I would check if the amplifier is in stock condition first and then fault find from there if there is a fault.
Do you have any test equipment to look at the output ?
0.1 uF should be from each power supply rail to 0V if you are using to decouple the leads to the output stage.Hi guys! I am rebuilding a DH200 presently, have made a huge pile of notes thanks to many of you, and printed out all the build and circuit diagrams, its a pretty easy amp to study. Bear in mind I am not a trained tech for electronics, Industrial Design is my background and have self taught all my electronics knowledge over the past 30 odd years.
There have been quite a few interesting mess-ups with this particular unit, one of which was it was being run on 120v step down transformer when I got it (Aussie 240v here) yet it has the international transformer and it was configured for 240! So how do you ask is this possible? Well after sitting staring at it for an hour and going over the drawings, I suddenly realised the switch had been wired back to front. Someone replaced the switch, and wired the active directly to pin 2, with pin 1 going to the jumper link which is connected to the Tx windings BR & BK/W which I guess doubles voltage hence only needing 120vac input?!? The other side which runs through the TB's was connected to pin 3 when it should have been on pin 1.
Anyway reversing the switch wiring had it running on 240v again and things measured ok, dc offset was not too high, 10mv and 40mv, and the amp sounded pretty good.
I have both heatsink modules off in order to clean the horrible black paint that was sprayed all over the amp to "freshen" it upand I am rebuilding the amp boards, new caps, replacing some of the resistors that have been listed as needing to be spot on in order to keep the Q pairs happily balanced etc etc.
So here is the question I have for all the experts in here. The output transistors have base stop resistors of 470ohms, so these have been upped from the original circuits 220ohms. The 390pf mica cap C13 is present. But the 680pf mica cap C18, which appears to go from the + side? of the transistor is missing, instead there is a 47pf cap attached at the same point as the base stop resistor, going to the ground terminal of the tag strip (neither of which were bolted to the heatsink so not making proper ground anyway). This attachment point is different to every photo I have scoured online, and different to the actual circuit diagram showing where C18 should be connected. Please see attached photo, I have removed C13 and unsoldered the orange wire so things are more visible.
Now I read in my notes someone said the output transistors had power bypassing caps on the DH220, while the DH200 does not. They suggest adding these 0.1uf caps to chassis ground, but where do they attach to on the transistors? If someone could suggest how I should proceed here it would be much appreciated. I have replaced C13 with a 390pf silver mica, am not sure on what the 47pf cap is doing in the pic, and where I should attach the 0.1uf caps (getting rid of the 47pf at the same time I guess).
I wonder if these caps you mention were added at some point due to a stability problem ?
the amp was running fine once I rewired the switch correctly for 240v, I ran it for a few hours on and off and it sounded pretty good considering there are some mismatched caps between the boards, dodgy rear fuse holders amongst other little things.
I got it because I wanted to rebuild a DH200 or 220 and see what I could make of it.
I have done both boards with new caps throughout, new resistors in the places recommended, and got to the output device end of the circuit where questions popped up about what had been used and where. the cap was not on either 200 or 220 diagram and not in the spot the diagram shows, hence my questions.
I got it because I wanted to rebuild a DH200 or 220 and see what I could make of it.
I have done both boards with new caps throughout, new resistors in the places recommended, and got to the output device end of the circuit where questions popped up about what had been used and where. the cap was not on either 200 or 220 diagram and not in the spot the diagram shows, hence my questions.
yup I figured it was within spec, just no voltages in any of the documentation for the amp. 58-59v was what I saw on each rail with the old caps and 25A bridge, new kemet caps and 35A bridge I'm seeing 60.2v.
another interesting thing today, when testing the rebuilt supply the switch light (new illuminated spst) is lit whether amp is off or on.
Original wiring had the active running through the fuse straight to the black primary wire, neutral ran directly to the switch centre (2) then from the switched pole through the thermal breakers to the other side of the primary windings. also off the switch is the breaker lamp which runs to the 100k resistor then the winding. there is wire running from the earth side of the switch to the joined primary windings, IE exactly like the factory 240v drawing.
while rewiring and fitting an iec socket I switched things round, running neutral directly to the black primary winding, and active through the fuse then thermistor then into the switch. now the switch stays illuminated when switched off, but the power is cut to the circuit.
I'm trying to picture the path in my mind as to why the switch light is illuminated in the off or on position but not seeing it!
another interesting thing today, when testing the rebuilt supply the switch light (new illuminated spst) is lit whether amp is off or on.
Original wiring had the active running through the fuse straight to the black primary wire, neutral ran directly to the switch centre (2) then from the switched pole through the thermal breakers to the other side of the primary windings. also off the switch is the breaker lamp which runs to the 100k resistor then the winding. there is wire running from the earth side of the switch to the joined primary windings, IE exactly like the factory 240v drawing.
while rewiring and fitting an iec socket I switched things round, running neutral directly to the black primary winding, and active through the fuse then thermistor then into the switch. now the switch stays illuminated when switched off, but the power is cut to the circuit.
I'm trying to picture the path in my mind as to why the switch light is illuminated in the off or on position but not seeing it!
Your illuminated SPST switch has three terminals, hasn't it? Yolu need to find out the pair that connects to the switch points. One of these both terminals connects to the mains input, the other one to the power transformer. The 3rd terminal connects to the PT's other input lead as well as to tghe other mains. If the in-built lamp always is on, just swap the leads to the contact terminal pair.
A DPST switch is superior, btw.
Best regards!
A DPST switch is superior, btw.
Best regards!
Okay, well about inrush current limiting and gate resistors ....
For inrush current limiting, use a relay circuit that shorts a resistor. You want to minimize AC impedance. That improves voltage regulation.
Gate stoppers do not pass DC current, and as such are not noisy, plus the outputs are followers with slightly less than a gain of one. They are not noisy, you would be better off with carbon composition here. It's exactly the same concept as grid stoppers in a tube amp.
Mosfet matching isn't bad from the factory. Again, source followers so it isn't as critical. What is critical is the matching on the diff pairs, and the Vas transistors.
I have rebuilt tons of these over the decades. These are the things that make audible and measurable improvements. So if you haven't done these things, go back and do them. There is a matching jig for signal transistors that will help immensely.
- Chris
For inrush current limiting, use a relay circuit that shorts a resistor. You want to minimize AC impedance. That improves voltage regulation.
Gate stoppers do not pass DC current, and as such are not noisy, plus the outputs are followers with slightly less than a gain of one. They are not noisy, you would be better off with carbon composition here. It's exactly the same concept as grid stoppers in a tube amp.
Mosfet matching isn't bad from the factory. Again, source followers so it isn't as critical. What is critical is the matching on the diff pairs, and the Vas transistors.
I have rebuilt tons of these over the decades. These are the things that make audible and measurable improvements. So if you haven't done these things, go back and do them. There is a matching jig for signal transistors that will help immensely.
- Chris
yes I didn't just follow the numbers on the switch I measured it to be sure, the switch points are centre and lower terminal as I have the rocker going up for on. please take a look at the page in the build manual that shows the various AC configurations for input voltage, mine is wired identical to the 240v picture, my neutral is connected to black PT wire, active to the BR/W wire, with BR & B/W connected together to join the winding into a 240v one I guess. switch terminal 3 is connected to the BR-B/W windings.
ah I think I see what you are getting at, swap the ac in/out wires around on the switch points? leaving the 3rd connection as per the drawings.
thanks Chris, currently it has 470ohm resistors on all output devices, 1w carbon, I picked up some 220ohm 1w carbon today, in order to swap out the 2 resistors on the P? side, aka DH220 circuit.
what are your feelings on the type of cap used for gate to ground? I can get various cap types from local suppliers, mkp 0.1uf ok?
I also have 30pr of transistors coming, original Fairchild, and I have a transistor tester, that should be OK to match them up if needed? the amp didn't have much dc on the outputs and some of the resistors were a bit out from each other, I replaced all the 2.2k with matched beyschlag as I have NOS of them, got some 560ohm today as they are about 10 ohms out from each other.
Hi Sonic Art,
1/4 watt or better would be fine, so you're fine as long as they aren't too large. They do not dissipate very much power unless the mosfet fails. Then it would be good if they opened.
Your gate cap sees a large swing at high output powers. So you want a good dielectric especially. I'd go with a Polystyrene or Polypropylene. Silver Mica would also be fine along with an NP0 / C0G ceramic capacitor (other types of ceramic are terrible!). You don't want Polyester or anything similar. A 250 V rating or better (500V is normal and fine).
I designed a matching jig decades ago and later gave it to the community. A few different PCBs have been designed for it by different members. Look in an Adcom GFA585 thread and you might find it by searching. This is the only way to match signal transistors closely. Temperature is the big variable you have to eliminate. That means measuring them individually will not give you close matches. But that is good for a pre-sort.
-Chris
1/4 watt or better would be fine, so you're fine as long as they aren't too large. They do not dissipate very much power unless the mosfet fails. Then it would be good if they opened.
Your gate cap sees a large swing at high output powers. So you want a good dielectric especially. I'd go with a Polystyrene or Polypropylene. Silver Mica would also be fine along with an NP0 / C0G ceramic capacitor (other types of ceramic are terrible!). You don't want Polyester or anything similar. A 250 V rating or better (500V is normal and fine).
I designed a matching jig decades ago and later gave it to the community. A few different PCBs have been designed for it by different members. Look in an Adcom GFA585 thread and you might find it by searching. This is the only way to match signal transistors closely. Temperature is the big variable you have to eliminate. That means measuring them individually will not give you close matches. But that is good for a pre-sort.
-Chris
If this is the thread to which you refer, I can find no reference to a transistor matching jig -- can you illuminate those of us in the dark?
https://www.diyaudio.com/community/threads/adcom-gfa-585-problems-explosions.92926/page-5
I can get Dayton film & foil PP 0.1 caps, no idea on the sonic quality of daytons caps.
I have Solen metalised PP on hand as well.
With regards to PT primary windings, here in OZ if you purchase a transformer, the primary side will be colour coded blue/brown for neutral/active connection. I guess this is for correct current flow direction through the transformer?
So wouldn't the US transformer be the same, with the black wire being active, and the white/brown being neutral? I ask because there is no marking for active/neutral on any of the Hafler drawings for power circuit connection.
My concern is the active was/is connected through the fuse directly to the transformer black winding (at least on this amp) with the neutral going through the switch and thermal breakers.
So if I reverse this putting the neutral directly to the transformer, and active through the fuse - switch - thermal breakers, should I not swap the PT connections around so the BK primary is still connected to the active, and BR/W to the neutral?
I have Solen metalised PP on hand as well.
With regards to PT primary windings, here in OZ if you purchase a transformer, the primary side will be colour coded blue/brown for neutral/active connection. I guess this is for correct current flow direction through the transformer?
So wouldn't the US transformer be the same, with the black wire being active, and the white/brown being neutral? I ask because there is no marking for active/neutral on any of the Hafler drawings for power circuit connection.
My concern is the active was/is connected through the fuse directly to the transformer black winding (at least on this amp) with the neutral going through the switch and thermal breakers.
So if I reverse this putting the neutral directly to the transformer, and active through the fuse - switch - thermal breakers, should I not swap the PT connections around so the BK primary is still connected to the active, and BR/W to the neutral?
Here's a thread on that matching jig : https://www.diyaudio.com/community/threads/matching-transistors-measuring-the-results.307138/
cogeniac and Phloodpants both made boards for that design. They work well.
cogeniac and Phloodpants both made boards for that design. They work well.
Something else I stumbled across but cannot seem to find now, is mention of adding a second trimpot to the DH200, aka DH220 for adjusting the DC offset, does anyone have some photos of this and the circuit changes needed? I see the circuit on the DH220 diagram, but not sure how much of this needs to be copied and what needs to be changed on the 200 to add it in.
Hi Sonic Art,
No, don't do that. With matched pairs your DC offset should be lower than 5 mV, less than 10 mV is excellent. This also gives you the lowest distortion.
I generally regard less than 50 mV as acceptable (my personal maximum I'll allow out, no damage with speakers), and in fact less than a volt will not damage your speakers. It's not great at all but it will not cook anything. I think a designed offset of 50 mV or greater points to incompetent design.
Now I said my personal maximum for DC offset. At 50 mV and above it is a fault in my book and I take action. I have seen the odd design where the actual DC offset designed in with a matched pair was just shy of 240 mV! Cheap junk can run 150 mV, but it is well known how to achieve low DC offsets with matched pairs less than 10 mV.
Another pet peeve, 10 turn controls for bias and offset is just stupid. Use single turn controls and you can restrict the range of adjustment with the resistors in that circuit. You need to understand that bias is a relative thing and drifts with ambient temperature along with the temperature of the output stage. DC offset? Just get it low. Most amplifiers using a single turn control will adjust to under a couple mV (I always try for 0 mV, but accept higher offsets if the circuit is touchy or drifts a lot. Yamaha is famous for controls that have too much range and are therefore difficult to get close to 0 mV. YOu are further ahead if your circuit is naturally stable and has relatively (not zero) offset compared to one you unbalance the input pair to achieve a low offset. Unbalancing the input pair increases THD by the way, as does an unbalanced pair (see any connection here?).
No, don't do that. With matched pairs your DC offset should be lower than 5 mV, less than 10 mV is excellent. This also gives you the lowest distortion.
I generally regard less than 50 mV as acceptable (my personal maximum I'll allow out, no damage with speakers), and in fact less than a volt will not damage your speakers. It's not great at all but it will not cook anything. I think a designed offset of 50 mV or greater points to incompetent design.
Now I said my personal maximum for DC offset. At 50 mV and above it is a fault in my book and I take action. I have seen the odd design where the actual DC offset designed in with a matched pair was just shy of 240 mV! Cheap junk can run 150 mV, but it is well known how to achieve low DC offsets with matched pairs less than 10 mV.
Another pet peeve, 10 turn controls for bias and offset is just stupid. Use single turn controls and you can restrict the range of adjustment with the resistors in that circuit. You need to understand that bias is a relative thing and drifts with ambient temperature along with the temperature of the output stage. DC offset? Just get it low. Most amplifiers using a single turn control will adjust to under a couple mV (I always try for 0 mV, but accept higher offsets if the circuit is touchy or drifts a lot. Yamaha is famous for controls that have too much range and are therefore difficult to get close to 0 mV. YOu are further ahead if your circuit is naturally stable and has relatively (not zero) offset compared to one you unbalance the input pair to achieve a low offset. Unbalancing the input pair increases THD by the way, as does an unbalanced pair (see any connection here?).
Since we are talking about the primary circuit, your standards and rules in your country apply.
In Canada, I would interrupt the hot, with the neutral connected permanently to the transformer winding. So the fuse holder and switch would go in series with the hot lead and then on to the power transformer. A soft start circuit would interrupt the power in that section also, same with thermal breakers.
As for phase, do not worry about that. As far as the transformer is concerned, there is no difference at all. It is AC current, alternating. On the outside, maybe the neutral is physically wound closer to the core, but the insulation layers are very good. It isn't just the insulation on the wire (enamel). In any event, I can't see where that has any practical impact at all.
The important connection is your hot from your AC cord. Keeping the neutral connected all the time affords the highest protection for personnel who might come into contact with the primary circuit. The neutral in Canada is connected to earth ground at the breaker / fuse panel. The ground is also connected at that point, but the ground is not intended to carry any current. It's merely a safety ground and would only ever carry a fault current from the metal chassis of whatever equipment to protect the user(s). That would include the core of the power transformer in the event you had a winding to core short.
In Canada, I would interrupt the hot, with the neutral connected permanently to the transformer winding. So the fuse holder and switch would go in series with the hot lead and then on to the power transformer. A soft start circuit would interrupt the power in that section also, same with thermal breakers.
As for phase, do not worry about that. As far as the transformer is concerned, there is no difference at all. It is AC current, alternating. On the outside, maybe the neutral is physically wound closer to the core, but the insulation layers are very good. It isn't just the insulation on the wire (enamel). In any event, I can't see where that has any practical impact at all.
The important connection is your hot from your AC cord. Keeping the neutral connected all the time affords the highest protection for personnel who might come into contact with the primary circuit. The neutral in Canada is connected to earth ground at the breaker / fuse panel. The ground is also connected at that point, but the ground is not intended to carry any current. It's merely a safety ground and would only ever carry a fault current from the metal chassis of whatever equipment to protect the user(s). That would include the core of the power transformer in the event you had a winding to core short.
thanks, I think we are pretty similar to you guys, I connected neutral to the black primary directly, and ran the active through the fuse, then thermistor, then switch, from there it goes through the breakers then to the brown/white primary.
active was entering the switch at the middle pin, this was causing the light on the switch to stay on all the time. I swapped in and out around and now light stays off until you switch the amp on.
the original wiring was neutral to switch and active through the fuse then direct to PT black primary.
active was entering the switch at the middle pin, this was causing the light on the switch to stay on all the time. I swapped in and out around and now light stays off until you switch the amp on.
the original wiring was neutral to switch and active through the fuse then direct to PT black primary.