Why does the APT Holman preamp sound so good?

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dubiella

Member
Joined 2004
Question concerning C35 (left channel) and its counterpart C135 or CBS:

are both exactly the same type of cap (both polar electrolytics, no difference)?

The schematic says C35 and C135, the board layout (service manual) has them as "C35" (left) and "CBS" in the right channel, volume section.
And: in my APT C35 is the standard grey ICC type and the one called CBS is a blue cap (all seems to be original).

Any ideas?

Thanks,

Marc
 
D

dubiella

Member
Joined 2004
I do not think so.

There is only one electrolytic in each channel of the volume section:

P1160084.JPG


I have already replaced C35 with a 10mF / 25V Elna Silmic.
I would just like to be sure about the other channel to fit an appropriate type.
 
D

dubiella

Member
Joined 2004
If someone else had the same question: I have replaced both caps with Elna Silmic II and it works great.



Final question regarding the specific circuit of the Phono part:

there is a level adjust pot for the right channel of the Phono 1 section.

The service manual says it is for perfect balance between the two channels.

In which position is it nominally equal in signal to the other (left) channel? Fully clockwise, counter - clockwise or in the middle?

Thanks,

Marc
 
D

Danimal1969

Member
Joined 2015
Chickenwatt said:
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
Click to expand...


Hi Cesar,

If you're still following this thread, can I ask you a few questions?

1) Caps #52 and #152 you mentioned. I can't find those numbers on the board...can you point me to them?

2) There are 4 aluminum caps in the phono circuit...C15, C115, C16, C116. They are .0043 and .015 values. Should those be swapped out as well?

3) You recommended using Burr Brown OPA2132 Op-Amps. How about OPA2134 instead??

Thanks!
Dan
 
mlloyd1

mlloyd1

Member
Joined 2001
D

Danimal1969

Member
Joined 2015
Hi guys. Hoping to get some further advice here. I finished recapping my apt holman. Changed all 40 something electrolytics, I cleaned the switches and pots, and plugged it it.

Powered right up, no scary noises or anything like that. The pots are all quiet, the mute system works perfectly, but it's definitely not right.

Tone is very bright and just not full. I've compared it to my friends NAD preamp and there is no contest. The Apt just sounds weak.

The only things I can tell that don't seem to work, are the bass mode, high filter, and ifrasonic filter. None of those switches do a thing that I can hear.

Any suggestions for me??

Thanks.
 
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Danimal1969

Member
Joined 2015
rayma said:
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.
Click to expand...

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?
 
D

Danimal1969

Member
Joined 2015
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.

Sent from my SM-G900V using Tapatalk
 
R

Russell Dawkins

Member
Joined 2005
Danimal1969 said:
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?
Click to expand...

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.
 
D

Danimal1969

Member
Joined 2015
Russell Dawkins said:
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.
Click to expand...

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

Sent from my SM-G900V using Tapatalk
 
S

Sonic Inequlaity

Member
Joined 2017
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!
 
lflarry1

lflarry1

Member
Joined 2017
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.
 
rif

rif

Member
Joined 2003
Paid Member
lflarry1 said:
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.
Click to expand...

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.
 
planet10

planet10

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