Cache of reviews and performance data for the APT 1
Apologies if I'm resurrecting a thread that has died a natural death...
I happened to find a cache of reviews and test results on the APT 1 and thought I'd post here in case any of the APT 1 fans and rehabbers on this thread want to know any specific data from these tests.
After reading through these, I'm floored by the extent to which all of the reviews praised the amp. Quotes are along the lines of "It is the best sounding amplifier ever tested by Consumer Guide magazine's audio experts."
Not that I don't think it's not a great amp, it's just that I never realized how well it performed and was reviewed when it was released. Seems the reviewers were really blown away the performance test results which all measured better than the manufacturer's specs even. Apparently, that was a rarity in 1980.
These old reviews are great because unlike so many these days they also do in-depth testing and report the data and performance graphs. Imagine that, objective measurements!
Anyway I'll be building a Hypex NCore amp in a few weeks when they have stock again and had a crazy thought to get my old APT 1 fixed (recently lost a channel) so I can A/B these two very different amps from different ages that yet share a focus on excellent performance and distortion measurements.
Apologies if I'm resurrecting a thread that has died a natural death...
I happened to find a cache of reviews and test results on the APT 1 and thought I'd post here in case any of the APT 1 fans and rehabbers on this thread want to know any specific data from these tests.
- High Fidelity, March 1980
- Consumer Guide
- Stereo, 1980
- Stereo Review, November 1980
- Audio Magazine, March 1981
- Modern Recordings & Music, February 1980
After reading through these, I'm floored by the extent to which all of the reviews praised the amp. Quotes are along the lines of "It is the best sounding amplifier ever tested by Consumer Guide magazine's audio experts."
Not that I don't think it's not a great amp, it's just that I never realized how well it performed and was reviewed when it was released. Seems the reviewers were really blown away the performance test results which all measured better than the manufacturer's specs even. Apparently, that was a rarity in 1980.
These old reviews are great because unlike so many these days they also do in-depth testing and report the data and performance graphs. Imagine that, objective measurements!
Anyway I'll be building a Hypex NCore amp in a few weeks when they have stock again and had a crazy thought to get my old APT 1 fixed (recently lost a channel) so I can A/B these two very different amps from different ages that yet share a focus on excellent performance and distortion measurements.
Is this normal for a BJT, or is it for this device specifically or does it apply to the process used to manufacture this family of power devices?
This thread - undeservedly forgotten
This thread seems to be one of the best collections of information about the Apt Power Amp 1 and Holman Preamp, and I'm bringing it back to life to ask:
- did anybody ever get a scan of the service manual?
- did anybody get a parts list?
I recently was given the Preamp and Power Amp. The Preamp seems to work perfectly. The Power Amp is missing the right channel. I'd like to get the Power Amp working again, but I have no test equipment other than a good Fluke multimeter. I'm hoping that testing the power transistors and replacing the electrolytics on that channel will bring it back to life, but I was hoping to see this service manual that apparently exists.
Thanks!
Sean
This thread seems to be one of the best collections of information about the Apt Power Amp 1 and Holman Preamp, and I'm bringing it back to life to ask:
- did anybody ever get a scan of the service manual?
- did anybody get a parts list?
I recently was given the Preamp and Power Amp. The Preamp seems to work perfectly. The Power Amp is missing the right channel. I'd like to get the Power Amp working again, but I have no test equipment other than a good Fluke multimeter. I'm hoping that testing the power transistors and replacing the electrolytics on that channel will bring it back to life, but I was hoping to see this service manual that apparently exists.
Thanks!
Sean
)a scope - it would be very much worth your while for this endeavor. After opening up the amp and checking voltage in a few places, I had a hunch: I hooked it back up and rapped the top a few times. Sure enough, both channels came alive.
I believe the only current problem with my amp is the speaker relay, possibly the mono switch as well; when I used the mono switch, the sound would come and go in the right channel.
When I unplugged the input (I was using an iPad) I got a pop and hum out of the speakers until I unplugged the amp. Does this problem also sound like a flaky relay? That's my hunch, but it might be worth the minor effort of replacing the electrolytics on that board along with the relay.
Does anybody have an idea of a direct replacement for the relay? I wonder if Vince at Audioproz would be willing to sell me just the part?
Thanks,
Sean
I believe the only current problem with my amp is the speaker relay, possibly the mono switch as well; when I used the mono switch, the sound would come and go in the right channel.
When I unplugged the input (I was using an iPad) I got a pop and hum out of the speakers until I unplugged the amp. Does this problem also sound like a flaky relay? That's my hunch, but it might be worth the minor effort of replacing the electrolytics on that board along with the relay.
Does anybody have an idea of a direct replacement for the relay? I wonder if Vince at Audioproz would be willing to sell me just the part?
Thanks,
Sean
This weekend I cleaned the relay with 1200 grit sandpaper and Deoxit. Then I replaced all of the electrolytic capacitors, except for two which might have had diodes soldered across the leads - wasn't sure about those. Reapplied heatsink paste to the power transistors.
The amp now consistently plays on both channels and sounds pretty good, but a couple behaviors from before have not changed:
1) At power on, both channels leds glow red, then fade to black (green if a signal is present). The right channel led fades much more slowly than the left.
2) With the amp on, connected to speakers, and no input signal, there is a buzz/hum from both speakers, but the right is worse.You have to be less than a couple feet from the speaker to hear it. The right channel led sometimes faintly glows green with no input plugged in.
Does anybody have ideas/suggestions?
The amp now consistently plays on both channels and sounds pretty good, but a couple behaviors from before have not changed:
1) At power on, both channels leds glow red, then fade to black (green if a signal is present). The right channel led fades much more slowly than the left.
2) With the amp on, connected to speakers, and no input signal, there is a buzz/hum from both speakers, but the right is worse.You have to be less than a couple feet from the speaker to hear it. The right channel led sometimes faintly glows green with no input plugged in.
Does anybody have ideas/suggestions?
Not terminated. Should it be? Should I put a resistor across the input or a dead short? I notice in the service manual that the parts list includes two "phono shorting plugs." In fact, I might even have them in my parts box...
Replace the relay for one with hard silver contacts and it will be better (and it won't break down again anytime soon).
Okay, I did indeed find some rca shorting plugs. With the input terminated, the amp is pretty silent. With the input open, noisy. Is that normal?
Yes.
the input shorted places a zero ohms at the input and this allows the amplifier to amplify nothing and only add it's own noise to become the output.
When you disconnect the input cable, the amplifier sees the Rin value as the loading on the input. This can be 50k to 500k.
This resistance (Rin) creates noise and the amplifier amplifies that noise, adds on it's own noise and sends that total to the output. You will hear this as a hiss, a bit like white noise, maybe with a bit of extra Hum.
For future reference, in case anybody else is searching through this thread for help, I found a good replacement for the Power Amp's relay: TE 9-1419111-2 from Mouser. Has specs nearly identical to the original, seems to have a bit less current draw on the coil, and 6A silver contacts instead of the original relay's 5A gold plate. Easy drop-in (well, solder-in) replacement.
For what it's worth, I also just finished replacing all of the electrolytic capacitors on the Apt Holman Preamp, in addition to the mute relay.
The capacitor parts list was as follows (radial except where noted):
5 x 1uf 50v
6 x 22uf 25v (axial)
2 x 47uf 16v
4 x 100uf 16v
2 x 100uf 25v *probably not original
2 x 22uf 16v
12 x 10uf 35v
6 x 10uf 16v
2 x 1000uf 35v
Better to order all of the 100uf capacitors at 25v. I took a chance and used 16v as in the rest of the circuit, but am crossing my fingers that nothing pops when I power it up.
The exact replacement for the mute relay was RY2V-U-DC24-IDEC, from Galco.
Hope this helps someone!
The capacitor parts list was as follows (radial except where noted):
5 x 1uf 50v
6 x 22uf 25v (axial)
2 x 47uf 16v
4 x 100uf 16v
2 x 100uf 25v *probably not original
2 x 22uf 16v
12 x 10uf 35v
6 x 10uf 16v
2 x 1000uf 35v
Better to order all of the 100uf capacitors at 25v. I took a chance and used 16v as in the rest of the circuit, but am crossing my fingers that nothing pops when I power it up.
The exact replacement for the mute relay was RY2V-U-DC24-IDEC, from Galco.
Hope this helps someone!
Hi all,
Looking for some advice regarding Apt Model 1 power amp please.
I rebuilt Apt Power Amplifier Model 1 amplifier, but have this weird condition that I don't understand.
When no input is connected, there is loud buzzing (transformer-like) through only the right channel (it's much quieter in the left channel). As soon as I connect RCA input from my preamp to that channel (even with no signal), the buzz is gone completely.
Service manual has this note "The input jack chassis ground is the ONLY chassis ground in the amplifier". Well, OK, but still doesn't explain why only the right channel buzzes.
DC offset (not adjustable, measured at the output terminals) is 10mV per channel. Each channel has bias adjustment trimpots, but these have no effect on buzzing.
I traced ground connections from the power supply to both amp boards - on signal side, and on power side - both are well connected, I even resoldered them. If I lift the power board out of the amp (hence disconnect it from chassis), both channels buzz identically. But if I put it back (hence connect the chassis to the ground traces), only right channel buzzes. Not sure if it's the ground loop, or the way ground wires are ran through the amp to the board.
Thank you
Looking for some advice regarding Apt Model 1 power amp please.
I rebuilt Apt Power Amplifier Model 1 amplifier, but have this weird condition that I don't understand.
When no input is connected, there is loud buzzing (transformer-like) through only the right channel (it's much quieter in the left channel). As soon as I connect RCA input from my preamp to that channel (even with no signal), the buzz is gone completely.
Service manual has this note "The input jack chassis ground is the ONLY chassis ground in the amplifier". Well, OK, but still doesn't explain why only the right channel buzzes.
DC offset (not adjustable, measured at the output terminals) is 10mV per channel. Each channel has bias adjustment trimpots, but these have no effect on buzzing.
I traced ground connections from the power supply to both amp boards - on signal side, and on power side - both are well connected, I even resoldered them. If I lift the power board out of the amp (hence disconnect it from chassis), both channels buzz identically. But if I put it back (hence connect the chassis to the ground traces), only right channel buzzes. Not sure if it's the ground loop, or the way ground wires are ran through the amp to the board.
Thank you