Hafler DH-200/220 Mods

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marc brown

marc brown

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Joined 2007
Hafler DH tube driver

vilfort said:
This thread has been a little quiet lately so I figured it was time to post an update to my Hafler tube conversion project.

Today an old 220 arrived at my door from Ebay. It was a completely un-modified factory wired job so it gave me a nice chance to hear what a "clean" Hafler sounded like... Well what is there to say: it sounded a bit congested, un-elegant, clumsy and chalky... Sure, it likely could benefit from a re-cap but I cannot help feeling that the whole high open loop gain/loop feedback thing is messing up things.

I immediately hooked my Hafler tube mod up again and played the same CDs... Now, this was better: effortless, deep and wide sound stage, bass slam and silky highs.

This octal triode MOSEFET combo is becoming very easy to live with. It also seems very stable. I have run the amp for 10 days straight now and BIAS is rock solid. Sound wise the amp really started opening up after having been on for 3 days. I also noticed that tube rolling makes a huge difference. Russian surplus tubes sounded raw and harsh. The best combo was running Sylvania 6SL7 w/ GE 6SN7.

In case anyone out there wants to build this sweet little amp from an old Hafler (or build it from scratch) here is a cleaner and safer version of the schematic (version 2.5).

Cheers,

D.

PS: yes, all the parts do fit nicely in the chassis with a little finesse. I will post a pic later.
Click to expand...

Vilfort, I'm very interested in modifying a DH-500 with your tube driver stage. Do you have any pictures of your implementation? Would I need to make any changes to your circuit before implementing it in the DH-500?

thanks! :)
 
Algar_emi

Algar_emi

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Hi. Who said that helping people doesn't give you anything ;) I helped the father of one of my acquaintance a few months back, and look what does he gave me! Two Hafler amps in perfect working order, a DH-200 and a nice DH-220. The kit construction is very nice, the power transformer is huge and heavy. Bias is close to 0.3A (measured on each supply rails). Serious piece of a kit.

I'm an happy man :D

I already put the DH-220 to service within a nice little sound system for my wife's office, rotel CD, NAD tuner, VSE SVP-2 tube preamp and the Hafler.
 

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C

chrisb

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Joined 2002
Nice score Sylvain - looks like the one certainly had "some work done" to at least the power supply filter bank stage, and input jacks - so perhaps some of the numerous mods for these over the years as well .

Yup, one of DH's out of the park home-runs in terms of performance / value, and certainly spawned many an aftermarket upgrade / mod/ tweakers career.
 
Algar_emi

Algar_emi

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That was not all, I also got a very nice Sony CDP-338SE CD Player, built like a tank, sound very good, has a neat remote volume control by motor. The small red led on the headphone volume pot flash when varying the volume, changing the rear variable output at the same time. A real classic. I saw that Lampizator added a tube output to this particular model: Sony CDP338ESD

May give a try in a few years, if the CD player survive. Seem to work just fine for the moment, but we never know with old player.
 
WSJ

WSJ

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Joined 2009
public.fotki.com/WAYNEWANG/electric-car-beetle-ev-/
woody said:
Does anyone know the heat sink ratings for the 220 ? I am interested in the actual thermal resistance.
Click to expand...

That is easy to measure, just clamp a power resistor to the heat sink in the center inside opening and apply a fixed amount of power, then measure the heat sink temp rise. Done this many times, works great.

Heat sink temp rise test. Data recorded for use with Excel. Pic #2.

I'm using similar equipment to evaluate my Aquarium heater. Heat source, 200W, heat sink is the sides, top and bottom of the Aquarium. Pic #1

My Hafler Amp mods: http://public.fotki.com/WAYNEWANG/

Fluke 96 Scopemeter and Fluke 80TK Thermocouple Module
 

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A

AMRoberts

Member
Joined 2007
Do I need to replace power switch with lamp failure?

Hi,

I believe the neon lamp inside the power switch on my DH-220 has given up the ghost. Background - I don't actually use the switch, the amp is plugged into the switched outlet on the DH-110. Symptoms:
  • normal operation on both channels
  • several months of lamp operating when system was switched on for some hours, then intermittent, rapid, randomized flickering, then off
  • finally a transition to never lighting at all
I am looking at the schematic, and to the limited extent that I understand such things, it seems that the secondary purpose of the lamp would be to indicate if either of the thermal breakers was operating ... Is this correct? If so, I'm not convinced I want to open the cover just to change out the switch. If there is a more important purpose to having the lamp functioning, perhaps I'll have to give it a try.

While I'm looking at the schematic I have a second question (also probably a function my limited understanding). It seems to me that even with the amp switched off, there is a closed circuit through the transformer primary (albeit with high impedance??) via C407. Is there any purpose for this, or is C407 just acting as a snubbing circuit for any arc within the switch?

Thanks,
Alan
 
Algar_emi

Algar_emi

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Images I posted were for the DH220 with the newest PC-19c PCB and indeed the RCA and speaker binding posts were upgraded. The Supply caps also with a neat pcb assy, with snubber and electrolytic film cap bypass.

But what was my surprise when I opened the older DH200, it was upgraded too ;) Check the pictures. Mods include RCA & bindings posts replaced with better quality, signal coax input cable between RCA and PCB, same multicaps power supply upgrade pcb, and the pcb seem to be the two sides PC-19 as well, with quality film caps, two pots adjustments (offset & bias), etc.

Also the gentleman that had these amps came from HK, and his amps have the optional multi-voltages primary version :D

I'll just add a Surge Varistor at the transfo input to protect the power-on switch and no other upgrades will be necessary on these babies!
 

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Algar_emi

Algar_emi

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C407 is there to remove the 'Spark' sound when turning the amp off. It is installed on most power switches for this very purpose. On the DH-220 if one of the over-temp switched mounted on each each heatsink opens (over temp fault), the amp turn-off, and the lamp is off at the same time...

On the DH-200 there is a separate neon lamp on the left side of the power-on switch, normally it is off, in case of over-temp fault it turns on.
 
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