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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 4

post #46 of 1817
And I really can't compare against Don's build as his boards are different from our versions..
post #47 of 1817


Originally Posted by sachu View Post

You need 4.75k for R27, R28..look at the schematic , on the far right edge.

I think the supplied R32 R33 resistors are actually 2 W..there may be a mistake in the BOM.

You calculate RLed based on the LED you are using and the brightness/current you want flowing through it. The Formula for it is listed on the Cavalli Audio site.

Indeed R5, R7 seem to be supplied as 47.5k when the schematic is listing it as 47 ohm..

We need Alex to chime in and correct his for us .

I wil dig in my parts bin or go pick up a few of them from the surplus store just in case.

I do have a bunch of 22 ohm resistors to use in series to get 44ohms if I don't find the 47 ohm ones at the store.


Yes, all correct.

R5, R7 are 47R (RN55D is 47.5R).

R27, R28 are 4k7 (RN55D is 4k75)

R32, R33 are 2R2. 1/2W will do for headphones. 2W is in case you want to push 18W into speakers.

Is there anything else missing or seeming to be wrong?

On this amp I do recommend the heater-first power up sequence. This is because the tube is DC coupled to everything else. When the amp first turns on the tube is not conducting at all and the bjts just don't know what to do.

One thing about this amp, because of the design, it is blazingly fast. See the performance web page for the measurements that snoopy made on it.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
post #48 of 1817
For the 2705/1145's, do you use "O" or "Y" hfe class?

Yes I noticed the speed in your "performance" section. What software is the one with "Audio Spectrum" in the header?
post #49 of 1817
Originally Posted by MrSlim View Post
And since the internet is all about not re-inventing the wheel here's a circuit to do it:

LM555 Timer Circuits

I particularly like the one called: Delay circuit with flashing indicator LED.

Even the basic delay circuit would be useful..

It would be pretty simple to breadboard, and the main expense would probably be a relay with heavy enough contacts for the main power suppy..
You would probably need a transformer for the voltage supply to the LM555. To kill another bird with one stone, you can use AMB's e24 momentary switch driver. Once the power switch latches you can drive a relay for the heater and a 12V circuit (LM555) and in turn drive the power relay for the s22.
post #50 of 1817
Somebody asked about filament warm up in a thread somewhere and this was suggested:

Power Supply Delay Action Board 300B 2A3 KT88 tube amp - eBay (item 150342422865 end time May-06-09 14:51:43 PDT)
post #51 of 1817
hey, that's awesome. I didn't think there were heavy relays that actuate with such little voltage across the coils.
post #52 of 1817
Thread Starter 
I need to get one of those delays.

*oh sweetie, I just need one more little thing from ebay...*

post #53 of 1817
"what a coincidence! There's this really cute Prada bag..."
post #54 of 1817
Thread Starter 

So, slow progress so far.

at this rate I should have it complete by 2011.
post #55 of 1817
Double Post
post #56 of 1817
Smeggy, SLOW is better than BLOWN up I'm still working on my BoM and chassis design. I do have a few tubes... <Gloat>
post #57 of 1817
Also, Smeggy (you probably don't want to hear this now), might I suggest OpAmp Sockets? Just In Case...
post #58 of 1817
Thread Starter 
no you may not.. already in

What tubes have you collected? I'm not even sure what tubes arrived in the package, not like I'd know any different anyway being a toob noob. I'll probably wait until later to experiment Gotta finish this, millions of other things including the S22 before any of will work. Still, it'll be great having the EHHA and Beta 22 up and running.
post #59 of 1817
those tubes look like they need a special home now !! ..dB
post #60 of 1817
Originally Posted by dBel84 View Post
those tubes look like they need a special home now !! ..dB
yeah...mine!! 20$ for the 3 of them ought to cover eh?
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