[smeggy]

Quote:

Originally Posted by ShinyFalcon /img/forum/go_quote.gif smeggy, what resistor did you end up using for the zobel?

I used 2W 20 Ohm as there were no 22s in Frys.

 

[digger945]

Dang bubba, you come a long way to be givvin up now aint ya.
Jus think of the sound and you can muster the intestinal fortitude.

 

[amb]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif I used 2W 20 Ohm as there were no 22s in Frys.

While the resistance is ok, you need to make sure that it's a non-inductive type. I don't know which resistors you got from Fry's, but the Zobel network is intended to provide a form of high frequency compensation, and if the resistor is inductive, then it effectively nullifies the function of the Zobel.

 

[Gatsu]

Quote:

Originally Posted by DoYouRight /img/forum/go_quote.gif wow great way to introduce your own board! would you happen to have a spare?

I only had one board made as I knew I would make a mistake somewhere, and boy did I!

If you notice in the photo the board has V3.0 on it, the schematic I uploaded is V3.3. I made quite a few stuff ups on that first version.

Some changes from the V3.0 to V3.3:
* Fixed the picaxe programming circuit
* Added in the output switching relays (yes I managed to forget to include them)
* Changed the circuit from having 4 independant LEDs for showing status to using 2 bidirectional LEDs (I originally was going to have the status LEDs very similar to namaanf's, but I wanted all of the buttons on the two cases to be the same, so it made sense to use them as indicators as well.)

You can't actually see the changes I made for these in the final pictures as they are underneath the board.

 

[askforwhy]

I've tested 4 Sigma22s today and so far, 2 good, 2 dead

Problem Sigma22 No.1:
I reversed CR2-CR4 J508/J511. Holy crap, I guess I will have to replace ALL the CRDs/BJTs/MOSFETs then? I shouldn't have rush like this.
Problem Sigma22 No.2:
Everything seemed fine at first, I used DMM to check the DC Voltage then. Suddenly fire and smoke came up from Q15.
Maybe I shorted V- to G by my probe accidently.

Resistors seems OK, so I guess I am replacing the MOSFETs only.
Any advice will help, thanks.

 

[El_Doug]

Quote:

Originally Posted by askforwhy /img/forum/go_quote.gif Problem Sigma22 No.2: Everything seemed fine at first, I used DMM to check the DC Voltage then. Suddenly fire and smoke came up from Q15. Maybe I shorted V- to G by my probe accidently. Resistors seems OK, so I guess I am replacing the MOSFETs only. Any advice will help, thanks.

this sounds EERILY familiar (read: exactly the same things happened to me).

however, after replacing all 4 mosfets as well as Q1 and Q2, I still did not have a working s22. upon testing even more of the transistors, I found Q3 had somehow blown itself - however, all that desoldering caused me to lift a trace, and I called it quits on that board. I'm now in the process of building another one

 

[FallenAngel]

Could be my imagination but when since I installed the Zobel network in the balanced Beta22, I think it's been running hotter. Does this make sense?

 

[Nebby]

Take the zobel out and do some measurements with and without it

 

[FallenAngel]

Easier said than done

Oh, and of course it gets hotter with low impedance headphones.

 

[smeggy]

Quote:

Originally Posted by amb /img/forum/go_quote.gif While the resistance is ok, you need to make sure that it's a non-inductive type. I don't know which resistors you got from Fry's, but the Zobel network is intended to provide a form of high frequency compensation, and if the resistor is inductive, then it effectively nullifies the function of the Zobel.

I'm not certain I got the exact type specified on your site but I think so, however, the amp was set to no output when it was turned on, ie, the 'phone/speaker switch was set to off in it's center position. I don't know if this makes a difference.

 

[amb]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif the amp was set to no output when it was turned on, ie, the 'phone/speaker switch was set to off in it's center position. I don't know if this makes a difference.

It shouldn't make a difference, if everything is wired up correctly. Why not post some clear pics of your internal wiring?

 

[smeggy]

I can't, the whole thing is now stripped out and the S22 and EHHA are in another case so there is just a pair of Beta boards in an mostly empty case.

It's now an abandoned project as I really don't have the time or knowledge to continue with it.

 

[qkizz]

It has been very weird thing happening to one of my beta22 boards. When the board is placed horizontally 75mV on R34 is pretty much stable, but as soon I flip it to vertical voltage is skyrocketing (within few seconds) to 120mV and up, when I flip it back to horizontal it takes few seconds for voltage to drop to preset value. I've inspected board visually and found nothing wrong.

I've noticed it during heatsinks change for a larger ones 2.5". I have 5-ch balanced/SE version. Firstly I built 3ch and later on I decided to add 2 more boards and make balanced. To fit two more boards I had to place a new ones vertically and decided to add larger heatsinks to compensate for loss of heat dissipation. And than I've find out that one of vertical boards is overheating after few months of normal functioning. What could be the problem? Thanks

 

[amb]

qkizz, the heatsink fins dissipate heat most effectively when it's oriented veritcally (helps convection). If you change the board orientation then the temperature will inrease. Normally the MOSFETs should compensate for the increase a bit by their negative thermal coefficient, but you may still need to re-adjust VR2 to turn down the bias.

 

[qkizz]

amb, I understand that. What is surprising to me, is that voltage start rising (2mv/s) the same second I flip the board. Within few seconds when it is happening the temp on heatsink won't even rise and I'm already at about 100mV. Would such a sudden change in heat dissipation off heatsinks trigger sudden change in bias?