Just saw the info on Dick West's passing away...
I missed this before... very sad to hear.
While I got to know Dick back from modifying Haflers in the '80s, most of my interaction with him was around a small group that scratch-built PS-IV preamps. Dick did the boards and matched the transistors... I took mine out of my system in the early '90s, but still have the silicon and boards around somewhere. Was a fun project and Dick was a joy to work with on that. I came across some of our correspondence on that a few months ago... now doubly sad.
THANKS!
Greg in Mississippi
I missed this before... very sad to hear.
While I got to know Dick back from modifying Haflers in the '80s, most of my interaction with him was around a small group that scratch-built PS-IV preamps. Dick did the boards and matched the transistors... I took mine out of my system in the early '90s, but still have the silicon and boards around somewhere. Was a fun project and Dick was a joy to work with on that. I came across some of our correspondence on that a few months ago... now doubly sad.
THANKS!
Greg in Mississippi
Hafler DH-200 offset voltage problem.
I have a DH-200 that I bought non-working on EBay. I replaced bridge rectifier which was shorted out. I also replaced all the electrolytic caps on both boards as well as the 10,000uF caps with 18000uF. Now the problem is the channels have an offset of + 408mV and + 480mV. There is also a 60 Hz signal riding on top of the offset on both channels. It is independent of the input and power supply. The power supply has a slight 120Hz ripple, but that is not present on the output. The amp sounds ok, but has a definite 60hz hum and a little AM radio mixed in coming from the speakers. The wiring is not neat but the solder looks ok. I re-soldered some of it and will probably rework most of the wiring.
From advice from previous posts I plan to replace the matched pairs Q1/Q2 and Q5/Q6 to solve the voltage offset problem. It is interesting that both channels are so far off.
Does anyone have any other thoughts on any other fixes to do while it is taken apart?
I am hoping that rewiring it with new connectors and wires will get rid of the 60HZ and AM radio problem.
Any thoughts will be greatly appreciated.
-Steve
Oakland CA
I have a DH-200 that I bought non-working on EBay. I replaced bridge rectifier which was shorted out. I also replaced all the electrolytic caps on both boards as well as the 10,000uF caps with 18000uF. Now the problem is the channels have an offset of + 408mV and + 480mV. There is also a 60 Hz signal riding on top of the offset on both channels. It is independent of the input and power supply. The power supply has a slight 120Hz ripple, but that is not present on the output. The amp sounds ok, but has a definite 60hz hum and a little AM radio mixed in coming from the speakers. The wiring is not neat but the solder looks ok. I re-soldered some of it and will probably rework most of the wiring.
From advice from previous posts I plan to replace the matched pairs Q1/Q2 and Q5/Q6 to solve the voltage offset problem. It is interesting that both channels are so far off.
Does anyone have any other thoughts on any other fixes to do while it is taken apart?
I am hoping that rewiring it with new connectors and wires will get rid of the 60HZ and AM radio problem.
Any thoughts will be greatly appreciated.
-Steve
Oakland CA
Thanks djk, The 2.2ohm(R45) at the input is ok but R39 is open on both channels. Funny they don't look burned. I will look into this and either replace R39 or do an alternative ground modification.
Hi slogger,
For starters, just keep things the same until all the faults are cleared. You need R39, don't mess with that part of the circuit. After that you can play a little.
Blown R39 means you had a large current from the input jacks flowing into the chassis. I can think of a few things that could have done that. Right now you are probably getting a ground through the stuff you have plugged into the amp on the signal side.
Wire dress is important. See if you can find some pictures of the interiors of these amplifiers and run your wire the same way. This can be more important than you might think.
Hi djk,
Really good seeing you again. Open input ground resistors is a good call, and this open part (R39) is a related part.
-Chris
For starters, just keep things the same until all the faults are cleared. You need R39, don't mess with that part of the circuit. After that you can play a little.
Blown R39 means you had a large current from the input jacks flowing into the chassis. I can think of a few things that could have done that. Right now you are probably getting a ground through the stuff you have plugged into the amp on the signal side.
Wire dress is important. See if you can find some pictures of the interiors of these amplifiers and run your wire the same way. This can be more important than you might think.
Hi djk,
Really good seeing you again. Open input ground resistors is a good call, and this open part (R39) is a related part.
-Chris
Hi anatech, Thanks for getting back to me. I replaced the bad rectifier, checked out the transformer unloaded then reassembled it and brought it up with a variac. The amp works fine but is a little noisy kind of low level 60hz buzzing. This was before I noticed the R39 issue. Once I play music I don't notice any distortion. It is possible this amp was used that way for years before the bridge rectifier failed.
I did notice that the speaker negative output posts in my unit are not grounded to the chassis like in the schematic. They do go to the center tap. So with R39 gone the output is not grounded to the chassis. I was going to do a star ground like Dick West talked about below.
I did notice that the speaker negative output posts in my unit are not grounded to the chassis like in the schematic. They do go to the center tap. So with R39 gone the output is not grounded to the chassis. I was going to do a star ground like Dick West talked about below.
I suspect that the R39 would go either when the bridge rectifier failed or due to a heavy AC signal on the ground. The R39s do not look burned but are open. The star grounding looks consistent (electrically speaking) with the schematic so I don't think it could hurt anything.
R39 usually goes when 120V comes in to the RCA inputs.
When using for PA this is a common failure.
When using for PA this is a common failure.
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Thanks, I an believe that 120V on the RCA ins would do that. I did the star grounding fix and it worked like a charm. The DC V offsets on the speaker out puts now are with in +/- 10mV instead of 400mV no more 60hz noise. I'm glad I didn't order all the transistors to match Q1/Q2 and Q5/6. I left R39 open. The amp sounds very nice now.
The only other thing I was thinking about doing is adding some smaller value caps on the 18,000uF caps to smooth out the 120hz ripple at the the +/- 60V before going into the amp boards. I don't see the ripple at the output so it is probably being fitered out by C10 and C7. Anyone recommend doing that?
The only other thing I was thinking about doing is adding some smaller value caps on the 18,000uF caps to smooth out the 120hz ripple at the the +/- 60V before going into the amp boards. I don't see the ripple at the output so it is probably being fitered out by C10 and C7. Anyone recommend doing that?
I am very interested in the circuit used by Hafler/Dick West to match transistors. Any info on it?
Cascode the input stage makes a nice improvement.
THx-RNMarsh
Cascode the input stage makes a nice improvement.
THx-RNMarsh
Hi Richard,
I made a diff pair with resistors in the base and collector circuits, a CCS for the tail current. Measure for equal collector voltages. I routinely get extremely tight matches this way, tight enough for degeneration resistor matching to be required also. I have posted this circuit and PCB layout several times. Look for "beta matcher" and my screen name.
When building it, I used 0.1% resistors for the base and collector resistors, 10K0 for bases, 100R for collectors. Place the pair in thermal contact and use a foam cover. Let things settle and you can take your pre-assorted bunch and make them worth something. 🙂 Works for J-FETs and BJTs equally well. Due to the base resistance, you can also figure out the beta under those conditions. The tail current is variable.
The 0.1% resistors are not expensive these days, and using a good DVM is expected. I use an Agilent 34401A usually, but the 3478A is just as good for this. BTW, temperature is cancelled out of the equation so you do get honest matches from that method.
Yes, both the CCS circuits (NPN & PNP) use red LEDs.
-Chris
I made a diff pair with resistors in the base and collector circuits, a CCS for the tail current. Measure for equal collector voltages. I routinely get extremely tight matches this way, tight enough for degeneration resistor matching to be required also. I have posted this circuit and PCB layout several times. Look for "beta matcher" and my screen name.
When building it, I used 0.1% resistors for the base and collector resistors, 10K0 for bases, 100R for collectors. Place the pair in thermal contact and use a foam cover. Let things settle and you can take your pre-assorted bunch and make them worth something. 🙂 Works for J-FETs and BJTs equally well. Due to the base resistance, you can also figure out the beta under those conditions. The tail current is variable.
The 0.1% resistors are not expensive these days, and using a good DVM is expected. I use an Agilent 34401A usually, but the 3478A is just as good for this. BTW, temperature is cancelled out of the equation so you do get honest matches from that method.
Yes, both the CCS circuits (NPN & PNP) use red LEDs.
-Chris
DH 220 0 Volt Connections
Hi Guys, hope you can provide some clarity for me.
I have been carrying out some pretty basic servicing and mods to a standard DH220 Amp, upgraded smoothing caps, fitted uprated bridge rec, fitted soft start circuit, fitted isolated phono sockets, etc.
The query I have concerns the 0 volt connections.
At present I have fitted a heavy duty strap between centre point of capacitors and terminated transformer 0, power amplifier 0 and speaker return 0 to this junction, the chassis isolated phono connection screened lead go direct to pcbs, should I mske any additional connection to the input earth? and should I ground the 0 volt junction on the capacitors?
Many Thanks
Aug
Hi Guys, hope you can provide some clarity for me.
I have been carrying out some pretty basic servicing and mods to a standard DH220 Amp, upgraded smoothing caps, fitted uprated bridge rec, fitted soft start circuit, fitted isolated phono sockets, etc.
The query I have concerns the 0 volt connections.
At present I have fitted a heavy duty strap between centre point of capacitors and terminated transformer 0, power amplifier 0 and speaker return 0 to this junction, the chassis isolated phono connection screened lead go direct to pcbs, should I mske any additional connection to the input earth? and should I ground the 0 volt junction on the capacitors?
Many Thanks
Aug
Hi Aug,
These days we would normally make one of the input RCA connections the chassis connection as well. It wouldn't hurt to use a 10 ~ 100 ohm resistor for that as we don't expect or want current flowing through that connection.
Be aware that there are extremely high current pulses flowing between the transformer return and the outputs from the rectifiers to the filter capacitors. Therefore, create a separate common path for those circuits and make another as the returns for your amplifier boards. Be aware also that the speaker connector returns will also have high currents circulating. What goes out must also return to some very low impedance point.
Imagine that each ground connection has some signal on it that you don't want to become mixed with anything else. In the case of supply charging currents, this is very much the case. Same for your speaker returns. Now, the circuit board "ground" is more a low current reference, and your signal input common is precisely that, a reference for the signal to be differentiated against. Any noise on your input signal grounds (bad term for this really) looks exactly as if that signal was on the signal conductor. If both conductors have an equal signal (say - hum), that signal isn't amplified as it is common mode. However, common mode noise does get amplified in the imperfect real world, just not as much. The common mode signal can cause distortion in the desired signal too.
Anyway, just look at your "grounds" as being signal carrying conductors. Some with what you want and others with very undesirable signals you don't want. Keep the "good" signals on different conductors as much as reasonably possible.
-Chris
These days we would normally make one of the input RCA connections the chassis connection as well. It wouldn't hurt to use a 10 ~ 100 ohm resistor for that as we don't expect or want current flowing through that connection.
Be aware that there are extremely high current pulses flowing between the transformer return and the outputs from the rectifiers to the filter capacitors. Therefore, create a separate common path for those circuits and make another as the returns for your amplifier boards. Be aware also that the speaker connector returns will also have high currents circulating. What goes out must also return to some very low impedance point.
Imagine that each ground connection has some signal on it that you don't want to become mixed with anything else. In the case of supply charging currents, this is very much the case. Same for your speaker returns. Now, the circuit board "ground" is more a low current reference, and your signal input common is precisely that, a reference for the signal to be differentiated against. Any noise on your input signal grounds (bad term for this really) looks exactly as if that signal was on the signal conductor. If both conductors have an equal signal (say - hum), that signal isn't amplified as it is common mode. However, common mode noise does get amplified in the imperfect real world, just not as much. The common mode signal can cause distortion in the desired signal too.
Anyway, just look at your "grounds" as being signal carrying conductors. Some with what you want and others with very undesirable signals you don't want. Keep the "good" signals on different conductors as much as reasonably possible.
-Chris
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Hi, thanks for your reply, I found it quite informative and contradictory to what I believed to be the correct 0 volt termination process, mind you this is from previous experience of wiring high powered PA Amps.
The main reason I sought the correct termination for the Haffler is the fact that it appeared different to to the way I would have terminated these.
Normally I would terminate the centre tap of transformer along with pcb 0 volts and speaker returns via terminal lugs on a common nut and bolt, dead centre of the capacitor common bar, I would then terminate this connection via a 0.1 cap and 10 ohm resistor down to a chassis lug where I would also terminate the mains earth cable.
The input cables from phono or other connector would then go on to the pcb only, might be worth mentioning, the input 0 volts and pcb power 0 volts were already on same track on amplifier boards.
It worked very well with the boards I was using, but from what you have described and what I have read elsewhere, would not be suitable for the Hafflers.
The main reason I sought the correct termination for the Haffler is the fact that it appeared different to to the way I would have terminated these.
Normally I would terminate the centre tap of transformer along with pcb 0 volts and speaker returns via terminal lugs on a common nut and bolt, dead centre of the capacitor common bar, I would then terminate this connection via a 0.1 cap and 10 ohm resistor down to a chassis lug where I would also terminate the mains earth cable.
The input cables from phono or other connector would then go on to the pcb only, might be worth mentioning, the input 0 volts and pcb power 0 volts were already on same track on amplifier boards.
It worked very well with the boards I was using, but from what you have described and what I have read elsewhere, would not be suitable for the Hafflers.
Hi Aug,
My view of this may differ from other members.
This way should work with PA stuff or anything else. Read Douglas Self's books. He designs recording and broadcast consoles. If anyone knows how to ground things, he would.
I would think that you would rather keep the heavy wiring off the PCBs by following what I had posted. It tends to break thing up very naturally so that you end up with a more relaxed ground structure. Also keep in mind that nothing is perfect, and grounding is one of those things.
In the late 70's, the store were I worked sold ILP amplifier modules. Customers were blowing these things up all the time. It was only grounding problems that was causing these to go boom. I was able to rewire their constructions so that they didn't blow up. I even made a 60 watt version for myself, which I later sold to a "jingle" studio as a monitor amplifier. It was this generic grounding scheme that always seemed to work I used.
-Chris
My view of this may differ from other members.
This way should work with PA stuff or anything else. Read Douglas Self's books. He designs recording and broadcast consoles. If anyone knows how to ground things, he would.
I would think that you would rather keep the heavy wiring off the PCBs by following what I had posted. It tends to break thing up very naturally so that you end up with a more relaxed ground structure. Also keep in mind that nothing is perfect, and grounding is one of those things.
In the late 70's, the store were I worked sold ILP amplifier modules. Customers were blowing these things up all the time. It was only grounding problems that was causing these to go boom. I was able to rewire their constructions so that they didn't blow up. I even made a 60 watt version for myself, which I later sold to a "jingle" studio as a monitor amplifier. It was this generic grounding scheme that always seemed to work I used.
-Chris
Hi Chris, ILP Modules, that's not far off from where I started, the company I was working for in the seventies used to get custom made 500 watt plate modules made by ILP.
I'll probably go with your suggestion for wiring as the fact that I/p 0 and power amp 0 are not common on pcb would from past experience mean that the Amp would most likely be unstable.
I'm pretty sure they should be common somewhere, even if via a resistor rather than connected together.
I seem to remember a couple of Amps that linked input 0 to Power Amp 0 via an on board 10 ohm resistor to isolate from dirty 0.
Many Thanks
Clive
I'll probably go with your suggestion for wiring as the fact that I/p 0 and power amp 0 are not common on pcb would from past experience mean that the Amp would most likely be unstable.
I'm pretty sure they should be common somewhere, even if via a resistor rather than connected together.
I seem to remember a couple of Amps that linked input 0 to Power Amp 0 via an on board 10 ohm resistor to isolate from dirty 0.
Many Thanks
Clive
Hi Clive,
Yes, they are connected, but on a separate arm between the capacitor common so the high current pulses are mostly on the other arm heading towards the transformer.
You are quite right about the resistance to separate the power circuits from the input circuits. However, an amplifier doesn't have to be unstable to suffer from improper ground treatment. Connecting the ref ground to the speaker return ground alone can send most amplifiers into a death spiral. Adding the capacitor returns to that mess only means the amp can hum along as it dies. 🙂
-Chris
Yes, they are connected, but on a separate arm between the capacitor common so the high current pulses are mostly on the other arm heading towards the transformer.
You are quite right about the resistance to separate the power circuits from the input circuits. However, an amplifier doesn't have to be unstable to suffer from improper ground treatment. Connecting the ref ground to the speaker return ground alone can send most amplifiers into a death spiral. Adding the capacitor returns to that mess only means the amp can hum along as it dies. 🙂
-Chris
I found this NOS PC-29 driver board listed on ebay, is a balanced input board for the P-225/230 models supposedly. i didnt see anything about these in this thread(or anywhere else), but they looked interesting.
Downside is the seller doesn't have schematics, or values to enable one to build them out...
NOS Hafler PC-29 (BL200 Balanced Input Board) for P-225/P-230 Amplifier - Blank
Downside is the seller doesn't have schematics, or values to enable one to build them out...
NOS Hafler PC-29 (BL200 Balanced Input Board) for P-225/P-230 Amplifier - Blank
Thanks for that. I was thinking about updating my DH-500 driver boards or using Qua-Co's cascode fet boards. This makes my decision easier.