Ahh yes true, the question is not if its there, there is no way to avoid it, the question is what is the proposed solution? 
In anycase, I have listened to this pre for hours on end both with headphones and a variety of power amps, and I at least have not suffered from any fatigue.
Cheers!
Russ
In anycase, I have listened to this pre for hours on end both with headphones and a variety of power amps, and I at least have not suffered from any fatigue. Cheers!
Russ
Err if I may comment....
jackinnj does have a point about noise from the PIC's osc (internal osc in this case). At work, the EMI guys are always worried about oscillators in my designs. Done right, I doubt noise from a 4MHz osc would make its way into the audio chain but purists will be purists (I doubt my EMI guys too - it's ridiculous all the filtering they want me to implement but I digress).
There are ways to deal with it as jackinnj mentioned such as lowering freq, adding resistors, layout optimizations, etc. However, if we want to be purists, we can take a leaf from the big dogs and implement sleep mode. The PIC only wakes up whenever there's a change in the control (e.g. pot tied to ADC, pushbuttons), sends the new value to the PGA2310 and goes back to sleep.
At work, I use a similar EMI probe - a coil wrapped around the tip of a pencil. Makes a nice sniffer. All in all, Russ has made a nice little preamp - low cost but with high quality parts.
One last thing, I recall the PGA2310 datasheet mentioning about the need to drive the inputs from a low impedance source, otherwise distortion worsens.
jackinnj does have a point about noise from the PIC's osc (internal osc in this case). At work, the EMI guys are always worried about oscillators in my designs. Done right, I doubt noise from a 4MHz osc would make its way into the audio chain but purists will be purists (I doubt my EMI guys too - it's ridiculous all the filtering they want me to implement but I digress).
There are ways to deal with it as jackinnj mentioned such as lowering freq, adding resistors, layout optimizations, etc. However, if we want to be purists, we can take a leaf from the big dogs and implement sleep mode. The PIC only wakes up whenever there's a change in the control (e.g. pot tied to ADC, pushbuttons), sends the new value to the PGA2310 and goes back to sleep.
At work, I use a similar EMI probe - a coil wrapped around the tip of a pencil. Makes a nice sniffer. All in all, Russ has made a nice little preamp - low cost but with high quality parts.
One last thing, I recall the PGA2310 datasheet mentioning about the need to drive the inputs from a low impedance source, otherwise distortion worsens.
maxw said:
Believe me that fact did not escape me.
But think.... hmmmm how many people have 600ohm sources??? And if they did they would probably need/want a buffer/linestage of their own discrete from the preamp.
Yes, if you had something with greater than 600ohm output impedance on the input of the preamp you would indeed need an input buffer. No (well except one tube DAC I have but have not dusted off in years) source I (or most people) have comes even close to that high an output impedance. So I have no worries there, it would be easy to add one, but the cost would go up by about $8.50 for a buffer(AD8620) which most will not need. It would be better to allow those who really need the input buffer just to add a simple line stage.
I have tested and measure now with source from around 1 to 100 ohms, and the performance is excellent and the THD is well within the specs.
More later after I have compiled all the data and finished the board.
But rest assured with <600ohm source (which is most of them) no input buffer is necessary. My first version actually (which was then actually Mauro's) was modified with an input buffer, but it only helped with tube sources and such.
Cheers!
Russ
Ok I just got an email from a good friend who wants one of these, and he happens to have a tube CDP....
So, I guess sice I value his friendship very much I will consider a modification the PCB which will allow for an "optional" input buffer which can be omitted if it is not needed.
Thanks for all the good input.
Cheers!
Russ
So, I guess sice I value his friendship very much
I will consider a modification the PCB which will allow for an "optional" input buffer which can be omitted if it is not needed.Thanks for all the good input.
Cheers!
Russ
As you wish!
Here is a version which allows an input buffer. The input buffer can be omited by simply omiting all the components related to it and running a wire or low value resistor from the pad closest to the input header on R4/R5 to the pad just beyond the end of the resistor to form a jumper.
That should please those of you that need a buffer, and those who don't want an eatra component in the signal path that does not need to be there.
Cheers!
Russ
Here is a version which allows an input buffer. The input buffer can be omited by simply omiting all the components related to it and running a wire or low value resistor from the pad closest to the input header on R4/R5 to the pad just beyond the end of the resistor to form a jumper.
That should please those of you that need a buffer, and those who don't want an eatra component in the signal path that does not need to be there.
Cheers!
Russ
Attachments
After all this talk about input buffering for the PGA2310, Russ is right. Most sources have low output Z, so need for buffering is rare.
Case in point, the few hi-fi preamps that I do know uses this chip (e.g. CJ's Sonographe, Bel Canto) do not have an input buffer nor output buffer. They claim no "external" negative feedback other than what's inside the PGA2310.
Oh well, Russ did put in an optional buffer. Very fast work. Sorry Russ, I didn't mean to stir the pot but it's very nice of you to be so accomodating.
Case in point, the few hi-fi preamps that I do know uses this chip (e.g. CJ's Sonographe, Bel Canto) do not have an input buffer nor output buffer. They claim no "external" negative feedback other than what's inside the PGA2310.
Oh well, Russ did put in an optional buffer. Very fast work. Sorry Russ, I didn't mean to stir the pot but it's very nice of you to be so accomodating.
Thanks for that Arius.
I actually only added the output buffer for those who wish to use this as a headphone amp, but that actually be easily omitted by simply leaving out all the components for the outputbuffer and running a wire from the output to the pin header, or even more simply by forming a solder bridge or soldering a small piece of wire on the pads for the AD8620.
Cheers!
Russ
I actually only added the output buffer for those who wish to use this as a headphone amp, but that actually be easily omitted by simply leaving out all the components for the outputbuffer and running a wire from the output to the pin header, or even more simply by forming a solder bridge or soldering a small piece of wire on the pads for the AD8620.
Cheers!
Russ
GeWa said:
Yes true.
I have ordered the beta PCBs and have done a lot of coding. The PIC now sleeps until the pot is moved at which time it wakes up, sends the serial data to the PGA2311 and goes back to sleep. Wish I had it that easy. This thing is really really quiet and smoooooth.
Now with options for both input and output buffers you could use this thing with just about any source or poweramp/headphone.
Cheers!
Russ
Hey guys, would the kits be coming with a programmed chip for the poor bums (i.e. me) without a programmer? How much is the full kit going to cost?
Are we going to be able to order from the site? I wanted to have a go building a pre before I have a go at the full-blown Mauro amp
--Nathan
P.S. Sorry if you've covered that stuff, I'm supposed to be studying for exams so I didn't have time to read everything
::EDIT:: Fixing typos
Are we going to be able to order from the site? I wanted to have a go building a pre before I have a go at the full-blown Mauro amp
--Nathan
P.S. Sorry if you've covered that stuff, I'm supposed to be studying for exams so I didn't have time to read everything
::EDIT:: Fixing typos
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