LU1014D Pass stash contest

[wwwtttwww]

Thank you! EUVL.

The Rs is about 1.1 Ohm for one side in the sim.

 

[haiqu]

Thank you! EUVL.

The Rs is about 1.1 Ohm for one side in the sim.

Cool. That gives a DF of about 13.6 into a 15 ohm speaker. And since I'm trying to replicate a '50s valve sound it should be fairly real.

 

[haiqu]

From quick back-of-the-envelope simplistic calculations, a primary transformer impedance of 0.5 mH will give me a crossover at 5 kHz. Easy peasy, the transformer I already have here will probably do the job. And at that point the damping on the woofer is already falling, so it's ideal.

 

[xrk971]

Yeah. already found it. Here is my result for a single-ended circuit into 15 ohms at 1 kHz. This shows a certain amount of promise. 🙂

Now investigating the effect of inserting an inductor in series with the load, since I want to run an electrostatic tweeter with it and that will represent the primary of the transformer. It does look as if the rail voltages could go much higher as well, so a tube voltage gain stage isn't entirely out of the question.

A microwave oven transformer (MOT) that we often use as a choke load on these SE Class A amps has a 1:25 step up normally used to drive 2500v into the magnetron of the oven. You could tap into that secondary and easily get some pretty nice HV step up, depending on what voltage you need for your electrostatic tweeter, I am guessing a 20Vpp swing on the primary would be more than enough.

 

[EUVL]

> That gives a DF of about 13.6 into a 15 ohm speaker

Not for the balanced follower published.
In the balanced follower, each side only see half of the load impedance.
So that would be a DF of ~7.


Patrick

 

[haiqu]

> That gives a DF of about 13.6 into a 15 ohm speaker

Not for the balanced follower published.
In the balanced follower, each side only see half of the load impedance.
So that would be a DF of ~7.

Patrick

Yep, I was assuming unbalanced. Can't see the need for the other half in my application.

 

[haiqu]

A microwave oven transformer (MOT) that we often use as a choke load on these SE Class A amps has a 1:25 step up normally used to drive 2500v into the magnetron of the oven. You could tap into that secondary and easily get some pretty nice HV step up, depending on what voltage you need for your electrostatic tweeter, I am guessing a 20Vpp swing on the primary would be more than enough.

I had some electrostatic speaker transformers made about 25 years ago when I was consulting to a panel manufacturer in Melbourne. They're 30:1 so should do fine.

The microwave transformers I've seen for sale are far too large and heavy for the tiny panel I'm using. See So you want exotic? Check these out.

 

[haiqu]

I'm in a bit of a quandary about how to drive this thingy. To get 20 watts into 15 ohms the driver stage will need to swing +/- 25V. Bit of a tough call, op-amps are limited to 15V rails and that would only supply 7.6 watts which is a huge waste of good parts. Hmmmm. Still chewing this over. I didn't really want to design a discrete driver.

 

[wwwtttwww]

Mr. Pass' Jfet buffer + transformer might be your best friend.

 

[haiqu]

A transformer would be my last resort but yes, I had considered it.

 

[EUVL]

Just bump into this.
https://www.diyaudio.com/community/threads/zero-feedback-impedance-amplifiers.42259/post-1229438

Isn't it sheer ELEGANT ?

😉


Cheers,
Patrick