Hafler DH-101 preamp low right channel

[gnexus]

Somehow, at this point, I just KNEW there'd be some kind of issue with EVERY component! So no luck with this one either... But why is it ALWAYS the right channel?

Background for this post:
Those here who have read my Nakamichi threads should know that all of my audio components were in non-climate storage for 20 years. Very bad idea!

Basically ALL those components now are unfortunately damaged in one way or another. Flooding of 4 feet of water during hurricane Harvey did not help the situation. Fortunately most things were ok. But the audio components did not fare well due to excessive heat and humidity.

In this case this Hafler was REALLY screwed! It actually had water or condensation that leaked onto the box. It was visually the worst. But I was hoping it was all just cosmetic. No luck...

The top panel was very badly rusted. The back panel had surface rust. ALL the back panel RCA jacks were very badly corroded. So had to get a new back panel and the gold plated jack upgrade kit. Still must repaint the top cover on it along with half a dozen others...

I was postponing checking it out electronically. Such bad luck with the other components has me very wary of starting on another. But I finally broke down today and plugged it in...

It works!
That's a plus! Left channel sounds fine. Amazingly, none of the pots are scratchy! Another plus! But the right channel is very low and distorted. It's -12dB low compared to the left channel and has zero bass.

This should be a very easy diagnosis and fix. Compared to the other components so far this preamp is basically nothing. The hard part of replacing the jacks is done. But I'm wondering where to start without a scope?

(Yes. I know I should get a scope. But still waiting on my friend and don't want to end up with 2 scopes.)

Thanks in advance for any ideas.

Edit:
The right output is actually -30dB lower with a 330Hz test tone. It's only 6-12dB lower with music. The output is the same using every input. Tone in/out doesn't affect the levels.

 

[tadawson]

Lower at only low freqs . . . . check the tone circuits. I don't recall the cutoffs on these, but seems like a failed bass pot or circuit might do this. (P3 and associated stuff).

 

[gnexus]

Lower at only low freqs . . . . check the tone circuits. I don't recall the cutoffs on these, but seems like a failed bass pot or circuit might do this. (P3 and associated stuff).

It appears you unfortunately misread the post. It's NOT only lower at the low frequencies. It does seem to be much worse at the lower frequencies, however.

It's an IDENTICAL situation with the tone controls bypassed. The post also notes that all the pots are fine. So it's not a problem in the tone control circuit or amp.

It's a problem with the output preamp circuit. Unfortunately Hafler has a VERY rudimentary schematic that's not up to normal standards. The circuits are quite simple but their labeling is crap. That makes it considerably more difficult to diagnose.

 

[TomSc]

You are lucky that one channel is good, giving you a reference to compare each channel. Run some pink noise through it with a Y cable and probe each channel with your meter on AC. It doesn't have to be a particularly clean signal. This track from YouTube should work.

. You should be able to tell where things go South, even if it's just the bass losing amplitude.

 

[rickl]

I had a low channel in a 101 (or dh-110?) that needed a switch cleaning. I'd try cleaning before replacing any components.

I really like my 101.

 

[gnexus]

You are lucky that one channel is good, giving you a reference to compare each channel.

Yes. That made it MUCH easier to resolve the issue!

Thanks for the link. But I already have TONS of test tones. I have a CD I made and also separate FLAC files with 90 different calibrated test tones. So was using those for testing. That's how I already found the huge loss in the right channel.

The preamp is so simple that it was actually easier just to swap components until the problematic component was identified. I did that until I found that the right channel C11 (10uF 16V non polarized) was bad. I stole the C2 cap and replaced it with that since the turntable input is currently not in use.

Now the preamp works perfectly!

It also has very nice gold plated RCA jacks and a REALLY messed up top cover!

So still lots of work left to paint the top cover...

 

[gnexus]

I really like my 101.

Yes. Very simple and very clean output! It beats most preamps in sound quality.

I built this one from a kit long ago...
But this work restoring it is 4 times as much work!

I'm afraid to even touch the DH-200...

 

[rickl]

I'm afraid to even touch the DH-100...

check this out:

B

Thread 'Upgrading a Hafler DH-100'

Mar 13, 2017

I bought this DH100 to digitize my LPs. I needed a phono stage and the ability to control the output to my Analog-to-digital converter. It worked for a while but I wasn’t happy with the sound. I looked into the DH100 and discovered it was a series 1. And there was a series 2. Could this be the problem?



The original DH100 was Hafler’s model into the low-end. It used op-amps and was a minimalist design (my opinion based on parts count and size and price).
Insides look like:

• Bob
• dh100 hafler
• Replies: 45
• Forum: Solid State

 

[gnexus]

check this out:

Sorry. I meant DH-200 power amp.
The last thing I need or want is another preamp...especially that one...

I guess that's the later model lower end preamp. I've heard of it but never actually seen one til now.
That was released about the time Hafler started going way downhill. They were bought out shortly afterward, if I remember correctly.

When I bought my preamp/power amp I think that was really the only products they sold. Hafler had a very good high end reputation from his time at Dynaco. Unfortunately he killed it with products like that preamp.

 

[rickl]

here are a few links to updates

Post in thread 'Hafler DH-101 Phono Mods'

Nov 29, 2011

Couple of dh-101 links - first was for changing out the RCA connector boards.
http://www.audiokarma.org/forums/showthread.php?t=368705
http://www.audiokarma.org/forums/showthread.php?t=139165
http://www.audiokarma.org/forums/showthread.php?t=242673&

• sregor

Post in thread 'Hi Guys! Want To See A Mess?'

Mar 29, 2022

Hopefully you you got this

• rickl

• 

and this one

https://db.audioasylum.com/mhtml/m.html?forum=vintage&n=10150&highlight=DH-101+mods&r=&session=

 

[rickl]

Sorry. I meant DH-200 power amp.

No worries.

There are a lot of AKers that are dh-200 experts.

My 101/200 combo was used 10+ years when the kids were growing up. Great combo. I've built one or two and still have one on the shelf (next to my xl-280). Plus fixed a few.

Get the 101 going then we can focus on the 200.

 

[gnexus]

here are a few links to updates

Thanks very much for the links!

But the first order of business is just getting the top cover painted and getting it back together again.

My previous post shows the already completed gold RCA jack mod.

Checking and fixing my low end JVC turntable needs to be done before being concerned about any phono section mods, and the power amp and speakers must be done before that...
Hopefully those will at least be easier than the nightmares so far, and hopefully the turntable just needs a new mat.

 

[The Fuxtor]

The switches in these are the worst! I found eventually that I had to put a hole in them to get Deoxit inside and really flood them. Otherwise excellent sounding preamp!!

 

[gnexus]

No worries.

There are a lot of AKers that are dh-200 experts.

Now you have me curious about the DH-200.

Currently wondering if it even works? or if the caps are leaking like hell? or if it explodes at power on!

If nothing else it has ANOTHER top cover that needs to be painted. So i might as well take it off. I'm going to need a production line at this point with SEVEN top covers that must be sanded and painted...

It doesn't look too terribly bad inside. But the rubber pads on the transformer definitely must be replaced. No smoke or flames when powered on.

Will need to run speaker wires to test further...

 

[gnexus]

The DH-200 works!
But:
It also has very low right channel...
(why is it ALWAYS the right channel?)

Time for another thread I guess...

Edit:
No need for a new thread. It was the right channel C1(10uF 16V non-polarized) cap. So simply stole another from the preamp.

So now both the DH-101 and DH-200 are (almost) fully working!

 

[gnexus]

Just had a fun time fixing a loose nut on one of the DH-101 RCA connectors with the gold plated RCA upgrade kit... it's not easy once they are wired!

If anyone else installs that upgrade kit you need to make sure to tighten the crap out of the nuts AND also use loctite!