http://www.linear.com/prod/datasheet.html?datasheet=165
any comments on this. Its the chip that is used in Mark Levinson amps. Noise should be really low by specs and its ment for high quality audio.
any comments on this. Its the chip that is used in Mark Levinson amps. Noise should be really low by specs and its ment for high quality audio.
Werner said:The LT1028 is one of the three low-noise IC amplifier champions. Up to you to find the other two
Was used in the Michell ISO HR and in the first Trichord Delphini.
LT1115? AD797?
Maarten (Who will certainly try the LT1028 in a next project)
Hi,
apart from noise there´s imo not much to worry about the ´sound´ of the used OP. Sound of a Phono stage is in first case made by the precision and dimensioning of the equalizing network and a good power suply and grounding!
Even the topology of the circuit has a greater influence. I´d generally opt for a 2 or three-stage design, where You can optimize on gain, values and noise-figures.
jauu
Calvin
apart from noise there´s imo not much to worry about the ´sound´ of the used OP. Sound of a Phono stage is in first case made by the precision and dimensioning of the equalizing network and a good power suply and grounding!
Even the topology of the circuit has a greater influence. I´d generally opt for a 2 or three-stage design, where You can optimize on gain, values and noise-figures.
jauu
Calvin
none of the previosly mentioned op amps are low noise - when used with a typical mm catridge input Z
the low voltage noise in LT1028/1128/1115, AD797, LM4562 is acheived by heavy bias of the input Qs which gives large base current noise and input current noise is multiplied by the source Z to give output noise
for mm source Z low noise FET inputs are best: AD743/745, OPA627/37 with input noise current order(s) of magnitude smaller than those "low noise" bjt input op amps
for bjt input op amps those with lower bias/base current noise such as LT1007, OPA227 are better than the high bias "low (Volatge) noise" LT1028, AD797 op omps in this application
http://www.diyaudio.com/forums/showthread.php?s=&postid=673663&highlight=#post673663
http://www.diyaudio.com/forums/showthread.php?s=&postid=674460&highlight=#post674460
http://www.diyaudio.com/forums/showthread.php?postid=328609#post328609
some Vnoise plots:
http://www.diyaudio.com/forums/showthread.php?s=&postid=843381&highlight=#post843381
the low voltage noise in LT1028/1128/1115, AD797, LM4562 is acheived by heavy bias of the input Qs which gives large base current noise and input current noise is multiplied by the source Z to give output noise
for mm source Z low noise FET inputs are best: AD743/745, OPA627/37 with input noise current order(s) of magnitude smaller than those "low noise" bjt input op amps
for bjt input op amps those with lower bias/base current noise such as LT1007, OPA227 are better than the high bias "low (Volatge) noise" LT1028, AD797 op omps in this application
http://www.diyaudio.com/forums/showthread.php?s=&postid=673663&highlight=#post673663
http://www.diyaudio.com/forums/showthread.php?s=&postid=674460&highlight=#post674460
http://www.diyaudio.com/forums/showthread.php?postid=328609#post328609
some Vnoise plots:
http://www.diyaudio.com/forums/showthread.php?s=&postid=843381&highlight=#post843381
jcx, you are right in theory but in real life the LT1115 has substantially lower noise than the vinyl itself. In other words: No noise is added and when the cartiridge not is in the grooves you won't hear any irritating noise.
BTW:Is it grooves or tracks when you talk about vinyl?
BTW:Is it grooves or tracks when you talk about vinyl?
jcx said:none of the previosly mentioned op amps are low noise - when used with a typical mm catridge input Z
the low voltage noise in LT1028/1128/1115, AD797, LM4562 is acheived by heavy bias of the input Qs which gives large base current noise and input current noise is multiplied by the source Z to give output noise
for mm source Z low noise FET inputs are best: AD743/745, OPA627/37 with input noise current order(s) of magnitude smaller than those "low noise" bjt input op amps
for bjt input op amps those with lower bias/base current noise such as LT1007, OPA227 are better than the high bias "low (Volatge) noise" LT1028, AD797 op omps in this application
A useful exercise is to calculate e/i. This gives you the impedance where the influence of current noise and voltage noise will be equivalent.
A FET input low noise amplifier is usually a good mm choice as mentioned since current noise will dominant. Make sure the 1/f noise is reasonable as well.
In my designs, I direct coupled the cartridge. You don't want large bias currents in this case. You might want to include about a 1K00 series R (assuming non inverting stage). This would be placed between the 47k and the + input. It's purpose is to keep from destroying the input FET from static etc. Sometimes the FETs will degrade but not die. You may start to get increased 1/f noise.
This may not be an issue these days, but it was with early FET input op amps.
I think the LT1028 and similar parts would be good for MC types since these are very low impedance. All the noise will be dominated by e in this case.
Al Clark
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