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Old 19th February 2012, 11:39 AM   #2621
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Quote:
Originally Posted by SY View Post
Simon, your tastes are quite affordable!

FLAGSHIP LUXMAN RECEIVER - MODEL RV 371 | eBay
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.
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Old 19th February 2012, 11:50 AM   #2622
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Hi,

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Originally Posted by DBMandrake View Post
Since there are paralleled pairs of output transistors, (eg Q730/Q734) when you say triple Darlington are you referring to all the way back to Q722 as being part of the Darlington triple ? What are the drawbacks of so many Darlington coupled stages - mainly loss of potential output voltage swing ?

....

Which transistors do you consider to be the Class A driver stage ? Q726/728 ? Q722/724 ? Or all 4 of them ?
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.

Quote:
Originally Posted by DBMandrake View Post
Interesting. I recognised the cascode stage but wasn't sure what its benefit or purpose might be at audio frequencies. My main exposure to cascode stages is in RF applications where its used to extend bandwidth by eliminating effects of miller capacitance.
Here to it helps with input capacitance but also corrects some other problems in the circuit.

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Originally Posted by DBMandrake View Post
Ok I'm a little bit confused as to which stage you're referring to as the second stage, do you mean Q712/714 ? By no degeneration do you mean because their emitters are tied directly together ?
Yes and Yes.

Quote:
Originally Posted by DBMandrake View Post
So you mean Q716/718, their 100 ohm emitter resistors are too low ?
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).

Quote:
Originally Posted by DBMandrake View Post
So are you saying that the 2SK389 is no longer available at all as a spare part (gulp) or just that it's not available for bulk orders for new designs ? And there aren't many modern alternatives ? So do not many audio amplifiers go to the trouble of having a monolithic dual for the first differential input stage ?
2SK389 is discontinued and becomes very hard to source, Linear Systems has the LSK389 2nd Source in production.

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Old 19th February 2012, 11:50 AM   #2623
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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 wouldn't be hard to rewire a bit and get the rear power amps into play. Might be useful for multiamping speakers.
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Old 19th February 2012, 12:11 PM   #2624
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Originally Posted by DBMandrake View Post
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:

Click the image to open in full size.
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Old 19th February 2012, 12:12 PM   #2625
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Quote:
Originally Posted by SY View Post
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)

Quote:
It wouldn't be hard to rewire a bit and get the rear power amps into play. Might be useful for multiamping speakers.
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.
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Old 19th February 2012, 12:43 PM   #2626
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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.
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

Quote:
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.
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)
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Last edited by DBMandrake; 19th February 2012 at 12:52 PM.
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Old 19th February 2012, 02:18 PM   #2627
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Poor Dr. Rod Rees, another PhD crushed under the heal of SY. He just taught courses at the University at the time on such subjects.
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Old 19th February 2012, 02:38 PM   #2628
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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.
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Old 19th February 2012, 03:04 PM   #2629
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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.
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Old 19th February 2012, 03:08 PM   #2630
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Quote:
Originally Posted by DBMandrake View Post
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.
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.
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