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M³ amplifier build discussions thread - Page 6  

post #76 of 828
3/10/05 at 2:25am
I asked this in the announcement thread, but I never got an answer, and now it's time to buy.

I definitely am going to populate D1. Can I use a Schottky diode, as long as the voltage specs are good enough? Or is it noisier than the 5 cent 1N4001 specified for D1?
post #77 of 828
3/10/05 at 2:50am
Thread Starter 
Quote:
Originally Posted by Syzygies
I definitely am going to populate D1. Can I use a Schottky diode, as long as the voltage specs are good enough? Or is it noisier than the 5 cent 1N4001 specified for D1?
Yes, you could use a schottky diode for D1, as long as it's rated at least 50V and 1A. Also make sure whatever you choose would actually fit on the pcb.

That said, since D1 is only for reverse voltage protection and not rectification, I could only think of one reason why you would use a schottky, and that is to choose one with a lower forward voltage drop (Vf) than the ~0.8V of the 1N4001. I had done some looking a while back, and could not find a schottky offering significantly lower Vf and rated at 1A or more. Maybe I didn't look hard enough, if you find a suitable schottky then I'd like to know which one.
post #78 of 828
3/10/05 at 3:02am
Edit: pics removed

I had a throw away Hammond 1455 T in the junk box and figured why not.
To echo what what was posted earlier... the square wave performance is very good from this amp and my DCoffset levels are a little higher then I usually see but they are still in the ok range.
post #79 of 828
3/10/05 at 3:33am
Thread Starter 
Quote:
Originally Posted by MisterX
I had a throw away Hammond 1455 T in the junk box and figured why not.
Ooooh, all those Cerafines...

Quote:
To echo what what was posted earlier... the square wave performance is very good from this amp and my DCoffset levels are a little higher then I usually see but they are still in the ok range.
Curious. My prototype with AD8610s measure -0.1mV, +0.1mV and 0.0mV DC offset on the L, R, and G channels.
post #80 of 828
3/10/05 at 4:37am

question

on the parts list guide, C1 is listed as:

multilayer ceramic capacitor 33pF 100V

but the DigiKey part number given later down in the page (BC1007CT-ND) is rated only at 50V. Is it okay to use a 50V cap here or should i use a 100V? It doesn't look like digikey stocks the Vishay/BC 33pF in a 100V variety; i could of course go with another brand.

[edit, another question]

in the C7 caps, is there any advantage to using either size? (12.5mm or 18mm)
post #81 of 828
3/10/05 at 4:47am
Thread Starter 
Quote:
Originally Posted by escher
on the parts list guide, C1 is listed as:

multilayer ceramic capacitor 33pF 100V

but the DigiKey part number given later down in the page (BC1007CT-ND) is rated only at 50V.
A 50V rated cap is fine.
post #82 of 828
3/10/05 at 7:24am
Thread Starter 
Quote:
Originally Posted by escher
in the C7 caps, is there any advantage to using either size? (12.5mm or 18mm)
Probably not in any sense that you could measure or hear. Use the appropriate size and number of capacitors to achieve the total target capacitance (this will depend on which brand/line of capacitor you use).
post #83 of 828
3/10/05 at 9:32am
Further to my last post, Nate submitted a more in-depth list of parts (panel components and crossfeed circuit). This files is now uploaded to http://www.nisbeth.dk/uffe/files/hea...rtssources.xls

/U.
post #84 of 828
3/10/05 at 10:08am
Thread Starter 
Quote:
Originally Posted by Nisbeth
Further to my last post, Nate submitted a more in-depth list of parts (panel components and crossfeed circuit). This files is now uploaded to http://www.nisbeth.dk/uffe/files/mcu...rtssources.xls
Nice list, although for this amp I would not recommend using any 1/8" jacks (either for input or output). Also, I would like to see Molex KK headers and/or terminal blocks added for the main pcb (perhaps marked as optional).

Some of the items like LEDs and jacks, etc., can be had from Mouser instead of Digi-key or Parts Express. Since most of the first section uses Mouser, it would be nice to keep as many items from the same vendor as possible.

Since the list contains such options as a crossfeed board, perhaps a section on the PSU would be nice.
post #85 of 828
3/10/05 at 10:25am
Geez, cut a guy some slack . I'm in the process of tweaking the spreadsheet to use as many Mouser links as possible. As I stated on the revised version, the additional information comes direct from Sanaka's PIMETA spreadsheet. I'll be making it more and more MMM specific as time allows and as I get closer to placing my own order.

Look for a new version with all optional parts having hot-links some time later this week. Also, I'll add a full parts rundown for a standard 24V STEPS (just built one so it's already done) along with an Elpac WM080.

I'll add the MOLEX headers as well to the main body of work.

N
post #86 of 828
3/10/05 at 10:30am
Quote:
Originally Posted by MisterX
I had a throw away Hammond 1455 T in the junk box and figured why not.
To echo what what was posted earlier... the square wave performance is very good from this amp and my DCoffset levels are a little higher then I usually see but they are still in the ok range.
Very nice work! What opamps are you using?
Quote:
Originally Posted by amb
Curious. My prototype with AD8610s measure -0.1mV, +0.1mV and 0.0mV DC offset on the L, R, and G channels.
I am also using 3xAD8610 and have one channel noticeably higher than the other two. Although the outlier is still fine at 1.6 mV, this amp is so good that I'm going to fiddle with it a bit when I get a moment and see if I can bring it in line with the other two.
post #87 of 828
3/10/05 at 1:36pm
Quote:
Very nice work!
Thank you.

Quote:
What opamps are you using?
OPA637/627 combo.

DC offset numbers are---->
Left = .87mV
Ground = .32mV
Right = 1.9mV

It kinda surprised me because I matched the resistors to stupid levels (.001%) but I have noticed that Q1+ runs noticeably hotter then rest so.....
post #88 of 828
3/10/05 at 2:22pm
Quote:
Originally Posted by MisterX
DC offset numbers are---->
Left = .87mV
Ground = .32mV
Right = 1.9mV

It kinda surprised me because I matched the resistors to stupid levels (.001%) but I have noticed that Q1+ runs noticeably hotter then rest so.....
I only matched mine to < 0.1%, and I have L and G < 0.1 mV, but R = 1.6 mV. Could a slight mismatch in the output transistors account for what MisterX and I see?
post #89 of 828
3/10/05 at 3:21pm
amb recently pointed out that the OPA604 works with ±24V power rails. This allows for a 48V supply with 50WV capacitors, which should provide over 30Vpp output swing, making it a great choice for driving the K1000. We would like to hear your opinions on the sound of the OPA604 in M³.
post #90 of 828
3/10/05 at 3:28pm
I used inexpensive resistors on a MINT the other day, to see how it sounded for friends who wanted best bang-for-buck, and matched them on a $50 RadioShack meter to its precision. I got better DC offset than my PIMETA, using 0.1% Vishay-Dale that I tried to match, but pretty much came already matched to the precision of the meter.

MisterX, what meter did you use, and how many resistors?

There's a famous math problem behind resistor matching: The "Birthday" problem. With 30 people in a room there's likely to be two people with the same birthday. Buy a bag of twenty resistors, there's likely to be an amazing match among two of them. A more interesting question is what one's high/low inventory levels should be, to always find good enough matches from what's left after years of cherry-picking and restocking.
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