Tubes draw some grid current all the time but it is more or less constant until the voltage approaching the zero grid line. Although this grid current will be very tiny for signal tubes but then we are dealing with 0.33mA of bias current. As long you make sure the max voltage swing is at least 3db more than what is required, you should be in safe category.
One observation is you have to watch out for the corner frequency of the RC in the voltage reference. Try to aim for 1~2Hz. Or just play around the cap value to see if you hear any differences.
The other way I see is to use DN2540 casocde instead of LND150 where you can then increase the bias current making it less affected by grid current. You can even replace the resistor with a LM329 if you are using jfet at the bottom of the cascode. In this case, I will suggest adding a RC filtering following the LM329 instead of strapping a big cap over LM329. A cap over LM329 is a no no to my ears when biasing at 3~5mA.
thats why
i had good results from the beginning using a 9V batery and sound improved when changing to 2 pcs of 4,5V batteries.
i had good results from the beginning using a 9V batery and sound improved when changing to 2 pcs of 4,5V batteries.
but
the whole rtp is abig preamp so i have enough space, my layout is similar to the official rtp3 and near the phonostage i use 2 batteries per channel, you can also try some lithium stuff this will last much longer but maybe sound different
the whole rtp is abig preamp so i have enough space, my layout is similar to the official rtp3 and near the phonostage i use 2 batteries per channel, you can also try some lithium stuff this will last much longer but maybe sound different
Could you please help me understand how to calculate the corner frequency? Is this the standard calculation of fc = 1/2πRC, where R is R12 + R13 and C is C4?
If I remember correctly, the RTP4 and RTP5 were similar in concept to the RTP3, but with MOSFETs in the bootstrap and constant-current positions of the SLCF output stage. Allen never felt they sounded as good as the all-valve RTP3 circuit.
All the versions of Allen's preamps are described in the Tube Preamp Cookbook (if you haven't got one, shame on you
)Alex
If I remember correctly, the RTP4 and RTP5 were similar in concept to the RTP3, but with MOSFETs in the bootstrap and constant-current positions of the SLCF output stage. Allen never felt they sounded as good as the all-valve RTP3 circuit.
All the versions of Allen's preamps are described in the Tube Preamp Cookbook (if you haven't got one, shame on you
Alex
I have the second edition, and I've only made it through about 1/4 of the book. It is a great resource
Hello VSE builders i have some questions about the RTP3D.
At the moment i build up a RTP3D with the instruction manual i get from Allen Wright.
It is a lot of work because there are some errors in the manual but i think i found them all (i hope so).
Is there a substitute for the MAT02/SSM2220? At the moment a MAT02 is build in.
The current sources uses BF 245C. How can i match them so that they deliver the right current with the given resistor in the manual.
Or should i use a trimmer poti to set it to the right current?Which value should the pot have?
I don´t know how much current the second stage in the line amp sucks.
Does anybody know it?
So that i can trimm the current source to the right value.
Thanks from Germany
Roland
At the moment i build up a RTP3D with the instruction manual i get from Allen Wright.
It is a lot of work because there are some errors in the manual but i think i found them all (i hope so).
Is there a substitute for the MAT02/SSM2220? At the moment a MAT02 is build in.
The current sources uses BF 245C. How can i match them so that they deliver the right current with the given resistor in the manual.
Or should i use a trimmer poti to set it to the right current?Which value should the pot have?
I don´t know how much current the second stage in the line amp sucks.
Does anybody know it?
So that i can trimm the current source to the right value.
Thanks from Germany
Roland
RTP3D questions
Why looking for a substitute? In the original C version Allen used 2SK170/369 matched pairs of Jfets. However according to him it turned out that MAT02 are much better, more gain for low output MC´s, less noise and above all better sonics. The only alternative he mentioned was LM394 as a possible replacement for MAT02 but if it is sonically beter? ???
According to the parts list there is no matching required, however I do not know if the parts Allen supplied with the kits were already "preselected". A matching device circuit was shown in his Tube Preamp Cookbook but can also be found here: Transistor matching
Of course you can also take a trimmer for adjustments. A possible implementation with the BF245C is shown in this blog under #54
In the old schematic of the SLCF with a 1 K resistor between ground and Jfet 2SK147/369 voltage measurement over this resistor gives 12.4 Volt. So according to Ohm's law that would be then 12.4 mA.
For sure trimming is possible here as well although maybe in this part of the circuit using matched devices for optimum symmetry of inverting and noninverting part could make sense although Allen Wright did not specify this in the manual.
airtangent
Why looking for a substitute? In the original C version Allen used 2SK170/369 matched pairs of Jfets. However according to him it turned out that MAT02 are much better, more gain for low output MC´s, less noise and above all better sonics. The only alternative he mentioned was LM394 as a possible replacement for MAT02 but if it is sonically beter? ???
According to the parts list there is no matching required, however I do not know if the parts Allen supplied with the kits were already "preselected". A matching device circuit was shown in his Tube Preamp Cookbook but can also be found here: Transistor matching
Of course you can also take a trimmer for adjustments. A possible implementation with the BF245C is shown in this blog under #54
In the old schematic of the SLCF with a 1 K resistor between ground and Jfet 2SK147/369 voltage measurement over this resistor gives 12.4 Volt. So according to Ohm's law that would be then 12.4 mA.
For sure trimming is possible here as well although maybe in this part of the circuit using matched devices for optimum symmetry of inverting and noninverting part could make sense although Allen Wright did not specify this in the manual.
airtangent