. There are 1mfd, .1s and .01s tucked against the PC19 card, intimate to the output stage... they give shape and snap to the musical image. Rest assured (I DID NOT ELIMINATE) power rail fuses, which are the only possible mounting point for the big Wimas and after the fuse blocks, closest and most intimate to the circuit...
All stock 200s have ~ PATHETIC power cords ~ so I wired a (fused) 14 gauge wire, the omit a current limiting source and any possible source of confusion, as all *stockish 200s always sounded so anemic to me. I also wanted to get all AC power cord runs out of the amps chassis, to see if there any influence on the sound, “infecting” the right channel… Undetermined result… but this FRANKEN’HAFLER with PC19 boards, is the best 200 series amp that I have ever built or heard… It drove the hell out of Maggies, was unflappable. Nothing like a stock model.
For note: I have (over 300) 5551 and 5401 transistors that I will eventually match up to 're-load' these boards... but it is so far down the list of priorities, list of actual interests... I have not completely written the original boards off, but am very close. I will for sure, redo transistors on some of the great many PC19 boards, but still way down the list of interests...
I am in the process of ordering my 4th set of Musical Concept PA7 boards [I really do like them] they represent a break through… I will use (2 sets) of remaining P230 6 output heat sinks, and connect them to the 200 series chassis’s and try the Mundorf MLytic HC caps, in place of the Nichicons shown in all other amps. Not sure if I will use the stock 625va transformers or (more likely try) the superlative TP202 400 va toroids used in the P230 monos. I kind of want to keep them identical - only changing (evaluating) the Mundorf caps, which I have been super curious about… The Mundorfs will most likely be the caps I use in the external power supply project later this year.
Image 4 is the only amp that I used most of the stock wire, it was in good shape, appear to be a factory build and due to the fact the I retained stock tranny and filter cap the wore lengths worked. Note the individual wire to the HEXFRED which was a different length and that there are 2 wires for each channel power feed to the fuse blocks. This has completely rebuilt driver boards... but still has an unacceptable 30mVDC on its outputs.
I will add Cardas RCAs and swap to Pomona 5 way binding posts, just like in the 'Farnken' 200 chassis, to make both chassis's ~ identical ~ for the mono amp model.
I figured that I would post a few more images of (DH200 based) amps.
I like my P230 mono amps SO MUCH, that I am going to cannibalize a few 200 chassis, that I built / rebuilt and will use them as a proof of concept with some new parts. *more on that later.
I post a picture of all 4 amps, (sadly, as proof, of current ownership and use) to support my comments, strong feelings and direct experience about the fundamental limits of using the stock boards. I have completely rebuilt many of the PC19 boards and used in a variety of chassis cores to eliminate variables that could otherwise influence my observations, when compared the the Musical Concepts PA4 board that I use to reference all work and as my ongoing reference (along with newer PA7 and OTL tube amps). These rebuilt stock boards are [disappointingly] veiled, lacking in transparency and dynamics ~ get in the way ~ of the musical experience... simply said. No negative bias, or overt supposition involved.
The 2 amps on the left are (completed, as shown in previous post) 220 based amps and the (2) 200 based amps on the right are completed projects that are the basis which serves to support my conclusions, as stated. I struggle to 'gut' them, they have served their purpose... sit unused and idle... sadly so. I can build them into something better...
The MM200 in the lower right (image 4) has everything that I could possibly try, the multiple (4) Wima were larger film bypasses, that would not fit any place but the fuse blocks, connected to ground at one end, but across the B+ and B- rails going to the board. There are 1mfd, .1s and .01s tucked against the PC19 card, intimate to the output stage... they give shape and snap to the musical image. Rest assured (I DID NOT ELIMINATE) power rail fuses, which are the only possible mounting point for the big Wimas and after the fuse blocks, closest and most intimate to the circuit...
All stock 200s have ~ PATHETIC power cords ~ so I wired a (fused) 14 gauge wire, the omit a current limiting source and any possible source of confusion, as all *stockish 200s always sounded so anemic to me. I also wanted to get all AC power cord runs out of the amps chassis, to see if there any influence on the sound, “infecting” the right channel… Undetermined result… but this FRANKEN’HAFLER with PC19 boards, is the best 200 series amp that I have ever built or heard… It drove the hell out of Maggies, was unflappable. Nothing like a stock model.
For note: I have (over 300) 5551 and 5401 transistors that I will eventually match up to 're-load' these boards... but it is so far down the list of priorities, list of actual interests... I have not completely written the original boards off, but am very close. I will for sure, redo transistors on some of the great many PC19 boards, but still way down the list of interests...
I am in the process of ordering my 4th set of Musical Concept PA7 boards [I really do like them] they represent a break through… I will use (2 sets) of remaining P230 6 output heat sinks, and connect them to the 200 series chassis’s and try the Mundorf MLytic HC caps, in place of the Nichicons shown in all other amps. Not sure if I will use the stock 625va transformers or (more likely try) the superlative TP202 400 va toroids used in the P230 monos. I kind of want to keep them identical - only changing (evaluating) the Mundorf caps, which I have been super curious about… The Mundorfs will most likely be the caps I use in the external power supply project later this year.
Image 4 is the only amp that I used most of the stock wire, it was in good shape, appear to be a factory build and due to the fact the I retained stock tranny and filter cap the wore lengths worked. Note the individual wire to the HEXFRED which was a different length and that there are 2 wires for each channel power feed to the fuse blocks. This has completely rebuilt driver boards... but still has an unacceptable 30mVDC on its outputs.
I will add Cardas RCAs and swap to Pomona 5 way binding posts, just like in the 'Farnken' 200 chassis, to make both chassis's ~ identical ~ for the mono amp model.
Attachments
"Some builders would be interested..."
Absolutely. We can only ask.
My sense is that if you're veering towards replacing the transformer then a dual secondary/bridge approach would be worth pursuing... if there's enough space.
For a DH-200 with its 25A bridge, doubling up the 22A-rated FBE22-06N1 in a dual secondary design would seem prudent. That rating disparity originally discouraged me from considering it. Just sayin'
Absolutely. We can only ask.
My sense is that if you're veering towards replacing the transformer then a dual secondary/bridge approach would be worth pursuing... if there's enough space.
For a DH-200 with its 25A bridge, doubling up the 22A-rated FBE22-06N1 in a dual secondary design would seem prudent. That rating disparity originally discouraged me from considering it. Just sayin'
[references to] Building Hot Rods...
I post all links in prior post, not sure exactly where they are in the thread (limited time at present, to search this out) you could search posts in my name, or scrub the threads (which I do often)
I cannot repeat / emphasize strongly enough... This is a FANTASTIC PART, struggle to imaging that it would not benefit any sort of project, whether it will easily fit into exact build, another question...
Tony, I do like the fuel lines analogy... LOS. We should also add large(r) intake manifolds, exhaust and even possibly braided brake line(s) to the collective... they all fit the intended example...
I post all links in prior post, not sure exactly where they are in the thread (limited time at present, to search this out) you could search posts in my name, or scrub the threads (which I do often)
I cannot repeat / emphasize strongly enough... This is a FANTASTIC PART, struggle to imaging that it would not benefit any sort of project, whether it will easily fit into exact build, another question...
Tony, I do like the fuel lines analogy... LOS. We should also add large(r) intake manifolds, exhaust and even possibly braided brake line(s) to the collective... they all fit the intended example...
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Rick, I had started to lay a foundation for things to come; a pair of Epcos B41550 22,000uf filter caps, new outputs from Profusion, adjusted gate resistors, replacement of nearly every small capacitor on the original boards, a proper snubber on the rectifier, a pair of Clarity Cap MR for input caps.
Being a car guy, I have spotted this syndrome from miles away in that arena, yet fell for it anyways!
I basically have replaced this Dodge Dart with a 90s Ferrari, at half the investment, and the hulk has been put out on the back 40.
Thank you for posting this additional information (and pics!)... I am about a week out from being able to start on my mods judging from the tracking info on my orders. I will follow up here when I have made some progress. Thanks again for all of your support!
Edit... I guess I spoke too soon. I dragged feet on placing the mouser order and now the 22,000uf filter caps are out of stock. Bummer. I guess this project is going to have to wait a bit longer.
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THATS IT Rick!
Thanks for finding the part... will be on my next order...
AWESOME!!!! TYTY!
Thanks for finding the part... will be on my next order...
AWESOME!!!! TYTY!
532-MAXCLIP07G --looks just like the one that Musical Concepts uses.
PS-100/220/500 (scroll down to the bottom... my picture illustration failed!)
Yes, thanks for that wonderful investigative work!
PS-100/220/500 (scroll down to the bottom... my picture illustration failed!)
Yes, thanks for that wonderful investigative work!
Building as mono amps
Please understand...
I am only interested in building as mono amps,
only using 1 heat sink, (2) leftover from
stock P230 stereo amp chassis.
1 toroid, 1 rectifier and 1 power module,
in a nice tidy uncramped chassis.
IS FAR BETTER THAN...
I .do urge you. to try your idea and
report back to everyone here
your actual result.
Please understand...
I am only interested in building as mono amps,
only using 1 heat sink, (2) leftover from
stock P230 stereo amp chassis.
1 toroid, 1 rectifier and 1 power module,
in a nice tidy uncramped chassis.
IS FAR BETTER THAN...
I .do urge you. to try your idea and
report back to everyone here
your actual result.
Examples of dual mono amps I've already built
Not trying to re-invent already well designed wheel(s),
I have done numerous dual mono amps.
with dual secondary toroids.
~ I am trying to *inspire* new ideas here ~
not really looking for any advice...
or direction... sorry to say...
The true MONO BLOCK is my goal,
shown picture 2 was the 'next step'
in my amp evolution.
I am 'converting' 2 additional 200 chassis
to try a few different ideal and 'newer parts'
in design stages. ordering parts.
*4 chassis, separate power supplies
with unrestricted working room
(an Pi filters) is next...
Sorry to say, this thread
has grown so stale...
Not trying to re-invent already well designed wheel(s),
I have done numerous dual mono amps.
with dual secondary toroids.
~ I am trying to *inspire* new ideas here ~
not really looking for any advice...
or direction... sorry to say...
The true MONO BLOCK is my goal,
shown picture 2 was the 'next step'
in my amp evolution.
I am 'converting' 2 additional 200 chassis
to try a few different ideal and 'newer parts'
in design stages. ordering parts.
*4 chassis, separate power supplies
with unrestricted working room
(an Pi filters) is next...
Sorry to say, this thread
has grown so stale...
Attachments
Please understand... you sound a bit paranoid. No one's out to get you. If you have something to share, fine. If not... that's fine too.
I built my DH-200 almost 40 years ago and I've been listening to music since then. I've only cracked it open now because it (and the preamp I built at the same time) is understandably sounding a bit noisy after all these years. Caps!
Pondering whether or not a 22A device is a sufficient replacement for a 25A one is patently reasonable. Since you've done that your rationale is of interest. So... ?
Employing dual secondaries rectification etc for separate voltage delivery isn't limited to providing one source per channel. For the preamp I'm looking at this dual secondary design one for positive and one for negative voltages (+24/-24VDC) -- but I might also "Vendetta" it too! I suspect that there might be a benefit to this approach for a power amp channel as well.
While I'm open to considering profound power supply changes to my DH-200 my chief objective is to get in and get out quickly -- signal cap replacement and, perhaps, the cascode upgrade and be done. For me, playing music is the ultimate objective, not tinkering.
Hope this helps.
I built my DH-200 almost 40 years ago and I've been listening to music since then. I've only cracked it open now because it (and the preamp I built at the same time) is understandably sounding a bit noisy after all these years. Caps!
Pondering whether or not a 22A device is a sufficient replacement for a 25A one is patently reasonable. Since you've done that your rationale is of interest. So... ?
Employing dual secondaries rectification etc for separate voltage delivery isn't limited to providing one source per channel. For the preamp I'm looking at this dual secondary design one for positive and one for negative voltages (+24/-24VDC) -- but I might also "Vendetta" it too! I suspect that there might be a benefit to this approach for a power amp channel as well.
While I'm open to considering profound power supply changes to my DH-200 my chief objective is to get in and get out quickly -- signal cap replacement and, perhaps, the cascode upgrade and be done. For me, playing music is the ultimate objective, not tinkering.
Hope this helps.
Thoroughly enjoyed
your addition to the automotive metaphor! Yeah I “changed the fuel lines” in one of my XL280s - low level detail most obvious improvement. I’ll get off my lazy ____ and search your posts for the links - thanks for your patience...A side note: some of these recently referenced builds move closer to a basic XL-280 as it’s front end uses higher voltage rails than the finals. That and except for a common transformer completely separate left & right channel secondary feeds, rectifiers, etc.
Tony
Hi All,
Please do not remove the thermal protection devices. Given half decent connections, they will not limit the performance of these amplifiers. The same part numbers are used in 500 watt + per channel amplifiers without any drop in performance.
There is never a good reason to delete or defeat a safety component. Not only that, but you can have a problem and not know about it. Now you're just rolling the dice - with someone else's equipment, house and life. Amps don't burn, but speakers do.
-Chris
Please do not remove the thermal protection devices. Given half decent connections, they will not limit the performance of these amplifiers. The same part numbers are used in 500 watt + per channel amplifiers without any drop in performance.
There is never a good reason to delete or defeat a safety component. Not only that, but you can have a problem and not know about it. Now you're just rolling the dice - with someone else's equipment, house and life. Amps don't burn, but speakers do.
-Chris
M200 mono amp layout
Still experimenting with the layout, with a goal of leaving room to work with additional parts... in the future, if I chose to. My initial goal, the first step... was to put the Cardas RCA inputs and retain the same Pomona 5 way binding posts like in the original #1 amp the one (a few posts earlier) the initial pictures has the Wimas in the P/S. Build amp 2 identical to mirror that layout.
I installed my first set of IEC plug receptacles, it was not as much of a pain as I thought it may be, it dulled the carbide bit pretty quickly. But, I got it straight and in the exact place that I had intended. I was going to install these IEC plugs on the P230m, but the captive cord, is pretty robust... the DH200 chassis 'needed' replacement of the tiny power cord. I was (less) afraid of "hacking up the chassis" with the router bit, on my first attempt at such... moving forward... all amps will have IEC plugs. I have some mondo 6 gauge power cords that I can finally try out on these amps...
I gotta say, that I do like the rear panel I/O connector placement on the the DH200 the best ~ of any Hafler brand amps ~ I will admit, I do like symmetry, keeping wiring the same in each channel. *I cannot stand the 500/600 layout, hate it...
I quit buying and sort of lost interest in the DH200 chassis (long ago) as the lip in the chassis pan dramatically impacts / limits the available working space... I had made a decision, early on to only use stock transformers, they fit better than toroids... however, the 45v/400va TP202 is slightly smaller in diameter, than the 45v/625 va 625 Avel Lindberg (for modeling likeness) shown in the image, I am using it to solidify some ideas...
For build cost, I am leaning toward using the stock transformers, both from XL280 (pulls) as it will permit more working room and more options for capacitors. I am thinking about the 80v / 22,000mf Mundorf MLytic HC, that is 75mm (the 80v 10,000 is 51mm, is the most sensible) Using the stock power transformers, saves budget helps to offset cost of my 4th set of PA7 driver boards.
If I do use the TP-202, it will be a closer build to the P230 mono amps, a portion to why I want to stay with the same value, but huge $$$ MHC 22K caps, matching the 80v / 22k Nichicons ...that have become really hard to get... like in the P230 which I really, really like, almost don't want to 'change the recipe'. But always want to try new things, to learn and grow...
[my head really hurts] weighting all the variables. For now, I wait... will talk with J. Hillig tomorrow, sort through some of this further. He too, is curious about the high current Mundorfs... a strong reason for my approaching this amp model in the first place. An even longer story...
**for record... a principle reason for these mono amps (single heat-sink design and build) is that it is ~ very difficult ~ to reasonably double up *what you see* into one chassis, or without "halving the power supply" Besides, I have the extra chassis(s) 'unused and sitting idle', to devote to such projects. This serves for answering many lingering questions, and to try a few different parts. Building the P230 mono gave me an "extra" set of 6 output heatsinks. Sooo, the DH200 is mono ~and~ will have 6 output devices... hard to explain, it is actually morphed from multiple amps.
***To minimize possible confusion, I have pictured the 80v / 15,000 Nichicons in this example, that would be very easy to use. They are the same size, I will use (evaluate them, in this role) while I make up my mind and waiting for the Mundorfs to arrive... replacing with the 80v/10K Mundorf HC that are the identical footprint, so this layout would work fine... And I am showing (modeling ideals) with 'older' musical Concepts PA4 boards, to approximate the actual working space in the amp...
These images will no doubt evolve, even more by the final build...
Still experimenting with the layout, with a goal of leaving room to work with additional parts... in the future, if I chose to. My initial goal, the first step... was to put the Cardas RCA inputs and retain the same Pomona 5 way binding posts like in the original #1 amp the one (a few posts earlier) the initial pictures has the Wimas in the P/S. Build amp 2 identical to mirror that layout.
I installed my first set of IEC plug receptacles, it was not as much of a pain as I thought it may be, it dulled the carbide bit pretty quickly. But, I got it straight and in the exact place that I had intended. I was going to install these IEC plugs on the P230m, but the captive cord, is pretty robust... the DH200 chassis 'needed' replacement of the tiny power cord. I was (less) afraid of "hacking up the chassis" with the router bit, on my first attempt at such... moving forward... all amps will have IEC plugs. I have some mondo 6 gauge power cords that I can finally try out on these amps...
I gotta say, that I do like the rear panel I/O connector placement on the the DH200 the best ~ of any Hafler brand amps ~ I will admit, I do like symmetry, keeping wiring the same in each channel. *I cannot stand the 500/600 layout, hate it...
I quit buying and sort of lost interest in the DH200 chassis (long ago) as the lip in the chassis pan dramatically impacts / limits the available working space... I had made a decision, early on to only use stock transformers, they fit better than toroids... however, the 45v/400va TP202 is slightly smaller in diameter, than the 45v/625 va 625 Avel Lindberg (for modeling likeness) shown in the image, I am using it to solidify some ideas...
For build cost, I am leaning toward using the stock transformers, both from XL280 (pulls) as it will permit more working room and more options for capacitors. I am thinking about the 80v / 22,000mf Mundorf MLytic HC, that is 75mm (the 80v 10,000 is 51mm, is the most sensible) Using the stock power transformers, saves budget helps to offset cost of my 4th set of PA7 driver boards.
If I do use the TP-202, it will be a closer build to the P230 mono amps, a portion to why I want to stay with the same value, but huge $$$ MHC 22K caps, matching the 80v / 22k Nichicons ...that have become really hard to get... like in the P230 which I really, really like, almost don't want to 'change the recipe'. But always want to try new things, to learn and grow...
[my head really hurts] weighting all the variables. For now, I wait... will talk with J. Hillig tomorrow, sort through some of this further. He too, is curious about the high current Mundorfs... a strong reason for my approaching this amp model in the first place. An even longer story...
**for record... a principle reason for these mono amps (single heat-sink design and build) is that it is ~ very difficult ~ to reasonably double up *what you see* into one chassis, or without "halving the power supply" Besides, I have the extra chassis(s) 'unused and sitting idle', to devote to such projects. This serves for answering many lingering questions, and to try a few different parts. Building the P230 mono gave me an "extra" set of 6 output heatsinks. Sooo, the DH200 is mono ~and~ will have 6 output devices... hard to explain, it is actually morphed from multiple amps.
***To minimize possible confusion, I have pictured the 80v / 15,000 Nichicons in this example, that would be very easy to use. They are the same size, I will use (evaluate them, in this role) while I make up my mind and waiting for the Mundorfs to arrive... replacing with the 80v/10K Mundorf HC that are the identical footprint, so this layout would work fine... And I am showing (modeling ideals) with 'older' musical Concepts PA4 boards, to approximate the actual working space in the amp...
These images will no doubt evolve, even more by the final build...
Attachments
It's not even about specs...
A more complete expression / description in prior post.
**Near the bottom.
Another option (I have not mentioned) is more related to amp placement
nearer to speakers, with longer interconnects shorter speaker lengths,
*don't even want to to try and explain or 'justify' my reasoning,
beyond the simple mention of it...
A more complete expression / description in prior post.
**Near the bottom.
Another option (I have not mentioned) is more related to amp placement
nearer to speakers, with longer interconnects shorter speaker lengths,
*don't even want to to try and explain or 'justify' my reasoning,
beyond the simple mention of it...
Hi Ozark HiFi Doctor,
Okay, cool. It's merely a practical thing. I can see that.
Comment on the amp by the speaker thing. From my point of view as an explanation.
The output signal to the speakers is the most robust signal in your system. The two most delicate signals exist between the cartridge and preamp, and between the preamp and the power amplifier. The signal levels to the power amplifier do include the same levels as the phono cartridge output (MM). We are talking in mV for the low detail sounds everyone tends to judge things on. So why in hell would you take that signal and run it 10 feet or more???
For your speaker runs, the highest resistance is the connections between the wire and amplifier or speaker terminals. The run length doesn't add anything much to that - and that is ignoring the impedance of the crossover elements in series with the drivers. Active crossover you say? There are still four more connections between the driver and speaker terminal jacks on the box. A passive crossover adds four more to that number. So you see, people are attacking the wrong problem as the problem doesn't exist compared to the actual connections of wire on the way to the actual driver. Also, food for thought. Slightly removed from the crossover frequency, the impedance of the crossover element is about the same as the driver. That's how a crossover works. Arguing about wire length is comparing a few ohms to 0.0<something> ohms for the actual wire if you're using thinner wire. You're orders of magnitude out whereas the added capacitance on the signal cables amounts to a far greater problem- as does noise pick up (not just hum).
Just saying here. It doesn't make any sense to place the amplifiers at the speaker end unless you're trying to save money on speaker wire and you have a four way or greater active crossover setup. Of course, even in that situation, the amps are in the wrong location completely!
-Chris
Okay, cool. It's merely a practical thing. I can see that.
Comment on the amp by the speaker thing. From my point of view as an explanation.
The output signal to the speakers is the most robust signal in your system. The two most delicate signals exist between the cartridge and preamp, and between the preamp and the power amplifier. The signal levels to the power amplifier do include the same levels as the phono cartridge output (MM). We are talking in mV for the low detail sounds everyone tends to judge things on. So why in hell would you take that signal and run it 10 feet or more???
For your speaker runs, the highest resistance is the connections between the wire and amplifier or speaker terminals. The run length doesn't add anything much to that - and that is ignoring the impedance of the crossover elements in series with the drivers. Active crossover you say? There are still four more connections between the driver and speaker terminal jacks on the box. A passive crossover adds four more to that number. So you see, people are attacking the wrong problem as the problem doesn't exist compared to the actual connections of wire on the way to the actual driver. Also, food for thought. Slightly removed from the crossover frequency, the impedance of the crossover element is about the same as the driver. That's how a crossover works. Arguing about wire length is comparing a few ohms to 0.0<something> ohms for the actual wire if you're using thinner wire. You're orders of magnitude out whereas the added capacitance on the signal cables amounts to a far greater problem- as does noise pick up (not just hum).
Just saying here. It doesn't make any sense to place the amplifiers at the speaker end unless you're trying to save money on speaker wire and you have a four way or greater active crossover setup. Of course, even in that situation, the amps are in the wrong location completely!
-Chris