Hafler DH-110 Preamplifier Refresh

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.

Checking THD after capac­i­tor replacement

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.

Hafler DH-110 capac­i­tors and rib­bon cables in the phono section
Hafler DH-110 switch­es, capac­i­tors and rib­bon cables look­ing to front

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.

Hafler DH-110 Noble 204Y50KΩX2 poten­tiome­ter

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

Hafler DH-110 pow­er sup­ply section
Hafler DH-110 line ampli­fi­er sec­tion look­ing to front

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.

Hafle DH-110 main board C119 capac­i­tor module

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.

Hafler DH-110 pow­er sup­ply sec­tion added heatsink for IC1 and IC2

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.

Hafler DH-110 long view of main board
Hafler DH-110 main board bot­tom view of phono side
Hafler DH-110 main board bot­tom view of pow­er sup­ply side

26 Replies to “Hafler DH-110 Preamplifier Refresh”

  1. 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

    1. 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.

  2. 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

    1. 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)

      1. 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

        1. 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)

    2. 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

  3. 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?

  4. 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!

    1. 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)

  5. 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

    1. 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)

  6. 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.

    1. 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)

  7. 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

    1. 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)

      1. 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.

        1. 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.
          Hafler 0.82 uF capacitor C19

  8. 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.

    1. 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)

  9. 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

    1. 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.
      Replacement surface mount type C19 and C119 board prototype

  10. 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 !!!!

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