hafler dh110

[gene french]

my dh 110 preamp seems to be passing the signal through as the volume and balance dont work....noticed the power light monitor light were not working....changed out f100 fuse...got lights back but still no volume or balance...swapped it for another that had working lites and good fuse...same thing...swapped it for a dh 101 and it worked with notable increase in volume...
any suggestions where to start lookin???

 

[George S.]

Switches and pots, any small signal transistor. Occasionally a opamp.

 

[wattsabundant]

Other than the possible selector switch issues there is a time delay mute circuit with a fet, Q1, driven by an opamp. You can try pulling the fet. Be advised there may be a turn on thump even if the volume is turned down.

 

[George S.]

Also check polarity of all polarized components that were replaced since it last worked.

 

[62vauxhall]

Those things have a muting circuit involving J112 FET transistors. I had a DH110 once, and those created a problem. I learned it is not uncommon for them to need replacing.

FWIW, when I owned the DH110, it was in conjunction with several other pre-amps. I thought I had too many and did a mini-shoot out between it, a Yamaha, a Kenwood, a DH101 and a NAD. I kept the DH101. Found I regretted bailing on the NAD so got another. It's gone now too but I still have the DH101.

 

[gene french]

Those things have a muting circuit involving J112 FET transistors. I had a DH110 once, and those created a problem. I learned it is not uncommon for them to need replacing.

FWIW, when I owned the DH110, it was in conjunction with several other pre-amps. I thought I had too many and did a mini-shoot out between it, a Yamaha, a Kenwood, a DH101 and a NAD. I kept the DH101. Found I regretted bailing on the NAD so got another. It's gone now too but I still have the DH101.

worth a lot to me...thank you so much...
i also read about that being the most common failure in 110...i will order some...i had a spare 101 also....it works fine...

 

[gene french]

Also check polarity of all polarized components that were replaced since it last worked.

hasnt been worked on...other than contact cleaner...

 

[GeorgeP]

I have 2 of those preamps. I removed the 2 muting JFETs, and installed relays. No more issues. Any body who wants that mod can ask, Ill post a schematic. Implement it on a small perf board. Easy and no non-linear issues with a hard contactor...fet has potential distortion/frequency issues when the start to go bad.
I ALSO HARD BYPASSED THE TONE PUSHBUTTON WITH TONE CONTROLS ON PERMANENTLY, AND ALSO THE EXTERNAL PROCESSER SWITH...USING JUMPERS ON THE SEND/ RECEIVE JACKS ON THE BACK.
THOSE SWITCHES ARE VERY PESKY AND INTERMITTENT, NOW...OUT OF THE SIGNAL PATH. FREQUENCY RESPONCE AT CENTER DETENTS, STILL MEASURED TO BE THE SAME ON BOTH BASS AND TREBLE CONTROLS...SO NO REASON TO SWITCH THEM OUT

 

[gene french]

Other than the possible selector switch issues there is a time delay mute circuit with a fet, Q1, driven by an opamp. You can try pulling the fet. Be advised there may be a turn on thump even if the volume is turned down.

dont see a q1...my schematic shows the fet as q15...
if i remove both q15s....that will disable the muting....correct???
thanks for taking your time...

 

[gene french]

I have 2 of those preamps. I removed the 2 muting JFETs, and installed relays. No more issues. Any body who wants that mod can ask, Ill post a schematic. Implement it on a small perf board. Easy and no non-linear issues with a hard contactor...fet has potential distortion/frequency issues when the start to go bad.
I ALSO HARD BYPASSED THE TONE PUSHBUTTON WITH TONE CONTROLS ON PERMANENTLY, AND ALSO THE EXTERNAL PROCESSER SWITH...USING JUMPERS ON THE SEND/ RECEIVE JACKS ON THE BACK.
THOSE SWITCHES ARE VERY PESKY AND INTERMITTENT, NOW...OUT OF THE SIGNAL PATH. FREQUENCY RESPONCE AT CENTER DETENTS, STILL MEASURED TO BE THE SAME ON BOTH BASS AND TREBLE CONTROLS...SO NO REASON TO SWITCH THEM OUT

i would be very interest in your mods....i did not recap these....do i need to??
i dont know as much as i wish i did...
please document the changes....dont take for granted that i know anything...
thank you for taking your time to help...

 

[gene french]

removing q15 and q115 made no difference....

no volume control...no tone control...no balance control...
and more volume when connected to the dh 101...

 

[gene french]

course of events....
q 15s both tested good out of circuit...reinstalled...
in circuit, checked every diode...none shorted or open...in circuit every transistor checked good...i did it twice...in circuit no resistors showed short or open...rail voltage + and - 23v....
opamp????

 

[George S.]

I'd input a sine wave of appx 500 Hz at the input jack and start checking the circuit with a scope to see where the signal is lost.
With only a DMM, you can still do resistance checks through various circuit legs, checking for bad joints, switches, pots, ribbon cables.
The opamp. Print out the data sheet and do the voltage checks. Voltage checks can be found by Googling opamp voltage checks.
The unit should work with the mute function disabled by pulling the two J112 FETs, at least that what was reported on one site.
I did see lot's of reported jack issues with these.
Looks like there were 4 different boards used in these.
Never seen one myself. Good luck.

 

[gene french]

I'd input a sine wave of appx 500 Hz at the input jack and start checking the circuit with a scope to see where the signal is lost.
With only a DMM, you can still do resistance checks through various circuit legs, checking for bad joints, switches, pots, ribbon cables.
The opamp. Print out the data sheet and do the voltage checks. Voltage checks can be found by Googling opamp voltage checks.
The unit should work with the mute function disabled by pulling the two J112 FETs, at least that what was reported on one site.
I did see lot's of reported jack issues with these.
Looks like there were 4 different boards used in these.
Never seen one myself. Good luck.

pulled both fets...no difference...checked them with dvm...checked good....forward and reverse bias ...d to s was about 35 ohms each...checked all in circuit...no problems detected ..rail voltage 23v and -23v...as it should be....
it makes sound....but about half as much....
it used to work...i kept preamp volume at 1/2...to prevent accident ... lots of power....well i never noticed a change until i wanted to dent some eardrums...like mr. laatsch...maybe shatter a glass or two ...
went to preamp to turn up volume...and didnt increase as it normally did...noticed power light did not work either....nor balance or tone controls...my other 110 exhibited same behavior...except power light worked...
swapped 110s out for my schiit preamps....worked...could again break glass...
plugged in my spare dh 101...it works as expected too...
strange...

 

[Gepetto]

pulled both fets...no difference...checked them with dvm...checked good....forward and reverse bias ...d to s was about 35 ohms each...checked all in circuit...no problems detected ..rail voltage 23v and -23v...as it should be....
it makes sound....but about half as much....
it used to work...i kept preamp volume at 1/2...to prevent accident ... lots of power....well i never noticed a change until i wanted to dent some eardrums...like mr. laatsch...maybe shatter a glass or two ...
went to preamp to turn up volume...and didnt increase as it normally did...noticed power light did not work either....nor balance or tone controls...my other 110 exhibited same behavior...except power light worked...
swapped 110s out for my schiit preamps....worked...could again break glass...
plugged in my spare dh 101...it works as expected too...
strange...

Your rail voltages pass through the LM117 and LM337 regulators that are strapped to that metal rail to provide the regulated voltages you need. DId you check your regulated voltages?

 

[gene french]

Your rail voltages pass through the LM117 and LM337 regulators that are strapped to that metal rail to provide the regulated voltages you need. DId you check your regulated voltages?

no sir...i will read how/where to check...i have really studied...
thank you

 

[gene french]

Your rail voltages pass through the LM117 and LM337 regulators that are strapped to that metal rail to provide the regulated voltages you need. DId you check your regulated voltages?

lm337= -23.12 (pin 3)
lm317= +23.42 (pin 2)
these readings were read directy from regulators

originally i read the rail voltage where it was labeled on foil side of main board....

 

[George S.]

Earlier thought you said no sound and rail voltage is correct at +-23 v. The PL2000 preamp will reduce output as rail voltage is reduced. Maximum I run is appx +-17 VDC because of the opamps. The higher level inputs play just fine at 1/2 normal rail voltage, but at reduced output.
Are you sure it's correct VDC, and don't forget that third rail, the ground rail. Do your voltage checks using that ground rail at the appropriate position. Don't use chassis ground as the ground rail may have a open or different potential.
And use the opamp data sheet to identify it's supply and ground pins for final voltage checks before calling it fixed. Note that a phono level opamp usually is supplied lower voltage because it's a low level signal.

 

[George S.]

Just saw your regulater VDC post. And those readings are the same further out the board away from the regulators, using the ground rail?

 

[VSAT88]

Hang in in there Gene. I know you can do it!