Line preamp using 2 ECC88 per channel

[Mikewong]

This circuit is taken from the Stereo VOL:66 march 1995 (Hi-Fi magazine published in Italy) and presented by Fulvio Chiappetta.

V DC=225V
Both tube V1 & V2 =6922 or ECC88
C1 100nf 400v
C2 2,2mf 400v
C3 1000mf 400v
C4 100nf 400v
C5 2,2mf 400v
Specifications:
Amplification factor:20dB
Input resistance:22k
Input capacitance: can be omitted
Output resistance:< 100 ohm
Distorsion in audio bandwidth@ 1 Veff: II harmonics -62dB
III harmonics -68dB, IV harmonics -75dB V harmonics -81dB
Signal and noise ratio @1 Veff out: 90dB
Max output voltage:>100Vpp

Please debate and discuss this circuit, factors that affect this
circuit in term of electrical behaviour & etc that contribute to stability and sound wise.

[Giaime]

Hello! An Italian

Are you sure you need all that gain?

I must also add that ECC88 are not my best flavour. There are many better tubes out there, almost forgotten...

[Looneytunes]

Hi Giaime,
Not to pull the thread off track, but what are your favorite tube flavors for a preamp?

[lineup]

Originally posted by Giaime
Hello! An Italian

Are you sure you need all that gain?

Maybe better to put these two ECC88 in parallel.
Will lower gain and increase drive capacity to a nice level.

Not that I know much anything about tube circuits.

[Zen Mod]

I don't like SRPP

[leadbelly]

It's not really a line preamp at all, gain is too high, so high it could actually overspec some SS amps at 100Vpp. It's a high gain input section. Even the caption does not call it a line preamp.

6922's and ECC88's are great

[Zen Mod]

Originally posted by choky
I don't like SRPP

edit time just 30 min. ....

even if I don't like SRPP,I like ECC88

better way for line stage (even if gain with 88 is on highish side) is to use two systems in one envelope in parallel,and make that line stage as anode follower if Zout is adequate;
if lower Zout is needed,than CF must be used-say-just one system of 88 for that (1 per channel )

one bottle per channel in WOT configuration is almost a killer!

[andrei]

Getting back to the schematic rather than tube flavour chat...

It looks to me like the quoted distortion figures are a bit optimistic. For 1V input signal and 250V B+, it simulates to about 0.5% THD (-46dB). This is a factor of three lower than standard resistor-loaded common cathode stage would give you at the same bias, but the effect is almost entirely due to the negative feedback through unbypassed cathode bias resistors. The power supply noise rejection is nothing special - the usual 6dB. The output impedance is low (the output stage being cathode follower), but the bias current is only 6mA, so it will only drive 5k load at rated 100Vpp output (clipping sets in abruptly at about 4k load).

[marziom]

that's seems a SRPP stage that drive the upper valve (V1b) of a push-pull stage.....but the signal of the two drive are unequal....

marzio

[Giaime]

So I haven't seen a positive post on that design

Mikewong, I think it's better to change design. You have 3 options:

1) you're a Tube Guru (like me ) and you will/can experiment and draw your own circuit.

2) Get TubeCAD. It's wonderful.

3) Have you looked at the Aikido? Or the SY's Heretical Gainstage? There are many linestages out there, some of them use strange tubes (not so used for audio but easily obtainable) that can sound very good (and they're cheap).


About tube flavours, before you judge the ECC88, try a EL84 trioded