Hi Dave,
Greetings! That's exactly what I did. I've Dl'd the manuals and there should be enough info there in order to fix it. Circuit description is always good to have along with a block diagram. I did a little research where it was bought and I'm pretty sure the previous owner plugged something into it that took out the channel by pumping too much power into it. I'm just going to locate the test points with my sig gen and see if and whats coming through there. I'll start at the end of the chain and work my way back. Manuals much better than the schematic on the bottom.
Thank you,
Larry
Greetings! That's exactly what I did. I've Dl'd the manuals and there should be enough info there in order to fix it. Circuit description is always good to have along with a block diagram. I did a little research where it was bought and I'm pretty sure the previous owner plugged something into it that took out the channel by pumping too much power into it. I'm just going to locate the test points with my sig gen and see if and whats coming through there. I'll start at the end of the chain and work my way back. Manuals much better than the schematic on the bottom.
Thank you,
Larry
I think I am slightly confused by the posted schematics and my recollection of the JAES article. I only say "I think I am confused" because if I have not recalled the JAE piece correctly then the the problem goes away. (Alzheimers?)
Early in the thread reference was made to the APT pre' having good LF rejection. I thought I saw in the JAES article that Holman used the RIAA pre as an active filter with a feedback loop and two caps, in classic active high pass configuration, prior to the input transistor...........
(I have noticed the separate rumble filter in the schematics posted in this thread.)
Anyone able to confirm that.....or not.......I am simply curious....that's all.
Cheers Jonathan
Early in the thread reference was made to the APT pre' having good LF rejection. I thought I saw in the JAES article that Holman used the RIAA pre as an active filter with a feedback loop and two caps, in classic active high pass configuration, prior to the input transistor...........
(I have noticed the separate rumble filter in the schematics posted in this thread.)
Anyone able to confirm that.....or not.......I am simply curious....that's all.
Cheers Jonathan
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The "infrasonic filter" is 18dB/octave below 20Hz, the actual -3dB point is about 15Hz.
In his original demonstration of the preamp at a Chicago CES, Holman used a slightly warped record of a solo piano. With the filter off the infrasonic warp caused the woofer cones to move in and out which in turn caused a clearly audible doppler shift in piano notes pitch, effectively introducing a type of wow. Switching in the filter totally eliminated the doppler shift, but left the audible spectrum untouched.
The RIAA EQ is done in the feedback network, with one additional single pole filter added at the output in order to extend the RIAA rolloff curve accurately out to 36kHz.
Outside of the infrasonic filter there is no other low frequency filtering in the phono stage. The infrasonic filter is applied to all inputs, though it can be bypassed with the switch on the rear of the preamp.
In his original demonstration of the preamp at a Chicago CES, Holman used a slightly warped record of a solo piano. With the filter off the infrasonic warp caused the woofer cones to move in and out which in turn caused a clearly audible doppler shift in piano notes pitch, effectively introducing a type of wow. Switching in the filter totally eliminated the doppler shift, but left the audible spectrum untouched.
The RIAA EQ is done in the feedback network, with one additional single pole filter added at the output in order to extend the RIAA rolloff curve accurately out to 36kHz.
Outside of the infrasonic filter there is no other low frequency filtering in the phono stage. The infrasonic filter is applied to all inputs, though it can be bypassed with the switch on the rear of the preamp.
I remember the Apt-Holman well, and a musician I know bought one and used it for many years, and i've heard his system many times.
In many respects it was the most innovative preamp available, then or since.
The owner's manual is a textbook example of what every owner's manual should be, but sadly isn't. If the quality of the owner's manual determined the net value of an audio component, it would be the best preamp in the world.
Sonically it was a little veiled, very listenable (sins of omission, not addition) but the problem was at it's retail price it was competing with some very competent gear. At half the price it would have been a top 5 unit.
If you needed it's features there was no competition but if not, you probably would choose something else based on sonics alone at similar MSRP.
I wouldn't hesitate to own and run one today, although it probably would not find itself in the main system. I would probably use it on the test bench actually, for it's versatility with phono and processor (aka "tape") loops. But I know many people who would be quite happy to have one as part of their main HiFi.
In many respects it was the most innovative preamp available, then or since.
The owner's manual is a textbook example of what every owner's manual should be, but sadly isn't. If the quality of the owner's manual determined the net value of an audio component, it would be the best preamp in the world.
Sonically it was a little veiled, very listenable (sins of omission, not addition) but the problem was at it's retail price it was competing with some very competent gear. At half the price it would have been a top 5 unit.
If you needed it's features there was no competition but if not, you probably would choose something else based on sonics alone at similar MSRP.
I wouldn't hesitate to own and run one today, although it probably would not find itself in the main system. I would probably use it on the test bench actually, for it's versatility with phono and processor (aka "tape") loops. But I know many people who would be quite happy to have one as part of their main HiFi.
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I love the L-R to L+R dial, especially removing the common component. helps me understand what is actually happening in the sound.
the volume control modifies the gain, instead of attenuation. Don't know if it's a great method. but it's different. I think it's called a Bandaxal circuit.
it's the service manual that really drills down. an excellent learning tool even if you don't own the Apt. available in pdf online for free.
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