Power op amp driving valve in A2
#32
Yes, we did, didn't we? I learnt a lot tho', I may have another go at this again sometime. I think the idea is fundamentally sound.Nick wrote:If I remember correctly, we got through a lot of desoldering braid that dayAndrew wrote:I did this a while back, with Nick's help I managed to stabilize it, so it didn't continually blow up op amps, was proving a bit expensive up until then.Mike H wrote:Off-topic suggestion for Nick ~ as regards use of an op-amp to regulate a supply rail (low impedance negative as well as positive)
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#33
No grabs ?Mike H wrote:Oh-kay, how's my idea of what is effectively a power op-amp grab you?
Looks like the project will be downgraded and the patient moved off the operating table.
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#34
Tell me you weren't using the braid as fuse wire.............!Nick wrote: If I remember correctly, we got through a lot of desoldering braid that day
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#35
A solder sucker is an even better fuse, too, honest!
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#36
I don't really want to give up on this idea.
I tried e-mailing P Millett some while ago but no reply.
Trawling the interweb has not helped at all, so how about putting an interstage transformer between the driver amp and the 1626 grid ?
I tried e-mailing P Millett some while ago but no reply.
Trawling the interweb has not helped at all, so how about putting an interstage transformer between the driver amp and the 1626 grid ?
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#37
Perhaps I should be trying to understand the theory a bit more.
Thing is, how does an op amp driver deal with the grid current that flows in A2 ?
Thing is, how does an op amp driver deal with the grid current that flows in A2 ?
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#38
Very well and that is the opamps puropse in life. To provide a high input impedance and a low output impedance so that it can drive a power hungry stage. It is particularly suited to the task you have for it.
I think Jack Elliano does a kit of this nature.
I think Jack Elliano does a kit of this nature.
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#39
Thanks Paul.
I had a look at his web site, and it seems he uses a custom interstage (A2LD-7),23-30 ohms primary and 20K ohms grid load.
http://www.electra-print.com/specialuse.php
I had a look at his web site, and it seems he uses a custom interstage (A2LD-7),23-30 ohms primary and 20K ohms grid load.
http://www.electra-print.com/specialuse.php
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#40
You need to read the spec for the amp in question and see what current it can sink and source. Low output impedance is one thing, current drive is a different thing.pre65 wrote:Perhaps I should be trying to understand the theory a bit more.
Thing is, how does an op amp driver deal with the grid current that flows in A2 ?
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#41
Well, I was thinking of a couple of mono amp modules using the TDA2050 chip, but the data sheet does not mention current sinking. Or if it does I can't find it.
http://www.ebay.co.uk/itm/110712864225? ... 2530wt_957
http://www.datasheetcatalog.org/datashe ... s/1461.pdf
http://www.ebay.co.uk/itm/110712864225? ... 2530wt_957
http://www.datasheetcatalog.org/datashe ... s/1461.pdf
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#42
Can be worked out from the power figures on the TDA2050 datasheet:
E.g., 5% distortion, supply = +/- 22V, load = 8R, 25W r.m.s.
= 50W peak, x 8 = 400
Square root of 400 = 20V peak
20V / 8R = 2.5 Amperes (peak)
10% distortion, supply = +/- 22V, load = 8R, 32W r.m.s.
= 62W peak, x 8 = 496
square root of 496 = 22.27V peak
22.27 / 8 = 2.78 Amperes (peak)
So in other words, more than enough - for a valve grid anyway
Shouldn't be bothered by the bulk of the current mostly going in one direction only. And is wired up just like a op-amp. + in, - in, + supply, - supply, out.
E.g., 5% distortion, supply = +/- 22V, load = 8R, 25W r.m.s.
= 50W peak, x 8 = 400
Square root of 400 = 20V peak
20V / 8R = 2.5 Amperes (peak)
10% distortion, supply = +/- 22V, load = 8R, 32W r.m.s.
= 62W peak, x 8 = 496
square root of 496 = 22.27V peak
22.27 / 8 = 2.78 Amperes (peak)
So in other words, more than enough - for a valve grid anyway
Shouldn't be bothered by the bulk of the current mostly going in one direction only. And is wired up just like a op-amp. + in, - in, + supply, - supply, out.
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#43
Shouldn't be I agree, but I have my doubts, simple to check though, Simulate the valve grid with a resistor and diode in series.Shouldn't be bothered by the bulk of the current mostly going in one direction only. And is wired up just like a op-amp. + in, - in, + supply, - supply, out.
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#45
Err, you seem to be swinging beyond the supply rails. Mind you 10% distortion.10% distortion, supply = +/- 22V, load = 8R, 32W r.m.s.
= 62W peak, x 8 = 496
square root of 496 = 22.27V peak
You would need to be using a high µ valve if 20v was the peak drive on the grid.
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