Im building a commercial phono pre, im mostly a digital and mixed signal instramentation, with some rf type of guy. I have built a few preamps for guitars/mics and some head amps etc.
This amp has some hush hush features that have never been done and is a precusor to a 100% digital dsp model. As for this mostly analog design i have pretty much every chip ready to experiment with from lt1115s to 553*s and all kinds of audio buffers along with chips like the uaf42. I know how i want to implement everything special in this. The one thing i need to experiment with is the riaa stage either active or passive.
I was wondering is anyone could give me a list of values for the passives most used in passive and riaa networks. I know they all need to be .01% thin film resistors and polyester/film caps at 1%. Id just like a list of values that can cover most any design i want to play with. Is there any advice like this out there, like a passives kit list for phono designers?
This amp has some hush hush features that have never been done and is a precusor to a 100% digital dsp model. As for this mostly analog design i have pretty much every chip ready to experiment with from lt1115s to 553*s and all kinds of audio buffers along with chips like the uaf42. I know how i want to implement everything special in this. The one thing i need to experiment with is the riaa stage either active or passive.
I was wondering is anyone could give me a list of values for the passives most used in passive and riaa networks. I know they all need to be .01% thin film resistors and polyester/film caps at 1%. Id just like a list of values that can cover most any design i want to play with. Is there any advice like this out there, like a passives kit list for phono designers?
The classic Lipshitz papers derived the (Laplace) transfer functions of a few different RIAA topologies. They are only valuable because the algebra is error-prone and lengthy; thus Lipshitz instructed 100 grad students to do the work and 100 more grad students to check the work. Followed by 3 reviewers double-checking the work before publishing in JAES.
However this approach is now obsolete thanks to computer algebra software packages like Wolfram Alpha (which happens to be free). It will derive the transfer function of your preferred RIAA topology, including the amplifier output impedance, including the amplifier dominant pole, in seconds. You don't need to pay $35 for an AES reprint. You don't need to whip out a magnifying glass to read the print. Let Wolfram do the heavy lifting.
However this approach is now obsolete thanks to computer algebra software packages like Wolfram Alpha (which happens to be free). It will derive the transfer function of your preferred RIAA topology, including the amplifier output impedance, including the amplifier dominant pole, in seconds. You don't need to pay $35 for an AES reprint. You don't need to whip out a magnifying glass to read the print. Let Wolfram do the heavy lifting.
Thanks the responses I guess ill have to figure out how to do the filter calculations on wolfram, im use to just using Elsie for passive RF stuff.
@robo7
Thanks you for the tip on that opamp, it is speced almost as good as the 9 dollar LT ones, and the data sheet is great. I think Im gonna go with that opamp its specs just make sense for the price.
@robo7
Thanks you for the tip on that opamp, it is speced almost as good as the 9 dollar LT ones, and the data sheet is great. I think Im gonna go with that opamp its specs just make sense for the price.
Hey I couldnt find anything on WolfRam but I found this calculator It bases the passive EQ stage off the first resistor.
The problem is I dont know what effect the first resistor has on the filter, I know that the lower value will have less johnson noise, but other than that is there some type of reason to not just use a 1ohm metal film?? The other components dont seem to out of whack, I guess with one ohm you would have to use non polarized electrolytics... which isn't ideal but other than that is there something im missing as to the signifigance of the first resistor?
The problem is I dont know what effect the first resistor has on the filter, I know that the lower value will have less johnson noise, but other than that is there some type of reason to not just use a 1ohm metal film?? The other components dont seem to out of whack, I guess with one ohm you would have to use non polarized electrolytics... which isn't ideal but other than that is there something im missing as to the signifigance of the first resistor?
If the first stage is happy driving one ohm and has a negligible source impedance compared to 1 ohm, no problem. For more realistic circuits, 10k-20k isn't a bad place to start.
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