MJL21193 said:
Working with both the simulation and the actual amp, i haven't had any luck removing C4. Stability seems fine, but the DC offset is a real problem. Simulator shows 3.5VDC and the actual amp shows 2.1VDC or so offset. My attempts to bring this down in simulation have ended with worse overall performance.
A servo circuit would be the answer, but I'm not ready for such a complication right now.
On the bright side, I did find one improvement and that was returning the cascode bias to ground rather than the emitters of the LTP. This reduced offset (already very low), THD (mostly higher order) and noise. Noise reduction was a token one with the most gains at low frequency.
I also increased the cascode voltage to ~25V and reduced the current to ~1mA.
Bumped up the VAS current slightly also.
I have changed the schematic for the Abomination to suit:
MJL21193 said:
As usual, I was mistaken. Better results from leaving the cascode to the emitters of the LTP, but reducing the current and increasing the voltage to the cascode. I have fixed it and it can be seen in the schematic above. I also added decoupling and bypass caps to the output stage (already on the layout) and added a C to the R in the rail supply to the frontend.
I know how to determine PSRR in the simulation now. Here it is:
It seems as through ours design are converging a bit, MJL.
I too have found the cascode with all of it's benefits (and
problems). Try decoupling with a 47-100u at the cathode
of LED3 or 5 to the positive rail. That will get you many DB
of PSRR improvement to your CCS and the cascode points.
I didn't copy from your design but andy C. "turned me on"
to some of Cordell's early papers about FET amps and we are
on the right track as both yours and mine (ABOM and FA3)
sim fantastic with wonderful clipping behaviour and
almost immeasureable distortion.
I might ask you (if you wouldn't mind) some multisim8 questions
as I have it installed and have ported most of my work to it.
keep up the good work,
OS
I too have found the cascode with all of it's benefits (and
problems). Try decoupling with a 47-100u at the cathode
of LED3 or 5 to the positive rail. That will get you many DB
of PSRR improvement to your CCS and the cascode points.
I didn't copy from your design but andy C. "turned me on"
to some of Cordell's early papers about FET amps and we are
on the right track as both yours and mine (ABOM and FA3)
sim fantastic with wonderful clipping behaviour and
almost immeasureable distortion.
I might ask you (if you wouldn't mind) some multisim8 questions
as I have it installed and have ported most of my work to it.
keep up the good work,
OS
ostripper said:
Hi OS,
I don't know what effect that would have on the real amp but the sim doesn't like it. Exact opposite to what you said, I saw PSRR worsen.
The sim suggests that the PSRR is very good as it is (much better than my previous effort - Patchwork) in the -70 to -85db range and for the true die-hard purist the frontend can be driven by a separate regulated PS. I will not likely take this extra step though.
ostripper said:
Fire away.
Multisim is tons easier to use than LT so you are in for a treat. I'm still learning myself (see above) so we could help each other.
I only tried it on mine not yours, sorry. Since the bias chain runs off of the rails. decoupling somewhere along it should improve
stability, on mine it was at the main cascode (+VAS) . I did
find a wrong point along the chain to decouple it, even causing oscillations so I "played" some more.
The "biggie" How do you import / create your own .model database ??
By seeing your exquisite PCB artwork and how multisim "has it all" I'm sure to be impressed. I have the schema part almost
decyphered.. its the simulation and board layout that I might
ask a few on .. thanks
OS
ostripper said:
The "biggie" How do you import / create your own .model database ??
Thanks OS,
I use MS 10, so I don't know if there are some new features that 8 doesn't have.
Under the tools menu is there "component wizard"? If so, you can use this to create any type of component from simple to complex. Just follow the prompts.
A little eye candy - the very latest layout for the Abomination amp.
I have received my new PC board material (~27 square feet or so - enough to keep me occupied for a while
) and it's all double sided. It was an ultra splendid deal so I couldn't resist. Good for the double sided layouts or if your feeling adventurous, the silkscreen in copper:
Makes like a bit easier - iron on only once and the copper writing is more visible than the laser printer black.
ostripper said:That is crazy, silk screen in copper.. WTF..
shorts...
A first for DIY..
OS
I thrive living on the edge...
I have had it on my "to do" list for a while. I have done some text before on other boards but I went whole hog here. There isn't any chance of shorts though - I was careful to position everything to avoid that.
I'm having a problem - too many amps laying around. This will be the second of this design, plus I still haven't finished my 6 channel Patchwork project. Your Frugal II is waiting for a mate and a home and I also have Glen's K10A half done.
Poor me.
WOW, your multisim is a 'perdy site ..flashin' LED's ,realtime
instruments, double cool..
I just want 3 pairs of abuseproof standardized amps for my house one's the kids can't blow...
I think I know why your amp didn't like the cap I suggested,
because of your ground referenced cascode in the VAS...
I got rid of mine ,a further departure from the symasym.
OS
instruments, double cool..
I just want 3 pairs of abuseproof standardized amps for my house one's the kids can't blow...
I think I know why your amp didn't like the cap I suggested,
because of your ground referenced cascode in the VAS...
I got rid of mine ,a further departure from the symasym.
OS
ostripper said:
Hi OS,
The real Mona Lisa here is this VAS and I'm not about to paint a mustache on it
There is an old expression: "If it ain't broke..."
PSRR of this amp is at least 20db better than my Patchwork (I won't comment on other amps I've simmed
). If this is still not good enough, the door is open to supplying the front end separately.
ostripper said:SS (t-trak) porno...
the "other side"...awesome stuff... I WANT A laser printer..
OS
Thanks OS,
Did you get that email I sent you? Offer still stands.
AKSA said:Enough to make a hardened audio designer cry......
Beautiful work, John!
Hugh
Thanks Hugh,
If you can't make them better, at least make them prettier.
I'm now officially ruined. I can't do any better than this design and really there isn't any reason to try. I don't need or want a better amp than this - I (and most others) wouldn't hear the difference anyway. It has low noise, it has high speed, amazing stability, very good PSRR, beautiful clipping performance. It has high power and the ability to drive a low impedance load. Oh, and it sounds great.
It's like the first season of Californication - where to go for season 2 but down?
The above may sound like bragging but anyone who has been reading this thread will know the difference. This is just my adaptation, my lucky changes, my paint brush smearing the brown CIL latex on the Da Vinci masterpiece.
My Abomination!
You can do 3 things to keep busy..MJL..
1. Offer your splendid design (PCB,silkscreen,etc)
for all to do..offer occasional support for (noobs).
2. Port your design for more power (higher rails, more OP
devices , or FET OP's)
3. As you seem to be a "one man board factory" sell
some to prospective constructors.
I am only a couple months behind you and I plan for all 3..
OS
1. Offer your splendid design (PCB,silkscreen,etc)
for all to do..offer occasional support for (noobs).
2. Port your design for more power (higher rails, more OP
devices , or FET OP's)
3. As you seem to be a "one man board factory" sell
some to prospective constructors.
I am only a couple months behind you and I plan for all 3..
OS
John,
The work has just begun. OS is right. Stick with this power rating for the moment, now concentrate on the enclosure design, so you can offer plans, or even completed metalwork. Then you do all the assembly instructions; documentation is a long, difficult process and involves a lot of paraphrasing and photography.
Then you have to do advertising copy. 'Best amp in the world, biggest keeper in high end, yada yada, with sexy photos and endorsements.
Finally, you need reviews. This is another minefield, as you have to keep these guys on side. Be aware the product will be based on appearance first, perceived quality second. Reviews are very helpful, particularly if you can get some academic critic to rabbit on about the hermetic imaging, and elegantly encapsulated bass. A crystalline top end will help too!!
The product is technically very good, exceptional even, so you need to concentrate on presentation and marketing. If selling to the DIY crowd, the requirement is different, with more emphasis on performance and low cost.
Perhaps when you've negotiated this minefield we can all band together and form an association to protect our market position!!
Merry Christmas and thank you for sharing your lovely amp,
Cheers,
Hugh
The work has just begun. OS is right. Stick with this power rating for the moment, now concentrate on the enclosure design, so you can offer plans, or even completed metalwork. Then you do all the assembly instructions; documentation is a long, difficult process and involves a lot of paraphrasing and photography.
Then you have to do advertising copy. 'Best amp in the world, biggest keeper in high end, yada yada, with sexy photos and endorsements.
Finally, you need reviews. This is another minefield, as you have to keep these guys on side. Be aware the product will be based on appearance first, perceived quality second. Reviews are very helpful, particularly if you can get some academic critic to rabbit on about the hermetic imaging, and elegantly encapsulated bass. A crystalline top end will help too!!
The product is technically very good, exceptional even, so you need to concentrate on presentation and marketing. If selling to the DIY crowd, the requirement is different, with more emphasis on performance and low cost.
Perhaps when you've negotiated this minefield we can all band together and form an association to protect our market position!!
Merry Christmas and thank you for sharing your lovely amp,
Cheers,
Hugh
ostripper said:
AKSA said:
Pump the brakes, fellas!
I'm not in this to produce a sellable amp. I'm not even in this for the benefit of others - there are, after all, tons of good designs out there to build (including the one this is hacked from). My motives are purely selfish - it's all about me, me, ME!
I have been doing this for the challenge and my own enjoyment - to learn and do.I'm feeling postpartum depression here or some such. An anticlimax that has me wondering what I'll do next. I'll recover, maybe...
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