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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Why does the APT Holman preamp sound so good?
Why does the APT Holman preamp sound so good?
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Old 1st April 2010, 02:39 PM   #21
unclejed613 is offline unclejed613  United States
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i worked at APT from 1979 until they closed. the Holman phono preamp is a rather unique preamp. the phono stage is a discrete op amp with a JFET/BJT diff amp (the JFET is the + input, the BJT is the - input). the JFET is a device selected at initial test by testing for noise. about 1 out of 5 2N5484's passed this test, the remainder were used as integrator discharger switches in the APT-1 power amp.
the output stage of the phono preamp was a class AB, biased a bit "hotter"... more of a "class AAB" stage. the RIAA network used 1% resistors, and some of the values were determined at initial test, so the RIAA characteristic was accurate to better than 0.1%. the rail voltages for the phono stage were filtered with capacitance multipliers, and so tended to be very quiet.

with the addition of some stricter power rail bypassing, the TL072's can be replaced with TLE2072 op amps if you want to update to more modern op amps
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Old 19th June 2010, 05:10 PM   #22
xpablo is offline xpablo  Malaysia
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http://homepage.mac.com/planet10/TLS...nPreManual.pdf

service manual
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Old 19th June 2010, 06:45 PM   #23
aptquark is offline aptquark  United States
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Quote:
Originally Posted by djk View Post
"Is the Pass that bad?"

No

I have found 90% of people cannot hear in the audiophile sense, and of the 10% that can, 90% of those pick the worst unmusical sounding gear.

The 1% that could tell whether something was musical never seemed to have any money.

I would describe the APT as uncolored, but lacking in dynamics, lifeless.

"Any schematic ?"

Unfortunately, yes, but I am moving and not likely to find it anytime soon.

I completely agree. I loved that pre for what it could offer. But, sadly, when I could afford a newer pre...it got shelved.
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Old 13th July 2015, 07:27 AM   #24
Chickenwatt is offline Chickenwatt  ominican Republic
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Wao this post is from December 2004 but here I am

I own a APT Holman preamp and is true that is lifeless with poor dynamics but this is due to the use of cheap electrolytic capacitors and old TL072 op amp.
But replacing those capacitors where the signal passes with Nichicon or Black Gate capacitors and changing the TL072 with Burr Brown OP2132 it start to compete in the Audiophile territory.
This preamp have more features than any other preamp made, like dubbing, 2 tapes, ext processor, etc. and a enviable phono stage.
For those who own a APT Holman here I put a scan of schematic better than the ones available.
Change Ic1, Ic5, Ic6, Ic7, Ic8 if you are going to use Tone defeat but if you will like to use Tone controls change Ic 9, 10 and 11 also for OPA2132
Ic2,3 and Ic4 works with Tape input, if you are not going to use them can leave the TL072's
Change signal caps C24,C124,C31,C131,C33, C133,C40, C140,C43,C143,C52,C152,C68,C168,C69,C169 with Black gate or Nichicon caps
Change C12 and C112 0.47 uf with something good like Solen if you use Phono Stage and C13,C17,C113 and C117
In the power supply change the rail caps 1,000 at 35v even if you see them good and the 4 little 10 uF at 25v C60,61,63 and C64.

After that you will hear an audiophile preamp with the enviable functions that the Holman preamp gives.

Good luck, Cesar
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Old 13th July 2015, 07:29 AM   #25
Chickenwatt is offline Chickenwatt  ominican Republic
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Well it seems that this page doesnt allow to upload pics, sorry I could not upload the schematic
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Old 13th July 2015, 08:58 AM   #26
djk is offline djk
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Host the photo on an external site.
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Old 13th July 2015, 09:20 AM   #27
Chickenwatt is offline Chickenwatt  ominican Republic
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Here are the scans of the schematic better than the pdf's available elsewhere

https://app.box.com/s/26kw7n9u36iikyyhx3vomc4wy8xjhfqs

https://app.box.com/s/8falrxzxe1fw34lvfyyf61b7cm5hu4iy

Download it to see full size

Last edited by Chickenwatt; 13th July 2015 at 09:22 AM.
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Old 25th September 2015, 04:13 PM   #28
CRikiT is offline CRikiT
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Default Chickenwatt - NICE!

I have been dormant with my stereo hobby for a long time. Now being an empty-nester, I have rediscovered it.

I have an old Apt-Holman preamp that I have fired up after a long time. Yes it does sound a little lifeless but very smooth. I have been thinking of upgrading some internal components and came across this thread - an it is now fairly current!

About 22 years ago, I sent my Apt into GasWorks and they replaced some of the caps. Really made a big difference, especially on the high end. They took a highligher to indicate the replaced cap on the schematic on the bottom of the unit.

I'll take a look at your recommendations in the near future to upgrade the rest of the circuitry. My source selector, along with other switches need cleaning. And the Mute button sometimes needs to be fiddled with.

Thank you for the information!
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Old 26th September 2015, 10:39 AM   #29
AndrewT is online now AndrewT  Scotland
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These last two links are alive.
Shame all the previous links were not attached.

Can we get these two attached for posterity?

Any chance someone can resurrect any of the old links?
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Old 26th September 2015, 12:55 PM   #30
Antoinel is offline Antoinel  United States
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Why does the APT Holman preamp sound so good?
Quote:
Originally Posted by Chickenwatt View Post
Here are the scans of the schematic better than the pdf's available elsewhere

https://app.box.com/s/26kw7n9u36iikyyhx3vomc4wy8xjhfqs

https://app.box.com/s/8falrxzxe1fw34lvfyyf61b7cm5hu4iy

Download it to see full size
Hello Chickenwatt. As mentioned in an earlier post, the phono input stage is a diff amp of a JFET and a BJT; an interesting approach which is clear in the first link.
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