Patrick,
That is some awesome preamp! In line with Fred's Dogzilla. Without a lot of
details, what was your basic philosophy in designing with so much circuitry?
What additional benefits did you seek and how does your particular
philosophy stand up to the popular "Least circuitry from input to output?"
west

"Patrick Turner" wrote in message
...


A S Goh wrote:

Hi Patrick Turner

Where is the schematic of the regulated PS

I have never posted the schematic of the PS.

I did have a solid state regulator to produce +320v at 50mA,
and very low ripple, and this was further filtered by the RC infront of
each pair of L&R stages.

There was also a regulated 12.6 v DC supply for the heaters.

Since April 2,000, that amp has been reborn again without regulation.
There is really no need for it inh the B+ supply.
Now I have 470uF, 20H, 470 uF, then ecah channel has 470 ohms, 470 uF,
then another RC before each stage in each channel.
The phono stage has an extra RC with 470 uF as the final B+ C.
With all that RC, the hum is unmeasurable.
This proved to be more reliable and quieter than active regulation.
The regulator was series element LM350, but now it's a shunt type, using
"amplified" zener diode, ie, a zd to the base of a power transistor,
as well as lots of C.
The phono input stage has chokes to the heaters, and bypassed to 0V with
0.1
uF caps.

I hope to post the whole schematic when I upgrade the website soon.

But its not rocket science to make a good line stage.

I made mine on a chassis big enough to keep the PS away from the phono
input
stage.
The chassis is 500 mm long. The HT transformer is potted, ex navy, and
also
the heater trans, Both of these are inside sheet steel case, and the hum
from
the magnetic fields
is just low enough to not affect the fet input stage for MC which I now
have
instead
of the MM 12AX7 stage I have on the 2000 preamp.
That phono stage is hard to beat, but with MC at 20 dB lower output,
I needed something a little quieter.

With a line stage, you don't need to be so darn perfect, because the noise
of
a PS
won't affect the higher signal level so badly as it does with a phono
stage.
Nevertheless, don't be bashful or shy, build a good PS and you won't
regret
it.
Regulation isn't needed for the B+ for a class A amp.
The only supply variations seen are the very tiny slow moving variations
of
the B+
voltage due to mains levels variations.
But with my amp, you can turn it off, then back on after 5 seconds, and
hear
no sign of the B+ sliding down, then back up.

The April 2000 preamp uses shunt FB to control gain of the 12AT7.
The tone control uses 12AX7, but its gain is reduced to only 1 with the
tone
control
networks included in what's called a Baxandall network.
I don't mind some FB.

But for those who don't like shunt FB, or other loop FB, read on,
although with a cathode follower, you cannot escape the FB, since
all the output voltage is in series with the input; its a case of lotsa
FB.
But its very local, and somewhat the most blame free form of FB I know.

One line stage integrated amp I supplied a customer a couple of years back
uses two chassis about 220mm square each, one for PS, and one for the two
amp
channels.
The PS has an EL84 used as a shunt ripple reducer, about as effective as
a 30H choke.

The line stage uses 1 x 6CG7 per channel.
NOS Telefunken give the best sound.

The input comes via a 5 way source select twin wafer switch from DACT.
I have one triode loaded with 47k, cap coupled to a DACT switched
attenuator,
then this has a cathode follower output loaded with 47k; 2 uF to the
output.
Beyshlag resistors and Wima polypropylene caps are used.
6SN7 is the king of the signal triodes,
and is electonically identical to the 6CG7.
For a slightly warmer sound, use 12AU7.

The signal should come straight to the first tube and its level raised
from the maximum standard 0.2v line level to 2v.
Using 1/2 a 6SN7 with no cathode bypass cap give a gain of 10, (20 dB,).
12AU7 give a gain of around 7, with unbypassed Rk.
The 2v is then fed to a pot of attenuator, where the 12 o'clock
position reduces the level back down to 0.2v, and that is fed to a cathode
follower
output stage the same as shown at my site, and you get a nominal 0.18 vrms
output.
This is plenty for normal listening, and in fact if you measured the
input levels used for comfy listening, its usually around 20 mV.

If the power amp needs the standard 1v to make full power,
then the preamp with a gain of 7 can provide enough gain.
Even a gain of 4 is plenty, so balance controls can be also fitted.
If I am asked to fit them, I now place them on the input side of the gain
tube,
with volume after.
Its then I'd use 6CG7, gain = 10, or 15 with bypassed Rk
to compensate the drop with a balance control inserted.
Good systems don't need balance controls.


This is a very simple form of SET preamp, and despite trying lots of SRPP
and bootsrapped follower ideas, the simple thing sounds very accurate.
You have freedom to try ideas and build various things, and listen.
thd will be below 0.1%.

I have used CCS instead of the 47 k loads for the triodes.
I liked the sound of that.

I think its tube choice which governs the sound heard the most.
So if you make a circuit with ninepin sockets, different tubes can be
tried,
providing the heater voltage can be altered for either 6CG7 and 12AU7.

The use of good quality R&C also minimise likelyhood
of any cloudiness otherwise heard.

Patrick Turner.








Thanks
"Patrick Turner" wrote in message
...


Spade wrote:

Hello,

I planning to build tube line and phono pre amplifiers for my hi-fi
systems. Can you recommend me some good and simple schematics that
are
proven to work fine. I like to use tubes that can take 12,6 on
heaters, like ECC81-83, since I have couple of transformers that
give
230VAC + 12VAC, but sure I can regulate heater supply to 6,3VDC...

Any ideas?

Than you!

Best regards,
Spade

You could look at the complete preamp at
http://www.turneraudio.com.au/htmlwe...tubepreamp.htm

Then see the 12AT7 line stage which has a gain of 8, toprhs of the
schematic.

There is a volume control pot, log, with added balance pot, series,
after a tone control stage which can be deleted altogether.
My pre has two pair of LR outputs to suit trialing
different amps, but you could have just one cathode follower
output stage per channel.

Patrick Turner.