el84pse schem, need advice

oliezt_sayfu · 11th May 2011, 08:45 AM

hello......

i want to build an amp with the part that i have....
here the schem....
i need your advice or criticsm...
or maybe, there's better schem ...

nb : is it possible to make 6sn7 driver stage to drive el84 pse....

thanks

DF96 · 11th May 2011, 10:29 AM

What is the triode valve - the circuit does not say? The data on the circuit suggests that it is a low impedance triode: mu~30, gm~10mA/V.

The first stage uses an active load, which will reduce distortion there, yet most distortion will actually come from the output stage.

the_manta · 11th May 2011, 02:33 PM

6SN7, yes, but in term sof optics a desaster

6SN7 as single triode or SRPP has very low µ. But you need µ for feedback to get a good damping factor. So a 2-staged topology is the way to go.

DF96 · 11th May 2011, 02:38 PM

It doesn't have any feedback. Maybe it should.

oliezt_sayfu · 11th May 2011, 03:21 PM

hello
thanks for the input everybody...
the driver use 6922/6dj8

should i use global feedback or local feedback..?

oliezt_sayfu · 11th May 2011, 03:45 PM

Quote:

Originally Posted by the_manta

6SN7, yes, but in term sof optics a desaster

6SN7 as single triode or SRPP has very low µ. But you need µ for feedback to get a good damping factor. So a 2-staged topology is the way to go.

hello
how much B+ that 6sn7 needed to operate at optimum linearity...

is it 300v enough for 6sn7?

sorry for the bad english

thanks

DF96 · 11th May 2011, 04:24 PM

The 6DJ8 should give you a low distortion first stage. 6SN7 would definitely have less gain, and might have slightly higher distortion.

You don't have enough spare gain for enough NFB, so no NFB is better than insufficient NFB. I assume you prefer single-ended pentode outputs? I would use the two EL84 as P-P, but each to their own!

the_manta · 11th May 2011, 05:35 PM

Sorry sorry sorry....I thought you wanted to use the EL84 as Pentode Now I see it's triode conected. Well then you don't basically need feedback, but I always recommend at least a bit.

Whether you want to use local feedback (I mean like that) or global is up to you. With gobal feedback it's more difficult to get a stable amplifier because of the phase shift of the output transformer and all the coupling caps. (Ideal feedback doesn't have any phase shifting components in its way, look at typical Transistor amp schematics, they are more or less completely DC coupled)

to the driver: A 6SN7 needs a bit more supply voltage and current to sound good, but 300V is adequate. 6DJ8/ECC88 is a very good driver and matches the EL84 shape :-) ECC88 doesn't need much volatge but at least 7 to 8mA. This gives nice working points.

Withe the 6DJ8/ECC88 and little or no feedback you have plety of possibilities to design your driver. One tube for both channels would be the simple way. with two systems, there are many many more...grounded cathode followed by cathode follwer, µ-follwer, SRPP, Diff-amp, cascode etc.....

Just try a few and keep the one you like :-)

DF96 · 11th May 2011, 07:30 PM

Sorry, I had not spotted the EL84 triode connection. As long as you don't drive it too hard it may be fine without feedback. Given a simple output stage, it seems sensible to have a simple input stage too.

oliezt_sayfu · 13th May 2011, 09:00 AM

thanks again for great input....
i'm thinking about PushPull output, but i have to buy PP Trans..
is it worth to change to Pushpull compared to PSE...(el84) ?
the loudspeaker is fullrange at 90db sens...

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11th May 2011, 10:29 AM	#2
DF96 diyAudio Member Join Date: May 2007	What is the triode valve - the circuit does not say? The data on the circuit suggests that it is a low impedance triode: mu~30, gm~10mA/V. The first stage uses an active load, which will reduce distortion there, yet most distortion will actually come from the output stage.

11th May 2011, 02:33 PM	#3
the_manta diyAudio Member Join Date: Nov 2006 Location: Munich, Bavaria	6SN7, yes, but in term sof optics a desaster 6SN7 as single triode or SRPP has very low µ. But you need µ for feedback to get a good damping factor. So a 2-staged topology is the way to go.

11th May 2011, 02:38 PM	#4
DF96 diyAudio Member Join Date: May 2007	It doesn't have any feedback. Maybe it should.

11th May 2011, 03:21 PM	#5
oliezt_sayfu diyAudio Member Join Date: Aug 2009	hello thanks for the input everybody... the driver use 6922/6dj8 should i use global feedback or local feedback..?

11th May 2011, 04:24 PM	#7
DF96 diyAudio Member Join Date: May 2007	The 6DJ8 should give you a low distortion first stage. 6SN7 would definitely have less gain, and might have slightly higher distortion. You don't have enough spare gain for enough NFB, so no NFB is better than insufficient NFB. I assume you prefer single-ended pentode outputs? I would use the two EL84 as P-P, but each to their own!

11th May 2011, 05:35 PM	#8
the_manta diyAudio Member Join Date: Nov 2006 Location: Munich, Bavaria	Sorry sorry sorry....I thought you wanted to use the EL84 as Pentode Now I see it's triode conected. Well then you don't basically need feedback, but I always recommend at least a bit. Whether you want to use local feedback (I mean like that) or global is up to you. With gobal feedback it's more difficult to get a stable amplifier because of the phase shift of the output transformer and all the coupling caps. (Ideal feedback doesn't have any phase shifting components in its way, look at typical Transistor amp schematics, they are more or less completely DC coupled) to the driver: A 6SN7 needs a bit more supply voltage and current to sound good, but 300V is adequate. 6DJ8/ECC88 is a very good driver and matches the EL84 shape :-) ECC88 doesn't need much volatge but at least 7 to 8mA. This gives nice working points. Withe the 6DJ8/ECC88 and little or no feedback you have plety of possibilities to design your driver. One tube for both channels would be the simple way. with two systems, there are many many more...grounded cathode followed by cathode follwer, µ-follwer, SRPP, Diff-amp, cascode etc..... Just try a few and keep the one you like :-)

11th May 2011, 07:30 PM	#9
DF96 diyAudio Member Join Date: May 2007	Sorry, I had not spotted the EL84 triode connection. As long as you don't drive it too hard it may be fine without feedback. Given a simple output stage, it seems sensible to have a simple input stage too.

13th May 2011, 09:00 AM	#10
oliezt_sayfu diyAudio Member Join Date: Aug 2009	thanks again for great input.... i'm thinking about PushPull output, but i have to buy PP Trans.. is it worth to change to Pushpull compared to PSE...(el84) ? the loudspeaker is fullrange at 90db sens...

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