Depends on where you tie that common ground to.
How does that look on the amplifier side?
Does it have two separate connections to some central ground like PSU ground or are the amp grounds connection in another way?
A good point to check is the ground connections of the output snubbers which most amps have.
You could ask the same question for the input connection ground of course, that may affect the operation but not the sound quality.
Jan
How does that look on the amplifier side?
Does it have two separate connections to some central ground like PSU ground or are the amp grounds connection in another way?
A good point to check is the ground connections of the output snubbers which most amps have.
You could ask the same question for the input connection ground of course, that may affect the operation but not the sound quality.
Jan
When you look at Hafler 200/220, the speaker GND output should be tied to the midpoint between the two large 10,000/75V caps. A protectionn board certanly can be inserted bwteen the Positive speaker terminals and the amplifier's PCB. No need to worry about the GND on the protector board (unless you insist). While you are at it, remove the speaker fuses and sockets. So: PCB speaker out to protection board. GND directly to midpoint of power supply.
And oh, one more thing: your protection circuit still needs to have GND connected to the GND midpoint on the power supply. Otherwise it cannot detect anormalities in your speaker signal. Such as excessive DC...
The issue with a common ground is that current from one speaker, through the common ground wire resistance, generates a voltage for the other speaker.
This causes crosstalk.
In this case, where the designer of that protection board has made a fundamental error, the best you can do is use as thick a wire as possible and hope for the best.
Jan
This causes crosstalk.
In this case, where the designer of that protection board has made a fundamental error, the best you can do is use as thick a wire as possible and hope for the best.
Jan
Thanks Vilfort and Jan. Yes no SPEAKER output ground then no DC offset measurement/detection......
Once I get the board ,linked above, I'll try to figure out if it uses the star ground, or can be modded to use the star ground, for DC offset. Ed Fantasia/Quaco board does exactly that and does not have speaker in/out grounds connected directly. See link below:
https://www.ebay.com/itm/373031816632?_nkw=hafler+200+speaker+protect&itmmeta=01J605HXETPS4PG89QQGEEGZKX&hash=item56da6dcdb8:g:Ob0AAOSwcv9ejHPq&itmprp=enc:AQAJAAAA8HoV3kP08IDx+KZ9MfhVJKm6g6T+ix6PaWcEM5Y31rXo/xTWbfOxKXjTCIcUfCretkoaqkHSzTBZxvfk9L649ZDwvhdSAG80bQWgmb6b+d+xM/ZXg6aiRTf7++92LBGRV00YF3t19T3Qby4ZVqWvc+uL138lP94e01ifI3mXF5wQesr3d6C94bvsOk+GZbs+j30elKIrl10YHGrtYwHBkCQXGreMQOM/OKuM05dae0vYUT8T6eSUIQFkFUG3/Batb+WF4meRX4T4BRQR9vVBB6R/peH3r66gi3hS9aedRblTaRxZGEhDUc0nkjcN0YiPxg==|tkp:Bk9SR77Xx4WwZA
Once I get the board ,linked above, I'll try to figure out if it uses the star ground, or can be modded to use the star ground, for DC offset. Ed Fantasia/Quaco board does exactly that and does not have speaker in/out grounds connected directly. See link below:
https://www.ebay.com/itm/373031816632?_nkw=hafler+200+speaker+protect&itmmeta=01J605HXETPS4PG89QQGEEGZKX&hash=item56da6dcdb8:g:Ob0AAOSwcv9ejHPq&itmprp=enc:AQAJAAAA8HoV3kP08IDx+KZ9MfhVJKm6g6T+ix6PaWcEM5Y31rXo/xTWbfOxKXjTCIcUfCretkoaqkHSzTBZxvfk9L649ZDwvhdSAG80bQWgmb6b+d+xM/ZXg6aiRTf7++92LBGRV00YF3t19T3Qby4ZVqWvc+uL138lP94e01ifI3mXF5wQesr3d6C94bvsOk+GZbs+j30elKIrl10YHGrtYwHBkCQXGreMQOM/OKuM05dae0vYUT8T6eSUIQFkFUG3/Batb+WF4meRX4T4BRQR9vVBB6R/peH3r66gi3hS9aedRblTaRxZGEhDUc0nkjcN0YiPxg==|tkp:Bk9SR77Xx4WwZA
Many inexpensive options here. https://www.ebay.com/itm/115853243479
The UPC 1237 is a great little chip for this kind of work. Have used it for several years. Works like glue!
https://ia802708.us.archive.org/24/items/Datasheets/UPC1237.pdf
As you can see from the Typical Application schematic, only the positve speaker terminal is relay protected.
So the negative speaker terminal can be tapped at the power supply as previously suggested.
No need to spend $100 or so. A $10 kit will do. But you need a 12V sources with these cheap kits. I normally use a 12V transformer like this: https://www.ebay.com/itm/254832864558
As I said, many ways to skin the cat...
Good luck.
The UPC 1237 is a great little chip for this kind of work. Have used it for several years. Works like glue!
https://ia802708.us.archive.org/24/items/Datasheets/UPC1237.pdf
As you can see from the Typical Application schematic, only the positve speaker terminal is relay protected.
So the negative speaker terminal can be tapped at the power supply as previously suggested.
No need to spend $100 or so. A $10 kit will do. But you need a 12V sources with these cheap kits. I normally use a 12V transformer like this: https://www.ebay.com/itm/254832864558
As I said, many ways to skin the cat...
Good luck.
Thanks Vilfort. Both the previous linked board and the Fantasia board use mains AC for power i.e. built in PSU's. Because it's been 44 years since schooling I have been trying to refresh my memory with online electronics training courses and have watched countless hours of Xraytonyb vids on amp repair to jolt my memory. Lol
I fully intent to email Ed Fantasia to find out how exactly he's able to isolate AC interference from the speaker in/outs. I have no doubt that he has done a proper job of it but have no schematics for his board. Doubtful I will get schematics without purchasing his board.
Can one actually use the mains line AC and the amp's center tapped dc ground to power a speaker protect circuit without introducing ripple on the speaker terminal ground? Is it just a matter of having a ripple free dc output from the speaker protect PSU and then just tying the ground to the amp's PSU dc ground? Sorry for my dumb questions.
I fully intent to email Ed Fantasia to find out how exactly he's able to isolate AC interference from the speaker in/outs. I have no doubt that he has done a proper job of it but have no schematics for his board. Doubtful I will get schematics without purchasing his board.
Can one actually use the mains line AC and the amp's center tapped dc ground to power a speaker protect circuit without introducing ripple on the speaker terminal ground? Is it just a matter of having a ripple free dc output from the speaker protect PSU and then just tying the ground to the amp's PSU dc ground? Sorry for my dumb questions.
Last edited:
Update to previous post: The Hafler DH-200 has both speaker jack grounds and the transformer secondary center tap tied directly to the star ground between the two filter caps.
Then all you need is a wire from SP IN GND to the common star ground.
In addition, it were better to provide a twisted pair of leads per speaker terminal, with each GND wire connected to common GND and the hot wires interrupted to insert the protection board.
Best regards!
In addition, it were better to provide a twisted pair of leads per speaker terminal, with each GND wire connected to common GND and the hot wires interrupted to insert the protection board.
Best regards!
Something interesting. I bought a second Hafler DH-200 amp of the bay, cheap. The seller claimed "works as it should". I wanted something to run while I'm upgrading my first DH-200 with the Quaco upgrade.
Pulled the PC-6 boards that had several poly film cap upgrades and re-wetted suspicious soldering joints, DB tested the PSU and then the complete amp. Went to full mains power and after idling for a few hours it seemed too warm to the touch on the right channel and WAY too hot on the left channel. Checked the bias which was L=425 ma / R=335 ma. Before bias adjustments the DC offset was L=16 mv / R=49mv. Still within spec.
Now here's the interesting part. My impression from reading on the DH-200, here and on AK, is that this amp's bias adjustments do not really affect DC offset. On this particular amp adjusting the bias to 250ma +/- 5ma changed the DC offset on both channels to 0-1mv using a Fluke 8024A, unmeasureable really. Thinking this couldn't be right I checked it with my HP 34401A.....same thing, unmeasureable.
What gives? This amp has the original PC-6 boards with some obvious cap mods on the back of the PC-6 as well as some caps strapped to the speaker fuses but no apparent semiconductor mods. Is there some sneaky mod that I'm not seeing that would cause this behavior?
Thanks,
Lonnie
Pulled the PC-6 boards that had several poly film cap upgrades and re-wetted suspicious soldering joints, DB tested the PSU and then the complete amp. Went to full mains power and after idling for a few hours it seemed too warm to the touch on the right channel and WAY too hot on the left channel. Checked the bias which was L=425 ma / R=335 ma. Before bias adjustments the DC offset was L=16 mv / R=49mv. Still within spec.
Now here's the interesting part. My impression from reading on the DH-200, here and on AK, is that this amp's bias adjustments do not really affect DC offset. On this particular amp adjusting the bias to 250ma +/- 5ma changed the DC offset on both channels to 0-1mv using a Fluke 8024A, unmeasureable really. Thinking this couldn't be right I checked it with my HP 34401A.....same thing, unmeasureable.
What gives? This amp has the original PC-6 boards with some obvious cap mods on the back of the PC-6 as well as some caps strapped to the speaker fuses but no apparent semiconductor mods. Is there some sneaky mod that I'm not seeing that would cause this behavior?
Thanks,
Lonnie
OK, been running the new DH-200 for e few days now. Bias and DC offset has been stable. Sometimes it makes a higher frequency whine that I can hear from 18 ft away, sometimes only loud enough to hear with my ear close to the amp cover. I've tightened the transformer plate screws as well as the transformer mounting screws but it continues intermittently.
The frequency is a whine, maybe 120 hz?, and not coming through the speakers. Definitely higher frequency than the normal faint 60hz hum heard from my other DH-200. Rails are at 60.5v. Filter caps? They are the originals.
The frequency is a whine, maybe 120 hz?, and not coming through the speakers. Definitely higher frequency than the normal faint 60hz hum heard from my other DH-200. Rails are at 60.5v. Filter caps? They are the originals.
Whine? At 120Hz I would consider that a hum. 😉
If it does not come from the speakers, it could be the main transformer. Consider replacing with a toroidal if you cannot live with it.
Hafler added rubber dampers glued to the top of the main transfomer to limit the magnetic excitement of the steel cover. Try removing the cover and see if the noise reduces.
If it does not come from the speakers, it could be the main transformer. Consider replacing with a toroidal if you cannot live with it.
Hafler added rubber dampers glued to the top of the main transfomer to limit the magnetic excitement of the steel cover. Try removing the cover and see if the noise reduces.
Thanks, Vilfort. Removing the top cover does not help the transformer noise, even though the OG rubber pads atop the transformer have gotten rock hard. My other DH-200 hums but can only be heard with my ear over the top cover. This one hums so loud I can hear it from across the room.......but not always. It seems to be dead quite at first and then louder hour by hour. By hour to hour I mean regardless of volume. Just setting there with no inputs and no load it will get louder with time. I intend to remove the transformer and check for cracked/loose mounting bracketry, install rubber isolation and give it another go. If that doesn't quiet the thing I'll splurge for a toroidal as I can't just bring myself to file 13 the old girl.
I had the exact same type of noise coming from my Heathkit AA-1600 amp, obnoxiously loud hum!
I replaced it with similar spec'ed Antek toroid with steel cover. Quiet as a church mouse now 🙂.
I replaced it with similar spec'ed Antek toroid with steel cover. Quiet as a church mouse now 🙂.
Thanks, Vunce.
I have been looking at the Antek AN-6445.
Did the cover make a noticeable difference in noise suppression?
Did you find it necessary to rotate the toroid a certain way to minimize noise on the speaker outputs?
I have been looking at the Antek AN-6445.
Did the cover make a noticeable difference in noise suppression?
Did you find it necessary to rotate the toroid a certain way to minimize noise on the speaker outputs?
Last edited:
It so happens that I have a DH-220 that's been collecting rust and dust in a garage. A friend tested it and told me it works! All original, so may need full recap. So for the experienced DH-220 users I have a question, the wise way to proceed with this amp:
Invest significant time and money to modify with:
1. Cordell DH-220C .... or
2. Fantasia (formerly known as Qua-Co) PC-1 .... or
3. Just recap and keep original
Please share your thoughts on the above (if you have gone through the above considerations) keeping in mind that time is money 🙂 and knowledge is power and good sound is valuable.
thanks!
PS: Specifically curious if any of the modifications are trying to address sonic problems of the original design. Not much has been documented in the articles.
Invest significant time and money to modify with:
1. Cordell DH-220C .... or
2. Fantasia (formerly known as Qua-Co) PC-1 .... or
3. Just recap and keep original
Please share your thoughts on the above (if you have gone through the above considerations) keeping in mind that time is money 🙂 and knowledge is power and good sound is valuable.
thanks!
PS: Specifically curious if any of the modifications are trying to address sonic problems of the original design. Not much has been documented in the articles.
If you're going to take it apart, go full-on and install a modified circuit. I built the Cordell project and it is chronicled here:
https://www.diyaudio.com/community/threads/hafler-dh-220-taking-apart-a-perfectly-good-amp.407907/
It completely transformed the amp from a sleepy old 1980s relic (albeit a pretty good sounding relic) into a completely new experience.
I have nothing but good things to say about the change in sound quality, and in particular the transient response and imaging is far superior to the original.
https://www.diyaudio.com/community/threads/hafler-dh-220-taking-apart-a-perfectly-good-amp.407907/
It completely transformed the amp from a sleepy old 1980s relic (albeit a pretty good sounding relic) into a completely new experience.
I have nothing but good things to say about the change in sound quality, and in particular the transient response and imaging is far superior to the original.
I recently got the Quaco (Ed Fantasia) full upgrade for one of my DH-200's. Stuffed the PC-1B boards and waiting on a 600VA Toroidal transformer to arrive. I'll report back on how it AB tests against my refreshed stock DH-200. Honestly, my aged ears don't detect any sonic problems with the refreshed factory unit, albeit the factory PS section is not able to keep up at higher volumes into 6 ohm nominal impedance speakers.
I completed by 220C upgrade about a week ago, but my upgrade followed an unusual path. A couple of years ago, I upgraded my old DH-220 to the Fantasia version complete with upgraded power capacitors, diode bridge, and power switch. While I felt Fantasia project was very well documented, I had some difficulty. In my zeal to get the project over the finish line, I forgot to check the clearance between the power capacitor mounting ring screw clamp and the gate driver heatsink on the side closest to the clamp. (Note that this is a problem on one channel only.) When I powered up, bang went the flameproof resistor along with the gate driver transistor. Unsoldering that board to effect repairs was very difficult. I did get the job done, and I thought it sounded very good, but maybe a little bright.
So, when I saw the 220C upgrade option with terminal blocks for power and board interconnects, I was interested in giving it a try. I started the project in the spring and completed it in August. I think it sounds very balanced with good punch, and excellent clarity, and both channels are very quiet at no input. I'm very pleased with the results.
Some thoughts about the construction:
1. First of all, read the instructions provided in the audioXpress article closely, and read them again - before you solder components in the PC boards. Read them again when you're ready for testing.
2. Safety first - this point is not emphasized enough with this amplifier IMHO. This amplifier has relatively high DC voltage rails, the power caps in the amp have the lead screws facing up, and the +/- power rail fuses are directly adjacent to both AFE circuit boards. Be very careful, and don't take this project on unless you are experienced with complex projects.
3. Going back to reading the instructions. It would be a good idea when reading the instructions to note the various resistors that will be accessed during the testing process. I suggest that you make sure that you mount these resistors a little higher when you solder them in to make them easily accessible with clip leads.
4. In the instructions, it mentions that you can test the AFE board in each channel before connecting it to its associated OPS board. This is a really good idea. If you plan to use the DH-220 power supply when you do this, I recommend that you replace the 5A +/- power rail fuses on that channel with 0.25A versions, and switch back when you area ready to test with the OPS boards fully connected.
5. Both channels worked first time for me, and I had no issues dialing them in to the desired settings. Note that the instructions suggest making sure you start with both trim pots in the full CCW position. It took a lot of turns, especially on the VAS trim pot to get from 0V to its desired set point.
6. Let the amp run for a couple of hours and re-tighten the terminal block screws before putting the cover on and buttoning everything down.( Make sure you let the power supply voltages drop to zero before doing this🙂) It's tight inside that amplifier!
7. I debated upgrading the A/C wiring, installing an IEC connector, and grounding the unit on the primary side, but elected not to.
All I need now is a "C" to put on the outside.
So, when I saw the 220C upgrade option with terminal blocks for power and board interconnects, I was interested in giving it a try. I started the project in the spring and completed it in August. I think it sounds very balanced with good punch, and excellent clarity, and both channels are very quiet at no input. I'm very pleased with the results.
Some thoughts about the construction:
1. First of all, read the instructions provided in the audioXpress article closely, and read them again - before you solder components in the PC boards. Read them again when you're ready for testing.
2. Safety first - this point is not emphasized enough with this amplifier IMHO. This amplifier has relatively high DC voltage rails, the power caps in the amp have the lead screws facing up, and the +/- power rail fuses are directly adjacent to both AFE circuit boards. Be very careful, and don't take this project on unless you are experienced with complex projects.
3. Going back to reading the instructions. It would be a good idea when reading the instructions to note the various resistors that will be accessed during the testing process. I suggest that you make sure that you mount these resistors a little higher when you solder them in to make them easily accessible with clip leads.
4. In the instructions, it mentions that you can test the AFE board in each channel before connecting it to its associated OPS board. This is a really good idea. If you plan to use the DH-220 power supply when you do this, I recommend that you replace the 5A +/- power rail fuses on that channel with 0.25A versions, and switch back when you area ready to test with the OPS boards fully connected.
5. Both channels worked first time for me, and I had no issues dialing them in to the desired settings. Note that the instructions suggest making sure you start with both trim pots in the full CCW position. It took a lot of turns, especially on the VAS trim pot to get from 0V to its desired set point.
6. Let the amp run for a couple of hours and re-tighten the terminal block screws before putting the cover on and buttoning everything down.( Make sure you let the power supply voltages drop to zero before doing this🙂) It's tight inside that amplifier!
7. I debated upgrading the A/C wiring, installing an IEC connector, and grounding the unit on the primary side, but elected not to.
All I need now is a "C" to put on the outside.