LT1028 mm phono preamp?

[miziq]

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.

 

[x-pro]

Unfortunately, this circuit suffers from the same problem as most of one-OPAMP circuits of this type - the output is essentially loaded on a quite large capacitance with only 10 Ohm resistor in series. Good for low noise but not much else...

x-pro

 

[Werner]

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.

 

[platenspeler]

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)

 

[makinson1]

LT1028 vs. OPA227 or OPA627?

My Forte model two pre-amp has these op-amps in it also, and I was wondering if the 227s or 627s sounded better even thought the Linear Circuits LT1028 has lower noise.

 

[Calvin]

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

 

[peranders]

I have used LT1115 and LT1028 and am quite pleased with them. To avoid probelms I have used a buffer at the output. It gives me also less problems driving a lowohmish RIAA network.

Schematic here

Picture here

 

[jcx]

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

 

[peranders]

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?

 

[danville]

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