Super fast, low noise phono preamp

[dioklecijan]

Hi DIYers
This is a picture of my DIY Phono Preamp. Schematics as shown is MC section.


Value of resistors R7, R8, R12 and of capacitors C2 and C5 are critical components. It's important to match to original values as close as possible. Capacitor C5 is better to be MKP (poliprophylene). Potty P1 isn't necessary, but it's adjusted on DC component before resistor R7, to be as small as is possible. Potty P2 have to be adjusted on DC offset to be 0.That's simply to make. In the case, we want greater gain, R11 have to be smallest value. With value of 220 ohms, we obtain 6dB more on gain.

I expect your suggestions.

Best regards, Dioklecijan

 

[dioklecijan]

Inside

 

[dioklecijan]

Final front

 

[peranders]

Nice work! Nice looking hand drawn schematic also.

Just wondering about C5 When You have gain more than 5-10 or this capacitors isn't very necessary, my opinion, but what is your reason for it?. Have you seen my LT1115/1028 vinyl amp.

 

[jam]

Peranders...............

at it again.....................

 

[dioklecijan]

Congratulation Peranders,
you see exactly what I want.

In this case with LT1028 and OPA627 is not very necessary to put capacitor C5 here, but don’t forget there is MM section with OPA 2134 and more offset without trim.

I see your phono and other works before. Very nice! Beautiful works.

 

[dioklecijan]

LT1028 or LT1115 or AD797 what is your experience?

 

[peranders]

LT1115 and LT1028 is the same IC but with different DC parameters.... and different price. I haven't tested AD797 yet.

 

[dioklecijan]

Look this:

Upgrade version with unique SRPP J-FET output stage


http://www.hiendfi.com/modules.php?name=News&file=article&sid=102

 

[analog_sa]

I have mixed feelings about the split passive/actibve riaa. It never ever sounded good to me compared to either passive/split passive or active correction. Maybe i was just unlucky with that topology.

 

[dioklecijan]

My scheme is split passive RIAA.

 

[jan.didden]

Nice work! Nice looking hand drawn schematic also.

Just wondering about C5 When You have gain more than 5-10 or this capacitors isn't very necessary, my opinion, but what is your reason for it?. Have you seen my LT1115/1028 vinyl amp.

P-A,

There happen to be 2 capacitors in the diagram called C5. I guess you mean the one on the 1st opamp?

Jan Didden

 

[analog_sa]

My scheme is split passive RIAA.

Apologies. I should try keeping my eyes open

 

[peranders]

There happen to be 2 capacitors in the diagram called C5. I guess you mean the one on the 1st opamp?

This cap is only for trimming bandwidth (stability reasons) with low gains and in this situation is totally useless (my opinion). When you are going to use this pin, it's 100's of pF or even nF's.

 

[dioklecijan]

HA

Sorry, my mistake.

There is no significant influences at gain-bandwidth and slew rate with this capacitor here. Isn't very necessary to use this.

That was an experiment before and I forget to erase this.

 

[jan.didden]

Oh but there is influence. That cap when left in will degrade the performance. BTW, the other C5 (1uF) is that part of the RIAA? Like low-freq roll-off?

Jan Didden

 

[dioklecijan]

No with 10 pF, maybe with 100 pF or more.

 

[peranders]

Oh but there is influence. That cap when left in will degrade the performance. BTW, the other C5 (1uF) is that part of the RIAA? Like low-freq roll-off?

The size of the cap now will do nothing, not negeative either.

C5 along with the other resistors creates a drop at 50 Hz and a lift at 500 Hz. The last 2122 Hz is acheived by C4.

 

[dioklecijan]

C5 trim offset.

R7, R8 and C2 creates a drop at 50 Hz and a lift at 500 Hz.

 

[dioklecijan]

Treble pole is little higher than 2122 Hz maybe at 2170. Those sound better. If you want exactly 2122 Hz, R12 will be 7,5 kohm.