[ble0t]

I've added something nearly identical to what the DDDAC uses (i.e. an AND gate) to account for this...thanks for catching that dsavitsk

 

[dsavitsk]

Which part did you use? There is a single AND gate at Digikey made by toshiba, but they only have 80 in stock and it is being discontinued. Mouser has a similar one from Fairchild, but the sot-23 size is out until september and the only one they have is a so-70 size (I am unable to find anyting in Eagle with that footprint.) Did you go with the full size 4 gate version?

 

[ble0t]

TI to the rescue again...$0.39 part at Digikey and they have thousands in stock...

http://focus.ti.com/docs/prod/folder...74ahc1g08.html

 

[Clutz]

Any updates?

 

[Clutz]

How are we going to go about programming this thing.. It is a PIC isn't it?

Other than that, excluding the costs of various resistors, capacitors, a DC power source, the crystal and the crystek oscillator, it looks like the cost for the parts is going to be just under $100 ($110CDN). It seems to me that it's pretty much on track for cost.

Re: IC7 and IC12 - do you think the THS4631 would work well here, or would it have a problem with oscillations? I've got a bunch of these, thinking I was going to try them out in my PPA (but I haven't yet.. I don't really feel like buggering around with it, swapping resistors, etc), so I figured that this might be a good use for this - or is there going to be any benefit from using an opamp that's better than the 134? (e.g. 8610, which I also have two of, or 2227/2228)? My concern about anything other than the 132/134 is that they might oscillate, and since they're SOIC, it'd be a real PITA to swap them off if they did do that.

Sorry ,I'm just getting really excited about this. I have parts coming in for a TDA1541 DAC, and the dynalo.

 

[ppl]

Quote:

Originally Posted by Clutz How are we going to go about programming this thing.. It is a PIC isn't it? Other than that, excluding the costs of various resistors, capacitors, a DC power source, the crystal and the crystek oscillator, it looks like the cost for the parts is going to be just under $100 ($110CDN). It seems to me that it's pretty much on track for cost. Re: IC7 and IC12 - do you think the THS4631 would work well here, or would it have a problem with oscillations? I've got a bunch of these, thinking I was going to try them out in my PPA (but I haven't yet.. I don't really feel like buggering around with it, swapping resistors, etc), so I figured that this might be a good use for this - or is there going to be any benefit from using an opamp that's better than the 134? (e.g. 8610, which I also have two of, or 2227/2228)? My concern about anything other than the 132/134 is that they might oscillate, and since they're SOIC, it'd be a real PITA to swap them off if they did do that. Sorry ,I'm just getting really excited about this. I have parts coming in for a TDA1541 DAC, and the dynalo.

that THS4631 is made for this application with the exception of having a high input impedance as oposed to the low impedance that DA chip likes otherwise speed and open loop gain are all good as is the voltage noise whitch is similer to the AD-8610 however the input bias current of the Ti part is about an order of magnatude greater than the AD8610 however since you are operating at low impedances voltage noise is of more importence. its a trade off because you need high open loop gain so that eliminates most high speed opamps with the exception of this TI chip.

However i think the ideal Op amp for an I/V convertor stage is somthing like this http://focus.ti.com/lit/ds/symlink/opa860.pdf

 

[Clutz]

Quote:

Originally Posted by ppl that THS4631 is made for this application with the exception of having a high input impedance as oposed to the low impedance that DA chip likes otherwise speed and open loop gain are all good as is the voltage noise whitch is similer to the AD-8610 however the input bias current of the Ti part is about an order of magnatude greater than the AD8610 however since you are operating at low impedances voltage noise is of more importence. its a trade off because you need high open loop gain so that eliminates most high speed opamps with the exception of this TI chip. However i think the ideal Op amp for an I/V convertor stage is somthing like this http://focus.ti.com/lit/ds/symlink/opa860.pdf

Hi ppl,

Thanks for the feedback. I think I'm going to go ahead and use this THS4631 chip then. I'm not worried about the THS4631 having a high input impedence, because the DA chip is running into the OPA1632, so the OPA1632 will see high input impedence of the THS4631, not the DA chip itself.. Or do I have that wrong?

Cheers!
Clutz

 

[ble0t]

We're very close to presenting the 'final' version of board.

Yes, that is a PIC to control the CS8416...I have a friend who can easily take care of the code and burn a limited number of chips for our use. Even if the board is finalized by the end of the weekend, it's going to take a bit to get a proto or two done and fully tested, especially with the PIC involved. But, things are finally starting to move along.

I'll keep you all posted

 

[Clutz]

Great news ble0t! I'm very excited to see the revisions. Let me know how much it'll cost you to prototype the boards and I'll send some money your way to help offset the costs. I can either send it to you paypal, or if you prefer- via a cheque.

Looking forward to it!

Cheers,
Brad

 

[MegaMeee]

Quote:

Originally Posted by Clutz Great news ble0t! I'm very excited to see the revisions. Let me know how much it'll cost you to prototype the boards and I'll send some money your way to help offset the costs. I can either send it to you paypal, or if you prefer- via a cheque. Looking forward to it! Cheers, Brad

Yeah I will as well... Although only if you can it via paypal.

 

[00940]

Clutz, PPL : the I/V function is performed by the OPA1632. Its specs are not that bad compared to the ths4631 : voltage noise at 1.3nV compared to 7nV for the ths4631, open loop gain is at 78db to 80 for the THS4631, gain bandwith is 180mhz compare to 210 for the THS4631.

The opa134 afterwards is only a differential receiver to turn the signal to unbalanced. We used it rather than a drv134 to allow people to configure it as a second filter if they wish so and to change the output opamps to tailor the sound of the dac to their liking. If cost is no object you can use there any opamp which is comfortable with +/- 6VDC rails. Bypassing is quite good, so stability shouldn't be too much of a problem.

 

[Clutz]

Hi 00940,

Thanks for clearing that up. I knew that the OPA1632 was doing the I/V, but I had forgotten about converting balanced to unbalanced. I'm only going to use the THS4631 because I've got a bunch of them lying around (but I also have a bunch of 227s) in the SOIC format, and I don't have any 134s - so might as well! It'd still leave me with three - plenty to get some browndogs and try sticking them in my PPA at another time.

Re: schematic and layout.

 

[SnoopyRocks]

The input impedance is being misinterpretted here. With closed loop operation, you cannot simply take the input impedance. In fact, the impedance seen looking into the opamp small, roughly (Z_f+Z_o)/A_o, where Z_f and Z_o are the feedback and OpAmp output impedances. A_o is the loop gain. The impedance seen by the DAC would be the parallel combination of the actual input impedance and this effective impedance, resulting in a small overall impedance.

 

[Clutz]

Thanks Snoopy!


On an unrelated note, has anyone heard anything from Francis Vaughn lately?

 

[MegaMeee]

I'm sure he's busy doing at uni doing his job... I know i'm busy doing the assignments he has written