Haffler DH-220 upgrade path

[Plcamp]

First of all, it's "Cordell". Read his book. Read Self's while you're at it. I bought the PCBs off ebay and they look fine. The design is solid. Proceed with caution. The AudioExpress articles, Aug and Sept '21 I believe, have the performance and build details. This is a very good upgrade.

For those interested, this presentation by Mr Cordell describes why each component was chosen in the topology you get from the eBay site.

 

[tomelex]

I would not worry about the fuses, just replace them with new ones of the correct value and make sure the ears of the fuseholder make good contact. The fuse is in the feedback network on the DH 220 also so no audible affect on the music from human ear possible.

 

[tvrgeek]

Coredell has new boards as well as a gentleman on E-Bay who used to work for them. But,
I have a DH120 I have modded and really opened up without a major topology change

Removed the balanced and dynaquad stuff, input pots.
Paid very close attention to the grounding scheme. Star ground.
Power supply: Tripled the uF, but used a bank or 6600's.
Bigger caps means heavier rectifier. I used a HEXFRED
I split the resistor on the rails and added a second cap. Greatly reduced ripple to VAS and IPS.
Easy to do an LED for the IPS CCS.
Tweaked IPS and VAS currents
Easy to add degen to the IPS current mirror. I actually reduced the LTP degen
But the BIG change was converting from dominant pole compensation to Miller. Even more can be done with two-pole or output inclusive.

'Ol Erno knew his stuff, so be very careful of phase margin or you get a 200W oscillator for about three seconds.

Over in various DIY forums there are huge examples of mods and POOGE for the 220's. Do your GOOGLE homework.

If you don't know what this means, buy all means get Bob Cordells book and Doug Self's book on amplifier design. Remember, you can't buy replacement outputs, so don't blow it up! ( I converted mine to Exicons, but that required several changes for stability)

As much as we loved to mod them, they were and still are a very good amp right out of the box. You can pay several thousand today and not equal them. I don't need another project, but I am about half tempted to do another. My LTSpice model says I can half the distortion again without the exotic FET cascode and diff VAS.

 

[magconpres]

Thanks for all the replies.
Bot busy with other projects and work, but hope to get back to the Haffler soon. Currently, it's sitting on my workbench.
Based on the input here, I am going to do some of the recommended testing and take the "less is more" approach.

 

[Gringoaudio1]

I have two DH-220 amplifiers. I replaced the power supply caps on one as the voltage was varying but had to take the other to a shop. He replaced a few small parts (caps mainly) and it sounds great now. One channel was out. I stopped caring about details of the repair once it was in his hands.
The RCA jacks on these things are from another era and no RCA cable I have will fit snugly to them. Was there a different standard for RCA dimensions at some point? They could use replacement.
I also have a DH-200 with burnt out output transistors in one channel. If you dig there appear to be modern replacements. Finding the originals means a lot of money. The repair shop guy just looked at the originals and his quote was too expensive. Anyone replace the power transistors with the modern equivalent? How do they sound? I guess I should replace all of the output transistors in both channels if I go this way. Thanks.

 

[Doodski]

I guess I should replace all of the output transistors in both channels if I go this way.

How valuable is a DH-200?

 

[Gringoaudio1]

It has the Musical Concepts front end
So I always wanted to hear it. Never have. It is ugly and has nasty sharp heat sinks and would be a boat anchor if it didn’t have this upgraded front end.

 

[Plcamp]

I believe a company called Exicon produces these FETs now? Going by memory but I think that’s right.

 

[tomelex]

I have two DH-220 amplifiers. I replaced the power supply caps on one as the voltage was varying but had to take the other to a shop. He replaced a few small parts (caps mainly) and it sounds great now. One channel was out. I stopped caring about details of the repair once it was in his hands.
The RCA jacks on these things are from another era and no RCA cable I have will fit snugly to them. Was there a different standard for RCA dimensions at some point? They could use replacement.
I also have a DH-200 with burnt out output transistors in one channel. If you dig there appear to be modern replacements. Finding the originals means a lot of money. The repair shop guy just looked at the originals and his quote was too expensive. Anyone replace the power transistors with the modern equivalent? How do they sound? I guess I should replace all of the output transistors in both channels if I go this way. Thanks.

The RCA inputs can sort of corrode over time, so should probably replace them anyway. Also, I use mine in bridged mode, 350 watts at less than 0.040 THD across the band 20 to 20Khz and for various reasons they sound better too even at low volumes. Max measured power at 450 watts peak at 1Khz mono. However, don't expect that kind of power at lower impedances than 6 ohms, as the power is reduced in bridge mode due to the heat sink dissipation in that case. You can also increase the fuse size to max 7 amps for the amplifier, but your speakers might like less fusing for safety. Exicon was rumored to have replacements MOSFET for the amp as mentioned, but you might just buy a parts amp to hope to get a few of the good originals VMOS which were purpose built for audio.

google for how to connect up their recommended switch and wiring points for bridged operation.

 

[Plcamp]

The junction of the rca’s grounds is also the single point ground for the whole amp.

I repaired one, problems were few. Apart from just cleaning it, the series AC thermal cutouts on the heatsinks we’re both bad; thermal compound was desperately dried out, and I replaced the power switch. All else was ok.