Hi all!
I'm playng around with the project of my phono preamp.
After many schematics, now i'm thinking about a EC8010 -- RIAA network --
RCA 76, both tubes CCS loaded.
Maybe this isn't a good design, but i'm a rookie in this field, so be
patient...
At the operating point the plate current for the EC8010 is 25 mA and 4mA for
the 76, both are about at 120V on plate.
Therefore the EC8010 drives more power than the 76. I wonder if this makes
sense. Maybe i'm wrong, but it seems to me that usually every stage drives a
following more powerful stage. It has to be so, or there is no relation
between the power dissipated in a stage vs. the power dissipated in the
following stage?
I' didn't found much information about this.

V-Twin wrote:

Hi all!
I'm playng around with the project of my phono preamp.
After many schematics, now i'm thinking about a EC8010 -- RIAA network --
RCA 76, both tubes CCS loaded.
Maybe this isn't a good design, but i'm a rookie in this field, so be
patient...
At the operating point the plate current for the EC8010 is 25 mA and 4mA for
the 76, both are about at 120V on plate.
Therefore the EC8010 drives more power than the 76. I wonder if this makes
sense. Maybe i'm wrong, but it seems to me that usually every stage drives a
following more powerful stage. It has to be so, or there is no relation
between the power dissipated in a stage vs. the power dissipated in the
following stage?
I' didn't found much information about this.

Some folks use a lot of current in the input stage of their phono
amp to allow the chosen triode to work where its Gm is the highest,
and its noise the lowest.
Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a step up
tranny.

I used to use the circuit shown at
http://www.turneraudio.com.au/htmlwe...tubepreamp.htm
but now I have a 2SK369 in cascode with a frame grid pentode, the 6EJ7,
running in triode, with 6 mA of Ia and this gives me
20 dB less noise when MC is used, and 10 dB less noise with MM.

Once you have got past the first stage, there is no need for high current
following stages,
since the SNR isn't a problem, and a gain stage with 3 mA is ample.

CCS loadings can be achieved with transistors, j-fets, or pentodes.
The CCS load is a vet high impedance load, and thus the gain of the triode
becomes cloas to its Mu, and the thd falls to the lowest it can be
without using a balanced circuit, which reduces the thd even further.
IN phono input stages, thd isn't a main concern,
and typical thd figures at 100 mV of of output is maybe 0.01% of 2H,
even when the load is a resistor of say 5 times the RA of the tube.
The noise of the stage is determined by the grid input noise, the shot noise,
and the flicker noise of the tube, which is worst at LF,
and spoils many tube phono amps, so tube choice and
careful selection is very important.
The CCS needs to be low noise, as would the R used instead,
but the Ra is in shunt with the anode R load, so R has little effect
if Ra is a small fraction of it.
Same goes for the following grid bias R, which is effectively
in parallel with the load R supplying DC to
triode.

Patrick Turner.

Hi RATs!

I used a SV572-30 to drive a 2A3.

Nothing to do with phono amps, but, I just like telling that one

Happy Ears!
Al


Alan J. Marcy
Phoenix, AZ

PWC/mystic/Earhead

Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a step up
tranny.

But that won't work with a total max. gain of 600 x .....
Ec8010 (on ccs) x # 76 (on ccs) = 60 x 10 = 600 .....
Way to low ! Even for MM ......

Ronald .

OK, what am I missing? My Sumiko, which is a high output MC, has an output
of 3mV times a gain of 600 is 1.8V. Add a line stage and you have more than
enough gain for any amp. My amp drives to full output with a gain of .8V so
no line stage would be needed with this phono stage.

Sandy Brown


Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a step
up
tranny.

But that won't work with a total max. gain of 600 x .....
Ec8010 (on ccs) x # 76 (on ccs) = 60 x 10 = 600 .....
Way to (sic) low ! Even for MM ......

Ronald .

"Centifolia"

OK, what am I missing?


** Wait for it.


My Sumiko, which is a high output MC, has an output of 3mV times a gain of
600 is 1.8V.



** The output may be 3mV - but at 1 kHz !!!

At 25 Hz it will be only 0.3 mV - due to the RIAA recording curve.

A phono preamp needs at least 1000 times gain at low frequencies -
even when no NFB is used - much more if it is.





.......... Phil

"Phil Allison" ha scritto nel messaggio
u...
At 25 Hz it will be only 0.3 mV - due to the RIAA recording curve.

A phono preamp needs at least 1000 times gain at low frequencies -
even when no NFB is used - much more if it is.

I said i'm a rookie...i forgot to consider the 20dB loss of the RIAA
network... )

And it'll sound like sh*t since you don't use a Riaa correction .... ;-))
A total (unfiltered) gain of about 3600 for MM is quite normal ....


"Centifolia" schreef in bericht
news:Bchsb.128916$ao4.403701@attbi_s51...
OK, what am I missing? My Sumiko, which is a high output MC, has an
output
of 3mV times a gain of 600 is 1.8V. Add a line stage and you have more
than
enough gain for any amp. My amp drives to full output with a gain of .8V
so
no line stage would be needed with this phono stage.

Sandy Brown


Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a
step
up
tranny.

But that won't work with a total max. gain of 600 x .....
Ec8010 (on ccs) x # 76 (on ccs) = 60 x 10 = 600 .....
Way to (sic) low ! Even for MM ......

Ronald .

Ronald wrote:

And it'll sound like sh*t since you don't use a Riaa correction .... ;-))
A total (unfiltered) gain of about 3600 for MM is quite normal ....

"Centifolia" schreef in bericht
news:Bchsb.128916$ao4.403701@attbi_s51...
OK, what am I missing? My Sumiko, which is a high output MC, has an
output
of 3mV times a gain of 600 is 1.8V. Add a line stage and you have more
than
enough gain for any amp. My amp drives to full output with a gain of .8V
so
no line stage would be needed with this phono stage.

Sandy Brown


Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a
step
up
tranny.

But that won't work with a total max. gain of 600 x .....
Ec8010 (on ccs) x # 76 (on ccs) = 60 x 10 = 600 .....
Way to (sic) low ! Even for MM ......

Ronald .





I have used a 6DJ8 with a passive RIAA, followed by a 12AX7,
so total gain at 1 kHz is 30 x 70 /10 = 210, and the
divide by 10 is the loss at 1 kHz of the RIAA filter.

So if you have a 5 mV @1kHz cart at 1 kHz, you just over 1,000 mV at the
output.
But a cart of 2,5 mV, and a second phono stage gain of 35
would still make 250 mV.
But not so good with a Denon 103 MC, whose output is only 0.3mV.
Then you need more gain, or a step up transformer.

FB type EQ might have even greater demand for gain since even at 20 Hz there
is maybe 12 dB of FB operative, and 32 dB at 1 kHz, so an open loop gain
of 4,000 would be appropriate.

Many old phono stages just had two halves of 12AX7 cascaded for an open loop
gain of
about 4,000 at LF.
Some of the better ones had a CF stage added to the output of the second gain
1/2 of
the 12AX7, thus making the stage very low Ro, even at LF.

I prefer the passive RIAA, after a cascode stage, with mu follower topology
following .

Patrick Turner.

"Patrick Turner" ha scritto nel messaggio
...
Some folks use a lot of current in the input stage of their phono
amp to allow the chosen triode to work where its Gm is the highest,
and its noise the lowest.
Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a step up
tranny.

Therefore is a good idea, or?

Once you have got past the first stage, there is no need for high current
following stages,
since the SNR isn't a problem, and a gain stage with 3 mA is ample.

Ok.

The noise of the stage is determined by the grid input noise, the shot
noise,
and the flicker noise of the tube, which is worst at LF,
and spoils many tube phono amps, so tube choice and
careful selection is very important.

I only have very basic knowledge about this, i need to learn more. Any
suggestion (books, web sites...)?

V-Twin wrote:

"Patrick Turner" ha scritto nel messaggio
...
Some folks use a lot of current in the input stage of their phono
amp to allow the chosen triode to work where its Gm is the highest,
and its noise the lowest.
Hence the use of 6C45pi, 417A, and paralleled 6DJ8 tubes, etc,
and this supposedly allows the use of moving coil carts, without a step up
tranny.

Therefore is a good idea, or?

Not necessarily.
Some folks like this way of doing an amp.
Some folks don't, so I suggest you find by using a soldering iron
and your ears, and a CRO.



Once you have got past the first stage, there is no need for high current
following stages,
since the SNR isn't a problem, and a gain stage with 3 mA is ample.

Ok.

The noise of the stage is determined by the grid input noise, the shot
noise,
and the flicker noise of the tube, which is worst at LF,
and spoils many tube phono amps, so tube choice and
careful selection is very important.

I only have very basic knowledge about this, i need to learn more. Any
suggestion (books, web sites...)?

There is a fair bit around the web on phono tube preamps.

The old book like RDH4 don't have 6DJ8 circuits within it, but it does have lots
of applicable theory, which you should know about,
if you want to fiddle around with tubes.

Patrick Turner.

I use a 76 directcoupled 6be8 CF. The 76 sounds marvelous when
feeding another driving tube. It sounded even better without the CF
by a tad, but lower freq's really rolled off when driving cables to
the amp (100k input resistor). Maybe the CCS loading will help in
this regard. Let me know if it does, as the 76 is a really
nice-sounding tube.

Bob Hedberg

"V-Twin" wrote:

Hi all!
I'm playng around with the project of my phono preamp.
After many schematics, now i'm thinking about a EC8010 -- RIAA network --
RCA 76, both tubes CCS loaded.
Maybe this isn't a good design, but i'm a rookie in this field, so be
patient...
At the operating point the plate current for the EC8010 is 25 mA and 4mA for
the 76, both are about at 120V on plate.
Therefore the EC8010 drives more power than the 76. I wonder if this makes
sense. Maybe i'm wrong, but it seems to me that usually every stage drives a
following more powerful stage. It has to be so, or there is no relation
between the power dissipated in a stage vs. the power dissipated in the
following stage?
I' didn't found much information about this.


Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

"Bob Hedberg" wrote in message
...
: I use a 76 directcoupled 6be8 CF. The 76 sounds marvelous when
: feeding another driving tube. It sounded even better without the CF
: by a tad, but lower freq's really rolled off when driving cables to
: the amp (100k input resistor). Maybe the CCS loading will help in
: this regard. Let me know if it does, as the 76 is a really
: nice-sounding tube.
:
: Bob Hedberg

Your price, Sir

: : Bob Hedberg
:
: Your price, Sir
Err, never mind, see you've made yours up
Rudy

Pardon?

"Ruud Broens" wrote:


: : Bob Hedberg
:
: Your price, Sir
Err, never mind, see you've made yours up
Rudy


Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

(Think he meant "prize", referring to the contest)

Bob Hedberg wrote:
Pardon?

"Ruud Broens" wrote:


: : Bob Hedberg
:
: Your price, Sir
Err, never mind, see you've made yours up
Rudy



Bob H.

Just grab that plate in one hand, the chassis in the other,
and FEEL the power of tube audio!!!
(not literally, of course, just kidding. DON'T DO THAT!)

--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects, Vacuum Tubes & other stuff: |
| http://www.dogstar.dantimax.dk |
+--------------------------------------------+

it's hard to beat EC8010 with 20 to 25mA in any topology with any tube.
it's ****in' beast ,and I have just a pair-in my WOT ;(((
who want to donate at least 20 pieces to poor ZM?


--
--
.................................................. ........................
Choky
Prodanovic Aleksandar
YU

"don't use force, "don't use force,
use a larger hammer" use a larger tube
- Choky and IST"
- ZM
.................................................. ...........................
"V-Twin" wrote in message
...
Hi all!
I'm playng around with the project of my phono preamp.
After many schematics, now i'm thinking about a EC8010 -- RIAA
network --
RCA 76, both tubes CCS loaded.
Maybe this isn't a good design, but i'm a rookie in this field, so be
patient...
At the operating point the plate current for the EC8010 is 25 mA and 4mA
for
the 76, both are about at 120V on plate.
Therefore the EC8010 drives more power than the 76. I wonder if this makes
sense. Maybe i'm wrong, but it seems to me that usually every stage drives
a
following more powerful stage. It has to be so, or there is no relation
between the power dissipated in a stage vs. the power dissipated in the
following stage?
I' didn't found much information about this.