Hafler DH-101 gets new capacitors.

After 33-1/3 years (give or take a couple of weeks…seriously!), I finally refreshed the capacitors in the DH-101.  A year or two ago, I swapped out the DH-110 for a handful of reasons.  First, I always thought it was a little “softer” sounding, maybe even mushy.  Second, I bought it used, and the front panel and knobs tend to chip off.  Third, I hated the stepped volume control with a passion–at lower volumes, it was impossible to set to the desired level.  Fourth, the switches and potentiometers were quite noisy, and got noisy faster after a good cleaning.

That drove me to put the DH-101 back into the system.  I’d read comments from some owners preferring the 101’s sound over the 110, the background being “blacker.”  And upon hooking it back up, I noticed it was not only quiet, but sounded a touch more precise.  Faster, maybe?  At any rate, the 101, and the 110 for that matter, were both overdue for a refresh.  Time for some new capacitors in the 101!

Rather than buy them individually, I wound up buying a complete capacitor kit.  I might have preferred caps that were a little more high-end, but the advantage here was that these were electrically paired and matched for a much closer tolerance than what I could have bought on my own.  All of the electrolytics are now Nichicon.

The kit was only for PC4, the main audio board.  It did not include power supply caps.  No problem, as I had other plans.  The process went rather well, I’m happy to say, and it did not take long to replace everything.  A couple of days later, I was finally able to give it a listen.

Was there a huge difference?  No.  But I did notice the sound was cleaner and clearer than before, and the tonal balance was subtly better.  It also seems the highs lost a slight bit of roughness.  It did come out quieter than before, although I was also battling some substandard Audioquest cables at the time.

The power supply caps I ordered from Mouser.  The 101 originally had capacitors before and after the 7818/7918 voltage regulators.  Before the regulators were 1000µF 35 volt capacitors, and after were 100µF 35 volt.

Or, so I thought.  Many years ago, I had a similar problem where the power was intermittent, the preamp would only turn halfway on–the sound was distorted, and the LED was dimly lit.  Back then, I had replaced the caps on one side of the power supply.  That fixed it, for a while.

Only after I took the caps out did I realize I’d replaced the originals with 25 volt capacitors.  Which might explain why they failed again!

Nichicon Muse series capacitor

We’re good now, though.  The new caps are 50 volts vs. 35 (or, oops, 25).  I also read that increasing the value could help the sound, so I bumped them up–the 1000µF are now 3300µF, and the 100µF are 330µF.  What are the advantages?  Better filtering (lower noise), and more importantly, increased storage capacity, as that is one function that capacitors provide.  Luckily I found capacitors with the same lead spacing and diameter, as it’s a tight fit.

So, what happened to the sound?  The noise level is very slightly better, to the point of almost not noticing it (as it is already very quiet).  But the drive…the bass is subtly stronger and clearer now that the voltage does not sag.  Very nice!  The heft of the bass improved with the Nak PA-7 in the system (which has, I think, about 132,000µF total capacitance in its power supply), and this helped it along even more.  It’s subtle again, but the preamp has an even more effortless quality than it did before.  I can turn it up and hear no straining whatsoever.

I bypassed the external processor loop.  Doing so freed up a set of RCA jacks.  I have long wanted to have an attenuated output, so I could regain more of the volume control’s range.  One output is still full power, while on the other, I have two resistors per channel (33k, and 8.2k) in an L-pad configuration, giving me ~12dB-15dB attenuation.  Due to the power output of the preamp, I went with 1-watt resistors.

I will likely not take modifications much further, beyond some mechanical changes.  I may change to a star grounding arrangement to get rid of some stray EMI/RFI.  I might rewire it with premium wiring (even though I did a nice job of routing it when I originally built it up) from DH Labs.

Most notoriously are the horrid RCA jacks on the back.  Made of aluminum, the are quiet dull, and they are also loose to the point of rattling.  I need 22 panel mount gold-plated RCA jacks to make a change here, not so much for sound, but to prevent future problems.  All of my cables are now gold plated, so there will be no metal mismatch.

Despite its age, the little DH-101 still holds its own, and is refreshed for another couple of decades.  I am leaning towards a tubed preamp, but this 101 will not leave my possession.  I might match it back up with the M-500t, or I may find a Hafler DH-220 power amp to pair it with.  That would make for a nice-sounding system.