Audio Op Amp power

I need an amplifier front end for my dsp audio and I'm wondering what exactly I should do.

I think the main use will be for a guitar effects processor but I think I'll also want something that processes audio in general(not sure if I need to make a distinction?).

I'll be using the PCM1804 for the ADC conversion and I'll be putting an amplifier front end on it to try and get the max resolution. (So, say, it will be calibrated to the input signal).

On the datasheet for the ADC it says the analog input voltage is -0.3V to (Vcc + 0.3V).

I'm not sure whats up with the -0.3V but in any case Vcc is from -0.3V to

6.5V.

I think because of convience I'll be using Vcc at 5V and I'll want to minimize the power supply devices I'll need.

Now the op amps I've been looking at for audio say the min Vcc is 5V. I'm wondering if its a good idea to run at the min voltages?

Right now I need a power supplies of 3.3V for the DSP, ADC, and DAC; 5V for ADC and DAC and then the supplies with for the op amps(buffers, filters, and amplifiers). I'd like to use the same power supplies instead of creating a new one. I will of course need a negative rail also so I was hoping that all I need is 3.3V and +-5V but I'm a little worried about using the +-5V on the op amp since its the min supply voltage. Not sure if it will cause any problems?

Also, would there be any special considers I need to worry about for different types of inputs into the op amps? Are there better configurations than just the simple stuff you learn in any basic text book? (I was thinking of just using a fully differential op amp configured as an inverting amp)

Ultimately I rather not use the op amps if possible because it causes me to need to have a negative supply but maybe this isn't difficult with with some of the ic's available now days?

Is there any good books on audio circuits with mainly practical knowledge? I'm just really afraid of using some of the stuff I've learned from basic EE books and it not cutting it in the real world. (I do have the AOE which I need to re read again).

Thanks, Jon

Reply to
Jon Slaughter
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I guess a few things I'm not sure of besides running at the min voltage is if order matters and if I should do things even though its not necessary.

For example, I need to filter the input and amplify it. Does it matter which order? (of course it shouldn't but maybe it does in practice) Also, should I buffer the input first even though its going to an amplifier that I would imagine also is sorta acting like a buffer.

I think I could probably combine the filter, buffering and amp all into one circuit and just use one op amp?

Thanks, Jon

Reply to
Jon Slaughter

Jon, it's admirable to make a circuit from scratch, but you can first work with a professionally-designed circuit to see how it works and get some experience. One issue is making the hardware-software interface work. For example, many digital audio compaines, such as Creative and E-Mu, use 24-bit 48 or 96kHz A/D converters with a standard audio/digital interface data stream called ASIO. Most of the relevant hardware is available cheaply on eBay, to help you get off to an easy start.

For example, the Creative USB Sound Blaster, Audigy 2 NX, (model SB0300) has two stereo 24-bit A/D inputs and both USB and optical outputs, and meets the ADIO standards. You can get used ones on eBay for $40 to $70. This one went for $40, although that was likely a bit of a fluke.

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USB Sound Blaster Live! may be another possibility.

If you want better, more professional, but still cheap stuff, check out E-MU products on eBay, like the 0202.

Reply to
Winfield

It is really hard to hand wire the SSOP package. Not impossible, but I don't think I ever did a dead bug on a chip with so many pins.

A good trick if you can do it is to get the evaluation board for the part. I don't know about TI, but Crystal sells them, and they occasionally end up on the surplus market.

Looking at the TI design, I cringe at the 10uF polarized caps in the audio chain. Assuming you are willing to waste some space, you can go non-polarized.

I suspect you could just take an eval board and tweak it a bit (better components) and get better performance than some Creative or M-Audio box. But certainly at a higher price.

Just the fact that you don't use the USB port for a power supply would be an improvement.

Reply to
miso

Someone should write a book entitled "The Art of Designing Circuits for Art of Electronics Books". :P

I'll guess ... level shifter and rail to rail op amp for the front end.

When it comes to power supplies, I believe the dynamic range of the op amp output and the ADC conversion range should match up. The spec in your post looks like an absolute max spec (just before poof).

D from BC

Reply to
D from BC

On Fri, 10 Aug 2007 01:17:21 GMT, in sci.electronics.design "Jon Slaughter" wrote: snip

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and this is a bit expensive

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Martin

Reply to
Martin Griffith

If your saying I should first work in the software out I have already played with some FIR's(mainly delays) using matlab and non-real time processing. I long time ago I got interested in asio a bit but never really could find decent information on it. (Steinberg has some SDK or something. Although I thought about first doing my project entirely for the pc and using either VST's or asio I think I'd rather learn about the hardware(I'm mainly doing this for the hardware. Conceptually I think I got it down but I know thats only part of it).

Besides, the newer sound blaster cards are pretty bad. The Live and Audigy both have some type of "glitch" problem where they overload the pci bus and cause the computer to "stutter". (I do have the audigy 2 BTW)

In any case I do not think the software side is going to be an issue(simply convolutions) and I have done enough programming in my time that I can figure that part out on my own. What worries me is the hardware... but I guess that might be why I want to do it ;)

Thanks, Jon

Reply to
Jon Slaughter

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Thanks, I'll try and check them out.

Jon

Reply to
Jon Slaughter

How well do these USB widgets work in the unavoidable presence of ground noise?

Clifford Heath.

Reply to
Clifford Heath

The 24-bit A-D's used in the E-MU and Creative products have differential inputs, and this type of circuit connection can be continued all the way back to the input, but I don't know whether the E-MU and Creative products have done so. My gut feeling is they have a better chance of making quiet preamp circuits in USB modules, compared to PCI-bus boards.

But I should report that E-Mu's 1212 PCI-card stereo A/D type is working well for us in an extremely-sensitive experiment. BTW, the E-MU 1212 uses AKM's ak5394 24-bit 192kHz A-D chip,

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Our PC is a Lenovo (i.e. formerly IBM) minitower.

Reply to
Winfield

So are you feeding full-differential inputs? Or is your DUT only earthed through the sensor's earth connection? Otherwise what kind of connection is working for you?

Clifford Heath.

Reply to
Clifford Heath

I made sure the sensor doesn't have an earth connection.

Reply to
Winfield

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