Didi you actually read that chapter well? Cordell warns against the risks of DC servos degrading the sound. The phase shifts in the low-end are oblivious. I would consider its use only in a zero-global feedback amp. Is their evil a better one than GNFB? I dont know, but I hope to find out.
So was my ex-wife, but that's been taken care of. I'd put up with it in a phase shift though.
Reworked lyrics of one of France greatest : Jacques Dutronc Le fond de l’air est frais | NosEnchanteurs
And of the greatest of songs ever : Il est cinq heures Paris s'eveille - YouTube
(turns 70 in two weeks time, we all is getting old)
My goodness me, you really have trawled through this thread to pull that one up.
Sure servos can affect the sound. That's why I generally don't use them. I prefer none (as in sx an nx Amp) or an over sized electrolytic ( as in e-Amp or Ovation 250).
However, if your servo is causing problems, it's your design you need to look.
'sfunny - span-up (spun? spinned?) Brassens' Goriiiiiillia minutes before reading that!
I am 68 this year and lived in Paris during "les evenements". Brassens, Brel &co were a great way to really learn french (without realising it), and have left me with a deep love of the Chanson tradition.
An elegant way is by modulating a current source with the servo output, imo.
Still a loop, but some also still favor to differentiate between local and global.
(Mais les braves gens n'aiment pas, que des cons suivre une autre route que eux. La mauvaise réputation...sorta)
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Sorry, but I was reading the thread from the beginning, skipping some posts when it derailed.
I agree... I'm not sure what I would choose between a biig electro and a servo
Touché. I do differentiate indeed.
Hi all
Has anybody here listened to various DIY discrete opamps?
I have made a clone JE990 and it is very good but wondered if there is anything A LOT better out there - soundwise?
I looked at the various Sam Groner opamps as well as the line-up modified 918 as well as the plenty on the net.
I suppose I am asking what shouldn't I bother with as a DIY experiment
Rob
OK, you have to compare apples to apples. First, the JE990 and their ilk have output current capability of some 250mA. As far as I know, there isn't a normal chip opamp that can do that on it's own. You have to add something like a BUF634 buffer inside the feedback loop to achieve that kind of output drive.
So, if you compared, say, an LME49710 + BUF634 (@ +/-15vdc supply) to a JE990 (@ +/-25vdc supply), I think it would be unlikely that you could hear the difference (unless you want to drive something to 35 volts!). They would also probably measure about the same, given the same gain, etc. The difference is that the chips are probably more consistent than the discrete, and far cheaper too.
Still, I have been fooling around with a hybrid discrete opamp, where the front end is discrete and the diamond buffer is provided by a BUF634 (or equivalent). I don't see the sense in having two diamond buffers, one in the LME49710 and one in the BUF634.
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Discrete Audio Opamps
Hello all,
For that are interested I have been been building and experimenting with DOAs (Discrete Op Amps) for some time. I have built several projects using them. I have both the Sam Groner V2 BJTs and MOX JFETs (found on this forum) on hand. The MOX DOAs are built using NOS Toshiba LSK389 parts. Both are exceptional designs. Let me know if you are looking for them.
Hello all,
For that are interested I have been been building and experimenting with DOAs (Discrete Op Amps) for some time. I have built several projects using them. I have both the Sam Groner V2 BJTs and MOX JFETs (found on this forum) on hand. The MOX DOAs are built using NOS Toshiba LSK389 parts. Both are exceptional designs. Let me know if you are looking for them.
Considering the work and parts put into them I don't think they are. I price the DOAs that I offer at $48 each (single quantities) which is typical. At that price no one is getting rich.
The ones that I offer are assembled and tested. DOAs can be pesky buggers to build if you have not done it before and lack a good test bench. The ones I make conform to the old 2520 pinout standard (shown below)
There are other DOAs on the market that have the same pinout.
The most notable being the John Hardy 990 The John Hardy Company 990 Discrete Op-Amp as well as Discrete Op-amps and Classic Audio Products, Inc.
I built the headphone amplifier that Sam Groner includes in his paper describing his DOA. I use it as a test fixture driving my favorite headphones (Sennheiser 650s) or reference loudspeakers in my dev lab. Using a consistent fixture to test DOAs allows you train your ear to hear subtle differences in the DOAs and there are differences. I built the fixture to accept DIP packaged op amps as well as '2520 packaged' DOAs. That allows you to audition DIP packaged op amps in the same circuit. I could put up a picture later today should anyone be interested.
The ones I make conform to the old 2520 pinout standard (shown below)
There are other DOAs on the market that have the same pinout.
I can't use the odd pin out since all of my boards are set up to use DIP-8 ICs.
I can't use the odd pin out since all of my boards are set up to use DIP-8 ICs.
Sorry Ammel68,
The larger 2520 pin out is 'old school' finding its roots in vintage recording consoles and custom gear from the 70's. The format is big enough to allow the use of thru hole parts.
There are a few DIP-8 DOAs around. I've tried the Burson Audio DIP-8 DOAs. They are interesting enough.
Collective Cases offers an adapter that will allow a DOA in the 2520 footprint to fit into a DIP8 socket.
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