This is a really long movie with no plot... I hope you're OK Waki.
A lo-cost HT-supply true transformer-coupled tube headphone amplifier - Page 5
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- 505 Posts. Joined 3/2007
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Great to hear you're back and that your health is improving! We were beginning to wonder what happened. Hopefully your improvement is permanent and there'll be more amps in the future. There are very few of us DIY tube builders here and last thing we want is to lose one!
It's been a pleasure watching the evolution of your design and I'm happy to have played a small part in the process. Happy to hear it works.
The "clicking" you're hearing sounds almost like a decoupling problem, although this shouldn't be an issue with a two stage design. Can't hurt to try something like a 10uf electrolytic in the C9 position. I'd also be looking for a bad solder joint in the power supply or grounds.
Hey, there you are! It's great to see you back in action.
I once had a 'tick, tick, tick' in a circuit that turned out to be a hairline crack in a power trace on a PCB that kept arcing across. Discovered it with the lights out! You may have an arc in you HT circuit somewhere, turn off the lights and have a look; it won't cost a dime.
What was your solution on the filament supply?
Edited by elliottstudio - 11/24/12 at 9:17am
Turns out I couldn't re-use the CCS bias on the second channel because it makes the current drain assymetric, so it needs to be duplicated at the cost of another 10mA or so...
Good job that the PT and choke are overspecced.
You can see the most recent version of the circuit (arranged for PCB layout) in high detail and save an easy-to-manipulate copy (by right-clicking and selecting 'save image as...') by visiting this link:- http://wakibaki.com/audio.php#t11
If you change the coupling coefficient of the transformer to 1, the -3dB frequency response goes up to > ~100kHz. The transformer model is primitive, and the 0.95 coupling coefficient is arbitrary. I checked the low frequency rolloff by substituting in progressively smaller caps, you can see things going a bit awry when you put in about a tenth of the capacitance, so I have a bit more confidence that the low end simulation is meaningful, but I don't see much point in worrying about the significance of the top end.
Let's wait for the RMAA results for the rebuilt amp. I ordered some transistors for the CCS's, but I haven't ordered the new chassis yet.
Are you going to build it out on that PCB you designed? That would be a treat.
Looking at your first stage tube circuit, I've tried using a diode (and an LED too) for the cathode bias and measured more THD than with a plain resistor. Does the CCS load on the plate help alleviate some of the distortion?