Mini-As almost alive

winslow

Member
2005-08-05 6:27 am
If I wasn't missing 1 value of resistor, the Mini-As would be up and running tonight. I'm so sad. Got them built with the 1 amp bias resistors in, but that will probably get changed once the amps are making music and I'm certain they are operating properly.

I do have to give a big thanks to the guys who made the Mini-A- Nelson, Grey, Jason, and Brian. Those boards are slick and was pretty fun to put together. Probably took 3 hours to do both amp boards.

Anyways, finally off to bed dreaming about high biased single ended class A amps.
 
Re: Err

winslow said:
The power supply that I measured doing +/- 18 is going +/- 25 tonight, and she's set to be biased at 1 amp, but I'm getting .03 amps across the bias resistor.


:confused:

Are you running it at +-25 or +-18? .. +-25 is way too high for a mini. I doubt the devices could get rid of the heat. Bias is measured by checking voltage across a source resistor and using ohms law. example: .5v measured / .5r resistor = 1A bias <or> .62v measured / .47r resistor = 1.319A.

good luck..don't give up if you have problems, it's well worth it.

Marc
 

winslow

Member
2005-08-05 6:27 am
One side has nearly 14 volts, other side has .55 volts. So, .55 volts divided by .475 ohms gets me 1.15 amps. That makes me feel better. Now just have to figure out what do do about that voltage.

The power supply is from a car amp that I had laying around since this was going in the car. Have to find out if she's regulated or not.

Damn, she's hot...glad I didn't go full bias off the bat...and glad I have larger heatsink wanting to get drilled and tapped.
 

winslow

Member
2005-08-05 6:27 am
Yeah, I could scale it up to the A3/30...but Iwas really trying to keep the power down to a smaller level. Going to call Monolithic and see if I can get a schematic for the donor amp and see if I can adjust the voltage on the power supply.

Trying to kick some butt at the shows...and I think this amp has potential to do it.

On the side of the resistor closest to the edge (R11 or 12 I think, I'm at work and can't look at it) I got 14 volts. On the other side I got .55 volts. Is that not right? I'll go double check any DC on the output tonight...but that may explain that pop that I'm thinking is a turn on pop. I tried to find the posts where guys had posted their measurements, but I couldn't find them last night...search engine here is wierd and I'm not really used to it.

One thing is forsure, even with it being sick, she sounds good.

And sorry for all the questions, just a nursing student who tints windows for a living...and was a car audio installer prior to that. So, not the most technical person in he world...but I try.
 

winslow

Member
2005-08-05 6:27 am
Both are making music right now. Still have a nasty turn on pop that I haven't racked down yet.

They sound good and are running pretty hot. I'd like to try bring the bias up sometime.

Also, how do I lower the negative feedback on these boards? I've seen posts on lowering it with the Zen amps, but don't think that I've found one yet that relates to BrianGT's boards. Curious if lowering the feedback will sweeten up the topend some.
 

winslow

Member
2005-08-05 6:27 am
Switching noise in the PS...need to find a way to tackle that.

As I was looking for the noise powering components in the signal chain down to track the noise down (was present with the amps on and everything else off), I powered up the transport...nothing. Then powered the DAC up...pop. So I'm now wondering if my DAC has some DC on the outputs- Benchmark DAC1 if anyone has messed with it.

Amps sound awesome though.
 

winslow

Member
2005-08-05 6:27 am
Is this normal?

When I touch C1 while the amps are playing, it sounds like the amp grounds out. Bad solder joint, bad cap?

Also, what happens if you do not put C3 in? That is the feedback loop, correct? If you lifted R13 and left out C3 the amp would run high bias without feeback?
 

winslow

Member
2005-08-05 6:27 am
Yeah I got that. But I was curious about the sound when I touched the metal tops of both caps, meaning, is it supposed to do that?

And I have a few old posts saved where Grey is talking about changing a few parts around in the Mini-A and he mentioned a few part numbers...and I'm trying to understand which parts on his version are what parts on Brian's boards. Again, I'm no EE or anything close...so I want to ask questions before I blow something up.