rather than stamped. Sorry to hear about your 
experience, but thank you for the warning.keep it simple
OK, time to simplify things for a newbie, and non electrical engineer type like me.
I own 2 Hafler DH 220's and have on that's not in use to modify, then I will swap out and do the other.
I need to know the essentials, I have tried to make notes as I read the thread, but its way to confusing for someone who is not an electronics tech.
Lucky for me my brother is an electrical engineer and says that he sometimes neds to keep his tech's busy, so if I have any projects he will have them done for me and all I have to pay for is parts.
SO I need to know which mods to make to get the most bang for the buck.
So far I have the following parts:
2 new power suply caps 27,000 mf nippon
2 new pairs of speaker binding posts ( gold plated vampire) mostly because my 12 AWG speaker wires are too big for the cross drill holes in the original terminals
2 new gold plated RCA jacks.
EIC socket and plug, 3 conductor shielded mains cable & 3 prong plug .
I have printed the schematics posted by Fab, but frankly I don't know if I need to get any more parts to complete this job.
I certainly would like to get rid of that thump when I turn on the amp, so I think the thermistor across the AC adresses this, but I don't really know ? Can I assume that a competent electronics tech will be able to acomplish this or should I give him detailed instructions and a schematic ?
I Understand in principle about the " star Ground", this makes sense to me for eliminating hum, but again do I need to give detailed instructions to the tech? If so What do I tell him? What about the extra ground in my new 3 conductor mains cable? is it superflous ? I assume that the shield drain wire should be connected to this " earth ground" at the " wall " plug end only. Is this correct ?
What about the other capicitors on the PC board ? should I have them checked ? Replaced? THey are 20 years old.
Then when I start talking to my brother about fred diodes for the power supply he tells me " they are only for the anal" . Personally I have no idea what they are or what they do, so I just have ot trust someone's opinion here.
OK, time to simplify things for a newbie, and non electrical engineer type like me.
I own 2 Hafler DH 220's and have on that's not in use to modify, then I will swap out and do the other.
I need to know the essentials, I have tried to make notes as I read the thread, but its way to confusing for someone who is not an electronics tech.
Lucky for me my brother is an electrical engineer and says that he sometimes neds to keep his tech's busy, so if I have any projects he will have them done for me and all I have to pay for is parts.
SO I need to know which mods to make to get the most bang for the buck.
So far I have the following parts:
2 new power suply caps 27,000 mf nippon
2 new pairs of speaker binding posts ( gold plated vampire) mostly because my 12 AWG speaker wires are too big for the cross drill holes in the original terminals
2 new gold plated RCA jacks.
EIC socket and plug, 3 conductor shielded mains cable & 3 prong plug .
I have printed the schematics posted by Fab, but frankly I don't know if I need to get any more parts to complete this job.
I certainly would like to get rid of that thump when I turn on the amp, so I think the thermistor across the AC adresses this, but I don't really know ? Can I assume that a competent electronics tech will be able to acomplish this or should I give him detailed instructions and a schematic ?
I Understand in principle about the " star Ground", this makes sense to me for eliminating hum, but again do I need to give detailed instructions to the tech? If so What do I tell him? What about the extra ground in my new 3 conductor mains cable? is it superflous ? I assume that the shield drain wire should be connected to this " earth ground" at the " wall " plug end only. Is this correct ?
What about the other capicitors on the PC board ? should I have them checked ? Replaced? THey are 20 years old.
Then when I start talking to my brother about fred diodes for the power supply he tells me " they are only for the anal" . Personally I have no idea what they are or what they do, so I just have ot trust someone's opinion here.
DH-220 thump at turn-on
Hi Tommy7
Do you actually have 10000 uF caps or 27000 uF installed?
Higher caps value may be sometimes harder for power-up on the amp...
If you have read some specific posts of mine, you will notice that the best noticeable change on the sound improvment on my side was the voltage regulators of the driver board. Of course, the increase of the main power supply caps to a higher value gives more bass control.
If you have 2 DH amps and have separate connection for bass and mid/hi on your actual speaker, I suggest that you "bi-amp" your system and you could be very happy of the result.
I think for other stuff on mods, this can be subjective and you may need to set your own mind based on comments on this forum unless you have very specific questions.
Regarding the instructions to the tech, maybe just ask the tech and he should give you his/her requirements!
Good luck
Hi Tommy7
Do you actually have 10000 uF caps or 27000 uF installed?
Higher caps value may be sometimes harder for power-up on the amp...
If you have read some specific posts of mine, you will notice that the best noticeable change on the sound improvment on my side was the voltage regulators of the driver board. Of course, the increase of the main power supply caps to a higher value gives more bass control.
If you have 2 DH amps and have separate connection for bass and mid/hi on your actual speaker, I suggest that you "bi-amp" your system and you could be very happy of the result.
I think for other stuff on mods, this can be subjective and you may need to set your own mind based on comments on this forum unless you have very specific questions.
Regarding the instructions to the tech, maybe just ask the tech and he should give you his/her requirements!
Good luck
New driver circuit for DH-2xx amp
Hi
I was very curious on another thread about a new Amplifier Guru amp design which uses an original topology. In fact this amp has 3 threads on this forum!
See this link for the disclosed schematics topology:
http://www.diyaudio.com/forums/showthread.php?postid=736240#post736240
I have decided to adapt this principle to the DH-2XX amp keeping the existing Lateral Mosfets instead of using vertical mosfet as Greg does in its design. Of course, added to the fact that the complete Greg new design is not disclosed I had to adapt it to the Lateral mosfet characteristics. I have also included the Low Memory input stage I have already disclosed in earlier posts. So far, I have a prototype built but I need to improve some characteristics like stability for cap loading and distorsion before first trying a sound check with music.
Here is a picture of the prototype installed for one channel in a DH-200 AMP:
It includes tweaking components temporarily installed for quick testing.
I may request this forum help trying to finalize the improvement althoug Greg Ball may not appreciate this quest...
I could continue to inform you on my progress or I could start a brand new thread.
Hi
I was very curious on another thread about a new Amplifier Guru amp design which uses an original topology. In fact this amp has 3 threads on this forum!
See this link for the disclosed schematics topology:
http://www.diyaudio.com/forums/showthread.php?postid=736240#post736240
I have decided to adapt this principle to the DH-2XX amp keeping the existing Lateral Mosfets instead of using vertical mosfet as Greg does in its design. Of course, added to the fact that the complete Greg new design is not disclosed I had to adapt it to the Lateral mosfet characteristics. I have also included the Low Memory input stage I have already disclosed in earlier posts. So far, I have a prototype built but I need to improve some characteristics like stability for cap loading and distorsion before first trying a sound check with music.
Here is a picture of the prototype installed for one channel in a DH-200 AMP:
It includes tweaking components temporarily installed for quick testing.
I may request this forum help trying to finalize the improvement althoug Greg Ball may not appreciate this quest...
I could continue to inform you on my progress or I could start a brand new thread.
Attachments
thanks
Thanks, Fab
thats exactly what I am loooking for somthing simple, with biggest bank for the buck application.
Right now both amps have the original 10,000 mf caps as far as I know ( i've only taken the cover off one, and I got them both "pre-owned" )
Voltage regulators on the driver board, I sort of know what that is, but is that a simple circuit across the input voltage, or do I need to have a seperate boadr built and installed ?
Also, my speakers are not bi-ampable now, but I am building a new set of Mini- Utopia clones, from some Focal drivers I got before they stopped selling to the public. They are from the top of the line Audiom series of a few years ago. I will be making them bi- ampable by keeping the x- over boards totally seperate and having a set of Cardas terminals for each tweet and mid bass.
My plan is also to have a local counter-top manufacturer make me a pair of MTM ported cabinets out of solid granite. ( They think I am completely off my rocker, but I just about have them talked into this project)
I do want to tighten up the mid bass of this amp ( although I don't know how it will sound with the new speakers ) it's a bit "loose" with my current Cobalt 807 clones . Although to be fair I haven't had time to completely tweak the speakers yet. They definately tightened up when I plugged the port tubes with convoluted speaker foam.
Sorry, I know too much speaker talk for an amplifier forum.So as soon s I am allowed, Fab, I would like to e-mail you directly for more info.
I would like to ask, though does anyone think that commercially available driver boards or kits from a place like Musical Concepts or Borbely are worth the money ? I have looked at them, but it would be nice for someone like me who has no electronics background to put something like that in my amp than to start building my own if the sonic bennefit is worth it.
Thanks, Fab
thats exactly what I am loooking for somthing simple, with biggest bank for the buck application.
Right now both amps have the original 10,000 mf caps as far as I know ( i've only taken the cover off one, and I got them both "pre-owned" )
Voltage regulators on the driver board, I sort of know what that is, but is that a simple circuit across the input voltage, or do I need to have a seperate boadr built and installed ?
Also, my speakers are not bi-ampable now, but I am building a new set of Mini- Utopia clones, from some Focal drivers I got before they stopped selling to the public. They are from the top of the line Audiom series of a few years ago. I will be making them bi- ampable by keeping the x- over boards totally seperate and having a set of Cardas terminals for each tweet and mid bass.
My plan is also to have a local counter-top manufacturer make me a pair of MTM ported cabinets out of solid granite. ( They think I am completely off my rocker, but I just about have them talked into this project)
I do want to tighten up the mid bass of this amp ( although I don't know how it will sound with the new speakers ) it's a bit "loose" with my current Cobalt 807 clones . Although to be fair I haven't had time to completely tweak the speakers yet. They definately tightened up when I plugged the port tubes with convoluted speaker foam.
Sorry, I know too much speaker talk for an amplifier forum.So as soon s I am allowed, Fab, I would like to e-mail you directly for more info.
I would like to ask, though does anyone think that commercially available driver boards or kits from a place like Musical Concepts or Borbely are worth the money ? I have looked at them, but it would be nice for someone like me who has no electronics background to put something like that in my amp than to start building my own if the sonic bennefit is worth it.
thumps
Dick:
I'll have to investigate this a bit more, I can't tell you right now if the speaker cones move . No I have not checked DC offset.
I also just realized that the thump could also be coming form powering on the pre-amp? I never really thought about it too much, just assumed it was coming from the power amp due to its age/ degredation of some component. As I mentioned to Fab, both my amps have the original ps caps and I plan to replace them 1 set at a time. Honestly I have never connected the amp which is slated for the workbench to anything so I don't know if it thumps or not, but I am going to have a tech check it all out first.
Thanks for your comment I really need a lot of help here.
Dick:
I'll have to investigate this a bit more, I can't tell you right now if the speaker cones move . No I have not checked DC offset.
I also just realized that the thump could also be coming form powering on the pre-amp? I never really thought about it too much, just assumed it was coming from the power amp due to its age/ degredation of some component. As I mentioned to Fab, both my amps have the original ps caps and I plan to replace them 1 set at a time. Honestly I have never connected the amp which is slated for the workbench to anything so I don't know if it thumps or not, but I am going to have a tech check it all out first.
Thanks for your comment I really need a lot of help here.
There are not too many mods one can make to a DH-220 that give you a quick bang for the buck. The amp's circuit is quite well done. What version of PCBs do you have? Are they PC-19-C?
The only mods I would recommend are to:
1. Replace all the electrolytic caps with similar value devices.
2. Use a quality pair of filter caps in the PS, such as 22,000 uF devices.
Other than these changes not much will alter the sound. Using an IEC socket may satisfy your fastidious needs but will not improve the sonics.
If you really want a major improvement in sound replace your present PCBs and filter caps with those from Musical Concepts. Study the installation manual for them for the PA3-C circuit cards at MusicalConcepts.com.
The only mods I would recommend are to:
1. Replace all the electrolytic caps with similar value devices.
2. Use a quality pair of filter caps in the PS, such as 22,000 uF devices.
Other than these changes not much will alter the sound. Using an IEC socket may satisfy your fastidious needs but will not improve the sonics.
If you really want a major improvement in sound replace your present PCBs and filter caps with those from Musical Concepts. Study the installation manual for them for the PA3-C circuit cards at MusicalConcepts.com.
best bang for buck
Thanks again Dick, I sort of suspected that was the right tack to take. The ps caps I aqiured appear to be the same ones that are sold through Musical Concepts site, although I got them on an ebay auction from Chris Sherman who has posted in this thread I believe. I have a couple more questions, though. I noted earlier in this thread that Fab did some swapping of transformer to a torroid model, at the time he did not notice any significant difference, but Musical Concepts rave about their toroid transformer as if it were the " cats ***" does anyone have any further experience with this? I'm quite sure if I put a $200 toroid transformer in the box of parst and ask my brother to have his tech install it for me he'll tell me I'm being anal again. Furthermore has anyone looked at the toroid transformers at Apexjr website. There are a couple there for only $25 that look like they might do the trick . But I don't know enough about it to tell for sure. For example they have one with +_ 52 volt and +_10 volt secondary windings. Can you sum the two secondaries for 62 VDC ? Forgive me for sounding completely ignorant, but you have to understand that ... in fact... I am!
Also I would like to know if there is a optimal setting for the bias pots, or do the factory settings work best ?
Thanks again Dick, I sort of suspected that was the right tack to take. The ps caps I aqiured appear to be the same ones that are sold through Musical Concepts site, although I got them on an ebay auction from Chris Sherman who has posted in this thread I believe. I have a couple more questions, though. I noted earlier in this thread that Fab did some swapping of transformer to a torroid model, at the time he did not notice any significant difference, but Musical Concepts rave about their toroid transformer as if it were the " cats ***" does anyone have any further experience with this? I'm quite sure if I put a $200 toroid transformer in the box of parst and ask my brother to have his tech install it for me he'll tell me I'm being anal again. Furthermore has anyone looked at the toroid transformers at Apexjr website. There are a couple there for only $25 that look like they might do the trick . But I don't know enough about it to tell for sure. For example they have one with +_ 52 volt and +_10 volt secondary windings. Can you sum the two secondaries for 62 VDC ? Forgive me for sounding completely ignorant, but you have to understand that ... in fact... I am!
Also I would like to know if there is a optimal setting for the bias pots, or do the factory settings work best ?
board version
Sorry again, Dick for sounding stupid, but I know I read in a prev. post the difference between the pc19 versions, but now I can't find it. How Do I tell again ?
Also I investigated the " thump a bit more. It seems to have two sources, the pre-amp ( a very old NAD unit) and the amp. Actually it's more of a quiet,muted pop. When I turn on the Amp the woofer cones move dramatically and make a soft pop noise. But if I turn on the pre-amp after the amp is on the cones move again , and there is another pop followed by a scratchy hiss that fades after a second or two. If I turn on the pre amp first and wait a second or two before turning on the Amp, there is very little noise, but the woofer cones still move.
I think I can atribute most of the power-up noise to the pre-amp as it has a compromised volume pot. So, I'm wondering if I should rebuild the preamp and replace the pot, or just scrap it altogether and just get a new pre amp for the turntable only and just a volume pot for the CD player ? balance ond tone controls, while seemingly convenient are seldom used. In fact the only controls on the pre that are regularly used are the selector switch, volume, and the bass boost curcuit for low listening levels.
What are your thoughts?
Finally Do you think the MC pa-3c is really worth the money?
Assuming I do get it and iunstall the new ps caps which I already have is there anything else note worthy I should consider?
Sorry again, Dick for sounding stupid, but I know I read in a prev. post the difference between the pc19 versions, but now I can't find it. How Do I tell again ?
Also I investigated the " thump a bit more. It seems to have two sources, the pre-amp ( a very old NAD unit) and the amp. Actually it's more of a quiet,muted pop. When I turn on the Amp the woofer cones move dramatically and make a soft pop noise. But if I turn on the pre-amp after the amp is on the cones move again , and there is another pop followed by a scratchy hiss that fades after a second or two. If I turn on the pre amp first and wait a second or two before turning on the Amp, there is very little noise, but the woofer cones still move.
I think I can atribute most of the power-up noise to the pre-amp as it has a compromised volume pot. So, I'm wondering if I should rebuild the preamp and replace the pot, or just scrap it altogether and just get a new pre amp for the turntable only and just a volume pot for the CD player ? balance ond tone controls, while seemingly convenient are seldom used. In fact the only controls on the pre that are regularly used are the selector switch, volume, and the bass boost curcuit for low listening levels.
What are your thoughts?
Finally Do you think the MC pa-3c is really worth the money?
Assuming I do get it and iunstall the new ps caps which I already have is there anything else note worthy I should consider?
It is not unusual for a preamp to cause a thump when it is turned on. This is why most people religiously follow the routine of first turning on the preamp and wait for its voltages to settle before turning on the amplifier.
Get out your VOM and check for DC offset at the outputs from the preamp and also at the speaker jacks on your amp. I think you have some DC offset running around somewhere in your system. Speaker cones should not noticeably move in and out when an amp is turned on or off, especially the DH-220 which has a very neat way to null out DC offset.
Good to hear about your large PS cap replacements. They should make a positive difference in the sound, especially in the lower frequencies.
A toroid's value is questionable and there is some dispute about it compared to the traditional old timey EI transformer. Check the archives here as there was a recent thread about it. There is no magic to a toroid and it will not improve the sound. A transformer with higher current capacity can make a bit of a difference if you can shoe horn in the larger transformer into the chassis, but is it worth $200? Of course Mus Concepts glows about them as they are a high mark up item sold.
As for the value of the MC PA3-C cards, their value lies in the ears of their beholders. I like them. I have had many Hafler amps, even dual mono DH-220 with really big caps in the PS -- which sounded quite good. But, nothing compares to what I hear with the MC PCBs. Too bad you can't audition a pair.
Try to determine if your DC offset or "thump" symptom is in both channels equally or only one channel. That will help you sleuth out the cause. Your electrolytic caps are 20+ years old so they would be my first suspect. Solve the thump thing, install your larger PS caps, and enjoy your amp. Then, later, if you still have a burning desire to modify think about about further electro cap replacements and maybe a MC PA3-C PCB installation.
Cheers............
Get out your VOM and check for DC offset at the outputs from the preamp and also at the speaker jacks on your amp. I think you have some DC offset running around somewhere in your system. Speaker cones should not noticeably move in and out when an amp is turned on or off, especially the DH-220 which has a very neat way to null out DC offset.
Good to hear about your large PS cap replacements. They should make a positive difference in the sound, especially in the lower frequencies.
A toroid's value is questionable and there is some dispute about it compared to the traditional old timey EI transformer. Check the archives here as there was a recent thread about it. There is no magic to a toroid and it will not improve the sound. A transformer with higher current capacity can make a bit of a difference if you can shoe horn in the larger transformer into the chassis, but is it worth $200? Of course Mus Concepts glows about them as they are a high mark up item sold.
As for the value of the MC PA3-C cards, their value lies in the ears of their beholders. I like them. I have had many Hafler amps, even dual mono DH-220 with really big caps in the PS -- which sounded quite good. But, nothing compares to what I hear with the MC PCBs. Too bad you can't audition a pair.
Try to determine if your DC offset or "thump" symptom is in both channels equally or only one channel. That will help you sleuth out the cause. Your electrolytic caps are 20+ years old so they would be my first suspect. Solve the thump thing, install your larger PS caps, and enjoy your amp. Then, later, if you still have a burning desire to modify think about about further electro cap replacements and maybe a MC PA3-C PCB installation.
Cheers............
About setting the bias, there are differences of opinion. I like my DH-220 biased to around 300 mV of idle current. This makes the amp run quite warm, but that's OK in the winter
.
I had an amp come by me here that was biased up to 425 mA of idle current. It did seem to sound a little smoother but it sure got hot. My small amount of experimentation has not proven to me that going beyond the factory spec of 280 mV markedly improves the sound.
Heat is the enemy of solid state circuits so you have to make a choice about what is the most important thing to you. A very slight sound improvement or possible reduction in life span of the amp's components.
I compromise on 300 mV if the amp is very well ventilated and it is winter.
.I had an amp come by me here that was biased up to 425 mA of idle current. It did seem to sound a little smoother but it sure got hot. My small amount of experimentation has not proven to me that going beyond the factory spec of 280 mV markedly improves the sound.
Heat is the enemy of solid state circuits so you have to make a choice about what is the most important thing to you. A very slight sound improvement or possible reduction in life span of the amp's components.
I compromise on 300 mV if the amp is very well ventilated and it is winter.
Good news again...
I got that second XL-280 working this evening. I started checking voltages a few weeks ago and got a bit frustrated with it and too many other things, so I put it aside for a while. After a fairly productive day
around the house today and a good meal late this afternoon, I went at it again.
The worst thing about this particular amp is that both PC-40 circuit boards had ridiculous amounts of solder flux all over their undersides. At first glance, it resembled corrosion from excess moisture or salt air. Carefully cleaning up all the excess and wiping things down with 91% isopropyl alcohol revealed several less than acceptable solder joints. A clean 20 watt soldering iron and many touch-ups with fresh 60/40 solder helped troubleshooting things greatly. I wound up replacing D5, a 1N4003 diode and Q14, a 2N3440 transistor.
Total parts cost: less than two bucks.
Time spent tonight: less than four hours.
Pristine Hafler XL-280 sound once again: priceless
I got that second XL-280 working this evening. I started checking voltages a few weeks ago and got a bit frustrated with it and too many other things, so I put it aside for a while. After a fairly productive day
around the house today and a good meal late this afternoon, I went at it again. The worst thing about this particular amp is that both PC-40 circuit boards had ridiculous amounts of solder flux all over their undersides. At first glance, it resembled corrosion from excess moisture or salt air. Carefully cleaning up all the excess and wiping things down with 91% isopropyl alcohol revealed several less than acceptable solder joints. A clean 20 watt soldering iron and many touch-ups with fresh 60/40 solder helped troubleshooting things greatly. I wound up replacing D5, a 1N4003 diode and Q14, a 2N3440 transistor.
Total parts cost: less than two bucks.
Time spent tonight: less than four hours.
Pristine Hafler XL-280 sound once again: priceless
Intrepid?!? ME???
You are too kind, sir.
I almost gave up a few weeks ago and fortunately rediscovered some timeless wisdom. (That's when I put it aside a while.)
I've never seen so much hardened brown rosin all over a PCB in my life. When I finally cleaned it all, it was plain to see where several solder joints were poor/weak. I've never seen one like this before. These were PC-40D revs of the board, so newer/later/younger than my first amp. Is it possible the factory had a horribly bad run of solder, or simply missed removing the excess rosin? It really didn't look like a bad repair job because it was consistant over the entire board. It certainly explains the brittle and loose wiring I found in this amp, though.
I also must admit, I was completely encouraged by Shawn's amazing effort
resurrecting his Crown DC300A. I couldn't possibly give up in the presence of such determined effort.
Dick West said:Congrats. You are intrepid
You are too kind, sir.
I almost gave up a few weeks ago and fortunately rediscovered some timeless wisdom. (That's when I put it aside a while.)
I've never seen so much hardened brown rosin all over a PCB in my life. When I finally cleaned it all, it was plain to see where several solder joints were poor/weak. I've never seen one like this before. These were PC-40D revs of the board, so newer/later/younger than my first amp. Is it possible the factory had a horribly bad run of solder, or simply missed removing the excess rosin? It really didn't look like a bad repair job because it was consistant over the entire board. It certainly explains the brittle and loose wiring I found in this amp, though.
I also must admit, I was completely encouraged by Shawn's amazing effort
resurrecting his Crown DC300A. I couldn't possibly give up in the presence of such determined effort.
mmerig:
I replaced the rectifier, but this did not solve the buzzing problem, and the voltage difference (.03 vs .003) I reported earlier was an artifact of my meter (I get this reading on other power supplies too). Larger filter caps on the VR don't help, either.
The buzzing (noticeable, not intolerable, 120hz) seems to be related to a ground loop. The buzzing increases if I touch the positive input wire or the input cap with my finger (and my other hand not touching anything). The same finger effect happens on the other channel, which is not connected to the VR and has it's own separate power supply, but the residual buzz is barely audible when I stop touching the cap or input wire.
Will getting rid of the ground plane on the voltage regulator board solve this? The VR ground is connected to the star ground of the main power supply. The buzzing is much louder if the VR is not grounded (no surprise). Grounding different points of the VR ground plane to the star ground makes no difference.
Any ideas?
I replaced the rectifier, but this did not solve the buzzing problem, and the voltage difference (.03 vs .003) I reported earlier was an artifact of my meter (I get this reading on other power supplies too). Larger filter caps on the VR don't help, either.
The buzzing (noticeable, not intolerable, 120hz) seems to be related to a ground loop. The buzzing increases if I touch the positive input wire or the input cap with my finger (and my other hand not touching anything). The same finger effect happens on the other channel, which is not connected to the VR and has it's own separate power supply, but the residual buzz is barely audible when I stop touching the cap or input wire.
Will getting rid of the ground plane on the voltage regulator board solve this? The VR ground is connected to the star ground of the main power supply. The buzzing is much louder if the VR is not grounded (no surprise). Grounding different points of the VR ground plane to the star ground makes no difference.
Any ideas?
Here is a summary of how the voltage regulator in my Hafler 220 worked out.
I put a 33 volt zener aross each voltage regulator to keep the maximum voltage down. Apparently, there were some high surges that broke several transistors on the main board. This worked, as I had no problems after several weeks of use, with the regulator connected to the right channel only.
For a listening test, I placed the two speakers next to each other about 20 feet away from me. I did A-B comparisons by turning the balance knob quickly back and forth every few seconds or so. My source was a CD player, and I combined the stereo signal into mono. I did this after using the amp several weeks.
First I used sine wave tones (20, 40, 100, 500, 1k, 8K, 10K, 12K, 15K, 18K, 20K). I also used short clips of music with big transients. Each sequence was a few seconds, repeated several times for about 30 seconds total. The first clip was a hammer on steel (from Johnny Cash's "The Legend of John Henry's Hammer"), the second was the first drum beat from B. Dylan's "Like a Rolling Stone", the last was a bass-heavy section from Jack Johnson's "Wasting Time".
The last track was symbolic for the whole effort, as I hardly heard a difference on any test, except a subtle one on the hammer track. The volume was as loud as I could stand, and I blew two speaker fuses.
When I took out the regulator, I tested it and realized that the LM337 had broken on the negative rail. The 33 volt zener was also broken. C4 (0.1 uf, 630V, film) looked like it got warm, as the wound label had distorted. The output voltage was about 80 volts rather than the desired 70. So there are still some reliability issues. There is no short circuit protection on the regulator, but other than low resistance as capacitors are charging, I cannot think of what would cause this problem. There is only about 500 uf on each rail after the regulators.
The imbalance in rail voltage may have been a factor, but I think the main reason I could not hear much difference was that my amp has twice the capacitance and a larger transformer (625 Watts) compared to stock, and the main power supply is adequate for any listening level I would need. Speaker efficiency is 92 db at 1 meter.
Because of these problems, I learned alot, and that was the main reason for doing this. Thanks to all that helped me. Any further comments or questions are welcome.
I put a 33 volt zener aross each voltage regulator to keep the maximum voltage down. Apparently, there were some high surges that broke several transistors on the main board. This worked, as I had no problems after several weeks of use, with the regulator connected to the right channel only.
For a listening test, I placed the two speakers next to each other about 20 feet away from me. I did A-B comparisons by turning the balance knob quickly back and forth every few seconds or so. My source was a CD player, and I combined the stereo signal into mono. I did this after using the amp several weeks.
First I used sine wave tones (20, 40, 100, 500, 1k, 8K, 10K, 12K, 15K, 18K, 20K). I also used short clips of music with big transients. Each sequence was a few seconds, repeated several times for about 30 seconds total. The first clip was a hammer on steel (from Johnny Cash's "The Legend of John Henry's Hammer"), the second was the first drum beat from B. Dylan's "Like a Rolling Stone", the last was a bass-heavy section from Jack Johnson's "Wasting Time".
The last track was symbolic for the whole effort, as I hardly heard a difference on any test, except a subtle one on the hammer track. The volume was as loud as I could stand, and I blew two speaker fuses.
When I took out the regulator, I tested it and realized that the LM337 had broken on the negative rail. The 33 volt zener was also broken. C4 (0.1 uf, 630V, film) looked like it got warm, as the wound label had distorted. The output voltage was about 80 volts rather than the desired 70. So there are still some reliability issues. There is no short circuit protection on the regulator, but other than low resistance as capacitors are charging, I cannot think of what would cause this problem. There is only about 500 uf on each rail after the regulators.
The imbalance in rail voltage may have been a factor, but I think the main reason I could not hear much difference was that my amp has twice the capacitance and a larger transformer (625 Watts) compared to stock, and the main power supply is adequate for any listening level I would need. Speaker efficiency is 92 db at 1 meter.
Because of these problems, I learned alot, and that was the main reason for doing this. Thanks to all that helped me. Any further comments or questions are welcome.
DH-220 Mods, PA3 Boards Installed
I recently modified a DH-220 with Musical Concepts PA3 driver boards. With one channel stock, and one using the PA3, there was a big difference (night and day) between the stock PC-19 boads (circa 1985, all original parts) which sounded fuzzy and compressed, compared to the Musical Concepts PA3B's (fitted with 100uF/100V Black Gate FK rail caps and a 33u BG-N input series cap) much more clear, natural and dynamic without being overly bright.
Bias current for both setups was set to about 250mA, and used the stock Hafler (Hitachi MOSFETS, 2 per rail).
Also, I replaced the main filter caps (20 year old 10,000u Sangamos) with 26,000uF parts at the same time.
Does anyone know of a soft-start module available? I'm thinking of adding a replacing diode bridge (a pair 20A schottky setups-- one per channel) and adding 2 more main filter caps to allow dual mono operation.
Also, I've heard that BlackGates production is discontinued again (this time for real).
-Bruce
I recently modified a DH-220 with Musical Concepts PA3 driver boards. With one channel stock, and one using the PA3, there was a big difference (night and day) between the stock PC-19 boads (circa 1985, all original parts) which sounded fuzzy and compressed, compared to the Musical Concepts PA3B's (fitted with 100uF/100V Black Gate FK rail caps and a 33u BG-N input series cap) much more clear, natural and dynamic without being overly bright.
Bias current for both setups was set to about 250mA, and used the stock Hafler (Hitachi MOSFETS, 2 per rail).
Also, I replaced the main filter caps (20 year old 10,000u Sangamos) with 26,000uF parts at the same time.
Does anyone know of a soft-start module available? I'm thinking of adding a replacing diode bridge (a pair 20A schottky setups-- one per channel) and adding 2 more main filter caps to allow dual mono operation.
Also, I've heard that BlackGates production is discontinued again (this time for real).
-Bruce