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Swapping class AB amp linear supply with a SMPS - incl measurements

restorer-john

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That M-Audio Audiophile192 was one of the best PCI cards you could get at that time at almost a bargain price.

Yeah, it sits in an old Win7 backup PC next to my lab bench and to be honest, I only fire up that PC to keep the RTC alive and check on my old faithful machine every now and then. But, that card (and the Delta 24/96) cards were really good. Better in many ways than the outboard USB Focusrites etc.
 

Sokel

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Interesting. I killed the WiFi, bluetooth and all my SMPS/LED supplies etc and ran the PC on the LAN and it was still there back when I got the sh#ts and just left it. But... there was an internal PCI WiFi card in the PC, right near the M-Audio card. I'm gonna pull it out and see if that does the trick.

This is what the old M-Audio AP 24/192 will do on loopback:View attachment 264476
Is your PC case painted?
I had the same and I fixed it after the advise of my nephew's PC enthusiast friends.
My case is a little strange with absorbing panels inside,anodized alu and the PSU on the bottom.
So they made me scratch the metal a little at the points that the PSU screws on the case and tighten it with copper screws instead the nice black alu ones.
They also bended a little the I/O panel,scratced the edges of the case so it contacts nicely with each other.
This fixed almost every noise related issue,see my noise floor with the poor EMU (no averages):



NS.PNG


Edit: Plus with 128 averages so we can see every little spike,the one at 2Khz is probably fan or something:



128.PNG
 
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Chrise36

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That M-Audio Audiophile192 was one of the best PCI cards you could get at that time at almost a bargain price. 12 years ago I modified mine a bit by placing extra RC's at the + an - 12V lines and replaced the NE5532 by LM4562 op-amps. My Lab system PC was a dual core Athlon at that time running XP on an Asus mobo, Matrox entry video card next to the Audiophile card and a no-name 450W standard power brick. No special measures apart from careful audio cabling (balanced loop-back). The result:

View attachment 264493

I think AKM was way ahead with their AD/DA converters. Nearly no PC related harmonic spurs! Only a slight 3rd harmonic. You will have hard times to get a better result with external USB cards today. My current Topping D30Pro - E1DA measurement combo does not better! (But also not worse ;) )
Any idea how it measured before your impovements?
 

Piere

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It's a long time ago. As far as I remember THD improved the most by replacing the op amps by around 20 dB.
 

Piere

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Duh, is this a memory exam? It is what you see. Note that noise in measurements is usually a matter of noise bandwidh.
 

Chrise36

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Duh, is this a memory exam? It is what you see. Note that noise in measurements is usually a matter of noise bandwidh.
Ofcourse not just asking to know how capable one of these would be to do some basic measurements because i see some used ones dirty cheap
 
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Piere

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It's in the unobtainable box for many year now. They were sold out at the time for about 75 - 95 bucks or so. Regarding soundcards there is not much progress last 10 years IMHO.
 

egellings

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The Hypex does not. The DC rails fluctuate up and down with the incoming mains AC, exactly like a linear supply does.
Then the switchmode supply must be varying the on-time pulse width of the output signal to correct for that.
 

Piere

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No, it is by design. Most Hypex SMPS are just a HF transformer and not regulated.
 

restorer-john

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Ofcourse not just asking to know how capable one of these would be to do some basic measurements because i see some used ones dirty cheap

If you have an older PC with an actual PCI slot (not PCIe), find the AP (Audiophile) 24/192 card and make sure you get the wire dongle with the 6 1/4" TRS leads.

It's perfectly valid as a measurement device now, but remember, it will need a Win7 install. The Vista drivers work perfectly with Win7. I've never tried to use those old cards in a win10 box, because none of mine have a legacy PCI slot.
 

restorer-john

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It's a long time ago. As far as I remember THD improved the most by replacing the op amps by around 20 dB.

That's a huge difference to an already great performance. I have a soft spot for those old M-Audio cards- the SPDIF in/out is good too.
 

Chrise36

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If you have an older PC with an actual PCI slot (not PCIe), find the AP (Audiophile) 24/192 card and make sure you get the wire dongle with the 6 1/4" TRS leads.

It's perfectly valid as a measurement device now, but remember, it will need a Win7 install. The Vista drivers work perfectly with Win7. I've never tried to use those old cards in a win10 box, because none of mine have a legacy PCI slot.
Ok thanks i have to check it out
 

Piere

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A Mobo with that old legacy PCI becomes rare nowadays. The beak out cable of the card was not that good. The female jack connectors did not make reliable contact. I replaced the cable wich a better one with XLR connectors. For comparison the current MOTU M2 I have in use today in loop back. Concerning distortion not as good as that old M-Audio Audiophile192. But not bad either.

Motu M2.png
 

Chrise36

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I have a fairly old pc with the ASUS M4A78 mobo i think it does the job
 

JonP

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WIFI and/or Bluetooth - I think it was. I did find the source but now I forget, but pretty sure it was WIFI. Switch off all radios - routers, laptops, desktops, phones, repeaters, taplets etc anything that transmits OR receives WIFI.
Heh.. yep... Any strong enough RF source can mess with the gear, thru getting rectified/detected by diode junctions in the gear and making AF noise.
One time at a company designing a implantable defibrillator, with sensitive ECG inputs... we had a noise problem. Strange, intermittent, hard to track down. But we had to, this was a implantable medical device. Whole R&D group are involved. Finally, after a couple of weeks, I discovered it was the RF from the cell phone in my pocket, being picked up by the HV differential probe on the scope, NOT our device, and only when you were standing very close! A phone, even when not on a call, will blip out a "here I am" every so often so the cell system knows about it.
I'd experiment with looking at your measurement system's baseline noise, but with all the normal leads, etc. I would say you probably don't have to turn off all your wireless stuff, but the nearer it is the more likely it is to interfere. So, yes the wifi in the test laptop would be more likely to cause issues, but the house router 20-30ft away possibly not. Don't put your phone down on the test bench. ;-) And, just about always, there is no RX only wifi devices, they all talk back and forth, so watch your wireless plugs and other less expected things.

With the E1DA ADC, I'm seeing all kinds of cray sheet. I see a rolling HF noise floor if I have the cheap LED garage lights turned on, above the measurements. I have to turn my lights off!
Now, there's a lousy/badly filtered SMPS! Good thing you're not a Ham or SWL... some of those cheap products are terrible RF noise generators. But if you can save 5-10% of the unit cost by skipping decent filtering, and fake a Gov cert label (since Gove checking is spotty) think of the money you would make! And, I've heard of some lights being pretty quiet... problem is you pretty much have to test them yourself.

Anyway, good work on trying the supplies and measuring the results. Its the only way to really know.. well, its better than just hearing hum and hiss or not. And, can teach you what needs to be done to improve it even more.
 
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Chrise36

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A Mobo with that old legacy PCI becomes rare nowadays. The beak out cable of the card was not that good. The female jack connectors did not make reliable contact. I replaced the cable wich a better one with XLR connectors. For comparison the current MOTU M2 I have in use today in loop back. Concerning distortion not as good as that old M-Audio Audiophile192. But not bad either.

View attachment 264825
Hi i just received mine where did you buy the cables? i find them quite expensive
 
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