My understanding is that the resistor lowers the Q of the external inductance that forms the resonant circuit in conjunction with the input capacitance of the the FET. We both know that the resistor must be as close as possible to the gate of the FET, but if the resistor was forming a low-pass filter in conjunction with the input capacitance, then its exact physical (not electrical) position would be immaterial, and simply driving the FET from a higher impedance source would work. What I am suggesting is that the undamped loop into the Zener may just be enough inductance to cause oscillation. OK, you may be sceptical, (and so am I), but you seem to have tried everything else.
One can theorise about this sort of thing all day. The proof is in the pudding. You will only know what was the cause of your problem when you eliminate it.
One can theorise about this sort of thing all day. The proof is in the pudding. You will only know what was the cause of your problem when you eliminate it.
PREAMP.
Hi,
Mains isolation is an important factor, so if other members want to I can design regged PSUs from 50V up to 450....Good PSU design make or breaks a good circuit IMHO...
Cheers,😉
Hi,
Mains isolation is an important factor, so if other members want to I can design regged PSUs from 50V up to 450....Good PSU design make or breaks a good circuit IMHO...
Cheers,😉
Power supplies
...........so if other members want to I can design ...............
Hi Frank,
That is a very good idea. You are right about the supply being very crucial to the circuit. Go ahead and design one or some really good ones. We could give you feedback on how good they turn out to be.
Cheers,
Ashok.
...........so if other members want to I can design ...............
Hi Frank,
That is a very good idea. You are right about the supply being very crucial to the circuit. Go ahead and design one or some really good ones. We could give you feedback on how good they turn out to be.
Cheers,
Ashok.
REGGED PSU.
Hi,
When I proposed to do so, I had your particular needs in mind...so if you let me know the current and voltage requirements
for your phono stage I'll see what I can do....
Keep in mind, if you regulate one part you need to also regulate the other, otherwise it's not worth it.
Cheers,😉
Hi,
When I proposed to do so, I had your particular needs in mind...so if you let me know the current and voltage requirements
for your phono stage I'll see what I can do....
Keep in mind, if you regulate one part you need to also regulate the other, otherwise it's not worth it.
Cheers,😉
Riaa.
Hi,
In case anyone feels more comfortable with passive RIAA stages:
Let me know what you think of it.
Ciao, 😉
P.S. The loss of the cathode bypasses reduces the gain, introduces some local degenaritive FB, all in all this circuit should sound faster and more open, I expect bass to be tighter too.
This is my choice for a MC cart combined with the MC Hammer headamp it has a lot going for it, if I may say so.
Hi,
In case anyone feels more comfortable with passive RIAA stages:
Let me know what you think of it.
Ciao, 😉
P.S. The loss of the cathode bypasses reduces the gain, introduces some local degenaritive FB, all in all this circuit should sound faster and more open, I expect bass to be tighter too.
This is my choice for a MC cart combined with the MC Hammer headamp it has a lot going for it, if I may say so.
Attachments
Hi Frank
Interestingly, i am not a big fan of unbypassed cathode resistors. Don't know if it's the feedback or the resistors but even a high quality cap bypass, with the unavoidable added colourations sounds more open and dynamic to me. If i had to improve this circuit (according to my taste 🙂) i'd replace the first cathode resistor with a nicad and have fixed grid bias on the second stage. Of course this will change the output impedance of the first stage and slight adgustment of the 210k will be in order. Another interesting aspect is whether to implement the RIAA before or after the coupling cap. As shown the circuit has the advantage of using potentially low votage riia caps but they are obviously not biased. I wonder if you have tried both positions for the coupling cap and whether you find a difference.
regards
peter
Interestingly, i am not a big fan of unbypassed cathode resistors. Don't know if it's the feedback or the resistors but even a high quality cap bypass, with the unavoidable added colourations sounds more open and dynamic to me. If i had to improve this circuit (according to my taste 🙂) i'd replace the first cathode resistor with a nicad and have fixed grid bias on the second stage. Of course this will change the output impedance of the first stage and slight adgustment of the 210k will be in order. Another interesting aspect is whether to implement the RIAA before or after the coupling cap. As shown the circuit has the advantage of using potentially low votage riia caps but they are obviously not biased. I wonder if you have tried both positions for the coupling cap and whether you find a difference.
regards
peter
SUBJECTIVE OBJECTS...
Hi,
Whenever possible, I try to avoid bypass caps.
They slow down transient response and, depending on the animal in use, definetely colour the sound. No amount of bypassing electrolytes ever worked to my ears, all that did was disrupting coherency.
In my OTL amps, no bypass caps at all and just one coupling cap per signal polarity...naturally I have the PSU caps in the signal path too if you must but that doesn't seems to have much of an impact on the sound, probably due to the PP and CF topology used.
I'd rather use local NFB by not bypassing the cathode Rs than using global NFB.
All of these measures sound more open, faster and dynamic to me, usually bass is tighter too.
Sure, you could do that...never tried it though.
What I have tried is tie the cathode of the first triode to ground and bias the grid through a 10M or higher gridleak, worked great when combined with the MC Hammer headamp.
No, I haven't tried it but I follow you on this one.
I should try this, good idea...if anyone wants to try make the voltage rating at least 400VDC for the RIAA caps and I hope you still find some nice copperfoil polystyrenes for it.
All coupling and RIAA caps are precision matched both on value and between channels in the case of my own preamps.
Actually, I do follow that philosophy throughout the entire system, even for the PSU caps, resistors and wire lengths and xformers....up to the x-overs in the speakers...
Friends call me "Le Puriste"...
Cheers and thank you for the contribution,😉
P.S. Did you buy that Thorens vinyl spinner?
Hi,
Whenever possible, I try to avoid bypass caps.
They slow down transient response and, depending on the animal in use, definetely colour the sound. No amount of bypassing electrolytes ever worked to my ears, all that did was disrupting coherency.
In my OTL amps, no bypass caps at all and just one coupling cap per signal polarity...naturally I have the PSU caps in the signal path too if you must but that doesn't seems to have much of an impact on the sound, probably due to the PP and CF topology used.
I'd rather use local NFB by not bypassing the cathode Rs than using global NFB.
All of these measures sound more open, faster and dynamic to me, usually bass is tighter too.
Sure, you could do that...never tried it though.
What I have tried is tie the cathode of the first triode to ground and bias the grid through a 10M or higher gridleak, worked great when combined with the MC Hammer headamp.
No, I haven't tried it but I follow you on this one.
I should try this, good idea...if anyone wants to try make the voltage rating at least 400VDC for the RIAA caps and I hope you still find some nice copperfoil polystyrenes for it.
All coupling and RIAA caps are precision matched both on value and between channels in the case of my own preamps.
Actually, I do follow that philosophy throughout the entire system, even for the PSU caps, resistors and wire lengths and xformers....up to the x-overs in the speakers...
Friends call me "Le Puriste"...
Cheers and thank you for the contribution,😉
P.S. Did you buy that Thorens vinyl spinner?
Frankstein series reg
Frank,
Did anything ever scome of the series reg you were going to design for the RIAA stage?
David
Frank,
Did anything ever scome of the series reg you were going to design for the RIAA stage?
David
Hi,
Actually it's here already:
REGGED PSU.
If you build the complete MM phonostage with the linestage as a buffer you need that circuit x 4.
There's also an add on tubed headamp to cater for MC cartridges that's in a separate box so you can put it close to the TT.
Cheers,😉
Actually it's here already:
REGGED PSU.
If you build the complete MM phonostage with the linestage as a buffer you need that circuit x 4.
There's also an add on tubed headamp to cater for MC cartridges that's in a separate box so you can put it close to the TT.
Cheers,😉
Hi fdegrove
I'm interesting to build the phono stage plus the buffer line stage.
But you post two phono stages.One with passive riaa and the other with the feedback network.
Which from the two is the best?
Is it possible to use 2*PSUs?
One for the line stage and one for the phono stage?
4 PSUs is too complicated.4 trannies,16tubes!!
Or one for the L channel and one for the R.
Same PSU for preamp and phono in each channel.
Do you have a foto of the complete project?It will be interesting to see it.
I'm interesting to build the phono stage plus the buffer line stage.
But you post two phono stages.One with passive riaa and the other with the feedback network.
Which from the two is the best?
Is it possible to use 2*PSUs?
One for the line stage and one for the phono stage?
4 PSUs is too complicated.4 trannies,16tubes!!
Or one for the L channel and one for the R.
Same PSU for preamp and phono in each channel.
Do you have a foto of the complete project?It will be interesting to see it.
Have you ever tried MC step up transformers?
What is better,step up with trannies or with tubes?
Regards
What is better,step up with trannies or with tubes?
Regards
Hi,
The one with the passive network hasn't been built by me so I can't tell you what that sounds like.
Technically, yes.
It defies the purpose of the design depending on where you cut corners.
Actually, I think you misread; the preamp uses one regulated supply per channel for the phono stage and an identical one for the buffer.
So, in total that's 4 HT supplies, 4 regulated 12V heater supplies and 4 6.3 VAC supplies for the regulator valves.
Sorry, I haven't.
Ten to fifteen years ago xformers were probably not as good as they are today.
I always preferred the active stage to an xformer coupled stage, YMMV.
Cheers,😉
The one with the passive network hasn't been built by me so I can't tell you what that sounds like.
Technically, yes.
It defies the purpose of the design depending on where you cut corners.
Actually, I think you misread; the preamp uses one regulated supply per channel for the phono stage and an identical one for the buffer.
So, in total that's 4 HT supplies, 4 regulated 12V heater supplies and 4 6.3 VAC supplies for the regulator valves.
Sorry, I haven't.
Ten to fifteen years ago xformers were probably not as good as they are today.
I always preferred the active stage to an xformer coupled stage, YMMV.
Cheers,😉
12 xformers?Ok the filament xformers were small right?
How you connect 4*B+ and 4*12Vdc from the PSU chassis to the circuit chassis?
How much current can one PSU delivers?'Cause I'm planning to use one for the phono-line for the L-channel and one for the phono line for the R-channel.
And if I remember well you said the volume control effects to the riaa filtering.I'm planning to use an other volume control so I'm thinking to build a phono with passive riaa network.Any good schem?What about Bob Danielak's phono stage?What the other experts say?
How you connect 4*B+ and 4*12Vdc from the PSU chassis to the circuit chassis?
How much current can one PSU delivers?'Cause I'm planning to use one for the phono-line for the L-channel and one for the phono line for the R-channel.
And if I remember well you said the volume control effects to the riaa filtering.I'm planning to use an other volume control so I'm thinking to build a phono with passive riaa network.Any good schem?What about Bob Danielak's phono stage?What the other experts say?
Hi,
Actually, only six. Four for B+ and heaters for the regulators. Two more for the heaters of the preamp proper.
In the preamp the value of the volume control is the same as g'.
This value can't be changed and needs to be 1M. You can still use a regular potentiometer but it has to be 1M.
The Danielak should be a good preamp too.
Cheers, 😉
Actually, only six. Four for B+ and heaters for the regulators. Two more for the heaters of the preamp proper.
In the preamp the value of the volume control is the same as g'.
This value can't be changed and needs to be 1M. You can still use a regular potentiometer but it has to be 1M.
The Danielak should be a good preamp too.
Cheers, 😉
Schematic
Hi Guys,
Can one of you guys send me the schematic of this amp?
Thanks!
Audiofanatic 😉
GAK said:
Hi Guys,
Can one of you guys send me the schematic of this amp?
Thanks!
Audiofanatic 😉