Line preamp using 2 ecc88 per channel
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.
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.
Attachments
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...
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...
Hi Giaime,
Not to pull the thread off track, but what are your favorite tube flavors for a preamp?
Not to pull the thread off track, but what are your favorite tube flavors for a preamp?
Giaime said:
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.
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 🙂
6922's and ECC88's are great 🙂
choky said:
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!
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).
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).
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
marzio
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 😀 😀 😀 😉
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 😀 😀 😀 😉
Yes but they should be unequal.
It is a SEPP where the drive signal to the upper tube is taken from the SRPP stage in front.
A SEPP is unsymmetrical as the lower tube has higher gain than the upper tube and the idea here is to compensate for this difference. However the gain difference in the SEPP is not the same as the gain in the SRPP and the gain in the SEPP is dependant on the load the result is distortion even at quite low ouput levels, if the distortion level is given at 1V output level it is probably what can be expected.
There are other better circuits available that can compensate for the gain difference of the SEPP, my favorite is the inverted Futterman which also will give lower output impedance.
Regards Hans
If you're not afraid of iron...
This is my crack at an ECC88 linestage. I enjoy it.
All the details are at http://www.joeltunnah.com
Joel
An externally hosted image should be here but it was not working when we last tested it.
This is my crack at an ECC88 linestage. I enjoy it.
All the details are at http://www.joeltunnah.com
Joel
You can see some variations of SEPP drive circuits here http://www.tubetvr.com/otl.html but I should make clear that I would never use a SEPP for a line amplifier as I don't see the need for that.
My own line amp has an output impedance of about 1 ohm without a SEPP but I rely on feedback which is not everyones "cup of tea".
However, a SEPP using inverted Futterman drive circuit is a good choice for direct driving headphones, see here http://www.tubetvr.com/headphoneamp.html
Regards Hans
Hello Guys
I'have tried that kind of circuit with ECC82 and solid state stabilized pw supply, there is an example on an italian site of FANATICs of AUDIO.
May be that it's name is Gomes (z) configuration but this is not important.
I have done listening test with some audiophile and musician friend of mine, also compared with a classic line pre with E88CC (1st stage common cathde and 2nd stage cathode follower) and a line stage with E88CC in totem pole (200Vb and Rk 820).
Yes , It has an higher gain than others, but the problem was the sensibily to the quality and matching of tubes.
The simplificated rate of listening test was:
Ecc88 "classic pre" high
Ecc88 srpp medium - high
Ecc82 medium - low
I know that we have compared three circuits not with the same tubes but it was a listening test like an audio magazine,
some hig-end commercial ampli and loudspeakers and some people customed to listening test.
Regards, Giuseppe
I'have tried that kind of circuit with ECC82 and solid state stabilized pw supply, there is an example on an italian site of FANATICs of AUDIO.
May be that it's name is Gomes (z) configuration but this is not important.
I have done listening test with some audiophile and musician friend of mine, also compared with a classic line pre with E88CC (1st stage common cathde and 2nd stage cathode follower) and a line stage with E88CC in totem pole (200Vb and Rk 820).
Yes , It has an higher gain than others, but the problem was the sensibily to the quality and matching of tubes.
The simplificated rate of listening test was:
Ecc88 "classic pre" high
Ecc88 srpp medium - high
Ecc82 medium - low
I know that we have compared three circuits not with the same tubes but it was a listening test like an audio magazine,
some hig-end commercial ampli and loudspeakers and some people customed to listening test.
Regards, Giuseppe
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