Well whady'a know - bypassing the output resistor did the trick! And by using the center tap on the input coil, I can still show ~30R to the ACP. Now I just need to figure out how to do this inside the chassis so I don't have to live with a headphone cord out the front. Thank you, 6L6!
nicoch58 - thanks for pointing this out, it never occurred to me. It seems the solution is to have some idea how long you kept the ohmmeter on it, and then reverse the leads for the same duration to neutralize any field that might have stuck around. Or just drop in on a hard floor
nicoch58 - thanks for pointing this out, it never occurred to me. It seems the solution is to have some idea how long you kept the ohmmeter on it, and then reverse the leads for the same duration to neutralize any field that might have stuck around. Or just drop in on a hard floor
Thinking Out Loud
I have been thinking about the input circuits in the F6 and M2X amplifiers. I have a fine preamp with a surface mount op amp headphone output circuit.
I was thinking I could use the 1/4" headphone jack with two conductors surrounded by a foil shield. Especially easy would be to use an amplifier fed from the headphone jack across just the windings of the phase inversion transformers. If done right I suspect you could winding from the driver transformer for a pseudo balanced connection. I have my preamp on one side of a room and the power amp could be located in another place between the speakers and the power amp cables could be really short.
I know it is not a true balanced connection but I bet it might work.
Just an idea.
I have been thinking about the input circuits in the F6 and M2X amplifiers. I have a fine preamp with a surface mount op amp headphone output circuit.
I was thinking I could use the 1/4" headphone jack with two conductors surrounded by a foil shield. Especially easy would be to use an amplifier fed from the headphone jack across just the windings of the phase inversion transformers. If done right I suspect you could winding from the driver transformer for a pseudo balanced connection. I have my preamp on one side of a room and the power amp could be located in another place between the speakers and the power amp cables could be really short.
I know it is not a true balanced connection but I bet it might work.
Just an idea.
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ACP+ used as a current mode RIAA preamp
I have been intrigued by a couple of new current-mode phono preamps. They multiply current through a differential amp and they no longer have to deal
with loading resistors and caps. So I am thinking what if you ran the phono cartridge leads through shielded cable for each half of the cartridge and use a modified ACP+ as the differential amplifier and add an RIAA Equalization network and maybe a buffer for the output.
I just wanted to share what I was thinking about.
I have been intrigued by a couple of new current-mode phono preamps. They multiply current through a differential amp and they no longer have to deal
with loading resistors and caps. So I am thinking what if you ran the phono cartridge leads through shielded cable for each half of the cartridge and use a modified ACP+ as the differential amplifier and add an RIAA Equalization network and maybe a buffer for the output.
I just wanted to share what I was thinking about.
reducing bias in the circuit
I know enough to be dangerous and clearly not enough to get myself out of trouble
I am trying to implement this circuit into an integrated amplifier as a preamp only
as you can see the space is pretty tight and I had dropped the bias current a little based on another DIYAers advice [TungstenAudio] but it still runs too hot for this application. ( those tiny heatsinks are a scorching "&%$^&*%E$" on NPs finger test ~ 65 degC with an IR meter )
When I initially built the ACP, I dropped the bias by increasing R9 to 3K and increasing R12 to 3R2. Could someone help me understand the theory or the formula calculation for adjusting the bias and if there are other things to consider when changing the bias - my aim is to shoot for about half of the original bias in the circuit. It will not be used to drive headphones.
thanks..dB
I know enough to be dangerous and clearly not enough to get myself out of trouble
I am trying to implement this circuit into an integrated amplifier as a preamp only
as you can see the space is pretty tight and I had dropped the bias current a little based on another DIYAers advice [TungstenAudio] but it still runs too hot for this application. ( those tiny heatsinks are a scorching "&%$^&*%E$" on NPs finger test ~ 65 degC with an IR meter )
When I initially built the ACP, I dropped the bias by increasing R9 to 3K and increasing R12 to 3R2. Could someone help me understand the theory or the formula calculation for adjusting the bias and if there are other things to consider when changing the bias - my aim is to shoot for about half of the original bias in the circuit. It will not be used to drive headphones.
thanks..dB
thanks picoD, i tried doubling source resistors last night trying to figure this out and the moment I powered it up the supply voltage was pulled down and both those resistors started smoking - so it appeared as though I dramatically increased current flow by increasing the source resistors..dB
EDIT - for clarity, I changed R13 to 13ohms and R12 to 6ohms
EDIT - for clarity, I changed R13 to 13ohms and R12 to 6ohms