Hafler P1500: how to make volume down to zero (∞db)?

[jackup]

Hi Alls,

I own a Hafler P1500. I dont know why the volume can come down only to -15db. My concern is, how to mod this amplifier to make volume down to zero (∞db)?

Thank you very much,
Jackup

[Chartal]

Because it's an amplifier and not a integrated.
The knobs on the front are to fine-tune the gain.
You need a pre-amplifier for the volume control.

[stratus46]

Originally Posted by Chartal

Because it's an amplifier and not a integrated.
The knobs on the front are to fine-tune the gain.
You need a pre-amplifier for the volume control.

What you say is true but modding for down to 0 is no big deal. There are fixed resistors on the electrical 'bottom' of the pot that when shunted with wires will expand the range to infinity. KEEP in mind that the input loading might drop a LOT. Many units will be OK with that but not all. If it was mine I'd try for a load of at least 5K and not more that 25K. This may require changing the pots to a higher value. Solid state sources would be fine with this but tube gear would not be happy. Since I don't use tubes, I don't mind.

G²

[jackup]

Originally Posted by stratus46

What you say is true but modding for down to 0 is no big deal. There are fixed resistors on the electrical 'bottom' of the pot that when shunted with wires will expand the range to infinity. KEEP in mind that the input loading might drop a LOT. Many units will be OK with that but not all. If it was mine I'd try for a load of at least 5K and not more that 25K. This may require changing the pots to a higher value. Solid state sources would be fine with this but tube gear would not be happy. Since I don't use tubes, I don't mind.

G²

Could you please specify which resistors need to be shunted with wires?
Please refer to this Parts list: http://www.hafler.com/techsupport/pd..._P3000_man.pdf
Thank you very much

[djk]

That is a common mode volume control, it may not go to 0 even after modification, there may be some very low level high frequency present (-60dB~-80dB down). R6 is the part you want to remove and/or short out.

[jackup]

Originally Posted by djk

That is a common mode volume control, it may not go to 0 even after modification, there may be some very low level high frequency present (-60dB~-80dB down). R6 is the part you want to remove and/or short out.

Thank you very much! I'll try and report later!

[jackup]

Originally Posted by stratus46

What you say is true but modding for down to 0 is no big deal. There are fixed resistors on the electrical 'bottom' of the pot that when shunted with wires will expand the range to infinity. KEEP in mind that the input loading might drop a LOT. Many units will be OK with that but not all. If it was mine I'd try for a load of at least 5K and not more that 25K. This may require changing the pots to a higher value. Solid state sources would be fine with this but tube gear would not be happy. Since I don't use tubes, I don't mind.

G²

Originally Posted by djk

That is a common mode volume control, it may not go to 0 even after modification, there may be some very low level high frequency present (-60dB~-80dB down). R6 is the part you want to remove and/or short out.

Thank you all of you! Now the volume can down to zero with RCAs only. If i use XLRs, there is still low signal at speakers. I don't know why.

[djk]

Because it is a common mode volume control.

Try adjusting R8 (CMRR) for a minimum with the volume control all the way down. Unfortunately, there is no adjustable capacitor for HF CMRR, just the pot for LF CMRR. You should be able to get -60dB~-80dB.