I have rebuilt a number of Hafler amps from the DH220 on up. If something serious is wrong, my experience has been it is one or more of the output FETs, usually a P-channel.
Both TO3 and TO247 packages are available from the UK firm of Profusion at: Exicon Lateral Mosfets - Manufacturer Page | Profusion. They even have a dual die in one TO3 package to beef up the output. See Exicon Lateral MOSFETS for more details.
The fuses do get tired and especially the speaker output fuses tend to be too low in value. The factory installed 3 Amp fuses, but I replace them with 5 or even 7A for home theater use. Do watch your levels as these amps can put out a lot of current and blow speakers!
Have you checked the pin-out on the TO-3 package? You can't use them without a major rewire.
Also, if you're going to use 5 or 7 ampere fuses instead of the 3 ampere ones, why not just be honest and short the fuse holders out? I agree that fuses distort the output signal, the only real protection would be relays or a mosfet assembly.
-Chris
Also, if you're going to use 5 or 7 ampere fuses instead of the 3 ampere ones, why not just be honest and short the fuse holders out? I agree that fuses distort the output signal, the only real protection would be relays or a mosfet assembly.
-Chris
Hafler TO3 Packages
Hi Chris,
Thanks for the prompt answer. I have purchased both the TO247 & the TO3 FETs from Profusion. Both have worked well without any rewiring the Haflers they went into. I have not yet used the dual die versions in the TO3s, but I recall reading that they were drop-ins for the standard single die FET. One does need to readjust the bias and possibly fiddle with the drive for best P & N matching and even current draw from both haves of the affected channel.
Regarding the fuses, at some point a large enough fuse will be the same as a hunk of wire and I concur that no fuse is best. But, because I have sold a couple of my rebuilds to friends, I left them in as the lesser of evils.
Regards,
Ivan
Hi Chris,
Thanks for the prompt answer. I have purchased both the TO247 & the TO3 FETs from Profusion. Both have worked well without any rewiring the Haflers they went into. I have not yet used the dual die versions in the TO3s, but I recall reading that they were drop-ins for the standard single die FET. One does need to readjust the bias and possibly fiddle with the drive for best P & N matching and even current draw from both haves of the affected channel.
Regarding the fuses, at some point a large enough fuse will be the same as a hunk of wire and I concur that no fuse is best. But, because I have sold a couple of my rebuilds to friends, I left them in as the lesser of evils.
Regards,
Ivan
Hi Ivan,
Do you have a pic showing how you shoe horned in the TO-247 packaged mosfets onto the existing heat sink? I assume you had to hard wire them in and remove the original TO-3 sockets.
Using the dual die mosfets, your plan is to use one device to replace the original two or use four of them?
If using four dual die types, I wonder why? I would think you would be possibly running into the limits of the supply and heatsink delivering that sort of power into the load. I know the P230 uses 3-pairs of devices, same H/S but I think it has a bigger VA rated transformer, I’d have verify if so.
Can you elaborate on how you fiddle with the drive for best P/N matching? Why do you think it is necessary? Do you measure a performance difference? Please don’t tell me you hear a difference
On the TO-247 wiring, the new OPS board that we designed was done with the TO-247/264 package footprint. I showed a pic of it a few threads back, it adds features and makes the wiring neater.
Do you have a pic showing how you shoe horned in the TO-247 packaged mosfets onto the existing heat sink? I assume you had to hard wire them in and remove the original TO-3 sockets.
Using the dual die mosfets, your plan is to use one device to replace the original two or use four of them?
If using four dual die types, I wonder why? I would think you would be possibly running into the limits of the supply and heatsink delivering that sort of power into the load. I know the P230 uses 3-pairs of devices, same H/S but I think it has a bigger VA rated transformer, I’d have verify if so.
Can you elaborate on how you fiddle with the drive for best P/N matching? Why do you think it is necessary? Do you measure a performance difference? Please don’t tell me you hear a difference
On the TO-247 wiring, the new OPS board that we designed was done with the TO-247/264 package footprint. I showed a pic of it a few threads back, it adds features and makes the wiring neater.
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More on Hafler upgrades
Hi rsavas, I have thought about replacing the TO3 package with TO247, but sorry if I gave the impression that I had done it. The prices are not that different between a TO3 and TO247 and it would indeed be a messy job (and a long one). I have rebuilt later Haflers made by Rockford and they do use the TO247, like the P3000 and P7000.
As you know, matching The FETs is critical to avoid current hogging (P to P and N to N), but I'm also concerned if one side draws more power than the other--easy to see with an IR heatgun. This does show up as worse THD.
My mention of the dual die TO3 at this point was just informational--I have not tried them. The TO3 package is the real limitation to a lot more output. If you check the spec sheet, they do handle more power, but not twice.
My use in an existing design would be to increase reliability and reduce thermal stress on the part, which might give you a bit better specs given a somewhat lower operating temperature since the load is now split between the two dies. The specs improvement is conjecture on my part.
Since the PS voltages remain the same, it wouldn't increase stress on the parts.
When Hafler added additional FETs as you mentioned (DH-230, 280, 500, etc.), the transformer is sized to match the increased output power. The DH-220 has ~+/- 62V rails, and the DH-500 has +/- 95V rails.
It's been a while since I did additional matching, but I believe that I changed the O/P FET gate drive resistors (470 Ohms, N ch. & 220 Ohms P ch.). I think I changed the N ch. as there is a wider range to play with.
The list of mods is a whole other story and I believe there are threads from other Hafler fans on diyAudio covering this.
Hope this answers your questions!
Ivan
Hi rsavas, I have thought about replacing the TO3 package with TO247, but sorry if I gave the impression that I had done it. The prices are not that different between a TO3 and TO247 and it would indeed be a messy job (and a long one). I have rebuilt later Haflers made by Rockford and they do use the TO247, like the P3000 and P7000.
As you know, matching The FETs is critical to avoid current hogging (P to P and N to N), but I'm also concerned if one side draws more power than the other--easy to see with an IR heatgun. This does show up as worse THD.
My mention of the dual die TO3 at this point was just informational--I have not tried them. The TO3 package is the real limitation to a lot more output. If you check the spec sheet, they do handle more power, but not twice.
My use in an existing design would be to increase reliability and reduce thermal stress on the part, which might give you a bit better specs given a somewhat lower operating temperature since the load is now split between the two dies. The specs improvement is conjecture on my part.
Since the PS voltages remain the same, it wouldn't increase stress on the parts.
When Hafler added additional FETs as you mentioned (DH-230, 280, 500, etc.), the transformer is sized to match the increased output power. The DH-220 has ~+/- 62V rails, and the DH-500 has +/- 95V rails.
It's been a while since I did additional matching, but I believe that I changed the O/P FET gate drive resistors (470 Ohms, N ch. & 220 Ohms P ch.). I think I changed the N ch. as there is a wider range to play with.
The list of mods is a whole other story and I believe there are threads from other Hafler fans on diyAudio covering this.
Hope this answers your questions!
Ivan
Hi Ivan,
Yes, the TO-3 has lower thermal resistance than the TO-247, so go with the TO-3 if it does not cost too much more.
If the dual die device is a TO-3 with essentially two of the same die as the single-die device, you will get lower distortion for a given bias current, since gm at a given bias current is higher for a larger effective die area. If you were to use the dual die device and double the bias current, and ignored thermal considerations (which you can't), overall gm would be doubled and distortion would theoretically be halved from the output stage.
Be careful with changing the gate stopper resistors, as too small a value will result in parasitic oscillation bursts. These may not be seen under normal conditions, but can occur on the back porch of the sine wave at high signal levels into lower-impedance loads.
In a case with the DH-220C prototype, I did experiment with reducing those resistors and thought that I was successful in still not having parasitic oscillation bursts. However, when I tested it at high power levels into a 2-ohm load, they appeared.
Cheers,
Bob
Hi Bob,
Thanks for your response. I have a DH-220 that recently came from a thrift store ($20--I've got to crow a bit!). That is now back to working condition (bad Rt. Ch. P-FETs replaced + new caps). The right channel N-FETs are drawing more power, so a good time to check the gate resistor mod.
The imbalance may be from lower gm from a couple of late 70s, used FETs that I had handy.
I'd think that a simple, single pole low pass with a small value NPO cap would do the stopper resistor oscillation job. Did you try this? Do you remember at what frequency the oscillation occurred?
Regards,
Ivan
Thanks for your response. I have a DH-220 that recently came from a thrift store ($20--I've got to crow a bit!). That is now back to working condition (bad Rt. Ch. P-FETs replaced + new caps). The right channel N-FETs are drawing more power, so a good time to check the gate resistor mod.
The imbalance may be from lower gm from a couple of late 70s, used FETs that I had handy.
I'd think that a simple, single pole low pass with a small value NPO cap would do the stopper resistor oscillation job. Did you try this? Do you remember at what frequency the oscillation occurred?
Regards,
Ivan
I seem to recall it was above 10 MHz. It was definitely not a global feedback loop oscillation. Because it was a short burst on top of a large 40-V peak signal, it was difficult to isolate it on a scope. Not sure that adding a capacitor in that location would help, but it is something I would like to explore in the future. Those relatively large gate stopper resistors do slow down the output stage, and that is a shame.
Cheers,
Bob
Bob:
Did you ever try using your series R-C at the gate for the lateral MOSFETs that you use for the verticals in your old (but good) 50W design?
mlloyd1
Did you ever try using your series R-C at the gate for the lateral MOSFETs that you use for the verticals in your old (but good
) 50W design?mlloyd1
Bob:
Did you ever try using your series R-C at the gate for the lateral MOSFETs that you use for the verticals in your old (but good
mlloyd1
I did try the gate Zobel network quite awhile back, but my recollection is that I was not successful with it on the laterals in the Hafler. I don't know why, and I remember not spending much time on it. Also, the discrete fly-wire wiring of the output stage of the Hafler was not a very good environment for parasitic oscillation reduction experiments. Withe the new output board we have for the DH-220C, where there is better bypassing and more control of wiring inductances, and a local output Zobel network, it may be a more successful effort to try.
Cheers,
Bob
Yes, that may help with some drain wiring inductances. The next time I'm poking around in the DH-220C output stage I'll give it a try. I'll put it in and see how low I can go with the gate stopper resistors. In order to be most effective, this capacitor would likely have to be wired directly at the transistor socket, rather than on the output board.
Cheers,
Bob
Hello everyone!
I've recently purchased a Hafler DH-220 (ebay) to fill in for my vintage McIntosh MC2205 while I put it on the bench for the repair.
The good news is the MC2205 repair went really smooth even though it was quite extensive, that amp is a dream to work on (besides the weight!) and sounds OUTSTANDING!
The bad news is the DH-220 has a hum so bad I can't even listen to it!
I've put the DH-220 on the bench, decided to bridge it to mono and try it as an amp for a sub, if it goes well I will get another and give it the same treatment to run both subs.
I can see the power, speaker and input wire needs to be replaced, what I see is thin power wires and inputs aren't shielded? I also figure it needs to be re-capped, including the cans in the power supply and (the few) electrolytics in the amp circuit.
I figured I would bump up the cans to perhaps 22,000uf, replace the smaller electrolytics with some newer muse caps, not quite sure what to do about all of the other film, poly or other various caps all over this amp?
This thread is so vast, and I have read so much, about inrush limiters, soft recovery and FRED diodes, inrush limiters, it goes on and on....
What I am hoping is somebody that knows these amps and mods could throw some recommendations my way to beef up this amp to run a sub.
Topics of interest would be:
Is 22,000 good for the cans?
Any recomendations on PS cans? (available and affordable)
Should I bump up the amps on the bridge rectifier or use an inrush limiter? (or both)
For the bridge would you go easy route 35A package, or dual bridge, FRED's? I am out of touch on the rectifier options, fast, soft, FRED's etc. Looking for suggetions!
What about the films and poly's? Anybody have a good recipe to share on cap selection for the DH-220?
What Power and speaker wire gauge and type would you use?
How about for the Input wire?
Keep in mind, goal is mono sub amp, freshened up to be quiet and reliable with a solid thump!
If anyone cares to share recommendations with me that would be great, I have read so much about mods my head is spinning! LOL
Thanks a bunch to anyone who takes the time to read or reply!
I've recently purchased a Hafler DH-220 (ebay) to fill in for my vintage McIntosh MC2205 while I put it on the bench for the repair.
The good news is the MC2205 repair went really smooth even though it was quite extensive, that amp is a dream to work on (besides the weight!) and sounds OUTSTANDING!
The bad news is the DH-220 has a hum so bad I can't even listen to it!
I've put the DH-220 on the bench, decided to bridge it to mono and try it as an amp for a sub, if it goes well I will get another and give it the same treatment to run both subs.
I can see the power, speaker and input wire needs to be replaced, what I see is thin power wires and inputs aren't shielded? I also figure it needs to be re-capped, including the cans in the power supply and (the few) electrolytics in the amp circuit.
I figured I would bump up the cans to perhaps 22,000uf, replace the smaller electrolytics with some newer muse caps, not quite sure what to do about all of the other film, poly or other various caps all over this amp?
This thread is so vast, and I have read so much, about inrush limiters, soft recovery and FRED diodes, inrush limiters, it goes on and on....
What I am hoping is somebody that knows these amps and mods could throw some recommendations my way to beef up this amp to run a sub.
Topics of interest would be:
Is 22,000 good for the cans?
Any recomendations on PS cans? (available and affordable)
Should I bump up the amps on the bridge rectifier or use an inrush limiter? (or both)
For the bridge would you go easy route 35A package, or dual bridge, FRED's? I am out of touch on the rectifier options, fast, soft, FRED's etc. Looking for suggetions!
What about the films and poly's? Anybody have a good recipe to share on cap selection for the DH-220?
What Power and speaker wire gauge and type would you use?
How about for the Input wire?
Keep in mind, goal is mono sub amp, freshened up to be quiet and reliable with a solid thump!
If anyone cares to share recommendations with me that would be great, I have read so much about mods my head is spinning! LOL
Thanks a bunch to anyone who takes the time to read or reply!
Yes, I've had this experience also with a number of different lateral mosfet amps I've built over the years.
mlloyd1
mlloyd1
A stock Hafler DH-220 is a pretty good amplifier. I would recommend you first get it back to stock performance in stereo mode before doing a lot of other stuff. This is especially in respect to the hum. For example, is the hum in both channels or just one? If it is in both channels, there may be something bad in the power supply, like the reservoir capacitors or the rectifier. Re-capping is always a good idea, but find where the hum is coming from first.
Cheers,
Bob
Hi ToneMonkey2,
The first thing to do is stop reading for a bit, think about it and use common sense. For one, too high capacitance isn't your friend. For two, these were budget amplifiers that performed pretty well, so you aren't going to get super high end performance no matter what you do. What you can get is a reliable, good sounding amplifier if you use your head and don't go too nuts on it.
-Chris
The first thing to do is stop reading for a bit, think about it and use common sense. For one, too high capacitance isn't your friend. For two, these were budget amplifiers that performed pretty well, so you aren't going to get super high end performance no matter what you do. What you can get is a reliable, good sounding amplifier if you use your head and don't go too nuts on it.
-Chris
Hi ToneMonkey,
Before going nuts on mods... - there is something WRONG with your Hafler 220.
They are normally dead quiet... Even with the non-shielded wire.
https://hafler.com/pdf/archive/DH-220_amp_man.pdf
I own a few of the Hafler 200/220 and it might be that the previous owner messed with the internal grounding. Be sure that PCB connector 2 has a sold ground. Same is true for PCB connector 7.
Personally, I would connect the input RCA to PCB 1 and 2 and then only have PCB connector 7 go to GND while shunting C23 and making sure the RCA input ground did NOT go to the midpoint between the big caps. The input will be grounded directly via PCB connector 2->7->GND.
Good luck.
Before going nuts on mods... - there is something WRONG with your Hafler 220.
They are normally dead quiet... Even with the non-shielded wire.
https://hafler.com/pdf/archive/DH-220_amp_man.pdf
I own a few of the Hafler 200/220 and it might be that the previous owner messed with the internal grounding. Be sure that PCB connector 2 has a sold ground. Same is true for PCB connector 7.
Personally, I would connect the input RCA to PCB 1 and 2 and then only have PCB connector 7 go to GND while shunting C23 and making sure the RCA input ground did NOT go to the midpoint between the big caps. The input will be grounded directly via PCB connector 2->7->GND.
Good luck.
Hi Bob & Rick:
I've been lurking for a while, just watching progress. But now with lots of "anti-virus" spare time on hand, and an idle/spare DH-200 in need of TLC, I'm about ready to bring it back to life, and very intrigued with your design.
Is an updated schematic/parts list available?
Sean
Any news/progress?
I've been lurking for a while, just watching progress. But now with lots of "anti-virus" spare time on hand, and an idle/spare DH-200 in need of TLC, I'm about ready to bring it back to life, and very intrigued with your design.
Is an updated schematic/parts list available?
Sean
Hi Sean,
Almost ready to go. I am itching too, as it has been a long road to get to this point. One thing holding me up is building a fixture to select the jfets. It is not an absolute requirement, but something we want to have in place, Bob as come up with a method to tweek a resistor value in the IPS to assure that the VAS current is within spec. The idea is to not have to do that by selecting and doing a match to pair them up.
I ordered a SOT-23-6 test socket almost a month ago now, from where else and it still has not arrived. I bought a bunch of jfets, got them this week.
I will make a kit of parts, boards, teflon wire, coil, jfets, that you can not get from Mouser. Yesterday I created a project BOM in Digi-key too, but a few precision resistors are not available there. But it is good for some items that maybe on back order at Mouser, like the 2N5401 which have been on back order for a long time now.
I tried a couple of samples of the SOT-23-6 jfets, on a board I soldered up, random selection, the VAS current was in spec. I sent the board to Bob to give his final okay, also try out the P230 OPS board that I soldered up for him to try in his P230. The shipment was held up with USPS, in Chicago, the package took almost two weeks to be sorted. I see today that it finally is on its way, so USPS is really slow. Even Mouser is really slow, it took a whole week to process my order this week. Mouser told me they are working with 25% staff, so they can keep their distances from each other.
I am going to only provide the documentation and the link to the google drive to people who get kits, that way I have some control on who gets it. We put too much work into this design to just giving it away for free. I think that is only fair. The core design is very close to what was presented, so no surprises, just a few tweeks to the components, special OPS boards to make for clean wiring and additional features.
I understand that everyone wants to keep busy and this is a perfect time to do these projects. Bob has the final say when I push the full release button.
I have one person that I sent boards too that will do a trial run, test the waters, so to speak. Documentation is complete.
Today I have soldered up another board and will run it at +/-90V to test it out for a DH-500 installation. Have to evaluate if P230 OPS can be used in DH-500.
So there you go for an update.
Thanks for your interest.
Rick
Almost ready to go. I am itching too, as it has been a long road to get to this point. One thing holding me up is building a fixture to select the jfets. It is not an absolute requirement, but something we want to have in place, Bob as come up with a method to tweek a resistor value in the IPS to assure that the VAS current is within spec. The idea is to not have to do that by selecting and doing a match to pair them up.
I ordered a SOT-23-6 test socket almost a month ago now, from where else and it still has not arrived. I bought a bunch of jfets, got them this week.
I will make a kit of parts, boards, teflon wire, coil, jfets, that you can not get from Mouser. Yesterday I created a project BOM in Digi-key too, but a few precision resistors are not available there. But it is good for some items that maybe on back order at Mouser, like the 2N5401 which have been on back order for a long time now.
I tried a couple of samples of the SOT-23-6 jfets, on a board I soldered up, random selection, the VAS current was in spec. I sent the board to Bob to give his final okay, also try out the P230 OPS board that I soldered up for him to try in his P230. The shipment was held up with USPS, in Chicago, the package took almost two weeks to be sorted. I see today that it finally is on its way, so USPS is really slow. Even Mouser is really slow, it took a whole week to process my order this week. Mouser told me they are working with 25% staff, so they can keep their distances from each other.
I am going to only provide the documentation and the link to the google drive to people who get kits, that way I have some control on who gets it. We put too much work into this design to just giving it away for free. I think that is only fair. The core design is very close to what was presented, so no surprises, just a few tweeks to the components, special OPS boards to make for clean wiring and additional features.
I understand that everyone wants to keep busy and this is a perfect time to do these projects. Bob has the final say when I push the full release button.
I have one person that I sent boards too that will do a trial run, test the waters, so to speak. Documentation is complete.
Today I have soldered up another board and will run it at +/-90V to test it out for a DH-500 installation. Have to evaluate if P230 OPS can be used in DH-500.
So there you go for an update.
Thanks for your interest.
Rick