Iv
Martin, that SAA7220's 1dB up is to compensate the dac's and around opamp filter's 1 dB down i reckon.
Simon: for a quick and good sounding solution you can also try a THS4032 opamp. But check in the datasheets & SM the voltages for the opamps. In a CD304 it plays and sounds really good. You have to solder an smd ths on a 8 pin socket. I soldered also 2 small MKS caps on the socket.
Martin, that SAA7220's 1dB up is to compensate the dac's and around opamp filter's 1 dB down i reckon.
Simon: for a quick and good sounding solution you can also try a THS4032 opamp. But check in the datasheets & SM the voltages for the opamps. In a CD304 it plays and sounds really good. You have to solder an smd ths on a 8 pin socket. I soldered also 2 small MKS caps on the socket.
No risk there Simon.
Well, it will have less in the signal path, and less opamps so it might be of benefit. I use it because my DAC was scratch built and it was simple to do to have something up and running.
The other option is to make a discrete IV stage, like Jocko's or similar. There's a few about on the forums.
Thomo, well its not exactly gain, as you're changing current to voltage.
I think its quite close to ohms law (also, you can think of it as an inverting op amp, with the input resistor set to 0 ohms), so Vo = -(Iin*Rf).
I know I have 1.6k feedback resistors, so I think that'll give me 4ma*1600ohms = 6.4V pk-pk ~= 2.24V rms.
Well, it will have less in the signal path, and less opamps so it might be of benefit. I use it because my DAC was scratch built and it was simple to do to have something up and running.
The other option is to make a discrete IV stage, like Jocko's or similar. There's a few about on the forums.
Thomo, well its not exactly gain, as you're changing current to voltage.
I think its quite close to ohms law (also, you can think of it as an inverting op amp, with the input resistor set to 0 ohms), so Vo = -(Iin*Rf).
I know I have 1.6k feedback resistors, so I think that'll give me 4ma*1600ohms = 6.4V pk-pk ~= 2.24V rms.
Its fairly easy to knock up a simple op amp IV - just make sure you don't forget the capacitor in parallel with the resistor in the feedback path - or you might get oscillation and heat 
and distortion.
(but don't worry, it can be simple to do).
Also, a servo might be pushing it, but instead, a current source into the IV stage can be used to bias the output so it has zero DC offset, and thus no capacitor required. The DAC output swings from 0A to -4mA (so the output swings from 0v to +6.4v, so if you add 2ma to the input, then the centre point will be output at 0V (so -3.2 to +3.2v).
I guess it can drift with temperature (hence a servo would be better), but its probably negligible.
and distortion.(but don't worry, it can be simple to do).
Also, a servo might be pushing it, but instead, a current source into the IV stage can be used to bias the output so it has zero DC offset, and thus no capacitor required. The DAC output swings from 0A to -4mA (so the output swings from 0v to +6.4v, so if you add 2ma to the input, then the centre point will be output at 0V (so -3.2 to +3.2v).
I guess it can drift with temperature (hence a servo would be better), but its probably negligible.
Correction?
I think the DAC swings 2mA and draws a constant current of 2mA with can be nulled with a 2mA Constant Current Source like in the Pedja Rogic DAC.
philpoole said:Its fairly easy to knock up a simple op amp IV - just make sure you don't forget the capacitor in parallel with the resistor in the feedback path - or you might get oscillation and heat
(but don't worry, it can be simple to do).
Also, a servo might be pushing it, but instead, a current source into the IV stage can be used to bias the output so it has zero DC offset, and thus no capacitor required. The DAC output swings from 0A to -4mA (so the output swings from 0v to +6.4v, so if you add 2ma to the input, then the centre point will be output at 0V (so -3.2 to +3.2v).
I guess it can drift with temperature (hence a servo would be better), but its probably negligible.
I think the DAC swings 2mA and draws a constant current of 2mA with can be nulled with a 2mA Constant Current Source like in the Pedja Rogic DAC.
Alas, looks like Pedja's site is essentially no more....
http://www.pedjarogic.com/index.html
Ho hum.
http://www.pedjarogic.com/index.html
Ho hum.
That site was there yesterday! Lee, I think he has better stuff to do than following every DIYer out there seeing if they're building his stuff!! (not-for-profit in our case anyway)
They may have accidentally broken the site, let's hope it's back up soon, it made terrific reading.. even if I only half understood most of it
Simon
They may have accidentally broken the site, let's hope it's back up soon, it made terrific reading.. even if I only half understood most of it
Simon
Hi Simon,
read his announcement, Im not sure I agree with all of it, but he has every right to take his pages down I guess. Still I liked his work and wish Id saved some of his schematics.
http://www.pedjarogic.com/announcement.htm
read his announcement, Im not sure I agree with all of it, but he has every right to take his pages down I guess. Still I liked his work and wish Id saved some of his schematics.
http://www.pedjarogic.com/announcement.htm
Hi Luke,
I saw that a couple of weeks ago and whilst it's very sad I do think it's also all very true, even inevitable. I think he is a little naive to even comment on how a Chinese company has copied some of his circuits... after all nearly all the world's counterfeit goods originate in China.
The thing he ought to remember is that without his free sharing of knowledge people wouldn't have the chance to admire and respect his designs, and then there'd be no incentive to buy anything from his company. Having built his wonderful-sounding and simple buffer I would certainly not hesitate to spend money with his company.
Simon
I saw that a couple of weeks ago and whilst it's very sad I do think it's also all very true, even inevitable. I think he is a little naive to even comment on how a Chinese company has copied some of his circuits... after all nearly all the world's counterfeit goods originate in China.
The thing he ought to remember is that without his free sharing of knowledge people wouldn't have the chance to admire and respect his designs, and then there'd be no incentive to buy anything from his company. Having built his wonderful-sounding and simple buffer I would certainly not hesitate to spend money with his company.
Simon
It just takes a little Googling to find things these days:
http://www.diyaudio.com/forums/showthread.php?threadid=22206
I can't paste it (the URL is incompatible with this forum lol) but if you Google for pedja rogic discrete i/v stage you can open Google's cached HTML version of Pedja's commentary on that I/V stage.
Simon
http://www.diyaudio.com/forums/showthread.php?threadid=22206
I can't paste it (the URL is incompatible with this forum lol) but if you Google for pedja rogic discrete i/v stage you can open Google's cached HTML version of Pedja's commentary on that I/V stage.
Simon