grege said:
There can be no excuse for obvious and avoidable flaws in this design...eg...no second stage bootstrap.....absent degeneration.....darlingtons at output without bleeder resistor and capacitor...just four diodes for adjustment-free class-AB biasing....etc...These extras cost insignificant money....so...no excuse for this design...at all.....
For minimum acceptable performance Rod Elliot's designs should suffice...
Sorry for the misquote mikeks, I got carried away with the cutting and pasting, naughty Greg. 
I believe Graham, the designer, made a design decision to make it as simple as possible for hobbiest to construct. IMHO he achieved this and I agree compromises have been made. The exercise of adding these extra components at a later stage, and hearing first hand the improvements, is what makes this amp such a valuable learning experience.
I've built a number of other "complete" kit amps including a P3A but haven't learnt as much as when I built the DIGI125.
Did that, and it made an improvement. The two things that made the biggest improvement was 1. a bootstrap on the VAS and 2. adding extra bias diode. The other fiddles made minor, subtle improvements. Bare in mind it hard to make blanket statements when things are done using a non-scientific method.
I tried 4 diodes for biasing on the DIGI125 and the output transistors run very hot and heat up quite quickly. I'm not sure if this is a result of overbiasing or oscillation, but dropping back to 3 solved the problem. Others have reported this as well. What do you think it casue may be Mike?
Thanks for the feedback
I believe Graham, the designer, made a design decision to make it as simple as possible for hobbiest to construct. IMHO he achieved this and I agree compromises have been made. The exercise of adding these extra components at a later stage, and hearing first hand the improvements, is what makes this amp such a valuable learning experience.
I've built a number of other "complete" kit amps including a P3A but haven't learnt as much as when I built the DIGI125.
Did that, and it made an improvement. The two things that made the biggest improvement was 1. a bootstrap on the VAS and 2. adding extra bias diode. The other fiddles made minor, subtle improvements. Bare in mind it hard to make blanket statements when things are done using a non-scientific method.
I tried 4 diodes for biasing on the DIGI125 and the output transistors run very hot and heat up quite quickly. I'm not sure if this is a result of overbiasing or oscillation, but dropping back to 3 solved the problem. Others have reported this as well. What do you think it casue may be Mike?
Thanks for the feedback
I have read all this iconoclastic criticism from the purists, and I sometimes feel they have lost sight of what the Digi125 amp was about. This is all the more poignant since I realize most here have not actually heard this remarkable design.
The Digi125 is an extraordinary amplifier. It sounds better than it has any right to. It was designed for absolute minimalism and bedrock low cost, yet with a good performance to satisfy all but the top end audiophiles. In this, it serves brilliantly, and I don't believe there are many amps anywhere which do so much with so little. For years here in high cost Australia it sold as a kit for less than $40. That is a supreme achievement in this world of kilobuck audio bull####.
I agree with all of the suggested improvements; base stoppers, bootstraps, charge suckout on the output stage, etc etc. They all work, as Greg has remarked. But Graham Dicker, the designer, is one of the cleverest and most creative audio designers Australia has produced; he has a huge repertoire, and has designed a host of digital and logic products, even novel single ended amplifiers, hybrids too, lots of vacuum tube circuits, the whole gamut. The man is an enthusiast and a genius.
Almost every audio circuit I see these days is verbose; things can be simpler, but seldom does one see it.
The comment should be: "How does an audio designer create such an incredibly simple circuit which delivers such extraordinary performance at such low cost?"
Cheers,
Hugh
The Digi125 is an extraordinary amplifier. It sounds better than it has any right to. It was designed for absolute minimalism and bedrock low cost, yet with a good performance to satisfy all but the top end audiophiles. In this, it serves brilliantly, and I don't believe there are many amps anywhere which do so much with so little. For years here in high cost Australia it sold as a kit for less than $40. That is a supreme achievement in this world of kilobuck audio bull####.
I agree with all of the suggested improvements; base stoppers, bootstraps, charge suckout on the output stage, etc etc. They all work, as Greg has remarked. But Graham Dicker, the designer, is one of the cleverest and most creative audio designers Australia has produced; he has a huge repertoire, and has designed a host of digital and logic products, even novel single ended amplifiers, hybrids too, lots of vacuum tube circuits, the whole gamut. The man is an enthusiast and a genius.
Almost every audio circuit I see these days is verbose; things can be simpler, but seldom does one see it.
The comment should be: "How does an audio designer create such an incredibly simple circuit which delivers such extraordinary performance at such low cost?"
Cheers,
Hugh
Pavel,
We have already established that, I believe. And besides, did we not agree to disagree?
Have you heard the Digi125? I'm not talking about the topology, I'm referring to the actual design, the kit, the component choices Dicker makes?
If you have, fine, I'll listen. But if you make a judgement based entirely upon the schematic, then I refute your point utterly. The amp sounds very good even in published form, MUCH better than other much more complex designs I've seen in magazines which are redolent in current mirrors, sinks, and cascodes.
No offense taken or intended, BTW.
The problem as I see it is this:
1. A minimalist kit design from a very clever designer is available in the public domain. This indicates some generosity on the part of the designer, some altruism, for which he deserves credit, just as I give you credit, Pavel, for publishing some of your circuits on your website.
2. Engineers and purists can the design because it is ridiculously simple. Can't possibly work, no audition necessary, crikey, anyone with SS Physics 101 knows that!!
3. Novices and non-engineers, in short potential buyers, get the impression it is sonically substandard, even though the simplicity appeals from a constructor POV.
4. No sale is made, the brilliant creative work of this designer in other, more complex areas is overlooked forever, the DIYer gets no valuable experience on something very simple and inexpensive, and he is left floundering around wondering what is acceptable, doable, and why.
It is precisely this scenario which hobbles DIY, in my opinion. I may be wrong, but the last thing we need is the seductive academic argument leading to high complexity and expensive parts lists. This approach bodes poorly for success right off the starting block. Nelson Pass published his Zen amplifier about a decade ago; it has serious shortcomings sonically, but I and countless thousands of others built one and it was a wonderful introduction to high end for many. No one canned this design before the ink dried on the magazine article; I believe it behoves influential people like you, Pavel, to encourage simplicity when starting out, so people can gradate the complexity of their projects towards something of outstanding technical AND SONIC merit.
Have a nice day!
Cheers,
Hugh
We have already established that, I believe. And besides, did we not agree to disagree?
Have you heard the Digi125? I'm not talking about the topology, I'm referring to the actual design, the kit, the component choices Dicker makes?
If you have, fine, I'll listen. But if you make a judgement based entirely upon the schematic, then I refute your point utterly. The amp sounds very good even in published form, MUCH better than other much more complex designs I've seen in magazines which are redolent in current mirrors, sinks, and cascodes.
No offense taken or intended, BTW.
The problem as I see it is this:
1. A minimalist kit design from a very clever designer is available in the public domain. This indicates some generosity on the part of the designer, some altruism, for which he deserves credit, just as I give you credit, Pavel, for publishing some of your circuits on your website.
2. Engineers and purists can the design because it is ridiculously simple. Can't possibly work, no audition necessary, crikey, anyone with SS Physics 101 knows that!!
3. Novices and non-engineers, in short potential buyers, get the impression it is sonically substandard, even though the simplicity appeals from a constructor POV.
4. No sale is made, the brilliant creative work of this designer in other, more complex areas is overlooked forever, the DIYer gets no valuable experience on something very simple and inexpensive, and he is left floundering around wondering what is acceptable, doable, and why.
It is precisely this scenario which hobbles DIY, in my opinion. I may be wrong, but the last thing we need is the seductive academic argument leading to high complexity and expensive parts lists. This approach bodes poorly for success right off the starting block. Nelson Pass published his Zen amplifier about a decade ago; it has serious shortcomings sonically, but I and countless thousands of others built one and it was a wonderful introduction to high end for many. No one canned this design before the ink dried on the magazine article; I believe it behoves influential people like you, Pavel, to encourage simplicity when starting out, so people can gradate the complexity of their projects towards something of outstanding technical AND SONIC merit.
Have a nice day!
Cheers,
Hugh
Hugh,
all I speak about is the following circuit:
http://www.diyaudio.com/forums/showthread.php?postid=458376#post458376
(please mention that it is not AKSA).
Yes - I have built the same circuit more than 20 years ago many times and I still have 2 channels. I think that it is the 1st solution that one will create independently when starting with LTPs, not knowing much about circuit design. This circuit is full of flaws as I described before. Compared to my class A amplifier in a listening test, this amp sounds horribly. Grainy, harsh, unfocused sound. You can hear it on every kind of music. You know that I love to listen to the classical music, and here the difference is the greatest.
I very strongly doubt about persuading about sound quality in written form. But it is very easily possible to uncover objective design flaws, and the amp I referred to is full of them.
Regards,
Pavel
all I speak about is the following circuit:
http://www.diyaudio.com/forums/showthread.php?postid=458376#post458376
(please mention that it is not AKSA).
Yes - I have built the same circuit more than 20 years ago many times and I still have 2 channels. I think that it is the 1st solution that one will create independently when starting with LTPs, not knowing much about circuit design. This circuit is full of flaws as I described before. Compared to my class A amplifier in a listening test, this amp sounds horribly. Grainy, harsh, unfocused sound. You can hear it on every kind of music. You know that I love to listen to the classical music, and here the difference is the greatest.
I very strongly doubt about persuading about sound quality in written form. But it is very easily possible to uncover objective design flaws, and the amp I referred to is full of them.
Regards,
Pavel
That's exactly what everyone is trying to explain all the time !
BTW: One more mod comes to my mind. I am not sure at the moment if it is detrimental to stability however (or more exactly: to what degree, since it definitely affects stability). One could connect the "hot" lead of the miller cap (C2) to the output node.
This has once been suggested for the ubiquitous LTP- VAS-emitter-follower topology by E. Cherry from down under.
Regards
Charles
Hi Graham,
Thanks for your permission. It's always difficult to discuss a circuit when you are unsure of the copyright situation.
Speaking of copyright, I have often wondered about the copyright situation when a designer like yourself publishes in a magazine. Obviously the IP and circuit design is yours (or do you sign it over) but the magazine must have some level of copyright of the actual article such as artwork and layout. So in this case, publishing the ETI schematic would be a ETI copyright infrigment. (hasn't Silicon Chip taken over most defunct Australian electronics magazine's copyrights?)
So we really need to redraw your DIGI125 schematic before we post it to keep everyone 100% happy.
BTW: What happened to your web page http://members.bettanet.net.au/~gtd/ . It looks like it was eaten by Word. Do you still sell the kits?
regards
Thanks for your permission. It's always difficult to discuss a circuit when you are unsure of the copyright situation.
Speaking of copyright, I have often wondered about the copyright situation when a designer like yourself publishes in a magazine. Obviously the IP and circuit design is yours (or do you sign it over) but the magazine must have some level of copyright of the actual article such as artwork and layout. So in this case, publishing the ETI schematic would be a ETI copyright infrigment. (hasn't Silicon Chip taken over most defunct Australian electronics magazine's copyrights?)
So we really need to redraw your DIGI125 schematic before we post it to keep everyone 100% happy.
BTW: What happened to your web page http://members.bettanet.net.au/~gtd/ . It looks like it was eaten by Word.
Do you still sell the kits?regards
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.