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Why does the APT Holman preamp sound so good?
Why does the APT Holman preamp sound so good?
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Old 28th February 2016, 10:12 PM   #51
rayma is offline rayma  United States
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Quote:
Originally Posted by Danimal1969 View Post
Tone is very bright and just not full. I've compared it to my friends NAD preamp and there is no contest.
Can you check the response on a scope with an inverse RIAA?
If not, try the tape out jacks into another preamp.
This may help localize the problem to either the phono or the line stage.

Last edited by rayma; 28th February 2016 at 10:19 PM.
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Old 29th February 2016, 02:48 AM   #52
Danimal1969 is offline Danimal1969  United States
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Quote:
Originally Posted by rayma View Post
Can you check the response on a scope with an inverse RIAA?
If not, try the tape out jacks into another preamp.
This may help localize the problem to either the phono or the line stage.
Thanks for the response. Unfortunately, I don't have a scope or, quite frankly, the knowledge to properly use one. I will try your suggestion to run the tape out jacks.

I was just reading on the kenrockwell site how all the controls are supposed to work (wanting to make sure I wasn't just being stupid). Plus, I had no idea what the "stereo mode" knobs and switches really did. Well, besides my previously described problems, here is one that is much easier to describe...when the stereo knob is straight up, sounds good. When to the left, in mono, sounds good. When turned to the right, when channel separation is supposed to be greater, I just about lose all signal. I pretty much hear nothing but a faint sound out of both speakers when all the way to the right. So since this is an obvious problem, I think I should start here. But I'm looking at the schematic and I am over my head.

Any ideas?
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Old 29th February 2016, 03:05 AM   #53
rayma is offline rayma  United States
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Originally Posted by Danimal1969 View Post
Thanks for the response. Unfortunately, I don't have a scope or, quite frankly, the knowledge
to properly use one. I will try your suggestion to run the tape out jacks.
What was the condition before the recapping, were these problems present then?
Are you using it only with a turntable?
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Old 29th February 2016, 03:19 AM   #54
Danimal1969 is offline Danimal1969  United States
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Right now, It's only being used with a turntable. And I don't know about before the recap...I just bought it a recently and it had a power switch issue. The guy I got it from said last time he used it, it had some capacitor hum. I saw it had original caps, so I did those while I had it apart to address the power switch.

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Old 3rd March 2016, 06:07 AM   #55
Russell Dawkins is offline Russell Dawkins  Canada
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Quote:
Originally Posted by Danimal1969 View Post
Plus, I had no idea what the "stereo mode" knobs and switches really did. Well, besides my previously described problems, here is one that is much easier to describe...when the stereo knob is straight up, sounds good. When to the left, in mono, sounds good. When turned to the right, when channel separation is supposed to be greater, I just about lose all signal. I pretty much hear nothing but a faint sound out of both speakers when all the way to the right. So since this is an obvious problem, I think I should start here.
Any ideas?
Apparently Ken Rockwell, surprisingly, did not understand the function of the 'stereo mode' control either, so don't feel bad.

The switches below simply do what the legend suggests, the left one (when depressed) sends the left signal to the right output and the right one sends the right signal to the left output. Both pressed in reverses the channels, i.e., L to R and R to L.

As to the oh-so-rare stereo mode control, when centered it does nothing, but this controls a circuit which has separated the signal into its sum and difference components, also know as mid and side or even mono and stereo components. Recordists among us (who, in my experience, don't understand M-S properly either, although tend to enjoy using the term) may recognize that this is the MS technique first proposed by Alan Blumlein, more or less at the same time he developed the first patented stereo recording technique, now named after him.

The thing is, any conventional stereo signal can be separated into two constituent parts—the sum of the two channels and the difference between the two channels. The sum is the M signal and the difference is the S signal.

If a pure mono signal is fed to the Apt Holman preamp there should be no difference between the left and right channels, so if you turn the stereo mode control all the way clockwise to the L-R position, you should hear absolutely nothing. As I suggest, if the mono signal were perfectly mono, i.e., identical in both channels, you would hear nothing at all. What you do hear is the imperfections somewhere along the line.

The easiest way to get perfect mono is to use a good Y-cord coming from one channel of a source and slitting into two inputs of the Holman preamp. This eliminates differences between any preceding amplification stages. Under these conditions, any sound heard will be imperfections in the Apt Holman's line stages which, apparently are very low in level. You can get a subjective impression of the amount of distortion introduced by the Apt Holman by comparing the level of the sound heard at full L-R on this control to the spl when the control in centered.

You can also assess the improvement made by changing caps as you go, by using the same method.

I have used this preamp to separate an M-S recording of a graduation recital into its constituent parts so it could be properly decoded. It had been recorded using a cardioid M mic and a figure of eight S mic, but the result had been decoded into stereo presuming that the S mic was the M and the M was the S. I ran the signal into two channels of a mixer and into the Apt Holman. I then panned the two mixer channels to the centre to derive the S signal which I sent to the S input of an analog M-S decoder I had. I sent at the same time the signal into my Apt Holman pre with the stereo mode fully clockwise to the L-R position and took the left output and sent that to the M input of my decoder. I took the output of the decoder and sent that to a recorder and was done - all in analog. The recording went from absurd to very good, since the mics were good and the placement was also good. I dont know of any other preamps which would have let me do this.

Today I would have done the same thing easier with my Metric Halo 2882, but I would still have to think hard.Today I would have done the same thing easier with my Metric Halo 2882, but it would still be a headache inducing process.

Tomlinson Holman's objective with the control was mainly to let the user have some control over, for example, the level of the vocals in pop music (which are usually mono - right down the centre), or the centre fill of an orchestral recording where the engineers played too loose with the stereo enhancement.
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Old 3rd March 2016, 02:07 PM   #56
Danimal1969 is offline Danimal1969  United States
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Quote:
Originally Posted by Russell Dawkins View Post
Apparently Ken Rockwell, surprisingly, did not understand the function of the 'stereo mode' control either, so don't feel bad.

The switches below simply do what the legend suggests, the left one (when depressed) sends the left signal to the right output and the right one sends the right signal to the left output. Both pressed in reverses the channels, i.e., L to R and R to L.

As to the oh-so-rare stereo mode control, when centered it does nothing, but this controls a circuit which has separated the signal into its sum and difference components, also know as mid and side or even mono and stereo components. Recordists among us (who, in my experience, don't understand M-S properly either, although tend to enjoy using the term) may recognize that this is the MS technique first proposed by Alan Blumlein, more or less at the same time he developed the first patented stereo recording technique, now named after him.

The thing is, any conventional stereo signal can be separated into two constituent parts—the sum of the two channels and the difference between the two channels. The sum is the M signal and the difference is the S signal.

If a pure mono signal is fed to the Apt Holman preamp there should be no difference between the left and right channels, so if you turn the stereo mode control all the way clockwise to the L-R position, you should hear absolutely nothing. As I suggest, if the mono signal were perfectly mono, i.e., identical in both channels, you would hear nothing at all. What you do hear is the imperfections somewhere along the line.

The easiest way to get perfect mono is to use a good Y-cord coming from one channel of a source and slitting into two inputs of the Holman preamp. This eliminates differences between any preceding amplification stages. Under these conditions, any sound heard will be imperfections in the Apt Holman's line stages which, apparently are very low in level. You can get a subjective impression of the amount of distortion introduced by the Apt Holman by comparing the level of the sound heard at full L-R on this control to the spl when the control in centered.

You can also assess the improvement made by changing caps as you go, by using the same method.

I have used this preamp to separate an M-S recording of a graduation recital into its constituent parts so it could be properly decoded. It had been recorded using a cardioid M mic and a figure of eight S mic, but the result had been decoded into stereo presuming that the S mic was the M and the M was the S. I ran the signal into two channels of a mixer and into the Apt Holman. I then panned the two mixer channels to the centre to derive the S signal which I sent to the S input of an analog M-S decoder I had. I sent at the same time the signal into my Apt Holman pre with the stereo mode fully clockwise to the L-R position and took the left output and sent that to the M input of my decoder. I took the output of the decoder and sent that to a recorder and was done - all in analog. The recording went from absurd to very good, since the mics were good and the placement was also good. I dont know of any other preamps which would have let me do this.

Today I would have done the same thing easier with my Metric Halo 2882, but I would still have to think hard.Today I would have done the same thing easier with my Metric Halo 2882, but it would still be a headache inducing process.

Tomlinson Holman's objective with the control was mainly to let the user have some control over, for example, the level of the vocals in pop music (which are usually mono - right down the centre), or the centre fill of an orchestral recording where the engineers played too loose with the stereo enhancement.
Wow, thank you Russell for that explanation!! I was totally ignorant about what this control did and that cleared it up quite nicely.

It appears I was chasing a ghost then. Since most music, as you suggest, is very center heavy, there is not much left as the control is turned to L-R. I will have to find something in my collection that is very over the top stereo (Bowie's Space Oddity comes to mind) and see how the preamp responds. I will also try your idea with the "y" cable and see how it goes.

In theory then, if I was to feed 2 totally unique signals into the preamp, like from two different turntables, one into the left, one into the right, then the output even at full L-R would be the 2 different signals, correct?

Overall, I can't see the reason to ever use this in normal playback, but it certainly helped you with the editing you spoke of.

Thanks again!!
Dan

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Old 3rd December 2017, 05:28 AM   #57
Sonic Inequlaity is offline Sonic Inequlaity  United States
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Hello- I am new to this forum. I have a completely rebuilt and upgraded APT-Holman and two (2) rebuilt and upgraded APT-1 Power Amps- configured as mono blocks. This was a very kind, but a very expensive proposition by my dearest significant other; love you honey!!! Truly I do! The sound is excellent and the power amps where the work was completed;, did a side by side with a 10K Bryson, the sound was very comparable and the measurements were quite similar as well.

With that said, cosmetically the units really need a facelift. My dearest really didn't think it mattered, but given the updates I would really like to find either new old stock faceplates for the units or have reproductions made (obviously keeping the originals for purists - probably a purist would not be interested in upgraded equipment though, would they now.). Can anyone point me to a possible source, old APT vendor or a a one stop shop where I can send the original face plates and they can be copied. By the way this gift was quite a surprise for me as I was looking at Krell... Which may just sendup being my TH set up and APT equipment in as small listening room wth many different speakers running through a russ sound speaker selector so I can enjoy some of my upgrade classic speakers. Any ideas, information? Any help would be greatly appreciated. Thanks - Sonic Inequality- in a not so egalitarian world!
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Old 11th December 2017, 07:11 PM   #58
lflarry1 is offline lflarry1  United States
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Question apt holman preamp right channel no output

Hey Guy's,
I bought an Apt Holman at a discount audio store here in philly. One channel is dead. At first both channels were dead but I replaced the relay which is a known problematic area. Well, I turned it on the relay works but one channel is dead. Before I start to troubleshoot it,I thought to ask on here if anyone can point me to a good starting point. Since both channels have different tech as to signal paths I can't just compare the two. I have mostly all the parts like caps Ic's and even sockets to go with them. I believe there's Tl032's and rc4558 op amps in there. So before I break out a signal tracer and scope I thought that someone would know a "common failure" to save me some time. It's mine so the customers stuff comes first and I haven't gotten any spare time to work on it. Thanks in advance to anyone who can help.
Normally some older gear isn't worth the time and trouble of resuscitating them but this preamp is quite nice for what it is, and still brings $300 on e-bay.
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Old 12th December 2017, 12:15 AM   #59
rif is offline rif  United States
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Why does the APT Holman preamp sound so good?
Quote:
Originally Posted by lflarry1 View Post
Hey Guy's,
I bought an Apt Holman at a discount audio store here in philly. One channel is dead. At first both channels were dead but I replaced the relay which is a known problematic area. Well, I turned it on the relay works but one channel is dead. Before I start to troubleshoot it,I thought to ask on here if anyone can point me to a good starting point. Since both channels have different tech as to signal paths I can't just compare the two. I have mostly all the parts like caps Ic's and even sockets to go with them. I believe there's Tl032's and rc4558 op amps in there. So before I break out a signal tracer and scope I thought that someone would know a "common failure" to save me some time. It's mine so the customers stuff comes first and I haven't gotten any spare time to work on it. Thanks in advance to anyone who can help.
Normally some older gear isn't worth the time and trouble of resuscitating them but this preamp is quite nice for what it is, and still brings $300 on e-bay.
First off, get a copy of the service manual, it's available freely online as a pdf. It's really a good read.

Before pulling out a dmm or scope, try to find which section the fault lies in. The preamp is a buch of blocks in a chain, where the internal circuits follow the external controls. I think the first real block is the external processor. See if you get a signal there. If not, then try it with a bunch of different inputs selected. Then open it up and start digging. Be prepared to shocked by the poor quality soldering!

Replacing the relay with a nice Omron (the kind used in input selection/volume control), solved a lot of my problems.
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Old 12th December 2017, 01:00 AM   #60
planet10 is offline planet10  Canada
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Why does the APT Holman preamp sound so good?
Quote:
get a copy of the service manual, it's available freely online as a pdf.
I scanned these and put them online some time ago.

http://p10hifi.net/planet10/forum/Ap...nPreManual.pdf (2002, 8MB)
http://p10hifi.net/planet10/forum/apt1-manual.pdf (2006, 3.5MB)

I really liked these when we were selling them, but subsequent owenership (a half dozen pres and at least a couple amps) left me wanting. Hard to beat the pre when it comes to features thou.

dave
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