hi everyone,
ok i know people have already asked all the questions i'm about to ask, but i'd like to pick everyone's brain and have a nice open discussion about some high-level as well as finer points of designing a DIY line stage...
so i'm thinking of building a simple preamp for my system... first thing that comes to mind is to use IC opamps. i know a lot of audiophiles hold their nose when you mention "IC opamp" but i think if you lay out your circuit properly and use the proper devices you can get pretty good sound out of ICs. in particular, the OPA627 seems to be a popular pick. however, i'm also interested in how the Pass Labs projects sound (e.g. DIY discrete opamps, Zen line stage), and how they would compare with a properly-executed IC design.
if i use a OPA627, i am going to go with the surface mount components and get the very shortest signal path possible - i intend to have my entire feedback path less than 1cm long and with very short leads to signal and power supply bypasses. i think if the layout is super-tight, the performance of the device can be maximized. furthermore i will be using a choke-regulated power supply and LT1085/1033 regulators at the very least.
that said, i have a couple questions:
<ul>
<li>should i use two active stages, one before the volume pot (for input buffering) and one after? or just one after the volume pot? i prefer the latter (less is more) but there are performance considerations...
<li>if i use two stages, how should i split the gain between the two? maybe 6dB at the input buffer and 12dB at the output stage? or just buffer the input? i guess i am looking for the best balance between noise performance (more gain up front) and distortion (more gain at the output). since i am limited to using +/-15V rails w/most ICs, most of the gain probably needs to be in the output.
<li>Walt Jung, the opamp guru, seems to favor always buffering the output of gain-stage opamps due to current-drive, thermal, and distortion considerations. like i said though, i hate having more circuitry than is absolutely necessary. do the benefits of a buffer outweigh the drawbacks?
<li>if i pull it off the way i said i would, do you think my suface-mount IC design (using probably OPA627) will sound ok?
<li>will the Pass Zen design, if properly built, still kick my opamp's ***?
</ul>
ok those are my thoughts for now... if anyone cares to add additional questions or comments, feel free! i'd really appreciate any input whatsoever, not only for my own benefit but also because i'll probably be writing a technical column for Bound for Sound magazine in the near future so this would be good research...
thanks,
dorkus (marc)
ok i know people have already asked all the questions i'm about to ask, but i'd like to pick everyone's brain and have a nice open discussion about some high-level as well as finer points of designing a DIY line stage...
so i'm thinking of building a simple preamp for my system... first thing that comes to mind is to use IC opamps. i know a lot of audiophiles hold their nose when you mention "IC opamp" but i think if you lay out your circuit properly and use the proper devices you can get pretty good sound out of ICs. in particular, the OPA627 seems to be a popular pick. however, i'm also interested in how the Pass Labs projects sound (e.g. DIY discrete opamps, Zen line stage), and how they would compare with a properly-executed IC design.
if i use a OPA627, i am going to go with the surface mount components and get the very shortest signal path possible - i intend to have my entire feedback path less than 1cm long and with very short leads to signal and power supply bypasses. i think if the layout is super-tight, the performance of the device can be maximized. furthermore i will be using a choke-regulated power supply and LT1085/1033 regulators at the very least.
that said, i have a couple questions:
<ul>
<li>should i use two active stages, one before the volume pot (for input buffering) and one after? or just one after the volume pot? i prefer the latter (less is more) but there are performance considerations...
<li>if i use two stages, how should i split the gain between the two? maybe 6dB at the input buffer and 12dB at the output stage? or just buffer the input? i guess i am looking for the best balance between noise performance (more gain up front) and distortion (more gain at the output). since i am limited to using +/-15V rails w/most ICs, most of the gain probably needs to be in the output.
<li>Walt Jung, the opamp guru, seems to favor always buffering the output of gain-stage opamps due to current-drive, thermal, and distortion considerations. like i said though, i hate having more circuitry than is absolutely necessary. do the benefits of a buffer outweigh the drawbacks?
<li>if i pull it off the way i said i would, do you think my suface-mount IC design (using probably OPA627) will sound ok?
<li>will the Pass Zen design, if properly built, still kick my opamp's ***?
</ul>
ok those are my thoughts for now... if anyone cares to add additional questions or comments, feel free! i'd really appreciate any input whatsoever, not only for my own benefit but also because i'll probably be writing a technical column for Bound for Sound magazine in the near future so this would be good research...
thanks,
dorkus (marc)