I should think that an unbypassed cathode resistor would provide even more distortion surely? Especially with such a small anode load. Characteristics all over the place I should think.
I agree with your second comment of course, valves are great and for using!
Paul
Variation of ra and its consequences (Rout etc.)
Much modern thought , using usually solid state devices, aims to nail down valve characteristics; I am doing it in a small way with the pre-amplifier I mentioned. For a most interesting approach see the thread concerning type 3A5.
Paul
Guys be nice to the OP. 
A few well directed comments about potential improvements (with examples) would be nice - even if the OP chooses to ignore all of the excellent knowledge on tap here.
Led bias, CCS loads, white followers, etc. You know the score. Referencing Allan Wright's (RIP) excellent writings is a prod in the right direction.
In theory when RL is a lot less than the degenerated rp of the triode in question.. The RL in this design is already far too low for good linearity even without cathode degeneration. (The minimum RL for an ECC88 for acceptable linearity IMHO is in the range of 10 - 12K)
I've found there was an improvement in linearity in most cases with the addition of local cathode degeneration, but I don't deliberately load them below rp so I am not certain this would apply in a case where RL was significantly less than degenerated rp - probably a quick sim would indicate what to expect in this case. I've also found no reason to use degeneration for any reason other than to reduce stage gain..
I think one thing we're saying in different ways is that there are better ways of loading the anode than a resistor, whatever the value. 7N7 together with many others is advocating anode loads and solid state devices and the #26 preamp thread is advocating either a good plate choke or an output transformer. When it comes to the cathode, the #26 pre amp thread has been promoting filament bias with cathode resistors as small as 5 ohms, so bypassing such a resistor isn't even an issue. Kevin and many others have been using battery grid bias for ages.
You can't just slap the term "high end" on generic anode resistor+bypassed cathode resistor stages without having done some intelligent exploration of all the more advanced topologies modern preamp designers have been developing and using. Look at all the work that's gone into the Aikido project, for instance. By all means use generic gain stages that date back to the Bronze Age if you want to and like the sound. Drive them with water mills and mice going round in wheels, but don't trivialise the huge amount of work that so many designers have put into optimising the simple tube gain stage. And as 7N7 says, we haven't even started on the power supply.
Andy
You can't just slap the term "high end" on generic anode resistor+bypassed cathode resistor stages without having done some intelligent exploration of all the more advanced topologies modern preamp designers have been developing and using. Look at all the work that's gone into the Aikido project, for instance. By all means use generic gain stages that date back to the Bronze Age if you want to and like the sound. Drive them with water mills and mice going round in wheels, but don't trivialise the huge amount of work that so many designers have put into optimising the simple tube gain stage. And as 7N7 says, we haven't even started on the power supply.
Andy
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The problem, unfortunately, is that if you use anode and cathode loads more appropriate for linear operation, as recommended above, is that you will end up withtoo much gain.
Please note how this design already has "tapped" the anode resistor (taken the output from the mid point of the 2 anode resistors) to throw away about half of the gain of the 1st stage. ECC88 in Grounded Gathode has too much gain for a line preamp.
An anode follower as 1st stage will do the job i think. It has adjustable local feedback.
Please note how this design already has "tapped" the anode resistor (taken the output from the mid point of the 2 anode resistors) to throw away about half of the gain of the 1st stage. ECC88 in Grounded Gathode has too much gain for a line preamp.
An anode follower as 1st stage will do the job i think. It has adjustable local feedback.
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Hi formula 22!
If you accept the idea of changes, then maybe you could go right back to the beginning and start by defining what your actual needs are. How much gain do you need? What output resistance do you need? What is this typically going to be driving? Is the amp close or far away, so what length of leads? Will you need to receive or drive a balanced stage at all, i.e. is there an argument for it to be balanced? Might this be driven directly from a balanced DAC output so there will be something like 0.5v DC on each leg? Do you need a line preamp at all, or would this stage be better integrated into the amplifier you are using? Is there any compelling reason to use a ECC88 or could you use another kind of tube? You're kind of designing in a void here, so it's a bit hard to make useful recommendations. Maybe you could start by giving us the above information?
Andy
If you accept the idea of changes, then maybe you could go right back to the beginning and start by defining what your actual needs are. How much gain do you need? What output resistance do you need? What is this typically going to be driving? Is the amp close or far away, so what length of leads? Will you need to receive or drive a balanced stage at all, i.e. is there an argument for it to be balanced? Might this be driven directly from a balanced DAC output so there will be something like 0.5v DC on each leg? Do you need a line preamp at all, or would this stage be better integrated into the amplifier you are using? Is there any compelling reason to use a ECC88 or could you use another kind of tube? You're kind of designing in a void here, so it's a bit hard to make useful recommendations. Maybe you could start by giving us the above information?
Andy
You have one of the finest cleanest sounding amplifiers out there - in the form of the F5. I say learn to appreciate these outstanding qualities and build a preamp which preserves them.
My first option would be one of Allen Wrights designs in the form of the FVP5, or one of the later incarnations. That would be one of the best sounding - purest designs available and relatively easy to build if you restrict yourself to the Line stage component and don't include the superregulator.
Shoog
My first option would be one of Allen Wrights designs in the form of the FVP5, or one of the later incarnations. That would be one of the best sounding - purest designs available and relatively easy to build if you restrict yourself to the Line stage component and don't include the superregulator.
Shoog
Ah right - missed the F5 bit. Another alternative is the 26 preamp with a LL1660/5mA output transformer in 4.5:1. This is being used a lot and I can guarantee it sounds great! All details in the "#26 pre amp" thread.
7N7 has mentioned his own preamp circuit, which he hasn't published yet. It's extremely neutral and detailed and if he does publish it, it's worth taking a look at. It has a cathode follower so low output impedance.
andy
7N7 has mentioned his own preamp circuit, which he hasn't published yet. It's extremely neutral and detailed and if he does publish it, it's worth taking a look at. It has a cathode follower so low output impedance.
andy
FVP5 schematics have 6922 (E88CC) or 5687 tubes in the line stage.
A 5687 version will give enough voltage gain for an F5 (F5 needs a little over 4 VRMS for full power).
A 6922 version would give too much voltage gain as a stand alone line amp; remember the 6922 line stage section of the FVP5 was to amplify a relatively low gain phono stage.
Hi the heater supply is not the best . adjustable voltage regulator set at 12volts then each tube set with a constant current feed to each tube raised about 40 volt ablove ground will quiet the set way down. there is not a need I see for the input cap since the grid is a ground . There is no cap like no cap . 1000 dollar silver teflon caps only get chose to a straight piece of wire. But if you like the sound go with . The magic is in know where the line is between too little and too much .
In theory when RL is a lot less than the degenerated rp of the triode in question.. The RL in this design is already far too low for good linearity even without cathode degeneration. (The minimum RL for an ECC88 for acceptable linearity IMHO is in the range of 10 - 12K)
I've found there was an improvement in linearity in most cases with the addition of local cathode degeneration, but I don't deliberately load them below rp so I am not certain this would apply in a case where RL was significantly less than degenerated rp - probably a quick sim would indicate what to expect in this case. I've also found no reason to use degeneration for any reason other than to reduce stage gain..
Ok, I can buy that. In a pathological case the degeneration resistance would consume a significant part of available output swing, which would already be too low.
Maybe we just need to help move this design a little further from this danger zone. A good teachable moment as they say.
Thanks,
Chris
Silk purse sows ear !
To quote an old Irish Proverb;
When the lost man asked for directions the reply was "I wouldn't start from here".
Shoog
Part of this of-course is matching your preamp to the power amp to get the COMBINED sound you want.
I have a pre amp which has a SS front end to volume control to tube buffer. When I'm using a really clean SS power amp I take the preamp output from the tube buffer output for some additional mostly 2nd harmonic distortion. When using a tube power amp I take the preamp output directly off the volume control bypassing the tube buffer because the tube power amp has enough "warmth" of it's own.
Oh! the tube buffer is a ECC88 cathode follower thing with a phase inverted slave drone so that the total power supply draw is constant. Then for a bit more "warmth" substitute an ECC189 (6ES8) VARIABLE Mu tube instead. Is it HiFi? Who cares it's lovely.
With an F5 power Amp some "warmth" from the preamp is probably required to suit most of our tastes (we would not be on a tube amp forum if we were happy with that cold sterile and boring SS sound).
Cheers,
Ian
I have a pre amp which has a SS front end to volume control to tube buffer. When I'm using a really clean SS power amp I take the preamp output from the tube buffer output for some additional mostly 2nd harmonic distortion. When using a tube power amp I take the preamp output directly off the volume control bypassing the tube buffer because the tube power amp has enough "warmth" of it's own.
Oh! the tube buffer is a ECC88 cathode follower thing with a phase inverted slave drone so that the total power supply draw is constant. Then for a bit more "warmth" substitute an ECC189 (6ES8) VARIABLE Mu tube instead. Is it HiFi? Who cares it's lovely.
With an F5 power Amp some "warmth" from the preamp is probably required to suit most of our tastes (we would not be on a tube amp forum if we were happy with that cold sterile and boring SS sound).
Cheers,
Ian
Hi,
With 2k2 and 2k7 resistors in the anode Vta (1/2ECC88) is obtained by Gain of 18dB or 8x.
Output resistance preamplifier is abaut: Zout=140ohm
NOTE:
Otherwise, I wanted to create a preamplifier will have a gain of up to10x with the output impedance (Zout) to <1K (for F5-amplifier), where will be the second (2H) harmonic is about 1% and 3H <0.05%, for Vout = 1.5V preamp. There have 2 pieces ECC88 and 2 pieces PCC88. That is why I want to I create preamplifier with ECC88.
Thank you for your cooperation and cheers!
With 2k2 and 2k7 resistors in the anode Vta (1/2ECC88) is obtained by Gain of 18dB or 8x.
Output resistance preamplifier is abaut: Zout=140ohm
NOTE:
Otherwise, I wanted to create a preamplifier will have a gain of up to10x with the output impedance (Zout) to <1K (for F5-amplifier), where will be the second (2H) harmonic is about 1% and 3H <0.05%, for Vout = 1.5V preamp. There have 2 pieces ECC88 and 2 pieces PCC88. That is why I want to I create preamplifier with ECC88.
Thank you for your cooperation and cheers!
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Gingertube,
You indicate that a tube amp per definition is adding "warmth" to the sound. This is the case for most unbalanced amplifiers and can be good for lots of listeners.
I prefer the "wire with gain sound" and the balanced RTP3D preamplifier is the one for me.
I also tried the FVP5 and remember it as very good but it didn't fit my philosophie (balanced end to end).
You indicate that a tube amp per definition is adding "warmth" to the sound. This is the case for most unbalanced amplifiers and can be good for lots of listeners.
I prefer the "wire with gain sound" and the balanced RTP3D preamplifier is the one for me.
I also tried the FVP5 and remember it as very good but it didn't fit my philosophie (balanced end to end).
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