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M³ amplifier build discussions thread - Page 10  

post #136 of 828
3/14/05 at 6:26am
What size screws should I use to secure the heatsinks to the board?
post #137 of 828
3/14/05 at 6:41am
Quote:
Originally Posted by amb
Your local hardware store should have what you need. Either use #4 self-tapping screws, or tap the holes on the heat sinks with a #4-40 tap about 1/2" deep, and then use #4-40 machine screws.
Nuff said?
post #138 of 828
3/14/05 at 6:55am
Thread Starter 
primer, seeing that you're in Australia, you would probably use metric hardware. This means 3mm self-tapping screws or M3 machine screws after tapping the heat sinks.
post #139 of 828
3/14/05 at 7:03am
Thanks, I have some M3 machine screws but they seems to be a bit big but maybe I bought the wrong ones. Back to the hardware store tomorrow.
post #140 of 828
3/14/05 at 7:14am
Thread Starter 
Quote:
Originally Posted by primer
Thanks, I have some M3 machine screws but they seems to be a bit big but maybe I bought the wrong ones. Back to the hardware store tomorrow.
The heat sink holes have no threads, so the M3 machine screws would be "too big" unless you use a tap and drill to make the threads.
post #141 of 828
3/14/05 at 7:59am
metric self tapping screws are available with 2.2mm, 2.9mm, 3.5mm, ...

3.5mm would be too big, the 2.9mm (x 9.5mm length) fitted well on my M³

if you want to bother with tapping threads you must tap M3 threads and pick M3 machine screws (12x)
post #142 of 828
3/14/05 at 2:27pm
My hardware store didn't have self tapping screws that small, but did have a tap bit for my drill. The bit was only $5, and it was easy enough to drill the threads into the heatsinks.
post #143 of 828
3/14/05 at 5:52pm
Quote:
Originally Posted by phobus
My hardware store didn't have self tapping screws that small, but did have a tap bit for my drill. The bit was only $5, and it was easy enough to drill the threads into the heatsinks.
Just for reference I managed to cram some 3mm self tappers in my heatsinks today. They didn't go in too easily but I think that was more to do with the length (12mm)
post #144 of 828
3/16/05 at 6:48pm
My cerafines have got lost in the post and today I finally run out of patience. I have a working M³ now, it has only 3x470uf Pana FC's and 7 Jamico (urgh) 100uf, all 25v

Despite that it sounds pretty good!! Early days yet, with only about 4hrs of runtime but it has more depth and punch than my pimeta, its not a massive jump though.

My trimpots had no 'clicks' which confused me some, I was turning them as per the guide waiting for a click that wasn't forthcoming

Anyway, I have it all running with 85mv/5mv of bias and 637/627's.

I have a question though but probably a very stupid one so don't laugh!

Amb says to measure the voltage at the opamp pins and it should be the same as the psu but less a volt or two (I have no diode). When I measure mine it reads 9.6v but my psu is putting out about 20.5v.

Is this right? Part of me says its fine because the TLE is splitting the power, so it should be +-9-10v, I suppose I'm not sure if my meter should show the full voltage? Is my M³ healthy?
post #145 of 828
3/16/05 at 6:53pm
Voltage should be fine..
post #146 of 828
3/16/05 at 7:06pm
Thread Starter 
Quote:
Originally Posted by Magsy
My cerafines have got lost in the post and today I finally run out of patience. I have a working M³ now, it has only 3x470uf Pana FC's and 7 Jamico (urgh) 100uf, all 25v
As long as you're not going to power the amp with a PSU over 24V then you're fine with 25V rail caps.

Quote:
My trimpots had no 'clicks' which confused me some, I was turning them as per the guide waiting for a click that wasn't forthcoming
Depending the brand of trimpot the "click" may be more felt than heard. Even then, it may be just a subtle feel.

Quote:
Amb says to measure the voltage at the opamp pins and it should be the same as the psu but less a volt or two (I have no diode). When I measure mine it reads 9.6v but my psu is putting out about 20.5v.
When I say measure the voltage at the opamps I refer to the voltage across pins 7 and 4 (not relative to virtual ground). If you're measuring at pins 7 and 4 relative to virtual ground then you should have 19.2V across. This gives 1.3V drop from your PSU's 20.5V which is about right.
post #147 of 828
3/16/05 at 7:17pm
Quote:
Originally Posted by amb
As long as you're not going to power the amp with a PSU over 24V then you're fine with 25V rail caps.


Depending the brand of trimpot the "click" may be more felt than heard. Even then, it may be just a subtle feel.


When I say measure the voltage at the opamps I refer to the voltage across pins 7 and 4 (not relative to virtual ground). If you're measuring at pins 7 and 4 relative to virtual ground then you should have 19.2V across. This gives 1.3V drop from your PSU's 20.5V which is about right.
I have another set of 35v Cerafines coming which will be going in!

May well of been a light bump in the travel, I was using pocket tool (little un) to twiddle them.

Not sure what I have done with the voltage readings, I was measuring one probe in pin4 and one in pin 7 and it was reading half voltage. I've just checked and its reading 18.8v now! I was measuring without the opamps in earlier, it must of been that?

By the way, thanks for the great product, site/guide and support, its been a pleasure start to finish
post #148 of 828
3/16/05 at 7:20pm
Thread Starter 
Quote:
Originally Posted by Magsy
Not sure what I have done with the voltage readings, I was measuring one probe in pin4 and one in pin 7 and it was reading half voltage. I've just checked and its reading 18.8v now! I was measuring without the opamps in earlier, it must of been that?
Yeah, you have to have at least one opamp in place to do that measurement. Without any load the cap multiplier that supplies the rails won't be biased and you won't read the correct voltage.
post #149 of 828
3/16/05 at 8:56pm
Quote:
Originally Posted by Magsy
Early days yet, with only about 4hrs of runtime but it has more depth and punch than my pimeta, its not a massive jump though.

Anyway, I have it all running with 85mv/5mv of bias and 637/627's.
I've been running mine for 4 days now, and I have a similar setup to you. I'm running with 637bp/627bp and 108mv/5mv, and I have to say that the MMM is a BIG jump over the Pimeta for me , so much so that I gave the Pimeta to my uncle. Hope to compare with the PPA v2 soon

Anyways, I'm trying the AD843JN opamps right now, and they definately don't sound as good as the 637BPs to me. However from these forums, it seems a lot of people like the 843s better. Should I change any settings on my M3 to accomodate these opamps?
post #150 of 828
3/17/05 at 2:57am
Thread Starter 
Quote:
Originally Posted by phobus
Anyways, I'm trying the AD843JN opamps right now, and they definately don't sound as good as the 637BPs to me. However from these forums, it seems a lot of people like the 843s better. Should I change any settings on my M3 to accomodate these opamps?
Even though I list some optimizations for the C1 value on my site (based on opamp choice and gain), it is there for academic interest. It affects the behavioe of the amp way up in the ultrasonics and is for those who want to tinker with the amp to get the best square wave performance. I doubt that there would be any audible difference.

I don't think there are any tweaks in this amp that would affect the fundamental sonic signature of the opamp, and it's boils down to personal preference and how it might synergize with your headphone and source combination. If you like the OPA637s better, then stick with them. At the same PSU voltage, the OPA6x7 will give you a bit more output voltage swing than the AD843. This means more headroom before clipping.
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