I apologize upfront for what may be a dumb question.
I have a PCB for a Pass Aleph 1.7 preamp. It is balanced input to balanced output. I don't run balanced gear. I know I can use it as designed to accept single ended input and output single ended, but am wondering if I can convert it to just single ended operation.
Attached is the schematic. Would it be as simple as just populating the left side of the schematic and using "+IN" and Gnd for the input and "-Out" and Gnd as the output? I realize this would invert the signal.
Thanks for your thoughts.
I have a PCB for a Pass Aleph 1.7 preamp. It is balanced input to balanced output. I don't run balanced gear. I know I can use it as designed to accept single ended input and output single ended, but am wondering if I can convert it to just single ended operation.
Attached is the schematic. Would it be as simple as just populating the left side of the schematic and using "+IN" and Gnd for the input and "-Out" and Gnd as the output? I realize this would invert the signal.
Thanks for your thoughts.
To use only half, possibly you could change the volume control to 1k and connect it to ground instead.
Don't know if anyone has tried this, but it may work ok. The distortion will probably increase.
The output capacitors can be reduced to 10uF, for a 10k or higher load, if you increase the 4.75k value
connected at the output to say 50k.
Don't know if anyone has tried this, but it may work ok. The distortion will probably increase.
The output capacitors can be reduced to 10uF, for a 10k or higher load, if you increase the 4.75k value
connected at the output to say 50k.
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May be better to use it as it was designed and just connect to the unbalanced source and amp (I think I know how to do that).
if you want to make it proper, to work as designed, it is necessary to have volume control in form of output attenuator (as original is built)
now, that also working as variable loading, just another reason to be made that way
regarding bal/se mode of operation - if you intend to use it strictly as SE in/SE out, you can really make just one half of circuit, call it SE Preamp and that's it
if you want to use its Bal input capabilities, thus serving as Bal/SE converter, you need to make it fully, including vol attenuator on both output phases**, even if taking signal from one output phase only
**for proper work, both halves need to be equally loaded
now, that also working as variable loading, just another reason to be made that way
regarding bal/se mode of operation - if you intend to use it strictly as SE in/SE out, you can really make just one half of circuit, call it SE Preamp and that's it
if you want to use its Bal input capabilities, thus serving as Bal/SE converter, you need to make it fully, including vol attenuator on both output phases**, even if taking signal from one output phase only
**for proper work, both halves need to be equally loaded
Thanks, ZM. I appreciate the detail. I only have SE components - sources and amps (a luddite, I know). so I think I'll build the preamp as SE. I was able to locate the service manual so I see that the volume attenuator is after the preamp. I don't have the wherewithal to build a microprocessor controlled relay attenuator so I thought I'd use a Goldpoint stepped attenuator. It appears to me that a 10k stepped attenuator would do the trick?
as I remember it is a 1k only attenuator and the leads after the preamp should be kept reasonably short. I use Dantimax RelVol3 boards.
Here is the schematic for the attenuator from the service manual I received when I bought the PCBs a few years back. I think I can make a control circuit using MCP23S17 and a couple ULN2803 (old technology, I know, but I somewhat understand it). Now I just need to decide the sequence of relay switching.
point is to use pot wired as shunt (practically between output hot and GND) variable resistor
it is practically acting as variable load for gain stage
it can be resistor matrix , switched with relays, or it can be regular pot wired accordingly
and, gain issue covered (local degeneration)
it is practically acting as variable load for gain stage
it can be resistor matrix , switched with relays, or it can be regular pot wired accordingly
and, gain issue covered (local degeneration)
