G600

Sounds good Birgir. As long as they use actual sand...

I'd be in for Joamat's T2 if there is a run.

Looks like a very nice way to use some 6SN7 !

Thanks !

Nice work Muskyhuntr ! Do you guys have an advice for 2N5564 testing ? I have scored a pair at a very low price from a regional seller, I was told they are genuine (and they were the last two in stock). How to verify that ?

Gentlemen, I've just read the first 70 pages of this thread. Beside the reading pleasure (yeah, I'm getting as crazy as you all, finding that reading technical things is enjoyable), I saw something extremely special... This project is something I haven't seen before, and my English is too short to put proper words on it. Dr Gilmore, you have been quite busy doing this between bottle washing. Congrats to everyone that finished their T2.

Thanks^^

Biggest problem is shipping fees. The BOM points Trendsetter, but they are charging 4 times the parts price for shipping... Everything works like that from here. Guess I'm not in the good person's little papers ! Nevermind.

So LSK389A (hard to source in old Europe !).

Will a pair of LSK489 fit in place of LSK389, and will there be an improvement ?

Are the plastic washers necessary for the MJEs ? I'm sure not using them I made a mistake that can explain my problems... why not a short with a heatsink !? At least I have aavid's thermal pads, but damn, I'm dumb

Thank you. Which ones are critical ? Can I match only small bipolars, or power transistor need to be matched too ? Another one : matched sand goes in the same rail, or each rail has to be matched with the other ? Regarding your experience, do you think that onboard Dynahi must be biased to only 50mA ? My first board (the one that stops at 74mA with 500 Ohm) becomes hot, but the second one's left channel goes hotter. I think there's something wrong with that one.

Hello there. I started biasing my two boards (onboard version), and need help... PSUs are two 30V S22 with 160VA transformers, boards have lowered gain, red LEDs, ON MJE15030G and 15031G, every sand is from Mouser, no matching as I don't have tools for that. The first one : no offset from start, easy as a pie, but the bias can't go above 0.4V with the 681 Ohm resistor. I've changed for 500 Ohm but I can't go above 0.74V ! Still no offset by the way. What can be wrong with it ? The second one : nightmare. The left branch goes well to 0.75V (681 Ohm resistor too), and becomes incredibly hot, while the right channel stops at roughly 0.5V (and stays cold). Then I started tweaking the THAT340 pots, I could bring the bias close to correct at the right branch, and suddenly I heard something like an intermittent short, plus a bad smell from this right branch... I guess I'm good for a BJT sanity check, but what can explain the odd behaviour at first start ? Thanks.

I had them at home, and Mr Gilmore came with this : So looks like the difference is way out of reach...

I chose 5pF.

Thank you !

I have some fine (silly) questions for you gentlemen I'm at the point of first power on. I'm OK with the biasing method. What's the most efficient method, biasing with the pot or with shorting resistors ? Shorting resistor = 1K between I- and Gnd, and another between I+ and Gnd ? Pot to minimum setting = full clockwise ? Is there any need of a switch or a soft start between PS and Dynahi ? What if the source brigs a few mV of DC offset ? Thank you.

You have an email, then ! Thank you fellas.

Thank you AIve. May I ask where you found a PCB for a quad pot ?

Aive, What kind of pot are you using ? Have you built the amp with defaut gain (balanced gain of 42) ? Thanks.

Thank you ! Time to order the last parts and finish the boards.

That's pretty clear given the formula. My problem is the compensation cap value, without a scope I can't be sure of the frequency response, unless somebody helps me. I read 5pf is OK for a balanced gain of 11 (10k - 55k).

Dr Gilmore; Have you calculated the exact value I need for a balanced gain around 11 ? Thanks !

Thank you Dr. Gilmore. I'm trying orthos for now (LCD-2 = 50 Ohm / 91dB), so I think they'll take benefit from the Dynahi with lowered gain. I'll probably try HE-6 and / or K-1000 in the future, so this upcoming balanced Dynahi will be on duty. When I switch to dynamic headphones (or higher efficiency stuff), I'll build a dynalo (or dynamid) for sure, thanks for the tip !

Can somebody help me by confirming this ? I'm populating my boards right now, and still don't know if this way to obtain a balanced gain of 11 ( (50k/10k)+1 <-> 5+5+1) is OK, especially for the compensation capacitor. Unfortunately I don't have no scope and not much skills to guess this... More generally, is a balanced gain of 11x more friendly to run headphones between say 30-300 Ohm ? Best regards.