Aleph J-X Amp Project

[Bill Fuss]

If the voltage across it is lower you are going in the right direction.

You aren't by chance measuring with a 10x scope probe, are you.

 

[dhole]

my calculation of current through the 100r is 3.645 but I have 10w resistors getting too hot.... i still dont get it.

By the way Bill i greatly appreciate the time you have spent holding my hand here. You can tell I am a complete novice just able to not electrocute myself.

dave

 

[dhole]

You aren't by chance measuring with a 10x scope probe, are you.

oh no , a cheapo multimeter

 

[Bill Fuss]

You better get a decent one before you go any further, it is lying to you. Where are you picking up the .9v? If it was 9v it would make sense, that would be around .8 watts. It would be pretty warm, without being bolted to something.

 

[Bill Fuss]

3.6A through 100ohms is around 1300 watts, I think your math might be off a little.

 

[Bill Fuss]

Are you still there? Try measuring a 9v battery and see what you read.

 

[dhole]

Hey Bill

Took out the thermistor and things seem ok now... The 100r are nice and cool and the voltage is down to 0.00 when tweaked ( changing as amp warms up ) . Heat sinks are nice and warm ... its looking good.....
dave

 

[dhole]

Power for Rg = Rail voltage square/Rg/2.
So if you use 24V rails and 33R, you need about 10W. If you use 100R you need 3W.

Bill I used this to calculate wattage.

 

[dhole]

whoo those sinks are getting toasty. I can keep my palm on em for a good 10 seconds..

 

[Bill Fuss]

So you had the thermistors in the return path instead of just for chassis isolation?

Have you checked the offset across the outputs yet?

 

[dhole]

The thermistor was from psu ground to earth. The outputs connected. 100r to psu ground. Offset is 0.008

 

[Bill Fuss]

The Rg voltage drop is zero on both sides and the offset across the outputs is .008v. I wish I could see that with my own eyes.

 

[dhole]

I lied about the voltage drop thats 24.4 v !

 

[Bill Fuss]

You must understand that you have to get each side operating correctly before you try to balance them to each other.

24.4v / 100ohms = .244a
.244a X 24.4v = 6 watts

Rg should be pretty hot

 

[dhole]

Think I might have to admit defeat here. Thought i was getting somewhere. My voltage to R11 and 12 on both sides is at 5v and my dc offset is drifting down into negative voltages constantly as the case heats up , and its getting hot!

 

[Bill Fuss]

I know you have built an Aleph in the past. Look at this as bridging two Alephs, because that is what it is.

For this thing to work properly every part needs to be well matched from side to side, and there will still be variances to deal with.

You may have bit off more than you can chew on this one, a firm grasp of Aleph current source operation is of utmost importance.

Why don't you disconnect the power to one side and treat the other side as a normal single ended Aleph until you get a handle on it.

 

[dhole]

Cheers Bill will do that I should think. Out of interest could you tell me the measurments i should expect for :
voltage drop over 100r
voltage over R11 12
acceptable offset
cheers
dave

 

[Bill Fuss]

V across Rg is your offset voltage

V at R11 will be around 4v, trim it til you get close to zero offset.

Under 50mv offset is great. Zero is better.

Record the drops across R16 and R17 at operating temp so you can trim the other side to match when you get to that point.

 

[dhole]

r16 and 17 on both sides are 0.49 or 0.5 . Is the v at r11 dependant on psu voltage ?

The amp does sound very nice regardless!

 

[Bill Fuss]

The V at R11 is dependent on how much current is going through it, nothing else.

Where do you have a speaker hooked up?