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Katodenfolgern difference amplifier for driving the push-pull stages.

Hello,
in this blog I want to show you a push pull driver stage. I build it in a 6 x EL34 Power Amplifier ( schematic ) and I am very satisfied with this kind of driver .
It consists of two differential amps. A conventional cathode coupled differential amplifier at the top and an anode coupled differential amplifier at the bottom. Both differential amplifiers are forming a kind of constant current draw to improve each other. There will be no change in charge of the coupling caps from the cathode coupled to the anode coupled differential amp. This prevents 'blocking' of the tubes and cross over distortions .
Experimental BJT bread board circuit

Differenzverstärkern muss oft ein Katodenfolger je Ausgang nachgeschaltet be in order to drive triode with sufficiently low impedance. With the help of 'Fourth Circuit Design' can be of two Katodenfolgern build a differential amplifier with anode coupling. Through a clever interconnection with the controlling differential amplifier in Katodenkopplung additional time constant grid current free limit is reached, there is no work-shift and Distortion come with that, not occur. The differential amplifier serve each other with a current source which improves the quality of the differential amplifier even further. The picture shows the interconnection of the two differential amplifiers.

The following are the various circuit components described and subsequently launched a example circuit for a power amplifier .

In a conventional differential amplifier with Katodenkopplung the output to the anodes of the tube is removed.

Katodengekoppelter differential amplifier
The cathode current is distributed, depending on the voltage difference between the bars on the anodes. When using a constant current source, as shown in the picture, there is complete common mode rejection. This means that even under asymmetric activation is obtained at the anode equal-phase signals. Condition for this is that the load is equal to the anodes. A current source requires at least one additional appropriately wired tube. A good compromise, come without this power source is charged with a DC resistance. This is called 'long tail' and the wired as a differential amplifier tube (or transistor) pair is therefore long tailed pair , briefly called LTP. The multiple stages connected in series provides a more common mode rejection. Another reason why you invest in the tubes rather than an additional LTP level in a power source.
is even more favorable to as in the circuit above, use the following differential amplifier as a power source for the previous difference amplifier. Serving as Katodenstromquelle triode control changes of the total current and get so effective against the desired current source behavior r> R by circuitry measures.

triode can be constructed with a differential amplifier in anode coupling.

anode coupled differential amplifier
case of symmetrical control is no signal voltage at the anodes. Any imbalance causes an anode voltage signal that controls the passage of the triode. When using a constant current source, as shown in the picture, there is complete common mode rejection. This means that even under asymmetric activation is obtained at the cathode equal-phase signals. Condition for this is that the load is equal to the cathode.
The output resistance between the cathode is, as between two different Katodenfolgern, 2 / s [s = slope]. They are measured in the sample circuit 570Ω. The anode-side 'long tail' at the anode-coupled differential amplifier is at the open circuit voltage gain μ 'worse' than the cathode-side 'long tail' at katodengekoppelten differential amplifier. Triode with a high penetration and low residual voltage enable a high-resistance anode resistance which improves common mode rejection. However
are triode with very high penetration as Katodenfolger not really suitable. How to find the best cathode follower. In the presented application, the anodes of the small signal Katodenfolger moderately differential amplifier with the grids of the Katodenfolger katodengekoppelten coupled as a grid-based amplifier. The above reduced action of the 'long tail', due to the μ anode coupled differential amplifier, is thus more than compensated. Through this Gleichtaktverkopplung both create differential amplifiers are mutually optimal operating conditions.

The following is an application example of this driver in a booster :
(Tubes along the signal path ECC82 → ECC88 → 6N6P → 6xEL34)

The control of output tubes to be avoided in the grid current range control. When controlling an electrically coupled Katodenfolger You hold the power grid by appropriate choice of anode voltage for the Katodenfolger of range. At the anode-coupled differential amplifier is determined by the resistance common anode or the anode power source the maximum grid current of the output tube. The grid current use at the Katodenfolger determines the grid current of the output tube. The well-known problem with the change in charge of the coupling capacitor and the associated operating point is thus moved from the output tube grid to the grid of the driving Katodenfolgers. This change in charge of the coupling capacitor prevents the circuit. The top differential amplifier detects the grid electricity used to power tubes as a change of the total current and limits the control of the Katodenfolger still energized grid area. This does not change the charge on the coupling capacitors. The operating point is stable. Now you can size the coupling capacitors generously without fear Nachkriechen the operating point must be. How

the circuit does that, you can Oscillograph to the grids of the output tubes. The oscillogram shows an overdriven 1KHz sine wave.

(The same oscilloscope also obtained from the secondary winding of a Zwischenübertragers, which receives its bias on balancing resistors, image .)
on the 0V line, here grid electricity use is flattened, the upper cap of the sinus. At the lower end is added for a bit. This happened here in the anode current-free area and therefore has no effect on the output, especially as the push-pull signal is unaffected. The output is as desired in overdrive top and at the bottom.

It's not the dreaded crossover distortion by shifting the operating point.

Appendix:
first calculating the internal resistance of the equivalent current source for the differential amplifier katodengekoppelten:
This is formed by the anode-coupled differential amplifier. The common cathode resistor is:
1:01 Rkges = R9j R9h II II II R15J R15h
= 1 / (2x (1/47KΩ 1/56KΩ +))
= 13KΩ. This is
μ-times multiplied to the anode side: 6N6P
μ = 22
1:02 μrkges = 22 x 13KΩ = 286KΩ
Since the voltage drop at the common anode resistance Rages of katodengekoppelten differential amplifier control the triode of the anode-coupled differential amplifier, this resistance Rages μ-times multiplied added to μRkges:
1:03 Rages = R9c II R9o NB The 1MW resistors are negligible.
= 1 / (+ 1/47KΩ 1/47KΩ)
= 23KΩ
1:04 μrages = 22 x = 506KΩ 23KΩ
added together
Both resistance values yield the internal resistance of the equivalent current source for the differential amplifier katodengekoppelten:
1:05 μ (Rkges Rages +) + = 286KΩ 506KΩ 792KΩ
r =
By 'long tail' on the other hand, only about
1:07 would Rlt = (50V + 135V) / 7 mA = 26KΩ achieved.
Duch, the combination of the two differential amplifier of the differential amplifier katodengekoppelte cheaper by a factor of 30 as a single with 'long tail resistance'.
is noteworthy that most of the equivalent current source resistance r = 792KΩ is formed here by the common-mode control via μrages = 506KΩ. This finding is very valuable and applicable to many of these differential amplifiers.

second determination the equivalent internal resistance of the power source for the anode-coupled differential amplifier:
recognize this, we must, that causes any change in current to the anodes in parallel a corresponding voltage drop at the common anode resistance Rages katodengekoppelten the differential amplifier. This controls the two triodes of the anode-coupled differential amplifier in common mode at the bars. This μ-fold more sensitive grid control circuitry replaces the power source to the common Triodenanoden. When anodal 'long tail' of the anode-coupled differential amplifier could be a 'long tail resistance' of maximum (360V - 50V) / 7mA allow = 44KΩ. The the 'long tail' corresponding equivalent current source internal resistance, which is formed by the grid control is, in contrast μrages = 506KΩ. By combining the two differential amplifiers of the anode coupled differential amplifier cheaper by a factor of 12 as a single with 'long tail resistance'.

third common mode rejection and CMRR:
Through the interconnection of the coupled differential amplifier of the differential amplifier katodengekoppelte Katodenfolger as common mode signals on the anodes of the anode-coupled differential amplifier. These are coupled according to the penetration of the cathode. The grid control on the katodengekoppelten Differential amplifier counteracts this. Therefore favors a smaller penetration and a large common-mode rejection Rages.

CMRR is 60 dB measured in the application example.

calculate CMRR:
To calculate first the common-mode gain vugl
3:01 vugl 1/μ-Rages/μ = (+ Rages Rkges)
condition: Rkges>> 1 / s, for μ the value of the anode-coupled differential amplifier.

with the values from the example circuit:
vugl = 1 / 22 - 23KΩ/22 (23KΩ 13KΩ +)
vugl = 0.045-0.029
vugl = 0.016 corresponds to-36dB

The push-pull amplification for the differential amplifier is calculated katodengekoppelten
3:03 vuggkd sx = (μ / s II Ra)
where for μ s and the values for the triode in katodengekoppelten have used differential amplifier. These are determined from the charts to the tube.
vuggkd = 5mA / V x (29 / 5mA / V II 47KΩ)
vuggkd = 5mA / V x 5163Ω
vuggkd = 26 times

The push-pull amplification for the anode-coupled differential amplifier is calculated as:
3:04 vuggad = (1 - 1 / μ) x (Rk (Rk + 1 / s))
vuggad = (1 - 1 / 22) x (26KΩ (26KΩ + 285Ω)) = 0.95 x 0.99
vuggad = 0.94

is the push-pull amplification of the circuit:
3:05 vugg = vuggad vuggkd
vugg x = 26 x 0.94 = 24 = 28dB
vugg

3:06 CMRR is:
CMRR = vugg / vugl
CMRR = 24 / 0.016 = 1500
CMRR = 28dB 36dB + 64dB =

With Long Tailed Pair and Katodenfolger contrast, only one would
3:07 Rlt / Rages = 26KΩ / 23KΩ
(see 1:07 and 1.03)
= 1.13 or 1.1 dB CMRR
= 1.1 dB + 27dB = 28dB reach.

CMRR is improved by the Gleichtaktverkopplung of Katodenfolger and Long Tailed Pair presented here provide the Anodnung in this circuit to the 63 - fold or 36dB.

4th output resistance:
rkk The output resistance between the cathodes is expected to be 2 / s because the internal resistance of both cathodes are comparatively small signal in series. From the measured value for RCC can calculate the slope s:
4:01 s = 2 / rkk
s = 2 / 570Ω = 3.51 mA / V
1 / s = 285Ω
The reciprocal of the slope is s multiplied by μ Riak the internal resistance of the triode.
4:02 Riak = μ 1/sx
Riak = x 22 = 285Ω 6270Ω
this value may be to control in Ia = f (Ua) chart to the nearest operating characteristics set as tangents.

A simplified formula for calculating the output resistance between cathode and ground brings rkm an extreme value analysis:
4:03 For Rages = 0:
rkm ≈ 1 / s
4:04 For Rages = ∞:
rkm ≈ Rkges

It follows:
4:05 rkm = (Rages + 1 / s) II Rkges

With the values of the circuit:
rkm = 23KΩ 13KΩ II = 8K3Ω

The measurement showed scarce 8KΩ. It is also interesting that the output actually behaves like the equivalent circuit in subscribed Anordunug with transformer. If an output short-circuited small signal moderate, the output voltage remains unchanged as desired. This means the amplitude doubled on the opposite side, then.

The Scoop: In
has a forum in the scene of well-known user in my opinion just trying to notch up this development. http://ebmule.de/showthread.php?tid=1147&page=10
quote from 'User' from post # 246:
"... To prevent further discussions from the outset: that which Darius here trying to sell as an innovation, I have the end of last Year, already presented in a completed device in a similar configuration. ... "End quote http://www.roehrentechnik.de/forum/gdgt-300B.png
In the picture,

he has added to the review, it shows the old arrangement known differential amplifier controls Katodenfolger. Of course, all beautifully colored, fitted with simulations and positions the tubes as in the circuit here in the blog. Did he really believe to get through it?
As the saying goes, if I do not get it that no one should have tried it in my opinion by all the advantages of one of the arrangement to ignore or talk away. While one tries to distract from the subject highlighting the advantages not to have to admit, the other looks for the current source and the target past the next simulated reality. Flaming worst form, as well as my real name, provided in an offensive context, have become one of them. Of course, all attempts to dissuade the user, this blog here to read! The
Thread is in the version 13.06.09. Pdf copy is available and can be sent privately by email on request. The following blog is