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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 7

post #91 of 1816
Thanks for the help Scott...

Turns out i made a rookie mistake
I had switched one each of IRFZ24 and Z34 on both rails.

I now have +/-28.8 volts DC
post #92 of 1816
Yep, that's why I'm shopping for a desoldering gun/station right now.
LOL
post #93 of 1816
Quote:
Originally Posted by digger945 View Post
Yep, that's why I'm shopping for a desoldering gun/station right now.
LOL
I don't know how I went about without the desoldering pump till now..

In any case switching the MOSFETs out was easy as they are air wired on to the chassis.

The same MOSFETs are going to be air wired for the amp section next.

I found a few metal oxide 2W 47 ohm resistors for R5,R7 on the EHHA..
going to use them and make do for now..
post #94 of 1816
Quote:
Originally Posted by sachu View Post
I had switched one each of IRFZ24 and Z34 on both rails.

I now have +/-28.8 volts DC
phew , now you can get down to the fun part ..dB
post #95 of 1816
Quote:
Originally Posted by TimJo View Post
So I read through the design section yesterday - very creative Alex.

I'm still working my way through the details of the schematic, and I'm sure I'll have a few questions down the road, but once again thanks for putting together so much info on the website. This is a unique design for sure, and it'll take awhile for it all to sink in. I really love the symmetry of the design...

I did notice one typo on the schematic I believe. The signal path between the second triode and the lower VAS (Q6) passes through a unity gain mirror. The transistor pair in the mirror is labeled Q2-Q3, but I think it is supposed to be Q2-Q4, based on the parts list. Correct?
Thanks!! You'll love the EHHA II.

You're right about the schematic. After all this time . . .
post #96 of 1816
Quote:
Originally Posted by runeight View Post
Thanks!! You'll love the EHHA II.

You're right about the schematic. After all this time . . .
ALex, as I have already let you know, of course I want to be in on the proto team for the EHHA2..
post #97 of 1816
Quote:
Originally Posted by sachu View Post
ALex, as I have already let you know, of course I want to be in on the proto team for the EHHA2..
That's all well and good, but I think Alex has some -Ahem- other protos -AHEM- to work on so he shouldn't be distracted!
post #98 of 1816
Yes, he does, and has been having a hard time getting into the workshop.
post #99 of 1816
Thread Starter 
It's not even built and you're already talking upgrades!

*sigh*
post #100 of 1816
We have a working heater supply. Using Pete Millet's heater supply without the choke filter

Set it at 6.4 volts unloaded. The transformer is capable of 4 amps into 6.3 volts each rail so this one is wired in parallel so plenty of current to run 6H30s on the amp.

Now Don as you say 'comes the fun part'.

going to use separate AC cords to act as switches to bring up heater first, then S22 for the time being. Once test phase is complete I will move to install separate switches or put the timer+ relay .
post #101 of 1816
Thread Starter 
Nice going sachu!
post #102 of 1816
Alright..brought up one board..tube lit up, LED lit up as well as I brought up the S22 a few seconds later.

Ran through the checklist..

Was hard finding resistor locations as the numbering is covered up by the resistors.

Also, the picture of the board up on the Cavalli audio website is not the current version which makes it even harder.

All the voltages checked out except for the two.

1> R32 and R33 measured 0volts and varying R21 made no difference. plus side though, no smoke

2> Also the voltage on pin 6 of the opamp measured 0.4 volts instead of 0 volts.


Kinda tired to hook up the second board...will report back with setup results for that board in a few minutes.
post #103 of 1816
Similar resuslts with the second board. Except here
1> Voltage across R32 R33 was at 0 volts regardless of the R21 trimpot position.

2> Pin 6 on the opamp was at 1.8 volts

Alex,Don, Where do we go from here?
post #104 of 1816
Sachu, I just stumbled upon your build pics and have a comment about air-wiring the MOSFETs on the heatsinks. The inductance in the wires form an LC resonant network with the MOSFET gate capacitance, and could lead to instability (ringing square waves or even outright oscillation). The gate wiring to a MOSFET should be as short as possible and the gate stopper resistor should be immediately adjacent to the gate pin, this is why MOSFETs should be directly soldered on the PCB.

This is not related to your current problems but I thought you might want to be aware of this issue.
post #105 of 1816
Quote:
Originally Posted by amb View Post
Sachu, I just stumbled upon your build pics and have a comment about air-wiring the MOSFETs on the heatsinks. The inductance in the wires form an LC resonant network with the MOSFET gate capacitance, and could lead to instability (ringing square waves or even outright oscillation). The gate wiring to a MOSFET should be as short as possible and the gate stopper resistor should be immediately adjacent to the gate pin, this is why MOSFETs should be directly soldered on the PCB.

This is not related to your current problems but I thought you might want to be aware of this issue.
Thanks for the info Ti. Will be keeping the length as short as possible (less than 2 inches).
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