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Old 10th April 2010, 08:20 PM   #401
Salas is online now Salas  Greece
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Salas,

I have tested the SSHV with IRF9610. I prefer this than the original because it gives a fuller sound and better resolution. Also heat is comparatively less. Thanks.
I agree that the resolution is better and its included in the final schematic for long now. The less heat thing should not be though. Probably a Vgs difference must have produced less drop across the setting resistor, thus less current than with your previous PMOS. Nice that you also got some appreciable subjective lift non the less.
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Old 10th April 2010, 08:21 PM   #402
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Does it work without the gyrator?

I don't use the LT108x regs in my amps, but I hear they need more voltage headroom than might be expected, especially at 1A+.

If that is so, you'll need more like a 9V trafo, or to use the transistor CCS, or FET CCS - it's not hard to build if you cut some plain copper board with a hacksaw.
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Old 11th April 2010, 09:58 AM   #403
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Originally Posted by Salas View Post
I agree that the resolution is better and its included in the final schematic for long now. The less heat thing should not be though. Probably a Vgs difference must have produced less drop across the setting resistor, thus less current than with your previous PMOS. Nice that you also got some appreciable subjective lift non the less.
Agreed. Less heat could be due to the optimization of voltage/current through SSHV.
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Old 11th April 2010, 10:04 AM   #404
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Quote:
Originally Posted by Rod Coleman View Post
Does it work without the gyrator?

I don't use the LT108x regs in my amps, but I hear they need more voltage headroom than might be expected, especially at 1A+.

If that is so, you'll need more like a 9V trafo, or to use the transistor CCS, or FET CCS - it's not hard to build if you cut some plain copper board with a hacksaw.
Rod,

I haven't tried it without the gyrator. Will check it BTW. Is there any claculation/ratio to figuerout the Vin for this setup? It is bit difficult to find STP55. Hence could you give any alternative whcih is easilly available to use with? Also appreacite if you could post the latest schematic optimized for 26 filament if you have. Just to make sure.

Last edited by coolzero; 11th April 2010 at 10:06 AM.
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Old 25th April 2010, 06:38 AM   #405
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What is the ouput impedance of a 26preamp like this? how do I calculate this? Can it drive at 10K load?
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Old 25th April 2010, 06:56 AM   #406
regal is offline regal  United States
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What is the ouput impedance of a 26preamp like this? how do I calculate this? Can it drive at 10K load?
Output impedance without an OPT is around 9k, needs an amp with at least 50kohm input impedance
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Old 1st May 2010, 05:02 AM   #407
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Output impedance without an OPT is around 9k, needs an amp with at least 50kohm input impedance
This could be a lame question. But can you explain what sort of adverse effects could arise if using a lower impedance amplifier, like something with 20K input impedance?
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Old 1st May 2010, 05:47 AM   #408
regal is offline regal  United States
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This could be a lame question. But can you explain what sort of adverse effects could arise if using a lower impedance amplifier, like something with 20K input impedance?
Probably high distortion from overloading the tube. Probably negating any benefit of using a finicky tough to build #26 DHT preamp. Better off with an Aikido.
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Old 1st May 2010, 12:36 PM   #409
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This could be a lame question. But can you explain what sort of adverse effects could arise if using a lower impedance amplifier, like something with 20K input impedance?
For AC, the load will be in parallel with the plate load. Look at the resulting load line. The distortion goes up as the load line becomes more vertical.

Sheldon
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Old 1st May 2010, 05:54 PM   #410
E.T. is offline E.T.  United States
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Would a 26 have enough grunt to drive a 6as7? I'm looking for that "liquid sound" of DHT's. Someone suggested that that sound comes from internally generated microphonics, which seems plausible considering how microphonic small DHT's are.
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