MOX builder’s thread

[TNT]

OK OK - but how does it SOUND ??

please a litter higher resolution on the pics ?!

/

 

[marsupialx]

Couldn't tell you how it sounds, still missing pieces, such as opamps.

 

[cowanrg]

jeff,

if you dont mind, i could host the big pictures you send me on my website. i have the space for them, and people could see them in high res

looks great though. even though im not 100% sure of why you are doing some of the things you are doing.

 

[marsupialx]

Hey Robert, that would be groovy if you would post them so people could see them. There are reasons for most decisions, one was visual, but one was easy availability of both boards for configuring, and 9v batteries (4 per side) fit into the outriggers. - Jeff (marsupialx)

 

[cowanrg]

sounds good. I'll toss them up on my site once i get home from work.

 

[tiroth]

Very impressive Jeff.

My apologies to you and everyone else who requested 1uF caps via Jens--I put all of them in the mail today. If you don't have them by the end of the week, shoot me some mail.

 

[cowanrg]

ok everyone, here are the bigger and prettier pictures on my website.

very nice job. i like the form follow function idea.

http://www.cowanrg.mesanetworks.net/projects/images/mox1web.jpg

http://www.cowanrg.mesanetworks.net/projects/images/mox2web.jpg

http://www.cowanrg.mesanetworks.net/projects/images/mox5web.jpg

 

[marsupialx]

Another reason decisins were made is the materials were laying around. I didn't go out and buy the aluminum, I just took stock on what I had and designed around that.Eventually I'm going to do another similar unit with 4 boards per side. Then six channels of tube amps and a tube preamp along similar design aestectics. But that is on down the road. - Thanks to everyone involved in making the boards available. Way cool. - Jeff

 

[marsupialx]

The triangle little unit 'logo thing' is a storage box for jumpers. I just needed to do something frivolous.

 

[Ed LaFontaine]

Sloshing through Slew Rate

I find an advisory in ADN003 that says an op-amp's slew rate should be greater than "2pi Vout p-p fc". Could someone shed some light on this for me? Is it frequency dependent (different for high or low fc)?

Also, has anyone measured the performance of the discrete op-amp?


I attach a worksheet for a better understanding of op-amp spec's. For an excel copy of the worksheet, send me an e-mail request.

 

[JensRasmussen]

Not sure if this is right, but it seems to me that SR = 2 x pi x f x A where

f = freq
A = amplitude [V]

An externally hosted image should be here but it was not working when we last tested it.

\Jens

 

[Ed LaFontaine]

Slew Rate

OK,
I get the part where 2 pi=6.2832.

My remaining question is: What p-p voltage should we expect going through the Mox op-amps?

3 volts p-p entered into the equation tells me the Slew Rate needs to be around 19. However some of the op-amps deemed acceptable, ie. NE5532 have a slew rate of 8.
I'm trying to understand if this indicates a shortcoming of some chips or is the voltage to high?

Mongo can hunt and gather but this is to high on the tree. Can I get a ladder?

 

[JensRasmussen]

I get 0.19 [V/µsek] at 20 khz 3 V pp (A=1.5V)

 

[moamps]

Re: Sloshing through Slew Rate

Also, has anyone measured the performance of the discrete op-amp?

http://www.diyaudio.com/forums/show...=32095&perpage=10&highlight=mox&pagenumber=20

post 193

Regards
Milan

 

[Ed LaFontaine]

I see.
So op-amps with a slew rate above 2 should be more than adequate.
Thanks, Jens
And also for the caps!

 

[Ed LaFontaine]

Thanks Milan,
I had forgotten that post.

OVER 4V/uS.

 

[JensRasmussen]

I see.
So op-amps with a slew rate above 2 should be more than adequate.

I suppose it’s a matter of opinion if it’s adequate or not. If you only look at slew rate and limit yourself to small signals below 20 kHz.

If Vpp = 24V and f=100 kHz you need a SR of 7.5 V/µsek.

This is a large signal case, and since the signal levels from a line out are much smaller, it should not be necessary with more than

Vpp = 10V and f=100 kHz you need a SR of 3.2 V/µsek.

\Jens

 

[chipco3434]

Bunch of newb Q's

This project has had some small issues...

Note to self: Try to keep those trimmed resistor leads out of wife's foot.

Now the questions:

1. Anybody have a Mouser part number for the 8 pin dip sockets? Being new to this, there are at least 50 variations on this theme. Ordering the correct part the first time will help me keep the price down.

2. It would appear that the dip sockets must be used to get the height of the discreet boards above the height of C801-4 & C901-4, right?

3. I am unable to identify the components associated with C001 and C002, C200 & C500, and C800 & C900. I could use the values and even better, some part numbers.

4. Is the nomenclature of a 4.7k resistor normally expressed as "4k7"? While we are talking about it, where does it go?

Thanks to all in advance!

 

[chipco3434]

I almost forgot...

parts list calls out a C1 of 100pF on the opamp but I don't see it on the board???

Could use the help.

Thanks

 

[tiroth]

Re: Bunch of newb Q's


1. Not offhand, but if you order a gold-flashed machined-pin socket you can't go wrong. Often available cheap as surplus.

2. It helps, but if that is the only reason you are using a socket it would be better to hard-wire and just lay the caps on their side, or on the underside.

3. These compensation caps are not needed with the discrete opamp, nor with the IC ones I've tried.

4. Yes. You can place it on the opamp board, or on the underside of the MOX board.

(5) I think you are mistaken--there is no part C1! Don't confuse moamp's designators with mine. I suggest you take a look at the opamp guide, there are some good pictures to help you out.

http://www.anidian.com/audio/construct/opa_1.shtml

Good luck, and don't be afraid to come back with more questions.