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Old 28th March 2013, 07:02 PM   #8741
dvv is offline dvv  Serbia
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@Nige

I think I fundamentally agree with you regarding a classic SE input stage, based on a differential pair, with all the bells and whistles (cascodes, FET/BJT combinations, current mirrors) far too often cannot match a properly done fully complementary input stage on sound quality.

Not automatic, of course, but by and large, I seem to prefer fully complementary on sound basis alone, even if it is more difficult to get just right.

Also, I would add that letting in a little more current simply sounds better. By that, I mean current per trannie of say 1.1-1.4 mA, although Dan D'Agostino didn't shy away from 1.6 mA per trannie in his older series of amps, from the mid 80ies. Sure, your nominal S/N ratio tends to be lower upon measurement, even if you use low noise trannies like 2SC2240/2SA970, or such like, but this can be offset somewhat by using fully regulated power supplies with serious filtering.

Generally, why go single ended and then spend time and money making it symmterical just before the current gain stages, when you can go symmetrical straight off the bat?

All very personal views, of course.
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Old 28th March 2013, 08:53 PM   #8742
tvrgeek is offline tvrgeek  United States
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Ah, now we cycle back to things we are pretty sure we hear, but can't say what objective measure we can use to quantify it.

Now SELF would say the "traditional" (read that his), input stage is so good you need not go further, and a simple SE VAS contributes so little to the overall signature it is good enough. My understanding of his publications of course. Well, my 1200's sound pretty darn nice; better than any of my "traditional" amps. Only four more old amps to sell on e-bay. I am keeping one Rotel 951 on my test bench as the modern protection circuit in it is a good thing on the speaker test bench where you might connect something wrong and the beguine but un-inspiring sound does not matter. I wish the Z3 power supply was not so terrible as being a small footprint amp gave me more bench space. Just not enough room for caps in there I guess. It hums right along with the music so bad you can't do LF measurements.
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Old 28th March 2013, 09:30 PM   #8743
mjona is offline mjona  New Zealand
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Nigel

Re the concept of a phase splitter driven NPN output - Godfrey seems to have arrived at the same point as Linsley Hood 40 years ago with his Class A amplifier.

The only real difference I can see in Godfrey's layout is his use of an NPN input transistor where Hood used a PNP one.

If you are looking for a Class AB development of the phase splitter concept to experiment with, I suggest you investigate MC33078 and MC34080 where there is an additional "pull down" transistor driven in parallel with the lower NPN output device.

With regard to MC1530 - PNP transistors were noisy when fabricated into IC's so all NPN is unnecessary in building a discrete component version.
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Old 29th March 2013, 09:44 AM   #8744
godfrey is offline godfrey  South Africa
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Quote:
Originally Posted by nigel pearson View Post
Any specs ?
Not very exciting - about 3% THD @ 4W output, IIRC (I didn't save the sim). Output impedance was about 1 Ohm (again IIRC), rising above 200KHz or so. Looked like it might need a Zobel network for stability with purely capacitive loads.

Quote:
Originally Posted by mjona View Post
Godfrey seems to have arrived at the same point as Linsley Hood 40 years ago
No coincidence. I started with the JLH design and just changed the input stage to make an "all NPN" circuit. No pretense at greatness - it was just a "for fun" attempt at a simplest possible circuit.

Last edited by godfrey; 29th March 2013 at 09:47 AM.
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Old 29th March 2013, 10:29 AM   #8745
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Hi Godfrey . My estimate was that ( >1 % ) . My friend John has hidden his bucket of 3055's which he has begged me to use . Otherwise I would have been soldering it up today .

Mjona . You read my mind . MC33079 is my favoutite cheap op amp . Also JLH . My DC offset adjustment was based on the later JLH . The only problem I had was making a DC point that didn't cause hum , my solution is impractical . I feel the Godfrey circuit in H bridge would be interesting .

I came across this design many years after choosing similar ideas . To be frank if chasing the last wisp of distortion it is hard to see how one could do better . Where would extra complexity help it ?

MJR7-Mk5 Mosfet Power Amplifier

Why did I choose Mc33079 ? I listened to it with my eyes , Motorola often give circuit diagrams . The circuit can match NE5532 except on current . It is a very simple design and under the microscope beats 5532 . So much so it is like one of those annoying football teams from a lower league that any would fear to meet .

Someone said those who do not know history make the same mistakes . I would also say history sometimes had better answers . Fashion has a lot to answer for .


Talking motorcycles . Harley Davidson and Triumph were dominant . Both were seriously flawed designs . The flaws were respected by owners as a price worth paying . The Harley twin is too narrow to get best advantage from it . The Triumph hopeless on vibration also . For the life of me I can not see how they succeeded with such awful designs ? . The only thing I suppose is not going away from a reasonable recipe saved them money . It also meant spares were available cheaply with no shortages due to obsolescence . The Triumph Bonneville is the biggest pile of rubbish I know of ( far better a 1960 6T Thunderbird , almost civilized ) . A Bonneville still is the one I most want to own .
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Old 29th March 2013, 05:51 PM   #8746
dvv is offline dvv  Serbia
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Nige, for the n-th time, forget 2N3055 and try out some BD 249C (NPN) and BD 250C (PNP)..

They will sound the pants off 2n3055/2N2955, they are not 60 or 80V but 100V, they continuous current is 25A, impulse 40A (50A if by SGS-Thomson) and they have a very reasonable price.

Well neigh indestructible, and easy monting plastic pack, too. Their only weakness is temperature, in line with 125W devices of that time - you have to cool them seriously.

Mark my words, one of the best transistors for audio, a true unsung legend, despite its relatively modest specs but uncommonly short Ton, Tstore and Toff times for their generation and time frame.
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Old 29th March 2013, 06:20 PM   #8747
bcarso is offline bcarso  United States
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Quote:
Originally Posted by godfrey View Post

No coincidence. I started with the JLH design and just changed the input stage to make an "all NPN" circuit. No pretense at greatness - it was just a "for fun" attempt at a simplest possible circuit.
Another design shown by JLH has promise for an all-NPN configuration, if not necessarily a power amp: the vacuum tube "ring of three", pg 83 of Valve and Transistor Audio Amplifiers, ISBN 0750633565. It's d.c. coupled and is two cascaded common-cathodes and a cathode follower, with series feedback to the input tube.
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Old 29th March 2013, 06:39 PM   #8748
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You should have seen the transistors I turned down yesterday Dvv . The 3055 in class A is very OK . JLH wrote extensively about other deceives . The big surprise was 3055 was least trouble . Some prefer the non H version !!!

Although 3 % distortion is above the bar ( 0.1 % ) it looks easy to graft it onto another stage . The idea of having feedback that early appeals to me . Perhaps a secondary loop to get a tad better distortion .

It makes me rather proud of my 4 transistor design above . JLH was getting 0.05% up to 20 kHz using Darlintons . If you look carefully I was getting 0.05% up to 50 kHz using 4 devices . It is hard to say exactly what I was getting as the oscillator might have had additive or subtractive traits ? I recon I was in the region of what I show . It was a real struggle to get below - 50 db at 50 kHz initially .

You can forgive anyone for believing negative feedback creates high order distortion as in the graphs I give it looks that way ( instability was miles away ) . If you look at my 0R VAS distortion verses 47 R it looks to be true ( see Dvv we are are not mad to do it ) . Reducing gain seems to have effected a cure ( see graphs ) . I still suspect it was loading the previous stage which caused it . If you take gain to be 400 and 8mA than give z = ( 25/8 ) 400 = 1250 R ( BC547C ) . The resistor feeding it 820 R . That is not too bad . Some would even have 1K feeding 300R in . When I add 47 that is then off the scale . 16 R = 6K4 .

DF 96 said if I prefer 16R it is because it weakens the grip of the amp at low frequencies . Doubtless true . See everyone , I thought in my amp to have covered that ( 820 R feeds > 820 R should work ) and would use 0R to the BC547 emitter . No I hadn't , the scope didn't lie . I would imagine 4R7 to already be a great compromise. Doesn't it make you think to see the horrid little spikes in my 0R graph . OK very low level and 50 kHz . Still , it isn't very nice . Surely if we look at - 80db they will still be there ? At - 80 db I can be happier .

I did try a Darlington VAS . It worked great but did not sound as good ( less open ) . I tried a complimentary feedback pair . It was better . The best was just a high gain transistor . I didn't try a cascode . From my experience with them I would assume it to be excellent ( BC547 , MPSA 42 ) . My design can be up scaled and bias reduced ( 100 ma is fine ) . As voltage increases so distortion is reduces to an extent ( stretching the VAS curve ) . I would guess even 100 W to be possible and far less than 1% distortion ( +/- 50 V , 2n 5551 , 5401 , 2SA 1085 2SD756 ) .

Dvv and DF96 said about fiddling . Nearly all amps use a VAS like this . None as far as I know will do anything wild if a VAS emitter resistor is fitted . I suspect 90% would sound better for 4R7 ? For some amps it would be joyfulness discovered . I will suggest if transistor sound ever existed it was this that caused most of it ? Slewing is a byproduct . A bit like using a shotgun when it needed one well placed bullet . JLH has from memory only about 100 uA to drive the VAS , not ideal . That was typical then .
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Old 30th March 2013, 08:09 AM   #8749
Mihkus is offline Mihkus  Estonia
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Damn!!

I want to build DAC out of PD2026B pioneer DAC ic but theres no circuits or anything
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Old 30th March 2013, 08:45 AM   #8750
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
You should have seen the transistors I turned down yesterday Dvv . The 3055 in class A is very OK . JLH wrote extensively about other deceives . The big surprise was 3055 was least trouble . Some prefer the non H version !!!
MOST power transistors do well in pure class A. However, all don't do equally well

Quote:
... It makes me rather proud of my 4 transistor design above . JLH was getting 0.05% up to 20 kHz using Darlintons . If you look carefully I was getting 0.05% up to 50 kHz using 4 devices . It is hard to say exactly what I was getting as the oscillator might have had additive or subtractive traits ? I recon I was in the region of what I show . It was a real struggle to get below - 50 db at 50 kHz initially . ...
I feel that's not easy no matter which design one uses.

Quote:
... You can forgive anyone for believing negative feedback creates high order distortion as in the graphs I give it looks that way ( instability was miles away ) . ...
Which is why I believe in more local and less global NFB. Distortion, I feel, is best dealt with locally so that it doesn'r happen excessively, rather than let it happen and cure it after the amp is already "sick". Prevent rather than cure.

Quote:
I did try a Darlington VAS . It worked great but did not sound as good ( less open ) . I tried a complimentary feedback pair . It was better . The best was just a high gain transistor . I didn't try a cascode . From my experience with them I would assume it to be excellent ( BC547 , MPSA 42 ) . My design can be up scaled and bias reduced ( 100 ma is fine ) . As voltage increases so distortion is reduces to an extent ( stretching the VAS curve ) . I would guess even 100 W to be possible and far less than 1% distortion ( +/- 50 V , 2n 5551 , 5401 , 2SA 1085 2SD756 ) .
Darlington transistors by and large tend to sound warmer than usual, but at the price of some detail. I have yet to hear an amp using Darlington trannies in its output stage which will match a classic say dual transistor pair for clarity and detail.

Quote:
... Dvv and DF96 said about fiddling . Nearly all amps use a VAS like this . None as far as I know will do anything wild if a VAS emitter resistor is fitted . I suspect 90% would sound better for 4R7 ? For some amps it would be joyfulness discovered . I will suggest if transistor sound ever existed it was this that caused most of it ? Slewing is a byproduct . A bit like using a shotgun when it needed one well placed bullet . JLH has from memory only about 100 uA to drive the VAS , not ideal . That was typical then .
Ah, but for the one bullet solution to work, one needs to be a good shot.

Personally, I just love degeneration resistors in the input stages and never fail to let the VAS work into relatively high value resistors. In my view, they offer advantages only with no setbacks. They make sure the VAS is always working into a stable, ground referenced load, which reduces the influence of the amp load variations. It also lets you program the gain stage to almost whatever, making sure your stage gain is exactly what you want and what it needs to be. Limiting gain to something sane also reduces distortion, which in turn reduces the need for global NFB, which reduces more or less odd behavior upstream (say, from 50 kHz upwards).
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