New Phono amp - developing stage

Giaime · 4th July 2006, 06:24 PM

Here is all the article:

http://www.giaime.altervista.org/SuperRIAA.html

I think the whole section on tube and resistor noise should be read from anyone serious about electronics.

The same question of all my recent threads: what do you think?

alexmoose · 4th July 2006, 06:42 PM

I like the simple desing, the ability to switch between a variety of cartidges, and the lack of capacitors. I am looking to make a phono preamp, and this might be exactly what I am looking for

Giaime · 4th July 2006, 07:52 PM

mmm... lack of capacitors?

I'm not sure what schematic are you referring to, however in this design low parts count hasn't been an objective, like DC coupling.

Better good polarized stages than the absence of a capacitor

lndm · 5th July 2006, 04:46 AM

Hi Giaime,
This circuit looks interesting. I use a hybrid cascode myself. I like what I hear, but don't fully understand why. I have some questions.

What is the reason for choosing a cascoded second and third MM stage? I thought they were best as the first stage. I remember when I mentioned the word cascode on the forum, the heavies questioned why I would want such a stage, I could only say I liked the sound.

If I wanted to try something other than the ECC88, would I just need to alter the plate resistors, cathode biasing, and adjust the output impedances for the RIAA EQ to work. Do you think it would be worth trying with 6SN7's?

Giaime · 5th July 2006, 07:31 AM

Hello Indm,

I admit I haven't tried yet the circuit. Like many of those designs, it's only a "paper" project, which can be tweaked by the brave fellow who tries. However in the future I'm already planning to build a new preamp so...

Why Cascode? This particular "cascode with nfb" as mentioned in Broskie's articles has particulary low distortion (and noise, very important), lower than what I would expect by just putting nfb. Spice has confirmed that.

Cascode for the second stage because I needed that gain, but obviously one could do in other ways, such a CCS loaded grounded cathode stage. They are like an ice cream: cascode is chocolate, grounded cathode is vanilla, etc etc, choose your favourite one. When PROPERLY IMPLEMENTED good gainstages should be indistinguishable

And no, I wouldn't try 6SN7. This dual triode, bear in mind, was "invented" long before low noise and microphonics were key objective. This isn't to say that 6SN7 is noisy, because many good expensive NOS ones are very quiet. But why I would make a project suitable only for pricy NOS tubes?

Also there's a reason about transconductance: the higher the better, as stated in the article. Possible other tubes (in current production) to be considered are 6H30 and 6S45, all pricier than ECC88/6922, and the good 6S45 isn't dual.

However please note that the output stage (the 6CG7 - I love this tube - totem pole) is in developing stage, and I surely will change it, probably dc-coupling it with the previous stage (there's only 76V on the grid if I remove the coupling cap). I was thinking about the Plate Follower stage I use in my preamp.

Thank you all for the interest!

Gluca · 5th July 2006, 08:44 AM

I used and liked the made-in-CCCP 6N6p. I won those lil double triodes on ebay for cheap (and I mean a couple of euro each). You can probably consider them

Ciao

Giaime · 5th July 2006, 10:25 AM

Hi Gianluca, yes I'm open to russian little critters

I will search for data.

Eli Duttman · 5th July 2006, 12:32 PM

Giaime,

Jim McShane who KNOWS about these things tells me that the ElectroHarmonix labeled 6922 variant out of Saratov is very good in the noise dept. The EH tube should be a good affordable choice in the MC gain blocks.

A way to improve the CRITICAL noise performance in the MC gain block is to use paralleled 6922 sections in each leg of the difference amp. You'd be taking advantage of 2X gm and 1/2 Rp. I know the idea requires 2 bottles per channel for the MC gain blocks alone, but this project is an all out assault on performance.

pedroskova · 5th July 2006, 01:51 PM

...never seen a cascode feeding another cascode.

You may want to look at Steve Bench's cascode phono designs, as well as Alan Wrights hybrid cascode with a j-fet on the bottom... if you haven't already.

Giaime · 5th July 2006, 02:06 PM

Oh yes I thougt about paralleling sections. SNR ratio should increase by 3dB if I'm not wrong.

Since EH 6922 are cheap (not for me, but for the one that needs those kind of phono pre in his rig

) it could be done.

Thank you pedroskova, I read all that I could on Steve's site, however I didn't pay attention too much to what Wrights said, I have to look better.

I still have to learn more about SS design, I strongly think that a FET MC stage can be a big improvement over tubes.

4th July 2006, 06:24 PM	#1
Giaime diyAudio Member Join Date: Oct 2004	New Phono amp - developing stage Here is all the article: http://www.giaime.altervista.org/SuperRIAA.html I think the whole section on tube and resistor noise should be read from anyone serious about electronics. The same question of all my recent threads: what do you think?

5th July 2006, 12:32 PM	#8
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Giaime, Jim McShane who KNOWS about these things tells me that the ElectroHarmonix labeled 6922 variant out of Saratov is very good in the noise dept. The EH tube should be a good affordable choice in the MC gain blocks. A way to improve the CRITICAL noise performance in the MC gain block is to use paralleled 6922 sections in each leg of the difference amp. You'd be taking advantage of 2X gm and 1/2 Rp. I know the idea requires 2 bottles per channel for the MC gain blocks alone, but this project is an all out assault on performance. __________________ Eli D.

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4th July 2006, 06:42 PM	#2
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	I like the simple desing, the ability to switch between a variety of cartidges, and the lack of capacitors. I am looking to make a phono preamp, and this might be exactly what I am looking for

4th July 2006, 07:52 PM	#3
Giaime diyAudio Member Join Date: Oct 2004	mmm... lack of capacitors? I'm not sure what schematic are you referring to, however in this design low parts count hasn't been an objective, like DC coupling. Better good polarized stages than the absence of a capacitor

5th July 2006, 04:46 AM	#4
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Hi Giaime, This circuit looks interesting. I use a hybrid cascode myself. I like what I hear, but don't fully understand why. I have some questions. What is the reason for choosing a cascoded second and third MM stage? I thought they were best as the first stage. I remember when I mentioned the word cascode on the forum, the heavies questioned why I would want such a stage, I could only say I liked the sound. If I wanted to try something other than the ECC88, would I just need to alter the plate resistors, cathode biasing, and adjust the output impedances for the RIAA EQ to work. Do you think it would be worth trying with 6SN7's?

5th July 2006, 07:31 AM	#5
Giaime diyAudio Member Join Date: Oct 2004	Hello Indm, I admit I haven't tried yet the circuit. Like many of those designs, it's only a "paper" project, which can be tweaked by the brave fellow who tries. However in the future I'm already planning to build a new preamp so... Why Cascode? This particular "cascode with nfb" as mentioned in Broskie's articles has particulary low distortion (and noise, very important), lower than what I would expect by just putting nfb. Spice has confirmed that. Cascode for the second stage because I needed that gain, but obviously one could do in other ways, such a CCS loaded grounded cathode stage. They are like an ice cream: cascode is chocolate, grounded cathode is vanilla, etc etc, choose your favourite one. When PROPERLY IMPLEMENTED good gainstages should be indistinguishable And no, I wouldn't try 6SN7. This dual triode, bear in mind, was "invented" long before low noise and microphonics were key objective. This isn't to say that 6SN7 is noisy, because many good expensive NOS ones are very quiet. But why I would make a project suitable only for pricy NOS tubes? Also there's a reason about transconductance: the higher the better, as stated in the article. Possible other tubes (in current production) to be considered are 6H30 and 6S45, all pricier than ECC88/6922, and the good 6S45 isn't dual. However please note that the output stage (the 6CG7 - I love this tube - totem pole) is in developing stage, and I surely will change it, probably dc-coupling it with the previous stage (there's only 76V on the grid if I remove the coupling cap). I was thinking about the Plate Follower stage I use in my preamp. Thank you all for the interest!

5th July 2006, 08:44 AM	#6
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	I used and liked the made-in-CCCP 6N6p. I won those lil double triodes on ebay for cheap (and I mean a couple of euro each). You can probably consider them Ciao

5th July 2006, 10:25 AM	#7
Giaime diyAudio Member Join Date: Oct 2004	Hi Gianluca, yes I'm open to russian little critters I will search for data.

5th July 2006, 01:51 PM	#9
pedroskova RIP Join Date: Dec 2002 Location: C'ville VA, USA	...never seen a cascode feeding another cascode. You may want to look at Steve Bench's cascode phono designs, as well as Alan Wrights hybrid cascode with a j-fet on the bottom... if you haven't already.

5th July 2006, 02:06 PM	#10
Giaime diyAudio Member Join Date: Oct 2004	Oh yes I thougt about paralleling sections. SNR ratio should increase by 3dB if I'm not wrong. Since EH 6922 are cheap (not for me, but for the one that needs those kind of phono pre in his rig ) it could be done. Thank you pedroskova, I read all that I could on Steve's site, however I didn't pay attention too much to what Wrights said, I have to look better. I still have to learn more about SS design, I strongly think that a FET MC stage can be a big improvement over tubes.

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