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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 3

post #31 of 1812
5/2/09 at 2:34am
Thread Starter 
Yes!
I have two of them
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post #32 of 1812
5/2/09 at 2:35am
Hey guys, I noticed on Alex's EHHA page, he mentions that it's a good idea to have 2 power switches, one for the heater supply to warm up the tubes for about a minute before turning on the main supply, so there isnt any funny business going on with the tubes as they warm up.

I said to myself, hey that sounds like a perfect place for a little delay circuit that would be controlled by the heater supply.. Turn on the 12 v supply. the delay counts down for a minute, then trips a relay to turn on the main supply..

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..
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post #33 of 1812
5/2/09 at 2:40am
if the tubes aren't warm, there is a slim chance that the amp could swing to one of the rails. I don't think it has ever happened to any of the prototypes but the possibility remains.

I have the math for the gain wiatrob - I will post the resistor values ..dB

so I cheated - this was from old e-mail communication (compliments of Steinchen) - R21 is currently R13 iirc - someone correct me if I am wrong

"R21 sets the gain, thus the ideal value depends on the headphone impedance
you're using. Usually 6 for low-Z phones (32 Ohms), around 8 or 9 for
high-Z cans (250 to 300 Ohms) and 12 or 13 for old 600R cans or K1000.
That means resistor values for R21: 2k, 1k5, 800R (roundabout)"
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post #34 of 1812
5/2/09 at 3:28am
Thread Starter 
Q, is 4752 the 4k7 or 47? I think its the 4k7 but want to make sure.

I seem to be missing 4 resistors and it one of the above, either R5,7 or R27, 28.

Also, R32,33 are reading 2.2 ohms. ??
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post #35 of 1812
5/2/09 at 3:32am
I thought you said you have 2 DMMs

4752 = 47500 = 47.5K = 47K5

..dB
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post #36 of 1812
5/2/09 at 3:42am
Thread Starter 
No, two drill presses, much less useful for electrics

Well in that case I'm even more confused, R5 and 7 want 47, R27 and 28 want 4k7... erm, so what I have isn't for anything?

Bugger, that means I need to get 4 of each!

One point of information you should probably be aware of. In high school, I came bottom of my class in math two years in a row... yeah, Mr Thicky, thick McThick
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post #37 of 1812
5/2/09 at 3:55am
aaaah , didn't click back to see what the 2 referred to

I need to check the schematic to see which ones you are referring to. You are right , I am sure Jeff will replace the parts not in the kit. The 47.5K would be good to play with in the global feedback position ( R22/23 ) ..dB
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post #38 of 1812
5/2/09 at 4:04am
Thread Starter 
Gah, the RLED resistors are missing too. I'll need to run through the whole board to make a list for Jeff.
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post #39 of 1812
5/2/09 at 4:27am
Quote:
Originally Posted by smeggy View Post
Gah, the RLED resistors are missing too. I'll need to run through the whole board to make a list for Jeff.
Make that list quickly smeggy, then send me a copy for when I'm ready to build one
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post #40 of 1812
5/2/09 at 5:13am
Thread Starter 
Hmm, I need to have the Glass Jar MOSFET BoM verified against the circuit diagram as there seems to be some discrepancies.

BoM doesn't list RLED, R27, r28.

R5, R7 are listed as 47.5k

R32, 33 are listed as 2R2

What is correct and what do I actually need?
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post #41 of 1812
5/2/09 at 6:19am
Quote:
BoM doesn't list RLED, R27, r28.
4.75kΩ for R27, R28

(those values are provided on the schematic and parts list page)

RLED should be somewhere around 10K depending on the LED.

Quote:
R5, R7 are listed as 47.5k
The schematic sez they should be 47 ohms.
The parts list sez 47.5
(the half ohm doesn't matter but 10X the specified value does...)

Quote:
R32, 33 are listed as 2R2
2R2 = 2.2ohms. And they should be 2Watt resistors
(they should be the big blew ones in the bag on the right in the picture you posted on the first page)

What parts were included?
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post #42 of 1812
5/2/09 at 6:43am
The 2.2ohms resistors are 1/2 watt resistors....
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post #43 of 1812
5/2/09 at 6:46am
Thread Starter 
This was from the glass jar BoM.

no RLED, R27, r28 listed or supplied.
R5, R7 are listed and supplied as 47.5k ohm
R32 and 33 are listed as 2.2 ohm 1/2 W

I'll need to check through the rest tomorrow.

Luckily I have some 10ks I can use for RLED.
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post #44 of 1812
5/2/09 at 7:03am
Smeggy,

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.

Cheers,
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post #45 of 1812
5/2/09 at 7:13am
Thread Starter 
Yeah, I can see that. I was more concerned about them being missing from the bom and the wrong values for the others.

That's why I was asking in the first place. Noobs like me can easily miss this stuff and go on regardless with wrong values etc. also, there is no value for the LED supplied so formulas don't help
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