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Old 6th June 2008, 11:36 PM   #21
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Quote:
Originally posted by Mooly
Hi,
Erm-- A few have asked this . As I have said earlier the originals were one off's in the truest sense-- have a look at the pics I mentioned at the start.
The best I can offer I am afraid is an untested layout-- which was really an exercise in using DipTrace for me. Having said that the whole design is extremely stable and not prone to any "nasties" and even on prototyping board it performs well, and I can not see any major problems with using this layout.

Your layout is way short on copper.

Beef everything thing as thick as possible leaving little copper spare. Especially ground, power rails and output tracks.
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Old 7th June 2008, 03:04 AM   #22
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Default very nice design

hi mooly,

how r u? i am looking your design and thinking to build it too.......oh no..dont be afraid......vroboard again....ha...ha....

anyway i will try your design until i get final design for it.

what is the max wats will be dlvr?

best regards
michael
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Old 7th June 2008, 07:14 AM   #23
Mooly is offline Mooly  United Kingdom
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Hi,
Any oscillations in the output--- None whatsoever. Absolutely stable and extremely forgiving of layout. Perhaps I better explain that a bit more
I don't use a PC simulator-- everything I design and build is all done the hard way, plugboard and proto board to begin with as the design is worked through and optimised. You can't beat seeing (and hearing) the effect of component changes.
If this design were changed to a long tailed pair the gain and phase margins would be greatly altered. The single ended input not only sounds better ( very much better IMO ), it also make the whole design very "docile".
R13 and R18 the 330 ohm and 270 ohm.
The 270 ohm gate stopper is higher than usually seen (47 or 68 ohm). No magic formula I'm afraid, just listening tests and making sure it does not impact on the full power bandwidth of the amp.
As the gate capacitance varies between N and P channel devices there is the intriguing possibility of making R18 and R21 unequal. You often see extra capacitance added-- why not alter the gate resistor instead-- and what would the effect be on the distortion produced by the output stage I wonder ?
R13 the 330 ohms-- these just provide a little "isolation" for the VAS from the loading and junction capacitance of the drivers Q6/7. Again no magic--- just a sensible value.
As I said at the start, the whole reason for being of this amp is to reproduce music in a domestic setting. Listening tests were of equal importance--- no MORE importance than technical perfection.
I can honestly say that if I had heard better I would crave it, but I have'nt.
And that I suppose is why I have not been spurred on to develop it further. Yet !!
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Old 7th June 2008, 07:27 AM   #24
Mooly is offline Mooly  United Kingdom
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Hi Nigel,
More copper (More power ). I know you are into real powerhouse amp jobs, multiple outputs etc. For a single output pair it's not that bad, although C10 and 11 on the layout---I should have used the next size "up" with DipTrace.
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Old 7th June 2008, 07:41 AM   #25
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Hi Space,
You always frighten me
Having seen what you can do with veroboard you are DEFINITELY the man for the job.
Power wise about 60 watts into 8 ohms is a sensible figure, but that has to be taken in context, the amp deliberately has no additional output limiting -- purely for sonic reasons -- and the fact that as I designed and would be using it, if I abused it or shorted it and blew it up, then thats my fault alone If it were a commercial product some protection at least would be desirable, even a pair of zeners to limit the Vgs of the MOSFET's.
The lateral MOSFET's are tough little beasts, no secondary breakdown etc, no thermal runaway, self limiting if over driven.
SPACE --- Get the Veroboard out ! And 60 watts is plenty for a domestic amp. Remember that doubling the power will only give a 3 db increase in level, and that is not very noticeable.
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Old 7th June 2008, 08:06 AM   #26
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Mooly, your description of the overall sound of your amp wants me to try it out. But just a question - is it better to lower the voltage and retain a single output pair or to have the supply as is and double the output devices for full drive into a 4 ohm load?

Regarding gate stopper resistors, Randy Slone uses 470 ohms for the 2SJ162 and 680 ohms for 2SK1058. I have tried these values with other circuits and I think they sound very good.
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Old 7th June 2008, 10:40 AM   #27
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hi mooly,

yes....just looked at your fantastic design i have all the parts at myhand only output mosfets i don't have. never mind i can arrange it any way (original). i understand it is for musical not for power house. i really want to try your this circuit.

may be i wll need some help from you to build it.

wait, just send sms to my parts supplier for 2sj and 2sk...ok ....this time no problem .....he supply to me original parts....


is this class A design amp?

best regards
michael
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Old 7th June 2008, 11:36 AM   #28
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Hi Sam,
From years of experience of making untried or untested changes, or perhaps thinking that this or that might be better I have to say build "as is" at least to begin with. You then have a "reference" with which to compare any mods to. Anyone designing boards can always add the option to fit an extra pair on the layout.
That said they are no mean performers, my B&W 703's have a 3 ohm minimum impedance ( As stated by B&W ) and the amp has no problems whatsoever driving these.
The supply voltage is not critical, but I would not go much higher than the +/- 45 volts D.C. I use. The amp will work well from +/- 30 volts or so up, obviously with less power available.
Just make sure that the Op Amp has a stable single -12volt supply--- do not substitute this part without realising the implications--- it's not in the audio path anyway.
I can't say I have studied Randy Sloanes designs, but that sounds interesting using the unequal values, the ratio sounds about right as the 1058 has around 600pF gate capacitance and the 62 around 900pF. It would be interesting to know how the distribution of the distortion products produced by the output stage are altered doing this.
Regards Karl
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Old 7th June 2008, 11:42 AM   #29
Mooly is offline Mooly  United Kingdom
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Hi Space,
If you can get the outputs, give it a try, I know you won't be dissappointed.
If you need any help I can do that via this forum. Another great thing is that it can all be run up and tested without the outputs in place, it's all reasonably high impedance so any errors etc should not cause a major "blow out".
It's not Class A --- and don't let that put you off , it runs as cool as a cucumber.
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Old 8th June 2008, 05:22 AM   #30
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I noticed the CFP-MOSFET output. Very nice. Does it clip closer to the rails then an EF or VAS driven MOSFET?
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