Hafler DH101 preamp repair and mods?

hi Wally5 ,
I sold my dh-101 on ebay ,I just wasn't using it anymore, (25 plus years old) ,B1 D1 salas others ,I don't own a turn table anymore,lol.
I did all the mods I could find ,Mostly made a new CCS and a power supply ,replaced volume control with light resistor coupled leds,bypassed all the switches,and eliminated the tone controls,I did change some small signal ceramic to films caps but didn't hear any improvements ,I did leave a coupling cap in the front input ,and did each mod one at a time and listened,I didn't have any hum so I didn't shield the wire's ,A torrid trans was on the outside of the box ,biggest was a new power supply and bigger better caps,I stacked 4 caps 18,000,1000uf,10uf and .1uf,
Good luck !
 
Made a new plexiglass carriers for the Gold-plated RCA connectors, the new quality PCB board, the wiring will be Van Den Hul CS-18, mains filter and torus transformer will be installed. After the completion of the modification will put new pictures.




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An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


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Where did you get the new PCB? Did you design it your self?
 

Really? When I built my kit DH-101 in '79 I made alterations as I built it. Chief was to NOT connect RCA jacks to the chassis (star grounded) and most importantly, I substituted a 5 way bing post connected to the PCB ground at the phono preamp for the turntable ground. The chassis functions as a shield and mechanical support but is not part of the signal path.

When I got the first CD player in '83 I had a problem with no more aux level inputs. At that point I removed the low-level phono 1 / 2 input selection and converted phono 2 to a high level input. There was an improvement in the phono input noise due to the removal of excess unshielded wiring.

Gold connectors are best suited to connecting to other gold connectors otherwise you'll set up a "dis-similar metals" condition that can cause more problems than solutions.

BTW it still works outstandingly well.

 
I remember when my Audio Research SP-6 pre was sent back for upgrades and I borrowed my roommates Dh 101 till it came back (early 80's)
For 2 weeks it was hard to believe how good it was for such a cheap preamp.
I can imagine a fully tweaked out version would sound very nice
 
Hafler DH-101 pcb board

I agree with you this little preamp really is amazing what we really like are incredible mid-range and highly accurate bass, and behold I found a draft of the plate it has a small mistake on the pcb board should be added to a short circuit between the two points marked white.

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Finally I took out all the cables and shortened signal path, set the input selector relays, signal capacitors changed for the better Black Gate NX entrance and exit set Mundorf M-cap, eliminated components are tons of control (Musical Cocept mode), the difference is incredible. Now everything sounds more natural bass is precise and rapid whole range of different sound somehow seems much warmer, I plan to existing power Replacement Sulzer / Borbely power supply, also waiting for Elna Silmic II capacitors to arrive.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
Small hum

Can anybody tell me what your level of hum on HAFLER DH-101 preamp, I'd like to eliminate it, but I have a lot of problems. It is almost impossible to completely eliminate hum and if I respected all the rules regarding the grounding and power supply input, I have found quite a low level hum but with open input power amplifier is quite noticeable. If someone has an idea or a completely successful in eliminating hum I would be grateful.
Thanks in advance.