Thanks, but I've already got one
Yes there are quite a few on ebay now quite cheap, unfortunately the reason is this model is notorious for the dolby prologic surround processor chips dying - mine worked on all channels when I got it about 8 years ago but it too has suffered the same fate where front left and right work perfectly but centre and rear channels no longer work. (The power amps themselves are fine, they're just not being fed anything from the dolby processor board any more) All the ones I've seen listed on ebay also have faulty prologic processors, including that one.
I've only ever used it as a 2 channel amp though, so it doesn't worry me that the other channels no longer work and I hang onto it because it works well with my other equipment and still sounds excellent as a stereo amp.
Last edited:
Hi,
The whole power stage Q721 to Q736 is referred to. Both Pre-Driver Q721 to Q724 and Drivers Q725 to Q728 operate in class A due to their arrangements of emitter resistors.
As we have pre-driver, driver and output transistors this is usually called a Triple (Darlington). A normal Darlington power stage (aka D. Self EF2) has a low and non-linear, signal dependent input impedance of around 40KOhm for a 4 Ohm load. This load limits the gain of the VAS stage, but worse, it adds strong non-linear loading to the VAS, making it usually the stage that dominates distortion for the Amp.
Using a triple increases the input impedance to around 4MOhm to 12MOhm (depending on Pre-Driver choice). This allows a much greater linearity and if desired greater gain from the VAS. We may also elect to trade the gain increase for more VAS linearity.
The drawback is that it is non-trivial to keep a triple stable in a feedback amp and often heavy handed compensation measures (C721 to C724 in this case) are adopted, at least partially negating the improvements (here we have an extra 200pF to charge/discharge which impacts on slewrate and we have 200pF to AC ground from the VAS Output which limits bandwidth.
Here to it helps with input capacitance but also corrects some other problems in the circuit.
Yes and Yes.
It is not necessarily that the emitter resistors are low, but increasing them is ONE possible way to improve the current mirrors, many others exist (see usual sources including wikipedia for more).
2SK389 is discontinued and becomes very hard to source, Linear Systems has the LSK389 2nd Source in production.
Ciao T
The whole power stage Q721 to Q736 is referred to. Both Pre-Driver Q721 to Q724 and Drivers Q725 to Q728 operate in class A due to their arrangements of emitter resistors.
As we have pre-driver, driver and output transistors this is usually called a Triple (Darlington). A normal Darlington power stage (aka D. Self EF2) has a low and non-linear, signal dependent input impedance of around 40KOhm for a 4 Ohm load. This load limits the gain of the VAS stage, but worse, it adds strong non-linear loading to the VAS, making it usually the stage that dominates distortion for the Amp.
Using a triple increases the input impedance to around 4MOhm to 12MOhm (depending on Pre-Driver choice). This allows a much greater linearity and if desired greater gain from the VAS. We may also elect to trade the gain increase for more VAS linearity.
The drawback is that it is non-trivial to keep a triple stable in a feedback amp and often heavy handed compensation measures (C721 to C724 in this case) are adopted, at least partially negating the improvements (here we have an extra 200pF to charge/discharge which impacts on slewrate and we have 200pF to AC ground from the VAS Output which limits bandwidth.
Here to it helps with input capacitance but also corrects some other problems in the circuit.
Yes and Yes.
It is not necessarily that the emitter resistors are low, but increasing them is ONE possible way to improve the current mirrors, many others exist (see usual sources including wikipedia for more).
2SK389 is discontinued and becomes very hard to source, Linear Systems has the LSK389 2nd Source in production.
Ciao T
Thanks, but I've already got one
Yes there are quite a few on ebay now quite cheap, unfortunately the reason is this model is notorious for the dolby prologic surround processor chips dying - mine worked on all channels when I got it about 8 years ago but it too has suffered the same fate where front left and right work perfectly but centre and rear channels no longer work. (The power amps themselves are fine, they're just not being fed anything from the dolby processor board any more) All the ones I've seen listed on ebay also have faulty prologic processors, including that one.
I've only ever used it as a 2 channel amp though, so it doesn't worry me that the other channels no longer work and I hang onto it because it works well with my other equipment and still sounds excellent as a stereo amp.
Until you hear even better.
Those were the days when audio companies really CARED, and the order of the day was that it must all come out as one coherent whole.
These days, they want something they call "analytical", meaning that you do not hear the band as a whole, but as s group of individuals struggling to keep it all together (applies to the popular industry only).
I must say I was never reallyimpressed by Luxman's work, my feeling is that a lot of the time it was art for art's sake. I never owned one, but some of my friends were nuts about them and owned lots of them. They always had an outstanding build quality externally, but internally - not so good sometimes. Their design was questionable on occasion, but that is of course highly subjective.
I am also a vintage freak, but my weakness is the Marantz 1978-1980 series, considered among the Marantz freaks as their best ever in terms of regular production models.
This kind of thing:
Still, for a couple of channels of high quality amplification, that's pretty cheap. I don't know that I could stand to look at it, though.
It looks a bit better in real life than those photos, especially when its clean
(Rule number one when trying to sell something, clean it before taking photos)Yep, that was my thought too.
All the power amps have pre-amp to main-amp connectors and link jumpers on the rear, so the unused power amps could be re-purposed for something like a 2 way active crossover design where the main channels drove the woofer and the rear channels drove the tweeter.
I've been thinking of setting up something like that to help me experiment more quickly with crossover designs, using something like a DCX2496 as the processor.
Possibly some of Luxmans designs went down hill a bit in the mid 80's as they were bought out by Alpine in 1984 and there was some tension between the two brands in terms of design philosophy and target market/image.
Their heyday was probably from around the mid 60's to the early 80's, although I think they're having a bit of a renaissance/rebirth since the mid 2000's now that they they're free of alpine again. (Although they're perhaps too far into the expensive and eccentric "boutique" area now for my liking)
My favourite vintage one is the L-309 from 1974, probably because that's what my Dad had and it was just always there when I grew up and became interested in audio and electronics, so I still have a soft spot for it. I still think its a great looking and sounding amplifier from the shiny brushed metal era of the 70's
Luxman L-309
I have to admit I've not heard any Marantz amplifiers of that era, (or if I did I don't remember the brand specifically) probably due to them not being a readily available brand in New Zealand at the time. (Neither was Luxman for that matter, I don't think I ever saw another one other than my Dad's L-309 for 20+ years)
Last edited:
He was tenured, so I doubt I crushed him.
At that time, I was teaching a course called "Physics of Hifi," which was popular among non-science majors who had to check off a science course box to get their degrees in philosophy or education or underwater basket-weaving. I was still naive about how real sensory testing was done and inexperienced at electronics engineering (I was about 24), so I'm afraid I filled my students with a lot of nonsense regurgitated from the (at the time) underground magazines.
At that time, I was teaching a course called "Physics of Hifi," which was popular among non-science majors who had to check off a science course box to get their degrees in philosophy or education or underwater basket-weaving. I was still naive about how real sensory testing was done and inexperienced at electronics engineering (I was about 24), so I'm afraid I filled my students with a lot of nonsense regurgitated from the (at the time) underground magazines.
On style, the older Luxmans, Marantz, Tanburgs, etc. Even a lot of the Pioneer stuff into the 80's. Style. They felt good to use. Thought was put into them. Aragon preamp, Mission amps, and of course B&O. Take the simple ML #26 preamp with the offset front section. They tried. I can't give style credit to Mac, as I just consider them gaudy. Even NAD is their own ultra cheap way had a unique look. Then we got the plain black rack mount generic panel. Only now is the art of industrial design coming back. Make it work, but make it pleasing too. Raymond Lowe, Trever Wilkenson, the Eames's, Giargio, to name a few.
A very good idea! If you bypass or modify the in/out circuits of the DCX you'll have a much more usable signal flow. The DCX is a great tool for designing crossovers.
Not related to the question of the faulty Luxman circuitry, the single freatest problem with vintage gear is that so few people even know that they must be refreshed if they are to truly show their colors.
My aforementioned Marantz brothers (two integrateds, one preamp and one power amp) made some very mediocre music "as is". Measuring their filter capacitors, instead of the nominal 15,000 uF, I got 7,200/7,100 uF - less than one half. Moreover, these were the idiot dual concentric caps, nominally from Elna, with impossible values, e.g. 2x15,000uF/56V. Fortunately, there was just enough space to fit in two BC Components 22,000 uF/63V caps (15,000 uF is a rare value in Europe, noth worh the trouble of locating it). The critical inputs, NFB and input stage resistors were changed from 5% carbon to 1% metal film. ALL other capacitors were exchanged for new and fresh ones.
And then it really came on song. It was not as I remembered it, it was WAY better, but then, I do have better speakers today than I did then, I do have a better speaker cable then I did then, and so forth.
There is NO WAY any of them will be leaving me - ever.
My aforementioned Marantz brothers (two integrateds, one preamp and one power amp) made some very mediocre music "as is". Measuring their filter capacitors, instead of the nominal 15,000 uF, I got 7,200/7,100 uF - less than one half. Moreover, these were the idiot dual concentric caps, nominally from Elna, with impossible values, e.g. 2x15,000uF/56V. Fortunately, there was just enough space to fit in two BC Components 22,000 uF/63V caps (15,000 uF is a rare value in Europe, noth worh the trouble of locating it). The critical inputs, NFB and input stage resistors were changed from 5% carbon to 1% metal film. ALL other capacitors were exchanged for new and fresh ones.
And then it really came on song. It was not as I remembered it, it was WAY better, but then, I do have better speakers today than I did then, I do have a better speaker cable then I did then, and so forth.
There is NO WAY any of them will be leaving me - ever.
It's been a few years since I looked at the specs of the DCX2496 (I have a DEQ2496 instead) so refresh my memory - do you mean bypassing the balanced to unbalanced stages that are unnecessary for use in an unbalanced environment, or are you talking about complete ADC/DAC replacement ?
My idea was to connect the DCX2496 between the front pre-amp post volume control output and the front/rear main amplifier inputs, thus creating a 2 way active crossover that would let me experiment with things such as dynamically varying the crossover frequency and relative driver attenuation with just a simple turn of a knob. (With the DEQ2496 also still in the post input switching pre volume control loop as it is now for overall EQ)
It's not something I would use permanently, but it sure would make a lot of "what if" scenarios VERY quick and easy to test compared to doing it passively...
Last edited:
By allowing very fast "prototyping" of proposed crossover changes which could then be later built as passive/dedicated networks...
Ok, that's what I thought.
I'm not sure if the DCX2496 and DEQ2496 have the same analog stage design or not, but on the DEQ2496 I find that operating the existing stages in unbalanced mode (by linking pin 1 and 3 on the XLR connector) matches my system quite well - with the rear panel switch set to +12dBu I can reach clipping with a 0dBFS signal from a line level CD player, however in the +22dBu position I have roughly 6dB of headroom above the highest level analog input device, which is the mode I use it in.
Of course I'm connecting it before the volume control in the input switching to volume control "signal processor" loop, which is line level, and in the case of the Luxman is also buffered.
In the case of connecting a DCX2496 after the volume control noise etc would be a problem as you say because of the much lower (and variable with volume control) signal level. I'm also a bit concerned about the possibility of high level switch on pulses being fed directly into the power amp input, which has the potential to damage it...
When I speak of theology, it seems true to me that a belief in what a given individual thinks of as the "scientific method" can be held as dogma. Note that qualification: not any and all scientific methods as variously conceived, but a given individual's conception.
Typically, people's notions of scientific method presume a belief in an objective, observer-independent reality. And for many, any attempt to tweak that premise even slightly "descends" into mysticism. I can hear Ayn Rand admonishing me for even mentioning it!
But let me give one example of beliefs that someone I know holds to suggest something a bit less than radical subjectivism. A friend went to a highly-regarded college that specializes in "hard" sciences, and while there took a course that purported to educate about good audio quality and the circuitry that might associate with it. Among the lab expeiments: construct simplest-possible gain stages, one with a vacuum triode, one with a transistor. Determine which one sounds better passing audio signals. Some will probably know who this was, and if I am less than accurate here I welcome correction.
I believe the individual wanted the students to take away the notion that tube electronics were inherently superior to sand-state. In any event, that was certainly the take-away for my friend. He also, whether through this class or outside of it, protests again the use of negative feedback, comparing it to "a dog chasing its tail".
But fast-forward to somewhat more recent times. Being an aficionado of vinyl and a connoisseur of cartridges, tonearms, and 'tables, despite this anti-feedback stance he found the most exciting, involving playback system for vinyl to be a laser-based machine. I'll venture that he didn't inquire into how this readout was being accomplished, as I'd think the cognitive dissonance resulting from those details would be most disturbing. To wit: the system has to necessarily employ a rather elaborate servo system to work at all --- negative feedback city!
I think it is very much to his credit that he does actually listen to things. When some piece of equipment sounds good to him, he reports honestly about it, even when he finds out that, in his audio world view, it ought not sound good.
Meanwhile, the same person who taught the course those many years ago co-authored a fairly recent paper about negative feedback's effect on intermodulation distortion. I brought it to my friend's attention as I thought the discussion worthwhile (despite the hard science part being based entirely on simulations, in turn based on unrealistic models of active devices). But he wasn't particularly interested. I didn't probe further, but I got the distinct impression of disappointment in his teacher, who among other things actually comes close to saying that maybe bipolar transistors aren't so bad after all
Typically, people's notions of scientific method presume a belief in an objective, observer-independent reality. And for many, any attempt to tweak that premise even slightly "descends" into mysticism. I can hear Ayn Rand admonishing me for even mentioning it!
But let me give one example of beliefs that someone I know holds to suggest something a bit less than radical subjectivism. A friend went to a highly-regarded college that specializes in "hard" sciences, and while there took a course that purported to educate about good audio quality and the circuitry that might associate with it. Among the lab expeiments: construct simplest-possible gain stages, one with a vacuum triode, one with a transistor. Determine which one sounds better passing audio signals. Some will probably know who this was, and if I am less than accurate here I welcome correction.
I believe the individual wanted the students to take away the notion that tube electronics were inherently superior to sand-state. In any event, that was certainly the take-away for my friend. He also, whether through this class or outside of it, protests again the use of negative feedback, comparing it to "a dog chasing its tail".
But fast-forward to somewhat more recent times. Being an aficionado of vinyl and a connoisseur of cartridges, tonearms, and 'tables, despite this anti-feedback stance he found the most exciting, involving playback system for vinyl to be a laser-based machine. I'll venture that he didn't inquire into how this readout was being accomplished, as I'd think the cognitive dissonance resulting from those details would be most disturbing. To wit: the system has to necessarily employ a rather elaborate servo system to work at all --- negative feedback city!
I think it is very much to his credit that he does actually listen to things. When some piece of equipment sounds good to him, he reports honestly about it, even when he finds out that, in his audio world view, it ought not sound good.
Meanwhile, the same person who taught the course those many years ago co-authored a fairly recent paper about negative feedback's effect on intermodulation distortion. I brought it to my friend's attention as I thought the discussion worthwhile (despite the hard science part being based entirely on simulations, in turn based on unrealistic models of active devices). But he wasn't particularly interested. I didn't probe further, but I got the distinct impression of disappointment in his teacher, who among other things actually comes close to saying that maybe bipolar transistors aren't so bad after all
Last edited:
Hi,
The ELP "Laser Turntable" does use servo systems for positioning and tracking, but the actual readout AFAIK is open loop, the output is supposedly directly from the photocell. Note, I have not opened one up, but looked at them quite closely as there was a possible linkup through the UK distrubutors discussed.
If my information is correct, then this would parallel an open loop (often called zero feedback) Amplifier with a DC servo.
Ciao T
The ELP "Laser Turntable" does use servo systems for positioning and tracking, but the actual readout AFAIK is open loop, the output is supposedly directly from the photocell. Note, I have not opened one up, but looked at them quite closely as there was a possible linkup through the UK distrubutors discussed.
If my information is correct, then this would parallel an open loop (often called zero feedback) Amplifier with a DC servo.
Ciao T
Ok , figured as much , can't agree this would be an effective way of designing xovers (passive) ....
What are you actually replacing ....
Hi,
If I may be forgiven the bible-waving, when I speak of religion or religious faith I apply the definition of Hebrews 11:1.
Ciao T
If I may be forgiven the bible-waving, when I speak of religion or religious faith I apply the definition of Hebrews 11:1.
Ciao T
- Status
- Not open for further replies.