SirPaulGerman
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Is the DBX-CX-3 Preamp very close or the same as the CX-1 ?
My understanding is that it is not.Is the DBX-CX-3 Preamp very close or the same as the CX-1 ?
Do you recommend another preamp at the same level of the DBX CX-1?My understanding is that it is not.
Rick “but they are cheaper and more plentiful” Denney
Interesting names--a regular blast from the past of 'high end. It was wild and wooly back then, for sure!My first "really good" (???) speakers were a pair of JansZen Z412HP hybrid electrostatics that I bought from a friend down the hall in the dorm. He owned the original Quad ESLs
The shop where I bought most of my gear had a huge grand re-opening when all that was done, and the guys who founded DCM were there along with Andy Rappaport, who put out several preamp and power amps for a few years. Pretty sure that the shop sold Audionics and Hafler electronics at some point.
However, when it comes to the other speakers that were popular then that friends owned or I was able to audition at length, I am kind of drawing a blank. I recall Fried...
Mr. Holman: SO nice to see you here at ASR. I have one question for you as I was scanning the preamp's schematic: Why is there an opamp hooked up as a negative resistor on the output? Looks like it compensates for the feedback network loading, freeing up the main opamp to supply the output load. If I change the opamps to OPA1656 (or OPA2156 depending on input CM range), can I safely leave off this negative resistor? The new OPAXX56 family have 100ma outputs so don't really need the current help.Thanks. See my response to your earlier post. One of the tests I introduced proved the test of time and is in the IEC standard. The pre-emphasized square wave test made signals much faster than poor little stylii could go so was wrong. However we were trying to find out why things sounded different and came up with two tests for which one was and one wasn't true. Not too bad a track record working at the fringe, and "but in the end is all came to nothing" is clearly wrong.
Just to clarify my point if I did not explain it well (which I might not have done). I was writing in the context of reviewers looking for an objective rule they could use to identify what they perceived as certain sound differences within preamps. That is to say, in spite of the new tests promulgated at the time, reviewers found no reliable correlation between how a preamp managed the test in question, and the subsequent 'sound' of the preamp, from a subjective standpoint. I certainly did not mean to imply that your research on phono preamp stages (in order to identify what is going on in the RIAA circuit under dynamic conditions) was somehow not worthwhile.Thanks. See my response to your earlier post. One of the tests I introduced proved the test of time and is in the IEC standard. The pre-emphasized square wave test made signals much faster than poor little stylii could go so was wrong. However we were trying to find out why things sounded different and came up with two tests for which one was and one wasn't true. Not too bad a track record working at the fringe, and "but in the end is all came to nothing" is clearly wrong.
A breath of fresh air from the past.The service manual is just a joy isn't it?![]()
Conclusions
The owner who sent me this has a knack for finding these past jewels with excellent engineering. Their performance post refurbishing is extreme good even by today's standard which sadly has sled backward. Hopefully no one sheds a tear next time I complain about an audio product producing SINAD of 70 dB and such which this level of performance was achieved years ago.
I am happy to recommend the Apt Holman preamplifier. I see one on ebay for $550 although it will likely need thorough service like the sample I tested.
"The price includes the matching of channel parts (FET’s, op amps, etc.) for noise and performance, as well as some “esoteric” modifications. The modifications are done to satisfy those “golden ear” types who may possibly hear the subtle difference of some very critical capacitors in the audio path (e.g., there are a few stages that can benefit from capacitor bypassing with high quality Mylar capacitors, improvement of subsonic filter for advanced wider frequency response, less phase shift, etc.). Admittedly, I don’t think the sonic improvements are immediately obvious and dramatic (unless the unit had major off-spec or failed parts), but it is true that listeners who do own high quality, reasonably phase correct speakers playing quality, acoustic-oriented program material will hear an improvement. Let me stress my opinion (which is based on factual A/B blind testing and reinforced by AES Journal testing competitions) that the subtle differences of improved spatial/depth or instrument timbre clarity are mostly perceived due to the quality of the speakers and their appropriate listening position. But moreover, the level 3 mod will probably extend the life of the product by many years."
I don't mean to disagree with that gorgeous labor-of-love but 'crash-worthiness' is not about the most rigid frame but one that will absorb the g-shocks involved during a frontal (or side or rear) impact without exposing the occupants to those g-forces occupying the cage.Chassis construction (likely way safer in an accident than anything bought from a car factory):
That is exactly what that frame is designed to do. Absorb & disperse over as much of it as possible, exposing the occupants to the least G-Forces possible.I don't mean to disagree with that gorgeous labor-of-love but 'crash-worthiness' is not about the most rigid frame but one that will absorb the g-shocks involved during a frontal (or side or rear) impact without exposing the occupants to those g-forces occupying the cage.
The good thing about audio is that it can be a two way street, so no one is to blame. Thus, you could say:I had one of these units in my hifi system from 1976 though most of the 1980's. Great performance and sound, very nicely made, super reliable, unlike the Dayton Wright SPS unit it replaced. The tone controls actually worked! It was paired with Holman's Amp 1, another well made great sounding very reasonably priced piece of gear. My only complaint about the amp was that I always wished it had been 200 watts/channel to better work with a set of somewhat insensitive Gale GS-401 speakers.
Please note the phono response of this unit is not as shipped. It has been tampered with by removing the final cap of the RIAA equalization that makes up for the +1 term in Zf=Zi+1 equation of a non-inverting feedback amp. Somebody liked it "brighter," but it's wrong. Spec was ±0.2 dB 30 Hz to 15 kHz as I recall, and I made it that because I once heard a +0.5 dB error at 10 kHz in a blind a/b. Stan Lipshitz, former president of AES did a survey of RIAA equalization in preamps published in the AES Journal and among production ones found only three correct: the Quad 33, the Advent 300, and the Apt/Holman. All other high-end ones he measured were wrong.This is a review and detailed measurements of the Apt Holman vintage preamplifier. It is on kind loan from a member and has been refurbished by QuirkAudio.
The look is a cross between hifi and pro gear:
View attachment 167044
Other than some scratches on top, the unit is a very good cosmetic shape. Rear connections are extensive:
View attachment 167045
Yes, there was a time we had outlets in the back of stereos. The more there was, the higher end the gear was said to be! Wonder what led to their demise.
In case you are wondering as I did when I was first contacted about this unit, Holman is Tomlinson Holman or the T in THX (now works for Apple). Owner sent me the service manual which is not only extensive but has excellent tutorials on the design, instruments to test it with, and pages and pages of detail. It is incredible what used to be available compared to now.
Apt Holman Measurements
Let's start with our dashboard input. I selected Tape 1 as input but oddly front panel selector doesn't have Tape 1. I set it to Aux 1 and then pushed Tape 1 switch:
View attachment 167047
Wow, this is excellent! I expected SINAD in 60s or 70s and here we have 90 dB. It is dominated by second harmonic at that level. Even more impressive is the signal to noise ratio with same unity gain:
View attachment 167048
Frequency response was dead flat in audible band:
View attachment 167049
Crosstalk is better than many devices I test today:
View attachment 167050
There is essentially no frequency dependency in distortion+noise:
View attachment 167051
Output level is optimized for about 0.4 volts or so:
View attachment 167052
So you may want to pair it with a power amplifier that puts out most of its power at the above level.
Apt Holman Preamplifier Phono Stage Measurements
I adjusted the volume control to give a nominal 40 dB level (higher than preamp tests):
View attachment 167053
While I like to see no visible distortion spikes in this test, its level at -100 dB is still very good. SINAD is set by the slight amount of mains noise which I could not get rid of with various grounding methods (typical).
RIAA equalization is very good but there seems to be a high frequency resonance that causes error above 10 kHz:
View attachment 167054
I did not look to see if there is an adjustment/compensation for this in the service manual.
Be sure to use the balance control to restore equal level in both channels.
Level of headroom is good:
View attachment 167055
And doesn't change a lot due to frequency:
View attachment 167056
Conclusions
The owner who sent me this has a knack for finding these past jewels with excellent engineering. Their performance post refurbishing is extreme good even by today's standard which sadly has sled backward. Hopefully no one sheds a tear next time I complain about an audio product producing SINAD of 70 dB and such which this level of performance was achieved years ago.
I am happy to recommend the Apt Holman preamplifier. I see one on ebay for $550 although it will likely need thorough service like the sample I tested.
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As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
It is nice to see the designer, and one particularly one of such renown, explain their great "vintage" gear!Please note the phono response of this unit is not as shipped. It has been tampered with by removing the final cap of the RIAA equalization that makes up for the +1 term in Zf=Zi+1 equation of a non-inverting feedback amp. Somebody liked it "brighter," but it's wrong. Spec was ±0.2 dB 30 Hz to 15 kHz as I recall, and I made it that because I once heard a +0.5 dB error at 10 kHz in a blind a/b. Stan Lipshitz, former president of AES did a survey of RIAA equalization in preamps published in the AES Journal and among production ones found only three correct: the Quad 33, the Advent 300, and the Apt/Holman. All other high-end ones he measured were wrong.
Also as noted the imbalance is due to a mis-adjustment probably post factory of the cartridge balance control, which is reached through the side. The units were supplied with a test disc for balance. You played it, turned the mode knob to L-R, and adjusted the side control for a null, getting super good balance. This because we also heard small imbalances, also the reason the volume control has a tracking spec.
Cheers and kudos to people who are still interested and have read this.
Congratulations. Repairs, updates & mod's are easy also.This is my first post on ASR, as I don't really know enough yet to contribute anything technical. I bought my Apt Holman preamp from my then brother-in-law sometime in the early 80's. It was a king's ransom for me at the time. I always knew it was special piece of gear. It got retired to a closet when I abandoned vinyl and went to home theater, and just recently revived when I decided to replace my dead Philips GA312 and set up a stereo. My Hafler 220 is not well and soon to be replaced with something new. I'm going to end up with hybrid system both phono and streaming, and with DSP running in the processor in/out loop on the Apt. So amazing to see T. Holman here! Thank you sir for this amazing, all original, still working preamp!
Quirk Audio (Peter) has also taken care of my APT/Holman (this site's review), as well as an ADVENT 300 (this site's review), and my three NAD 2200's (one of which is this site's reviewed)Just got mine back from restoration by Quirk Audio. Turns out it has the MC circuitry as I suspected. Down the road I may have to play with that but for now the MC sounds (subjectively) glorious. Now where is that Diane Krall album. . Actually I really like her stuff.
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