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M³ amplifier build discussions thread - Page 2  

post #16 of 828
3/5/05 at 8:02pm

Speaking of power supplies...

My current plan is to build two amps. The first configuration is with a STEPS set at 32v for OPA637 /627, and bass boost. The second will be with AD8610 and I happen to have one of these GHOF 1-28, 28v, 1a laying around, and plan to case it seperately.

Good, bad or ugly?
post #17 of 828
3/5/05 at 9:13pm
Thread Starter 
pabbi1, 28V will take you close to the absolute maximum voltage rating of the AD8610 even after accounting for the voltage drop of the cap multiplier Q5 transistors and D1 diode. You're leaving little margin for error. Be sure that the power supply really puts out no higher than 28V under any circumstance or you'll risk blowing opamps.

For everyone's reference, D1, Q5+ and Q5- should drop about 0.8V each. So that's a total of 2.4V drop. While 28V - 2.4V = 25.6V seems safe (AD8610 is rated at max 27.3V), prudence dictates allowing about 2V minimum for error.
post #18 of 828
3/5/05 at 9:41pm
Thanks... but 1.0a is OK? Any other way to reduce the voltage a bit, like adjusting D1, or Q5?
post #19 of 828
3/6/05 at 1:12am
Quote:
Originally Posted by amb
For everyone's reference, D1, Q5+ and Q5- should drop about 0.8V each. So that's a total of 2.4V drop. While 28V - 2.4V = 25.6V seems safe (AD8610 is rated at max 27.3V), prudence dictates allowing about 2V minimum for error.
So I fully charged my barbecue pit lead acid battery tonight, and it measured just under 14V. That's 28V for two, drops to no more than 26V by amb's computation, that's just barely safe.
post #20 of 828
3/6/05 at 1:37am
Thread Starter 
Quote:
Originally Posted by pabbi1
Thanks... but 1.0a is OK? Any other way to reduce the voltage a bit, like adjusting D1, or Q5?
There is nothing to adjust on these. Just measure your psu's output voltage to make sure it really is 28V and not 28.xV where x is a large fraction, and you'd be ok. If you're a little over, you could double up on D1 (i.e., put two 1N4001 diodes in series) to drop the voltage a bit more.

1A rating is fine, as long as you're not cranking the bias to exceed that.
post #21 of 828
3/6/05 at 1:58am
Dear AMB,

Is this a good idea?
Use two car battery makes a 24V to amp?
If it's possible, hope can gets more clean sound.

Thanks!

Pal
post #22 of 828
3/6/05 at 2:19am
Thread Starter 
Quote:
Originally Posted by palchiu
Is this a good idea?
Use two car battery makes a 24V to amp?
If it's possible, hope can gets more clean sound.
While it's possible to do that, you have to make sure that the car batteries aren't putting out more than what the opamps could tolerate. Also, even car batteries will eventually become discharged, and they do not like to be completely and repeatedly discharged (will shorten the lifespan). So, you will have to put the batteries on a charger when you aren't using the amp. To me that seems like a major inconvenience.

I also don't think a car battery will really offer "cleaner sound" than a good regulated power supply. A car battery actually could be noisier than a regulated power supply. While I haven't done any noise testing of a car battery myself, I point you to the following article about voltage regulator noise. The part of interest is at the end of Page 4, where a lead-acid battery is tested for noise. Car batteries are of the lead-acid variety, and this test shows worse noise performance than a regulated power supply under load:
http://www.tnt-audio.com/clinica/reg..._noise1_e.html
post #23 of 828
3/6/05 at 3:53am
To implement bass boost, only the pot and cbb are required? Any additional shunt/jumper?
post #24 of 828
3/6/05 at 3:54am
Quote:
Originally Posted by amb
Edit: I just checked and Mouser has Wima MKS-2 1uF 63V 10% in stock:
Mouser #505-MKS21/63/10, minimum order quantity is 10,
They lied .... got to order at least 50 of them.

Quote:
Originally Posted by Ed
LOL, are the Wima MKS-2's really that much better than the Vishay Roederstein's?
No... in fact i prefer the green ones but try dispelling the myth that Wimas are the best 5 times a day and it gets old real fast.
Sometimes it's easier when you don't provoke the questions.
post #25 of 828
3/6/05 at 3:59am
Thread Starter 
Quote:
Originally Posted by pabbi1
To implement bass boost, only the pot and cbb are required?
Yep.

Quote:
Any additional shunt/jumper?
Nope.
post #26 of 828
3/6/05 at 4:14am
Thanks! AMB
post #27 of 828
3/6/05 at 4:21am
Where are the 2w R9 available?
post #28 of 828
3/6/05 at 4:23am
Mouser #262-1.0 among others.
post #29 of 828
3/6/05 at 4:28am
I meant other than Xicon... is that all that's available? Everything esle I have is Vishay (or Holco), and wanted to keep that, if at all possible.
post #30 of 828
3/6/05 at 4:29am
What does changing the value of R9 to 10 ohms do the sound? It changes the output impedance of the amp right?
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