My head is spinning, congratulations!
Back in the '50s, a company called Stephens (or something like that), made a 500 ohm speaker. Perfect for an OTL, which coincidently they also made. It's a tough thing to do, if you want to keep the moving mass low, but it IS possible.
I've thought for a while about designing a driver with bifilar wound dual coils, tightly coupled, at a relatively high impedance. Perfect for push-pull OTL. Well, one of these days, I'll get off my lazy butt and do it.
Back in the '50s, a company called Stephens (or something like that), made a 500 ohm speaker. Perfect for an OTL, which coincidently they also made. It's a tough thing to do, if you want to keep the moving mass low, but it IS possible.
I've thought for a while about designing a driver with bifilar wound dual coils, tightly coupled, at a relatively high impedance. Perfect for push-pull OTL. Well, one of these days, I'll get off my lazy butt and do it.
ZIP.
Hi,
Yep, you'd better forget those...rest assured not many amps can drive them correctly though.
Those are current hungry beasties, especially the Apogees.
With a bit of bad luck either one can get killed in a flash (I mean either the OTL or the ribbons) leaving the user with a big repair bill.
Want to put your OTLs to the test?
Put a series network across the output terminals consisting of a 10uF filmcap and a 1R resistor 10W or more and crank up the volume...with the speakers connected too.
If your HT rail fuses don't blow and you see the terminals go glowing red hot I can assure you you have one hell of an OTL.
Thing is, OTLs can deliver current but contrary to a transistor amp they put out more power at higher impedances.
Let me know if the 80W OTL survived the test...mine does.
Ciao,
Hi,
Yep, you'd better forget those...rest assured not many amps can drive them correctly though.
Those are current hungry beasties, especially the Apogees.
With a bit of bad luck either one can get killed in a flash (I mean either the OTL or the ribbons) leaving the user with a big repair bill.
Want to put your OTLs to the test?
Put a series network across the output terminals consisting of a 10uF filmcap and a 1R resistor 10W or more and crank up the volume...with the speakers connected too.
If your HT rail fuses don't blow and you see the terminals go glowing red hot I can assure you you have one hell of an OTL.
Thing is, OTLs can deliver current but contrary to a transistor amp they put out more power at higher impedances.
Let me know if the 80W OTL survived the test...mine does.
Ciao,
That's true, but most users prefer to go "bareback"fdegrove said:Hi,
Mine have a perforated cage I put on to protect from probing fingers...even the heat of the valves alone can hurt a person.
Granted, they look better without that cage but, hey... better safe than sorry.
Cheers,
I imagine though, that the glass temperature of your OTL is a hell of a lot higher than some 2A3 amp.
Cheers,
Gee, my triodes run cool as a cucumber. Idle plate dissipation is about 1.5 watts per tube- less than the heaters.
But then again, I'm not using Model T stuff like DHT.
If I had sheet metal fabrication capability, I'd be all over the cage stuff. I probably will go that route for the new DD ESL amps, but we're talking CRUDE: my brake is the edge of the dining room table.
But then again, I'm not using Model T stuff like DHT.
If I had sheet metal fabrication capability, I'd be all over the cage stuff. I probably will go that route for the new DD ESL amps, but we're talking CRUDE: my brake is the edge of the dining room table.
Re: Food for thought
And his assertion that the (necessarily) distorted feedback signal sent back to the input of the amp to be re-distorted into ever higher harmonics; is that real fact?
The part where has this little test setup measuring distortion at different levels of feedback, it would seem that even a source follower with it's 100% feedback makes unacceptable distortion because the transconductance curve is not quite a perfect parabola. What are we to do then?Pan said:http://w3.mit.edu/cheever/www/cheever_thesis.pdf
Check this site out and learn some more my "audiophile" friends
/Peter
And his assertion that the (necessarily) distorted feedback signal sent back to the input of the amp to be re-distorted into ever higher harmonics; is that real fact?
who left the door open?
Holy cow! I leave you guys alone for a couple of minutes and the whole thread takes off somewhere else, and I thought I had gone off topic! I like the topic though, and if we want to keep it going, may I suggest www.diyaudio.com/forums/showthread.php?s=&postid=177278#post177278, I just posted Bruces response to me regarding the inductive vs non-inductive resistors in the output stage of his design.
See you there,
Chris,
Holy cow! I leave you guys alone for a couple of minutes and the whole thread takes off somewhere else, and I thought I had gone off topic! I like the topic though, and if we want to keep it going, may I suggest www.diyaudio.com/forums/showthread.php?s=&postid=177278#post177278, I just posted Bruces response to me regarding the inductive vs non-inductive resistors in the output stage of his design.
See you there,
Chris,
I've been out for some days...
Christopher, it's more complicated that you think, really.
When you enter high-end arena, some very good speakers are very hard to drive.
You'll have to spend even more money on an amplifier to drive them.
You may find, for instance (I've seen it happen) that a Chord 1200 amp is not man enough to drive a pair of B&W 805 Signature! 
You'll have to spend even more money on the amp.
So, forget the specs an listen, try it, or you may be fooled by numbers.
I didn't want to believe a gainclone with LM3875s would be man enough to drive my Epos 11 speakers.
Only looking at the specs of the chip, I thought "no way!".
When I made one and tried it, I had a shock...
It's fabulous!
Christopher, it's more complicated that you think, really.
When you enter high-end arena, some very good speakers are very hard to drive.
You'll have to spend even more money on an amplifier to drive them.
You may find, for instance (I've seen it happen) that a Chord 1200 amp is not man enough to drive a pair of B&W 805 Signature!
You'll have to spend even more money on the amp.
So, forget the specs an listen, try it, or you may be fooled by numbers.
I didn't want to believe a gainclone with LM3875s would be man enough to drive my Epos 11 speakers.
Only looking at the specs of the chip, I thought "no way!".
When I made one and tried it, I had a shock...
It's fabulous!
friends don't let friends drive tough loads...
Ok, I can accept all the above to be bad matches. However, I'm sure a quick glance at the amp specs and the impedence/phase graphs would eliminate most if not all of those combinations.
As was said earlier, once power and output impedence are taken into account with respect to the speaker load and sensitivity, most mismatches will become easily apparent.
As much as we all like to trash Stereophile, one thing they have over all the other publications is they still measure everything, (except cables.....) and JA will pick out an amp that will have a tough time driving a tough load. If you are considering an amp and you or someone you know can do these measurements, or better still, have a good idea what the weakness of any particular architecture will be, (I think you'll find many on this forum with these skills) then you'll know ahead of time if it will drive a particular speaker well, without even hooking them up. That's real knowlege, and that's my quest. I want to be able to look at a schematic and know what that designs strengths and weeknesses will be, one day I will, for now I'm still learning.
Simple.
If you would care to write out an explanation of how there is more to it than that, I'm all ears. I do have a beef with people telling me somthing is more complicated than I think without ever showing me how complicated it can become. SY slapped me around pretty good over my glib little 'damping factor' comment and I loved it. Real reasons, real examples, real causes. When someone tells me something is much more complicated than I think, without backing it up, I assume they don't know the topic very well.
Chris
Ok, I can accept all the above to be bad matches. However, I'm sure a quick glance at the amp specs and the impedence/phase graphs would eliminate most if not all of those combinations.
As was said earlier, once power and output impedence are taken into account with respect to the speaker load and sensitivity, most mismatches will become easily apparent.
As much as we all like to trash Stereophile, one thing they have over all the other publications is they still measure everything, (except cables.....) and JA will pick out an amp that will have a tough time driving a tough load. If you are considering an amp and you or someone you know can do these measurements, or better still, have a good idea what the weakness of any particular architecture will be, (I think you'll find many on this forum with these skills) then you'll know ahead of time if it will drive a particular speaker well, without even hooking them up. That's real knowlege, and that's my quest. I want to be able to look at a schematic and know what that designs strengths and weeknesses will be, one day I will, for now I'm still learning.
Simple.
If you would care to write out an explanation of how there is more to it than that, I'm all ears. I do have a beef with people telling me somthing is more complicated than I think without ever showing me how complicated it can become. SY slapped me around pretty good over my glib little 'damping factor' comment and I loved it. Real reasons, real examples, real causes. When someone tells me something is much more complicated than I think, without backing it up, I assume they don't know the topic very well.
Chris
Re: Re: Food for thought
There was years ago a study published in Wireless World by either peter baxandall or John Linsley-Hood showing that if you put feedback around an amp, initially the level of distortion RISES if you increase feedback, precisely because of this effect.
Then, when you continue to increase feedback, the distortion levels went down, until you get to the point where they were way down to the non-feedback case. And the higher the harmonic, the more feedback you needed to get below the non-feedback case.
So, for low feedback (<10dB or so), the feedback increases the THD. So the best choice seems to either have no feedback, or if you put it in, make sure you have at least 20dB or so.
For this reason I have never been able to understand how low feedback factors would be able to lead to better sound, as some claim.
Jan Didden
Circlotron said:
SY said:
There was years ago a study published in Wireless World by either peter baxandall or John Linsley-Hood showing that if you put feedback around an amp, initially the level of distortion RISES if you increase feedback, precisely because of this effect.
Then, when you continue to increase feedback, the distortion levels went down, until you get to the point where they were way down to the non-feedback case. And the higher the harmonic, the more feedback you needed to get below the non-feedback case.
So, for low feedback (<10dB or so), the feedback increases the THD. So the best choice seems to either have no feedback, or if you put it in, make sure you have at least 20dB or so.
For this reason I have never been able to understand how low feedback factors would be able to lead to better sound, as some claim.
Jan Didden
The man without ears
Christopher,
Let's say that for me, in the end, Audio is a subjective matter.
It's even a question of taste.
So, by looking to a schematic you will someday know how an amp sounds?
Impressive.
But sorry, I don't believe it.
Don't take me wrong, I'm always giving MY oppinion, and I know how to discuss without thinking I'm always wright.
You could bring a bottle and we could be talking all night and
listening to good music.
And I could show you that two cd-players with 20hz-20khz freq. response, and similar specs could sound very different.
So, as I already said, specs are an initial indication, never
a final judgement on a product.
You really have to hear it, and better still, compare it to other
similar products in the same price range.
Just bring the bottle.
My fridge is full of ice.
You'll hear a gainclone playing as a bird.
But looking at the schematic you won't get to any conclusion.
Know why?
You'll have to know how a Daewoo 1000uf cap sounds.
In the end, you'll have to use your ears.
Christopher,
Let's say that for me, in the end, Audio is a subjective matter.
It's even a question of taste.
So, by looking to a schematic you will someday know how an amp sounds?
Impressive.
But sorry, I don't believe it.
Don't take me wrong, I'm always giving MY oppinion, and I know how to discuss without thinking I'm always wright.
You could bring a bottle and we could be talking all night and
listening to good music.
And I could show you that two cd-players with 20hz-20khz freq. response, and similar specs could sound very different.
So, as I already said, specs are an initial indication, never
a final judgement on a product.
You really have to hear it, and better still, compare it to other
similar products in the same price range.
Just bring the bottle.
My fridge is full of ice.
You'll hear a gainclone playing as a bird.
But looking at the schematic you won't get to any conclusion.
Know why?
You'll have to know how a Daewoo 1000uf cap sounds.
In the end, you'll have to use your ears.
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