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The all DHT SET Headphone Amp
The all DHT SET Headphone Amp
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Old 14th March 2019, 10:32 PM   #871
45 is offline 45  Italy
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Quote:
Originally Posted by popilin View Post
Does about 3mJ worth the effort?
Juan it's just for looking at things comprehensively and actually a CCS might be even cheaper than a choke if one really wants to do it.
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Old 14th March 2019, 10:51 PM   #872
bondini is offline bondini  Australia
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The all DHT SET Headphone Amp
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Meanwhile, I think I'm going to plug the Sennheisers in and crank it up!
Now THAT'S and idea!!

Bondini
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Old 19th March 2019, 03:26 PM   #873
TheGimp is offline TheGimp  United States
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Your schematic does not show the 32 ohm load. Do you have a dummy load hooked up to the output?
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Old 20th March 2019, 02:59 AM   #874
bondini is offline bondini  Australia
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The all DHT SET Headphone Amp
Hi TheGimp,

I've tidied up the schematic to show the 32 Ohm load and the sealed lead acid battery that powers the filaments. This shows more clearly that the base of the type 30's cathode bias resistor and the top of the 6A4/LA's cathode bias resistor share the negative terminal of the battery. Similarly, the positive battery terminal is shared by filament heater pin 1 of both valves.

This arrangement was very much a matter of convenience (I was experimenting, running through several topologies, didn't want to build heater supplies, was relying on the only battery I had, a 6.3V SLA) and serendipity (hey, maybe this will introduce a bit of negative feedback via the cathodes?). As you can see from the measured output, it's below the 1V rms input for a circuit that could probably deliver open loop voltage gain of around 50, so there is probably a bit of feedback lowering the gain and the distortion.
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