Universal output HP amp with custom Lundahl transformers

[justin]

I met Per Lundahl at Capital Audio Fest last year, and in trying to figure out what I could use I'd have for Lundahl transformers I asked about winding something that can drive e-stats, planars, low impedance, speakers from separate taps. I had also just bought a bunch of 6336B dual triodes, so thought that might work. The transformers came and many months went by but finally rigged something up. 

Basically right now it's just 6336B with both triodes in parallel, running about 200mA with a B+ of 260V. There's an e-stat output that steps up, and also 50 ohm and 6 ohm outputs. The grid voltage is set by a bunch of 9V in series.

The black box in the middle on top of the Wendy's napkin is a little 4W 12V to 600V DC/DC converter for the e-stat HP bias.

I'm actually driving it from the headphone jack of a Ray Samuels Raptor right now 🤣 Have sound coming out but no chance yet to do much further testing 

 

[dsavitsk]

3 hours ago, justin said:

I met Per Lundahl at Capital Audio Fest last year, and in trying to figure out what I could use I'd have for Lundahl transformers I asked about winding something that can drive e-stats, planars, low impedance, speakers from separate taps.

Neat. Can you share the datasheet?

You can do this from existing Lundahls. For instance, with something like the LL1620 there are quad primaries. So you can use two of them as primaries, and the other two as e-stat outputs (you'd have to check with Lundahl whether the voltage differential from primary to primary is an issue). Then the 8x secondaries give all sorts of ways to combine them for driving speakers and phones of different loads. Similarly, with something like the LL2766 and a push-pull circuit, you can use the OPT as a choke and cap couple the plates for e-stat use, then use the secondaries however for speakers/phones. I've found those solutions to be more novelty than useful (the gain is never quite right for everything, and a fix is no better than a second amp), so I am curious how the specifically designed option will perform.

[justin]

This is all that was provided:

I think I would prefer to use our 2.5kg (5lb.)
> transformers, as the high voltage secondary needs to have a lot of insulation
> to keep capacitances down.
> 
>               Spec:
>               Transformer for SE amplifier, size as LL1620 etc.
> 
>               Primary 1.2k impedance, 280V anode voltage,
> standing DC current 200 - 300mA (you will need to specify)
>               Input signal power around 10W
> 
>               Secondary 1 (electrostatic speaker) 1600V P-P
> (turns ratio 1 : 6).
>               Does this output need a centertap for offset
> voltage or for ground reference?
> 
>               Secondary 2 (low sensity headphones) , 15W
> into 50 ohms -> approx. 27V rms (turns ratio 3:1 for 1.2k : 50)
> 
>               Secondary 3 (6 ohms loudspeaker and sensitive
> headphones), 15W into 6 ohms -> approx. 10V rms (turns ratio 14:1 for
> 1.2k:6)

 

3729_SE_connections.pdf

[dsavitsk]

1 hour ago, justin said:

>               Secondary 1 (electrostatic speaker) 1600V P-P
> (turns ratio 1 : 6)
 

Do you really need 1600V? The more you push a transformer to do extreme stuff, the worse it will do at the stuff that actually matters. I'd wager that relaxing that spec to something more reasonable would make for a much better sounding design.