Updating a Hafler DH-110 preamplifier from the early-80’s with new electrolytic capacitors, along with a cleanup and then testing.

The Hafler DH-110 came in both a partially assembled kit and fully assembled unit. I had purchased this unit as a kit back in the early 80’s. It was originally paired with a Hafler P‑500 amplifier and Dahlquist DQ-10 speakers.
I had packed this preamplifier away before an out of state move 17 years ago, and decided it was time to return it to service.
The electrolytic capacitors were over 36 years old, so I decided to replace all of them with high quality Nichicon electrolytics. All of the original non-electrolytic capacitors were in excellent shape and were placed back in their original positions and channels.

I had researched what modifications some other audio enthusiasts had performed on their DH-110’s and had decided that Hafler had already optimized the circuitry, and to leave well enough alone. Well almost …
One of the changes that I made was to replace the individual channel supply rail electrolytic capacitors (470 uF @ 25 V) with a non-polarized version of the same capacitance and voltage rating. These capacitors are physically larger and have a wider lead spacing than the originals.
If I was to do this again I would stay with high quality polarized electrolytic capacitors, and maybe increase the capacitance to 560 uF instead.


After replacing the capacitors I cleaned all the switches and potentiometers with the exception of the volume control unit, with DeoxIT D5 contact cleaner. The volume control is a sealed aluminum Noble potentiometer.

I also disconnected the ribbon cable connectors and cleaned those as well as the back panel RCA connectors.


Capacitors C19 and C119 are both on a circuit board module and are comprised of a 0.82 uF (0.86 uF measured) film capacitor with a series resistance of 0.4 Ω and a 4.7K Ω series resistor. The resistor is most likely R69 which is not shown on the PC-14 board layout. This module is located at the input of each line amplifier channel.

I did add a heatsink made from a piece of 3/4″ X 1/16″ aluminum angle stock for IC1 and IC2 the 23.2 volt regulators. I noticed during testing that both of these regulators were fairly hot and could benefit from some additional cooling other than the small section of steel frame they were attached to. I reused the original mica insulating washers and added some high quality thermal paste between all surfaces including the frame.

I used my recently built Ultra-Low-THD Sine Wave Generator for testing the performance of the DH-110. All tests performed were well within the original specifications of the DH-110, and I was extremely happy with the results.
The only thing that I would like to still like to replace are the original RCA jacks which are still usable after cleaning off some very light corrosion, but could benefit from new jacks especially in the phono section.



Hi, great pics and work. I’ve got the same DH110 with the same PC14A. I found it very bright and tried to replace the 0.82uf C19, with a Wima MKP 0.68uf. Significant tonal change: less crispy, more medium and bass. I may have lost a bit of high frequencies but I can’t say or measure if this is due to the additional medium and bass or a real loss in high freq. What would you suggest? I have not yet recapped the e caps. Maybe this would restore the high freq. that I may have lost along the way…
Many thanks for your advice,
Philippe
a rise in uf in that area will increase the treable and lowering it with decrease it; as it hppened to you. I tried the same but lost the right channel! Working on the issue now.
The .82uf cap was not making proper contact to board. Resolved.
Hi
I have a Hafler DH-110 Preamp & the Hafler P‑500 Amplifier. I have had it for over 25 years!! I refuse to part with them, as they make my Allison 1 speakers a pleasure to listen to.
I have never had any problems with them in all this time time, and they are stil functioning well. My DH-110 definitely needs a refresh though!! It has started to occasionally cut out on the left and right channels while playing music. When i turn the Balance or Volume Knobs I get static and cut-outs. It doesn’t happen all the time, but enough to be annoying, especially when you are used to hearing such beautiful sound from this equipment.
I am just wondering, what you would charge to overhaul my DH-110? I would love tp keep it for another 10 years at least!!!
If you would be so kind, I would greatly appreciate if you could do it? I will leave my info below
Regards and Stay Safe!!!
Jeff
Hi Jeff,
I understand what a pleasure it is to listen to a Hafler DH-110 Preamp and P‑500 amp combo, as that is the setup that I used to have.
I currently do not work on any equipment that I do not own. But I may consider taking on a few small projects next year(2021).
Greg (Barbouri)
Dear Greg:
I can fully understand your reluctance to take a ‘few small projects’ in 2021. If you should reconsider, do let me now if you might be interested in tackling my DH 110. Chances are I may still be in need of help
Your article on DH110 impressed me , and earned my trust in your expertise.
Be Safe!
Cordiallyu.
luke
Hi luke,
Still not accepting any external projects.
I currently have more internal and family projects, than I have time to complete. I don’t see this changing any time soon.
Greg (Barbouri)
Hi Jeff,
I’ve had a Hafler DH-500, DH-110 and tuner for years. I recently bought a used DH-110 online to potentially use as a part donor. You’re pictures caught my eye. As the ebay DH-110 I just bought has the same green capacitors. Are those the original capacitors or replacement. Thank you
I need the part# for the t0-92 transistors in the hafler 110 , Q3,4,5,6, they’re written up as 414c 416c, 556b and 546b do you have any idea? Equivalent?
Greetings, I have a DH110 that has been recently recapped and gone over, and I am popping its internal fuse randomly now. It will play fine for a week or so, then pop the fuse. I keep it on constantly, and plugged into a PA-grade line conditioner, so I don’t think it is reacting to a line surge or dip. Do you have any idea what the culprit might be? Thanks in advance!
Hi David,
If the issue started after re-capping, I would check to see if one of the new capacitors is possibly bad.
Just because it is new doesn’t guaranty it wasn’t bad or marginal from the factory.
After having the unit on for several minutes, I would unplug it and check for any capacitors that are warmer than the rest.
I would also verify the polarity on all polarized capacitors, and verify bi-polar capacitors are installed in the proper locations.
Greg (Barbouri)
Hi Greg,
Impressive work!
Would you be up for doing an upgrade on my Hafler 110? If not, is there someone you would recommend? Is there a kit for sale, you would recommend?
Thank you,
MIke
Hi Mike,
I don’t plan on taking in any external work again this year. As usual I am already over committed with projects and family.
I did find, what looks to be a good capacitor kit on eBay though.
Ebay Hafler DH-110 PC-14 Capacitor Kit
The kit looks nice, with good reviews and the seller has a 100% feedback rating.
Thanks for the coffee!
Greg (Barbouri)
Have two dh 110. Both are equivalent in phono gain. Volume required setting to 3/4 for full room sound. Looking at replacing transistors in phono. Has new Caps n resistors.
What do you gain by changing the 8 470uf capacitors with 570uf caps?
Hi Tom,
I am currently using Bi-polarized 470 uF capacitors in the DH-110.
But changing from 470 uF to 560 uF would reduce the impedance by 12 milliohms and add additional peak surge capacity at the channel drivers.
This is only 90 uF more than standard and would most likely only add very minimal improvements over the standard capacitors.
This would likely only be noticeable at high volume levels, and very fast slewing of the outputs.
Currently there is no cost difference for upgrading to the 560’s in the Nichicon series that I would install, so why not.
It is possible though to add too much additional capacitance and damage the voltage regulators and diodes from the initial turn-on surge to charge the capacitors.
Greg (Barbouri)
Greg, thank you. I did replace the 470 uf caps as well as others that are in the PC14 capacitor up kit kit listed on eBay. Based on your comments, I’ll leave the new 470 uf caps in place.
I do find that the high frequencies to be somewhat too high.
I’m running the DH-110 pre-amp with my upgraded DH-200 amo driving a new set of Vandersteen 2ce signature 3 speakers. The speakers are not known to be bright in the high frequencies.
I see that capacitors C19 and C119 are 470 nf (.470 uf). If I replace theses with a lower capacitor value will that decrease the high frequencies some?
By the way the PC capacitor upgrade kit in eBay is excellent and the c19 and c119 cap replacement is not part of this kit. But overall, it’s an excellent kit.
Thanks in advance for any advice.
Best regards,
Tom
Hi Tom,
Changing C19 and C119 will mostly affect the lower frequency 3 dB cutoff point and have negligible change in the high frequency response.
I have considered changing the value of C19 and C119 to some 1.5 uF Rubycon 63MU155MC44532 units for an even lower frequency cutoff.
I noticed that your capacitors are 0.47 uF capacitors, compared to my original capacitors at 0.82 uF.
Greg (Barbouri)
With regard to the 1.5 uf Rubycon capacitor — 63MU155MC44532„ I noticed the data sheet for this capacitor states that it is a surface mount and termination are solder pads. I don’t see 2 leads coming out if the capacitor when U was viewing it on line. It U assume their must be leads so one can solder it to the circuit board.
It is a surface mount capacitor and the same style as the original surface mount 0.82 uF capacitor.

I would end up using some clipped leads and soldering them to the sides of the capacitor, just as Hafler did on the originals.
Hi Greg,
Are there any cap or resistor or any other changes which would decrease the sharpness of the high frequencies? I’m looking to make the high frequencies less sharp. Of course I can use the tone controls to make sound adjustments when a CD is LP has emphasized high frequencies.
Basically I recently compared the DH-110 to a NAD 1240 pre-amp with the rest of my audio system and was surprised that the NAD sounded more natural on the high frequencies. I was playing some well recorded classical music.
Hi Tom,
Treble control will affect frequencies above 5 kHz and may be your best bet verses changing the line amplifier design.
Checked my DH-110 this morning and the results showed an extremely flat frequency response all the way out past 32 kHz.
I am using the DH-110 with my modified Nakamichi 420 amplifier and some Infinity speakers, which all sound great together.
Greg (Barbouri)
Greg,
Ok, thanks!
Best regards,
Tom
Hi Greg,
My capacitors for C19 and C119 are .47 uF.
Is there any problem replacing these with .82 uf or 1.5 uf Mylar capacitors? Just wondering if the sound quality will be decreased by using Mylar caps.
By the way thank you for your past comments and recommendations for the Hafler DH-110 pre-amp.
Bets regards,
Tom
The Mylar type will be good in a environment with low vibration, but my choice would be the Rubycon acrylic/polymer capacitors.

Replacing your 0.47 uF caps with the 0.82 uF units will lower the 3 dB low frequency by nearly 50%.
Replacement surface mount type C19 and C119 board prototype.
Excellent presentation! I plan on using your guidance here on my own Hafler pre amp, same year, same vintage. Your work is well thought out, precise, and highly useful to the community. Many THanks !!!!