About 30 years ago I tried a servo-driven resistor heating the VAS transistor
to control offset. Worked fine.
The CA3046 five transistor array used to lend itself to a variety of such stabilized circuits. I suppose one could do something with the THAT arrays, these days.
Christophe,
Is there any delay or threshold further down the line? How do you prevent this from triggering on an occasional clip?
jan didden
Of course, Jan. No delay (or µ/ms). But a threshold (Diode D0) that you can tune with the gain of the error signal amplifier and a very simple circuit to prevent protection from flip/flop. Once the protection has fired, it takes some seconds (i don't remember how much
to recover after the problem has disappeared.
About 30 years ago I tried a servo-driven resistor heating the VAS transistor
to control offset. Worked fine.
Hi Papa,
Do you still use it in your recent amplifiers, or do you find it unnecessary, or do you have better ways for amplifiers stabilization?
I don't need any delay.
My amp is running smoothly since decades with this protection. I have made hundred of short circuit demonstrations at all power levels with no damage, and no fear, and never heard any clic or parasitic noise. Just a very luxurious silence.
You can let the short circuit as long as you want, despite the > 1000VA power supply and 2X75 V rails, 5 seconds after you remove-it, the music is back again. That's all.
And my protection never fire in normal usage.
Even without soft start, there is never the slightness noise during power-on or off. And the amp only turn green when power rails are stabilised and caps charged. More than that, if i make some bad hot connection at the input, with the amp powered, no noise neither: the protection takes care of that.
Delay for the protection is something we don't need, only negative effects.
And if the protection fire because you are listening at home at 10% distortion level, who want to listen to any music in a high end system in such a situation ?
John doesnt want to go into the whys and wherefores of his decision -- So. I'll say that it is customer/market driven decision on how a protection circuit is implemented ---
I found that for commercial or consumer use... distortion is preferred to even brief shut-down - silence. And magazine reviewers will find the issue during clipping and report it as a negative for audiophiles. Granted for high-end we shouldnt be running our amps into clipping but a mfr wouldnt have control over that. I would use a soft clipper rather than a disconnect for commercial amps... esp PA amps for stage use. For Dc, of course disconnect. And, if the amp was designed for protection the error point pick-off isnt an issue.
Most amps already have dc and overload protection these days so when would an outboard be needed - I am not sure. Not too keen on disconnect on overload during recording either... again some soft clipping/current limiting feature and/or limiter is the accepted way to handle such mistakes during recording...
I found that during recording, musicians are never consistant with the loudness of their playing... guitar picking isnt that controlled, for example. mayby on sythn machines the level can be consistant enough. Otherwise a time delay in the protection circuitry is the next best thing in practice. IMO. RNM
I found that for commercial or consumer use... distortion is preferred to even brief shut-down - silence. And magazine reviewers will find the issue during clipping and report it as a negative for audiophiles. Granted for high-end we shouldnt be running our amps into clipping but a mfr wouldnt have control over that. I would use a soft clipper rather than a disconnect for commercial amps... esp PA amps for stage use. For Dc, of course disconnect. And, if the amp was designed for protection the error point pick-off isnt an issue.
Most amps already have dc and overload protection these days so when would an outboard be needed - I am not sure. Not too keen on disconnect on overload during recording either... again some soft clipping/current limiting feature and/or limiter is the accepted way to handle such mistakes during recording...
I found that during recording, musicians are never consistant with the loudness of their playing... guitar picking isnt that controlled, for example. mayby on sythn machines the level can be consistant enough. Otherwise a time delay in the protection circuitry is the next best thing in practice. IMO. RNM
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In Pyramid amps I don't allow them to clip: I sense currents of screen grids of output tubes by LEDs that control LDRs in input attenuators and "Overload" signals. As soon as it approaches clipping it compresses peaks instead of distorting them. Red lights signal that compression had been engaged.
MacIntosh does similar way -- auto input level control. reduces input level when input is sensed too high (which would correspond to clipping at the output). You get brief peak amplitude reduction to be held to just under clipping level without any distortion....... maximum undistorted output with no chance of ever clipping.
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Please, do not assimilate false positive with the fact a protection is fast, YOU have the choice. You can tune the sensibility of this protection by rotating a pot.
And if you like some delay (it will not gives-you more security against false positive, only less protection), you just have to add a resistance.
I used this on the Big PA system i managed (10 000 watts JBL Horns) decades ago, and it had saved our equipments several time, mostly during set-up. I don't remember a negative effect, or any cut during shows at normal use.
So, the advantage of it is you can tune this to alert-you against any problem in high end home usage (clipping, oscillation, short circuit, very low DC offset in output as well as input of the amp or anything going bad in your amp like transistors in short circuit or fused).
Or take a big margin if you need to run-it in hard PA situations.
You just chose your poison.
And if you like some delay (it will not gives-you more security against false positive, only less protection), you just have to add a resistance.
I used this on the Big PA system i managed (10 000 watts JBL Horns) decades ago, and it had saved our equipments several time, mostly during set-up. I don't remember a negative effect, or any cut during shows at normal use.
So, the advantage of it is you can tune this to alert-you against any problem in high end home usage (clipping, oscillation, short circuit, very low DC offset in output as well as input of the amp or anything going bad in your amp like transistors in short circuit or fused).
Or take a big margin if you need to run-it in hard PA situations.
You just chose your poison.
In mass or semi-mass manufacturing one wrong decision might cost big $. It is totally different to what could be done at home or when producing in small series.
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A bit related to this thread's subject .. look what I've found while browsing some places in Far East.
JC ULD !
John, what is it? One of your GD line drivers? What does ULD stands for?
Best,
Attachments
First, Esperado, let us not talk about ABSOLUTES or correctness. Parasound has a number of different customers and we have to worry about their complaints. However, I agree that a long delay could be damaging to the loudspeakers.
Electroj, WOW! Yes, I think you found an ORIGINAL GD driver, from 1973. Inside, it looks like the line amp for for the Levinson JC-2, except that it uses TO-5, 2A output transistors, and runs about 50 ma. How much did they want for it?
Electroj, WOW! Yes, I think you found an ORIGINAL GD driver, from 1973. Inside, it looks like the line amp for for the Levinson JC-2, except that it uses TO-5, 2A output transistors, and runs about 50 ma. How much did they want for it?
John,
I did my best to find the link and it turns out it wasn't in Asia, it was in the US of A:
InstrumentsFair.com - Mark Levinson discrete op-amp Model JC ULD
(Scroll down)
Unfortunately, the module is no longer available
, but you might know who the seller is ...Best,
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What the else do you want us to talk on a DIYer forum ?
I wonder witch complaints the Parasound's customers had done about my protection system ?
I have not the slightest opinion about Parasound, and i don't ever know when i could listen to one of their products, too expensive for my budget of poor retired man, i believe.
Remember, it was just a response to your "Where did-you share your original ideas ?"
I will be pleased to consider any argument from you on the thread i had opened at the subject of this protection system, and believe it is out of topic here, yes.
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