ive got a feeling that Tom Holman said they were actually Motorola parts back somewhere but i could be wrong. He might see your post and answer 
OnSemi seem to be missing a suitable mid-power TO-126 style VAS device... all they seem to have there is BD139/140, MJE243/253 and MJE340/350. Japanese stuff is always tricky to get here. The best offerings so far are from Fairchild.
OnSemi seem to be missing a suitable mid-power TO-126 style VAS device... all they seem to have there is BD139/140, MJE243/253 and MJE340/350. Japanese stuff is always tricky to get here. The best offerings so far are from Fairchild.
ive got a feeling that Tom Holman said they were actually Motorola parts back somewhere but i could be wrong. He might see your post and answer
OnSemi seem to be missing a suitable mid-power TO-126 style VAS device... all they seem to have there is BD139/140, MJE243/253 and MJE340/350. Japanese stuff is always tricky to get here. The best offerings so far are from Fairchild.
Thank you both for the responses. Fairchild might work....they have distribution in the US that doesn't require a min order size = ISO container.
Any recollections as to the Ft for the MJE340/350's? The datasheets I googled were mute on that spec.
Really? That's a lot better than I would have guessed. But I'm confused if we're talking about the MJE340 for the VAS or cascode position.
Let me ask refine my question and pose it in a slightly different way.
For the cascoded VAS circuit, like what was implemented on the APT1, are both devices exotic, high frequency, low Cob devices or can one typically be "relaxed" (i.e., an ordinary 2N5401 or similar)? And if so, which? I've seen an approach like this taken on Borbely's Servo 50, but that design implements a folded cascode VAS.
No doubt.
the NPN (Q11)was an MPSD01 and the PNP (Q9) was an MPSD51 i looked them up on datasheetarchive.com and there are cross references to both euro and japanese part numbers as well as another mot/on number
MPSD01=BF298, BF299, BFR88, MPSA42
MPSD51=2SA1371, 2SA1624, BF436, MPSA92
there may be japanese equivalents of the MPSD01, probably best found by searching for complements of the A1371 and A1624. the japanese transistors will have a different pinout. the D01 and D51's pinouts are EBC, all(almost) japanese TO-92 pinouts are ECB. the Baker clamp diodes are 1N4148. IIRC, the cascode zener is a 4.7V half watt zener. Q8 and Q12 are 2N3904/3906.
MPSD01=BF298, BF299, BFR88, MPSA42
MPSD51=2SA1371, 2SA1624, BF436, MPSA92
there may be japanese equivalents of the MPSD01, probably best found by searching for complements of the A1371 and A1624. the japanese transistors will have a different pinout. the D01 and D51's pinouts are EBC, all(almost) japanese TO-92 pinouts are ECB. the Baker clamp diodes are 1N4148. IIRC, the cascode zener is a 4.7V half watt zener. Q8 and Q12 are 2N3904/3906.
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there never was a model 2 preamp. there were preamps and power amps with XLR plugs for use with pro-audio rack equipment, but the engineering department had been closed for a couple of years by the time APT closed. Kevin Slowe and i were the last techs to work there. i think Kevin was tinkering with a scaled down preamp, and i was tinkering with an op-amp based input stage for the power amp, but neither went beyond the prototype stage.
it's weird, get me talking about the Apt 1 and it's like i was just working there yesterday. ask me when one of my son's birthdays is, and i don't have a clue.
i have recently reconstructed (on LTSpice) the op amp input stage (sorry. not on an Apt-1, as i don't currently have one) that i prototyped back in 1984 (or was it 1983?). when i tested the prototype, it was about 10db better on distortion as well as about 6 to 10db better on noise. it was better on distortion because it had less circuit board real estate to interact with the power supply wiring. the improvement on noise was probably due to the bifet input stage of the TL072. the op amp input stage was a strange "seesaw" arrangement, but it worked. when i made the prototype, i actually hand-etched a daughterboard for the op amp and wired it in to an existing rev 10 amp board.
i have recently reconstructed (on LTSpice) the op amp input stage (sorry. not on an Apt-1, as i don't currently have one) that i prototyped back in 1984 (or was it 1983?). when i tested the prototype, it was about 10db better on distortion as well as about 6 to 10db better on noise. it was better on distortion because it had less circuit board real estate to interact with the power supply wiring. the improvement on noise was probably due to the bifet input stage of the TL072. the op amp input stage was a strange "seesaw" arrangement, but it worked. when i made the prototype, i actually hand-etched a daughterboard for the op amp and wired it in to an existing rev 10 amp board.
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Apt 2 for sale
Check out this link on Ebay:
APT Holman 2 Audiophile Preamplifier Preamp THX Two NR! - eBay (item 120501977969 end time Dec-14-09 18:30:08 PST)
Is this maybe the prototype or a scam?
Check out this link on Ebay:
APT Holman 2 Audiophile Preamplifier Preamp THX Two NR! - eBay (item 120501977969 end time Dec-14-09 18:30:08 PST)
Is this maybe the prototype or a scam?
APT-1 Output Transistors
Hi! I got an APT-1 Revision 6 with the MJ15022 transistors in one channel burned out. The complementary MJ15023 are fine and have a Beta of 70 and 130. I ordered a set of both transistors and they have a beta ranging from 15 to 40. How should I match the transistors? Would it be better to use the newer 15024 and 15025?
Also, should I remove the white ground wire from each output board and wrap it around the blue -V power supply to reduce magnetic interference?
Thank you for any advice.
Antonio
Hi! I got an APT-1 Revision 6 with the MJ15022 transistors in one channel burned out. The complementary MJ15023 are fine and have a Beta of 70 and 130. I ordered a set of both transistors and they have a beta ranging from 15 to 40. How should I match the transistors? Would it be better to use the newer 15024 and 15025?
Also, should I remove the white ground wire from each output board and wrap it around the blue -V power supply to reduce magnetic interference?
Thank you for any advice.
Antonio
model 2 preamp? i didn't remember any of them, maybe a trial run. maybe if i saw a picture of one... Kevin or Vince would be the ones to ask, since they were the preamp techs.
the output devices should all have betas of less than 35 or 40. i'll bet this amp was worked on by somebody that didn't know any better. the betas can be matched if you want to buy a ton of transistors and weed through them. that's the reason for the 0.47 ohm resistors, the betas didn't have to be real closely matched to get good results.
leave the white wire as-is. the magnetically induced distortion is nulled out by moving the V+ and V- leads around between the board and heat sink while watching the 20khz distortion residual on an o-scope. once you find the best null, you lock them down with hot-melt glue. we used a BIC pen body (the hexagonal shaped ones were good and strong) with V-notches cut in the end to manipulate the wires with. just be careful around the bias transistor and the collector posts of the output transistor sockets.
the output devices should all have betas of less than 35 or 40. i'll bet this amp was worked on by somebody that didn't know any better. the betas can be matched if you want to buy a ton of transistors and weed through them. that's the reason for the 0.47 ohm resistors, the betas didn't have to be real closely matched to get good results.
leave the white wire as-is. the magnetically induced distortion is nulled out by moving the V+ and V- leads around between the board and heat sink while watching the 20khz distortion residual on an o-scope. once you find the best null, you lock them down with hot-melt glue. we used a BIC pen body (the hexagonal shaped ones were good and strong) with V-notches cut in the end to manipulate the wires with. just be careful around the bias transistor and the collector posts of the output transistor sockets.
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APT-1 Further Problems
I replaced all the output transistors on one channel but when I tested the amp the light on that channel remains red while the other turns green after a short while. Look like the blown transistors were not the only problem!
Any suggestion on how to troubleshoot it? I have multimeter, scope, signal generator etc.
Thank you in advance!
I replaced all the output transistors on one channel but when I tested the amp the light on that channel remains red while the other turns green after a short while. Look like the blown transistors were not the only problem!
Any suggestion on how to troubleshoot it? I have multimeter, scope, signal generator etc.
Thank you in advance!
does the speaker relay turn on?
is there DC offset or signal present at the output terminal of the board?
input a 1khz 0.5Vrms sine wave, with the amp UNloaded. look at the waveform at the output terminal of the amp board. if it's distorted in any way, or if there's DC offset, you will have a red light. the LED driver circuit acts like a simple distortion analyzer. if you had shorted output devices you could have a bad driver transistor, open emitter resistors on the outputs or drivers. the design of the driver stage usually limited any damage to the outputs and drivers, sometimes a predriver would short.. check the base resistors of the output devices also, and the 1N4007 diodes across the C-E junctions of the output devices. also recheck the fuses on the affected channel.
after the repair, you should NOT just apply power and go. factory procedure was to run it up slow on a variac with an ammeter. another good method for initial test after a repair is to apply power with a 200W incandescent light bulb in series with the AC line of the amp. the bulb should light up briefly, then go dim as the filter caps charge. if it remains lit, you have a problem that's drawing excessive current.
is there DC offset or signal present at the output terminal of the board?
input a 1khz 0.5Vrms sine wave, with the amp UNloaded. look at the waveform at the output terminal of the amp board. if it's distorted in any way, or if there's DC offset, you will have a red light. the LED driver circuit acts like a simple distortion analyzer. if you had shorted output devices you could have a bad driver transistor, open emitter resistors on the outputs or drivers. the design of the driver stage usually limited any damage to the outputs and drivers, sometimes a predriver would short.. check the base resistors of the output devices also, and the 1N4007 diodes across the C-E junctions of the output devices. also recheck the fuses on the affected channel.
after the repair, you should NOT just apply power and go. factory procedure was to run it up slow on a variac with an ammeter. another good method for initial test after a repair is to apply power with a 200W incandescent light bulb in series with the AC line of the amp. the bulb should light up briefly, then go dim as the filter caps charge. if it remains lit, you have a problem that's drawing excessive current.
Hello:
Please excuse a question from a total noob, but I was wondering about a strange aspect of the Apt-1. Owned mine since 1981, btw.
The specs for the Apt-1 state that the rated power into either 8 ohms or 4 ohms is "over 100 watts per channel". I recently got a pair of Magnepan MMG speakers, which are most definitely 4 ohm speakers and will suck up as much current that you can throw at them. The advice is to use an amp that doubles the output at 8 ohms when driving a 4 ohm load. So based on the published specs, the Apt-1 won't do that? Does this make the Apt-1 a bad choice for Magneplanar speakers? I hear some "struggling" when this combo tries to reproduce powerful low bass notes, so that got me to thinking along these lines.
I have read elsewhere that inserting an Autoformer between the amp and speaker would make the amp "see" the speaker as an 8 ohm (or higher) load. Does that seem like a viable way to continue using this amp in my present system? Even though the autoformer isn't cheap, it is definitely cheaper than the sort of amp I think I'd need for the MMGs. Thanks in advance for your advice!
MG-bert
Please excuse a question from a total noob, but I was wondering about a strange aspect of the Apt-1. Owned mine since 1981, btw.
The specs for the Apt-1 state that the rated power into either 8 ohms or 4 ohms is "over 100 watts per channel". I recently got a pair of Magnepan MMG speakers, which are most definitely 4 ohm speakers and will suck up as much current that you can throw at them. The advice is to use an amp that doubles the output at 8 ohms when driving a 4 ohm load. So based on the published specs, the Apt-1 won't do that? Does this make the Apt-1 a bad choice for Magneplanar speakers? I hear some "struggling" when this combo tries to reproduce powerful low bass notes, so that got me to thinking along these lines.
I have read elsewhere that inserting an Autoformer between the amp and speaker would make the amp "see" the speaker as an 8 ohm (or higher) load. Does that seem like a viable way to continue using this amp in my present system? Even though the autoformer isn't cheap, it is definitely cheaper than the sort of amp I think I'd need for the MMGs. Thanks in advance for your advice!
MG-bert