Anybody try this phono preamp ?

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gaetan8888

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Joined 2007
#1
Hello

I've just found that phono preamp this morning.

Phono Preamplifier - RED - Page10

I would use another opamp than the LM833.

Anybody try this phono preamp, any opinions or suggestions about it ?

Technical data:

Featuring low noise, good RIAA frequency response curve, low distortion and good high frequency transients behavior due to passive equalization in the 1 to 20KHz range.

Sensitivity @ 1KHz: 2.5mV RMS input for 200mV RMS output
Max. input voltage @ 1KHz: 120mV RMS
Max. input voltage @ 10KHz: 141mV RMS
Max. input voltage @ 20KHz: 127mV RMS
Frequency response @ 1V RMS output: 100Hz to 20KHz ±0.5dB; -0.75dB @ 30Hz
Total harmonic distortion @ 1KHz and 6V RMS output: 0.006%
Total harmonic distortion @10KHz and 1V RMS output: 0.02%

Thank

Bye

Gaetan
 

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#2
Its a typical 1980,s audio IC circuit and back then I did use some LM833 IC,s but it was superseded later and even JLH updated his LM833 designs as did I, THD shown was typical then for them .


Personally I don't like polyester and capacitor tests in EW showed that polycarbonate and good quality polypropylene exceeded the specs of polyester .


Zenner diodes are good noise generators ,plenty of circuits on building a noise generator using them , change them for more modern voltage regulators .


I tried fitting one in a 1940,s tube communications receiver RF section (Hallicrafters SX28 ) --had to remove it due to noise (hash ) when tuning.
 
#3
duncan2 said:
Its a typical 1980,s audio IC circuit and back then I did use some LM833 IC,s but it was superseded later and even JLH updated his LM833 designs as did I, THD shown was typical then for them .

Personally I don't like polyester and capacitor tests in EW showed that polycarbonate and good quality polypropylene exceeded the specs of polyester .

Zenner diodes are good noise generators ,plenty of circuits on building a noise generator using them , change them for more modern voltage regulators .

I tried fitting one in a 1940,s tube communications receiver RF section (Hallicrafters SX28 ) --had to remove it due to noise (hash ) when tuning.
Click to expand...
Very good points and all valid. It is really no reason to go back 40 years when the op-amp IC were getting introduced. Our understanding of op-amp application had gone a long way. The Analog Technology LT1115 application note is a very helpful read.
https://www.analog.com/media/en/technical-documentation/data-sheets/lt1115fa.pdf
 
#4
Hello

I don't have LT1115, but I have OPA627 and OPA637 for the circuit in my first post.

I can replace the zener by other regulation methods.

What I found interesting in that circuit are that it have a "good high frequency transients behavior due to passive equalization in the 1 to 20KHz range."

Thank

Bye

Gaetan
 
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#5
lt1115 is not very good for moving magnet carts due to its aw impedance although it can take higher max Vcc.lm833 is actually a very good op-amp for mm phono.The problem you have is that the 17.5v regulators are almost at the limit of max VCC of both lm833 and opa627...I'd suggest the usual ne5532 instead, or better m5220 if you can find some in a damaged casette player, but i've seen njm4580 and 2068 used at 17.5v in phono circuits so they might simply work as is depending on the max output current that's drawn out from them.Try 100v, anti-miller dc polyester for c4 and polypropylene (fkp)100vDC for C5. 63vdc capacitors might exhibit piezzo behavior if very low max DC specd.C1 should be at least 470uF to have a good low freq behavior.
 
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#7
dreamth said:
lm833 is actually a very good op-amp for mm phono.The problem you have is that the 17.5v regulators are almost at the limit of max VCC of both lm833 and opa627...I'd suggest the usual ne5532 instead, or better m5220 if you can find some in a damaged casette player, but i've seen njm4580 and 2068 used at 17.5v in phono circuits so they might simply work as is depending on the max output current that's drawn out from them..
Click to expand...
Other posters have been focusing on the DC regulation from +-30 supply in the circuit post 1, which is non-essential to the circuit and probably won't be used. There is no reason for even +-15 on a mm cart circuit. I'm using +-8v on a circuit similar to post 1, which I can't tell the difference on source between this circuit with a shure M97 HE era IV cart, and CD verson. Circuit was originally 4558 which hissed badly, when I upgraded to 33078 op amp I had to kill oscillation with 33 pf feedback cap and .1 uf ceramic disc across power supply, an inch away.
+-8v supply limits radio input to the mixer circuit to 6 vac, which is reasonable out the earphone jack of a radio. Works fine on CD player mixed in too. Got the hummy 17 vct transformer out of the RA88a case and moved to 18vdc race car wall transformer I bought for $2.
 

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#8
dreamth said:
lt1115 is not very good for moving magnet carts due to its aw impedance although it can take higher max Vcc.lm833 is actually a very good op-amp for mm phono.The problem you have is that the 17.5v regulators are almost at the limit of max VCC of both lm833 and opa627...I'd suggest the usual ne5532 instead, or better m5220 if you can find some in a damaged casette player, but i've seen njm4580 and 2068 used at 17.5v in phono circuits so they might simply work as is depending on the max output current that's drawn out from them.Try 100v, anti-miller dc polyester for c4 and polypropylene (fkp)100vDC for C5. 63vdc capacitors might exhibit piezzo behavior if very low max DC specd.C1 should be at least 470uF to have a good low freq behavior.
Click to expand...
You are right that L1115 or AD797 are good choice for moving coil phono stage which is low impedance, but are poor choice for moving magnet which is high impedance. LME49720 is cheap and readily available. It is an excellent choice for MM phono input stage.

I found a pretty good MM phono board on e-bay. It sound quite good as is with the 5532 chips, but sound even better with LME49720.
MM MC Phono Turntable Pre-amplifier Preamp Refer Dual Phono Preamplifie,Finished | eBay
e-bay sellers claim this board for MC too, but it is not. You cannot connect a MC cartridge to an 47K input.
 
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#9
Hello

Here's the opamps that I have in my part bin. Most of them will need good .1 uf caps across the power supplies pins and the caps need to be very close to those pins. I would use 15 volt for the supply.

LM4562
LM6172
OPA627
OPA637
NE5532
AD825
LME49720

I remember somebody who use LM6172 for mm phono preamp with very good result. (With good decoupling caps on the supply pins.)

Any suggestions ?

Thank

Bye

Gaetan
 
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#10
I thought lm49720 is 30k input impedance and 2...4 times higher noise than lm833...LM833 behaves better than ne5532 in i/v converters so maybe it should be better here too , but D. Self wrote no book around lm833 unfortunately 🙂 I never tried lme49720 .I have 4 unused pieces of lme49710 although I heard in the past people claiming that the passive riaa schematic in the lme49710 datasheet performs very well .For lower VCC than +_17.5v which became a classic voltage for active voltage feedback riaa i'd say that two things can make for an acceptable sound, one is the soft clipping behavior of the njm4558(4559) used in the past another would be a clean of dust record...
 
#11
Although on the high side of voltage noise, the low current noise and high input impedance might make lm6172 an acceptable choice for mm phono...never thought about it .It might have a very good behavior with low impedance passive or active network as it has huge power reserves.One very cool thing i discovered about lm6172 is that for its huge slew rate it's unusually stable with lower grades pcb artwork...What i found about it is that it needs 2...4db bass boost as it's kinda thin in that area, but that's easy to solve. You have the proof of how stable lm6172 is in the photos attached cause that circuit worked great with that messy pcb.Well..not that messy in fact , but clearly no ground plane there.



https://www.diyaudio.com/forums/digital-source/338152-nec-cd-810-revival-mods.html#post5812138
 

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#13
Well...the 47k input resistor is in paralel with that input impedance...yet there are so many guys pretending that 30k input op-amps sound terrific that i can't argue too much about it.Truth is that if you use lm833 and any other classical op-amp you'll instantly notice a higher output with lm833 using the same feedback network.
 
#15
As i already said...lm6172 has an incredible response on the high side but without that mild bass boost i couldn't make it sound right.At the same time that mod was an i/v converter and its input current bias is huge, 4...5 times higher than any other op-amp so it eats a lot of the signal current when biased directly from the signal source, but with an mm input you can safely use a capacitor on the input and the 47k resistor will do with the bias.So it might behave differently in your circuit.
 
#19
gaetan8888 said:
Hello

Here's the opamps that I have in my part bin. Most of them will need good .1 uf caps across the power supplies pins and the caps need to be very close to those pins. I would use 15 volt for the supply.

LM4562
LM6172
OPA627
OPA637
NE5532
AD825
LME49720

I remember somebody who use LM6172 for mm phono preamp with very good result. (With good decoupling caps on the supply pins.)

Any suggestions ?

Thank

Bye

Gaetan
Click to expand...
LM4562 is identical to LME49720. They will be my choice for a 2-stage passive-active MM phono stage. You need to verify that they are genuine from US/European manufacturer, not fake part from Chinese seller on e-bay.

You need to get something else for MC phono.
 
#20
The open-loop differential input impedance of an op-amp is basically irrelevant, as it is much increased by the feedback anyway. What does matter (to some extent) are the input noise voltage and current. An LT1115 is a poor choice for moving magnet while an OPA627 or OPA637 is fine because of the high noise current of an LT1115 and the high impedance of a moving magnet cartridge at high audio frequencies.
 
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