Strange both my CFA/VFA amps perform better today especially Redemption song / Brain damage (Bob Marley / Pink Floyd).
Arghhh! Another valuable contributer is leaving us. 
Good luck!
PS: And don't forget to ask for a refund. 😀
Cheers, E.
Good luck!
PS: And don't forget to ask for a refund. 😀
Cheers, E.
My first post in this thread: If you guys can stop the war of attrition long enough to advise me, I, like other members reading here, would be thankful. Am I incorrect to point out that the components used with any quality amp will be be audibly different? Not necessarily better but different. Alot of what we think is better is attributable to our personal tastes. For instance, I prefer my audio recipe with the following emphasis:
40% soundstage
40% timbral accuracy
20% PRAT
Using these parameters might highlight one of the amps over the others but won't necessarily make it a better amp. I've only ever built two amps and they are both very good but each has its own character. One is the go to for loud, gratifying playback and the other is for critical listening. One sacrifices a little soundstage for a more polite presentation but I still love to hear from it. If we can stop naming a winner and concentrate on defining its character like I've done above, we'd be less likely to lose valuable insights from our members. That's my two cents worth.
40% soundstage
40% timbral accuracy
20% PRAT
Using these parameters might highlight one of the amps over the others but won't necessarily make it a better amp. I've only ever built two amps and they are both very good but each has its own character. One is the go to for loud, gratifying playback and the other is for critical listening. One sacrifices a little soundstage for a more polite presentation but I still love to hear from it. If we can stop naming a winner and concentrate on defining its character like I've done above, we'd be less likely to lose valuable insights from our members. That's my two cents worth.
You have to decide if you want a straight wire with gain or want an amp that "colors" the sound. I believe, though you would have to ask OS when he gets back, that one of the goals of this project was to produce not only a fast amp, but an accurate amp as well. To my ears, that is what has been achieved. If you want a "warm" amp, maybe you need to look for one that isn't quite so accurate, or maybe you need to use a preamp with tone controls.
BTW, I don't think folks left because someone didn't agree with them. IMO, they left because they didn't like the rules of engagement. Their prerogative, I like rules.
Blessings, Terry
BTW, I don't think folks left because someone didn't agree with them. IMO, they left because they didn't like the rules of engagement. Their prerogative, I like rules.
Blessings, Terry
I am sad to see you go. I enjoyed a lot of your posts very much.
Your abserce is a great loss to the forum.
J
i know OS is still not back yet, but for the other members of the "rapid prototyping crew" out there, here's a question for you. as another VFA model experiment, any of you ever thought about or plan to build bob cordell's 50w mosfet amp front end and stick it ahead of OS' output stage? it's alleged to be very fast and have very low distortion, so fits in with some interests demonstrated in the audience on this thread.
not sure what thread it was in, but i remember bob even made some mods to his front end to handle balanced input (in response to a challenge from john curl).
mlloyd1
not sure what thread it was in, but i remember bob even made some mods to his front end to handle balanced input (in response to a challenge from john curl).
mlloyd1
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Hi mlloyd,
Do you have a link to that schematic. I would like to put in ltspice and see how it works. I am of course, interested if someone will make a layout of it.
Do you have a link to that schematic. I would like to put in ltspice and see how it works. I am of course, interested if someone will make a layout of it.
sorry, I forgot to come back and post some links.
here's a link to a pdf of bob's original article which contains the front end schematic and circuit description: cordell 50w mosfet power amp.
note that this was a technical article versus a project writeup.
i'll post a link to bob's updated front end when i find it, in case this editing session times out before i get back.
mlloyd1
edit: it didn't time out! ok, i found the link to bob's updated front end. thanks to pete b who was looking previously and posted the link. there is no way i would remembered the long name bob gave it 🙂
here's a link to a pdf of bob's original article which contains the front end schematic and circuit description: cordell 50w mosfet power amp.
note that this was a technical article versus a project writeup.
i'll post a link to bob's updated front end when i find it, in case this editing session times out before i get back.
mlloyd1
edit: it didn't time out! ok, i found the link to bob's updated front end. thanks to pete b who was looking previously and posted the link. there is no way i would remembered the long name bob gave it 🙂
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OK I attached the DCFQ (Cordell IPS) to the Slewmaster OPS but I have errors and don't know how to finish it. I probably have the NFB connected wrong and not sure about the output from the VAS either. Looks like we need a zener voltage source for the front end 15V supply but I'm not sure how to do that either. Anyway, I'm attaching what I have so far and hopefully one of you can make it work and post back.
Blessings, Terry
Blessings, Terry
terry:
brave guy you are 🙂
i took a VERY QUICK at the ltspice schematic; you may want to make the changes in red in my attached picture: add a connection dot and delete 2 wire segments.
also might want to be careful applying +/-85 volts with all those 2N4401/2N4403 devices sprinkled around
🙂
mlloyd1
brave guy you are 🙂
i took a VERY QUICK at the ltspice schematic; you may want to make the changes in red in my attached picture: add a connection dot and delete 2 wire segments.
also might want to be careful applying +/-85 volts with all those 2N4401/2N4403 devices sprinkled around
🙂
mlloyd1
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sorry, the editor time limit got me.
picture for the above message is called "changes_for_terry"
i had a few more minutes to take another look. probably don't need additional emitter followers at the output of the front end (OPS board is already a triple). so, i'd take them out as well as the 4v source. see picture "more_changes_for_terry"
mlloyd1
picture for the above message is called "changes_for_terry"
i had a few more minutes to take another look. probably don't need additional emitter followers at the output of the front end (OPS board is already a triple). so, i'd take them out as well as the 4v source. see picture "more_changes_for_terry"
mlloyd1
Attachments
Hi mlloyd1, looking at the attached pictures, I think I recognize Multisim 🙂
Can you please attach the multisim model here (if I'm right)?
Thank you,
Valery
I think I have made the changes. It doesn't run right so something is still amiss. I'm posting the updated model.
Question, what are I1, I2 and I3? Should those be replaced with resistors?
Thanks, Terry
Question, what are I1, I2 and I3? Should those be replaced with resistors?
Thanks, Terry
what error messages do you get?
the Ix are independent current sources; they supply a fixed value of current, no matter what - i.e. the proverbial ideal current source.
i wouldn't replace them with anything (yet) until we see how things are running.
i didn't try to run this file - i assume you have all the models in place?
i like to run a dc sim first to check that my bias point values make sense; i didn't look carefully at the file but I'd guess it's not set up to run just dc.
i'll look over the circuit more thoroughly tonight when I get home from work.
mlloyd1
the Ix are independent current sources; they supply a fixed value of current, no matter what - i.e. the proverbial ideal current source.
i wouldn't replace them with anything (yet) until we see how things are running.
i didn't try to run this file - i assume you have all the models in place?
i like to run a dc sim first to check that my bias point values make sense; i didn't look carefully at the file but I'd guess it's not set up to run just dc.
i'll look over the circuit more thoroughly tonight when I get home from work.
mlloyd1