[fillemon]

thanx amb, your last remark really did it, indeed needing 3db extra is going to require a lot of watts.

i was aware that i needed to build 4 times σ22 for a speaker driven ß22. and i would implement very big heatsinks (same dimension as the ß24) it is maybe not the way to go.

but maybe the other way around ? could there be a headphone out on a ß24, with the same quality as a ß22.
(i'm trying to save money, i can build one of them, but the both might brake the bank a bit).

thank you very much
greetz fillemon

 

[amb]

lol, the β22 is already quite an over-the-top headphone amp, and β24 would be borderline insane as one.

It has a gain of 20, which is appropriate for a speaker amp of its class (just a bit under 2Vrms input will drive it to full output), but this is too much gain for most headphones. Also, its 5K ohm input impedance does not lend itself well to having a volume control pot there, so it really needs to be used with a preamp, or a source with a volume control. Currently I use a Benchmark DAC1 (which has a volume pot) feeding the β24 directly in fully balanced mode.

 

[fillemon]

haha, indeed, let's go to a high end meeting and say the next thing: yes my headphones are 100db/1 mV, and yes my headphone amp is 170Watt/8ohm , theoreticly that would be 150db

well i'm looking at this moment at a full range open baffle system with 95-96db, so i might go with the beta22, i suppose that the amp is capable of putting out 8watt continue. that would be enough, if i decide later on to take an inefficient speaker, i will put a beta24 behind it.

i think any of your amps will be very good for an open baffle (at least that's what i think): a lot of times an open baffle is very musical but not as detailed as i like, combining it with your amps amb will deliver a stellar sound i suppose.

anyway i still need a absurd good usb source : so i'm already looking forward to a high end non portable gamma1. i'll check every once and a while.
thanks

 

[Chaos4]

I was wondering if there is another area to see the measurements for this amplifer as headwize forums are still down. Great looking amplifier! I was considering a build, but would like to see some more info is possible. How about a schematic at least? Thanks amb, for another great design!

 

[amb]

Schematic (v1.0):

 

[digger945]

Does the part in red keep the outputs from completely falling out of class A?

I am seeing the part in blue in other designs and have built it on breadboard to try and understand how it works. Is this used only to balance the positive and negative voltages going to the output mosfet's gates? Can it be used to limit the voltage or does that need to take place at the 74/170's?
I really like this schematic, thanks Ti.

 

[amb]

The resistors circled in red are there to set the VAS stage open loop gain. The portion circled in blue is a complementary Vbe multiplier (adjustable voltage source) used to bias the output MOSFETs.

 

[digger945]

You say a lot with few words.

Thanks again Ti, I look forward to reading more when HW is back up.

 

[qkizz]

AMB, I have to try to install output inductors in my Beta24 and I know you posted it already on headwize, which is dead at the moment. Could you please tell me again how to do it? I've just bought new electrostatic speakers, which are much bigger than my old ones and pretty much it doesn't sound right. I've tried my another amp, which have inductors at the outputs and it looks like it would be good solution.

Thanks

 

[amb]

qkizz, make a single-layer cylindrical coil of 18AWG magnet wire, about 10cm in diameter and about 16 turns. Scrape off the enamel off the ends of the coil, insert a 1 ohm to 2.2 ohm 5W metal oxide resistor into the center of the coil and solder its leads to each end of the coil. That's your inductor and you install one in series with each of the four output terminals. You can experiment with the coil diameter and number of turns, if you want.

 

[qkizz]

Thank you, I'll try this.

 

[qkizz]

I've read somewhere that inductors are limiting bandwidth. It looks like it's true statement. I did as instructed by amb and it took just one minute of listening to realize that this is no go. Sound became dull, less involving and most of the difference was in highs and some in mids.
With the previous post I've jumped in to the conclusion way too fast. I have to give back full credit to Beta24. The problem was positioning the speakers, which is critical with electrostatic panels. The amp handles my new bigger panels perfectly.

 

[amb]

qkizz, I am glad that no inductor was necessary after all. What electrostatic speakers are you using?

 

[qkizz]

Currently Martin Logan Vista and previously Clarity.

 

[luvdunhill]

Ti:

Looking at your drawings for the angle bracket attachment for the beta22 and sigma22, I notice that the very edge of the casing of the MOSFETs will actually be off the angle bracket a bit. You specify the hole being 0.4" from the edge of the angle bracket, and many TO-220 devices are ~0.5" from the center of the hole to the edge of the casing. Does this pose any thermal issues?