The issue with a SRPP in a preamp duty is that there is absolutely no guarantee that the correct load will be applied. I believe this is probably why they fell out of favour in the roll some considerable time ago.
This is not a major problem with a CCS load if the right rp and current is used.
Shoog
This is not a major problem with a CCS load if the right rp and current is used.
Shoog
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Joined 2009
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I'm sorry, but this doesn't sound right to me.
The maximum voltage gain from a triode is mu. You achieve mu once the load resistance is high enough to completely dominate over the internal (rp) resistance. Whether you use a CCS or an inductor to achieve this high load resistance the end result in terms of gain is the same.
I suspect the CCS is technically superior because it can be designed to provide a high resistance load over a wider frequency range than most practical chokes. Chokes have self-resonant frequencies, above which they become capacitive, and they have declining impedance at low frequencies.
The advantage of a choke over the CCS is that the it can store energy and in doing so allows a large signal swing at the plate to rise above the B+ supply. It allows for more headroom but at the same gain as a CCS. Perhaps this is the source of confusion in your understanding.
Rgds,
Gareth
Hi,
It can't be.
No idea what this infatuation with the SRPP is but I discarded that topology ages ago. It has it uses but it's not all that great and most certainly not the holy grail.
As for the noise factor of CCS loaded low Rp triodes, I can only confirm that its probably the most quiet of all other alternatives.
SY knows very well that I try to keep as much sand out as I can but there are applications where it is just what's needed for that particular application.
Not to mention the fact that it can (the CCS I mean, not sand per se) open a hole new avenue of applications that are almost impossible to achieve without it.
And yes, I'm still the same guy that also uses VR tubes in his regs....
Just like anything else, cascade the same thing over all gain stages and yes, it will show its signature (sonic footprint as they say). But then that goes for just about anything, from resistors to caps and so on.
Ciao,
It can't be.
No idea what this infatuation with the SRPP is but I discarded that topology ages ago. It has it uses but it's not all that great and most certainly not the holy grail.
As for the noise factor of CCS loaded low Rp triodes, I can only confirm that its probably the most quiet of all other alternatives.
SY knows very well that I try to keep as much sand out as I can but there are applications where it is just what's needed for that particular application.
Not to mention the fact that it can (the CCS I mean, not sand per se) open a hole new avenue of applications that are almost impossible to achieve without it.
And yes, I'm still the same guy that also uses VR tubes in his regs....
Just like anything else, cascade the same thing over all gain stages and yes, it will show its signature (sonic footprint as they say). But then that goes for just about anything, from resistors to caps and so on.
Ciao,
Me neither, but for some reason, it's very fashionable, especially in Asia. For its intended use (driving low impedances and highly capacitive loads), it can work well. In audio, it's almost never used for that purpose, but stuck in positions where other circuits can work much better.
Only if the choke has, by some magic, stable negative resistance so that it contributes significant gain itself. A CCS and choke can, to a first approximation, be considered to be alternative methods of providing the same high impedance load and so the same gain (=mu). The second approximation brings in issues like noise and frequency response, but not gain.dirkwright said:
A lightly loaded SRPP is essentially just a grounded cathode stage with an active load. To get balanced operation requires a surprisingly heavy load, as the 'optimum' load resistance for low distortion is likely to be much lower than the SRPP output impedance. This fact seems to be relatively poorly known.
My theories about why the SRPP is so popular in certain quarters:
1. herd instinct
2. myths:
2a: "The SRPP is balanced and so has low distortion" - actually even a balanced SRPP would only have low even-order distortion, and many SRPP you will see in audio circuits are not balanced.
2b: "The SRPP has low output impedance and that is a good thing" - actually the SRPP has a surprisingly high output impedance (typically around ra/3) but that doesn't really matter if the following stage has a high input impedance, as is common for many valve stages.
3. go-faster stripes
Any move away from bog-standard grounded cathode stages can vaguely suggest/imply that the designer has incorporated advanced technology, even when the change has no significant effect on performance.
1. herd instinct
2. myths:
2a: "The SRPP is balanced and so has low distortion" - actually even a balanced SRPP would only have low even-order distortion, and many SRPP you will see in audio circuits are not balanced.
2b: "The SRPP has low output impedance and that is a good thing" - actually the SRPP has a surprisingly high output impedance (typically around ra/3) but that doesn't really matter if the following stage has a high input impedance, as is common for many valve stages.
3. go-faster stripes
Any move away from bog-standard grounded cathode stages can vaguely suggest/imply that the designer has incorporated advanced technology, even when the change has no significant effect on performance.
Hi,
I totally agree, the load must be no higher than 1K if not distortion goes up considerably.
I think the entire topology owns its popularity to the (IMHO myth) that a CF degrades the sound of a system.
If you believe that and you want a single stage that needs to have relatively low Zout and still has some gain then, yes. Provided the SRPP drives a Low Zin.
I think I still have the measurements taken of several SRPP stages somewhere, I'll try to find them later on tonight.
One of my fav topologies (and again one should not overdo it) is the mu-follower, it looks similar to the SRPP but isn't one at all. It has much of the advantages of the solid state CCS without the sand...
Ciao,
I totally agree, the load must be no higher than 1K if not distortion goes up considerably.
I think the entire topology owns its popularity to the (IMHO myth) that a CF degrades the sound of a system.
If you believe that and you want a single stage that needs to have relatively low Zout and still has some gain then, yes. Provided the SRPP drives a Low Zin.
I think I still have the measurements taken of several SRPP stages somewhere, I'll try to find them later on tonight.
One of my fav topologies (and again one should not overdo it) is the mu-follower, it looks similar to the SRPP but isn't one at all. It has much of the advantages of the solid state CCS without the sand...
Ciao,
Yes, the mu-follower drops all pretence of balance and instead goes for higher anode load (so low distortion) and lower output impedance than SRPP. Also better PSRR. In almost all small-signal audio circuits a mu-follower can do better than SRPP - the only downside is a small increase in HT voltage requirement due to the extra voltage drop across the extra resistor.
No, will be pretty low at low volume. Output impedance will peak at about 13k at -6dB volume, which is nearly maximum sound.painted said:
There are too many negatives in your first sentence to know what you are asking or commenting.
The second stage could suffer from grid current, which will create distortion due to the high output impedance of the first stage. It would be valve sample dependent.
I might be wrong on this but isn't the major part of the pots resistance in series with the signal at low audio levels? The reason I praised the quality of this humble circuit was because its merits are not obvious. Driving a 6Vrms voltage across the (assumed) 1nF load of the power amp would require 6/7962 = 0.000753A rms ca. 1mA pp from the pre. How could that come from the high impedance ECC83 if not the circuit held some clever design. For me that is
The issue is not just how much pot resistance is in series with the signal but how much is shunting the signal too.
I agree, its merits are not obvious! It uses negative feedback to reduce output impedance, but this cannot increase current driving ability. The ECC83 is about the worst possible choice for a line stage output valve. It can only have been designed by someone who doesn't really know what he is doing, or had a very sensitive power amp so signal levels were guaranteed to be low.
I agree, its merits are not obvious! It uses negative feedback to reduce output impedance, but this cannot increase current driving ability. The ECC83 is about the worst possible choice for a line stage output valve. It can only have been designed by someone who doesn't really know what he is doing, or had a very sensitive power amp so signal levels were guaranteed to be low.
Ohh yeah. Now we're talking
I'm interested.Got so interested in this CSS after all talk. Can i use it with my tubes/preamp?
I wouldn't go all the way to a CCS load since you already have the twin triode in place. I would go Mu-follower. Read this and get a full understanding as well as seeing how easy the conversion would be;
http://www.fetaudio.com/wp-content/uploads/2003/09/Mu-Stage.pdf
Shoog
http://www.fetaudio.com/wp-content/uploads/2003/09/Mu-Stage.pdf
Shoog
Here it says a mu-fallower acts as ccs?
The Valve Wizard -Mu Follower
Yes, i will read and see how much i can understand. Thx
The Valve Wizard -Mu Follower
Yes, i will read and see how much i can understand. Thx
My back of the envelope guesstimate says you would want to keep 100V min over each valve and to keep your bias current at about 5mA would require the bottom bias voltage to be set at -1V. Adjust your top resistor to 200R and insert a 16K resistor on the plate of the bottom triode (dropping 80V).
If you can adjust your power supply a fraction to get a bit more voltage then all the better.
Shoog
If you can adjust your power supply a fraction to get a bit more voltage then all the better.
Shoog
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