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adding output tubes stage to the buffalo 2

mars2

Member
2003-12-19 2:45 pm
Basel
My implementation runs the Buffalos in current mode output into low-ohm resistors as I/V-stage (there is a lot of information in the "Buffalo II & transformers" thread), followed by stepup transformers and a high-transconductance parafeed tube output stage.
About liking and disliking implementations:
I think that one should really try several topologies, listen and believe his ears.
From a certain level of sound quality, it comes down to everybodies personal taste.
 
The problem with the lampizator with the Buffalo is two-fold. First, the input impedance is too high, which means the ES9018 is acting as a voltage source more than a current source.

Second, it's single ended, so you lose the benefits (performance) of the balanced outputs. Rigging two together into a "balanced" setup does not help, as the inputs are not truely differential. You get the voltage swing, but not the cancellation.
 

mars2

Member
2003-12-19 2:45 pm
Basel
Yes, the lampizator seems a really strange circuit.
By connecting the buffalos antiphase out to the non-bridged cathode of a typical common-cathode stage you simply parallel the equal-phased NF-voltages which have nearly the same level.
Because this one is still undistorted, there should be some distortion canncelation. This is the advantage of the circuit, I think. The other params should be nearly the same.
But, as Brian pointed out, you`ll loose the balanced performance feature!
The only workaround with such a one triode SE-stage would be using a transformer...;)
 

mars2

Member
2003-12-19 2:45 pm
Basel
There`s only one phase amplified, otherwise you would simply have two outputs.
The common mode rejection is a very important quality factor of a balanced stage. It directly shows the amount of cancellation common mode signals resp. amplifying explicitly differential signals and depends amongst others on the amplification factor of both signals (and logically, the higher the amplification, the better the rejection).
Furthermore, it`s the cathode resistor, which compensates the two antiphase-currents, so that in this resistor, ideally only DC flows (the higher this resistor, the more precise both signals are resp. the better the common mode rejection is. Best is a current source).
I was too fast with my previous reply, and digged a bit deeper into the subject:
The negative input is of course in antiphase with the signal at the cathode. So with the lampizator circuit you will have some kind of feedforward compensation, due to the fraction of the antiphase input signal, which is coupled into the cathode via a voltage divider. I`m not even sure about the distortion reduction: did some spice sims, which showed more than double the distortion, than with only one input signal. But mostly 2nd-order, which could have a positive influence on the sound.
The lampizator circuit cann`t be something else than a single-ended stage with the fraction of an antiphase signal connected to the cathode
- possibly without any further advantage.

Please correct me, if I`m wrong...
 
Last edited:

RollE2k

Member
2007-11-08 9:33 pm
if you want tube output, i would rather make it a parafeed output then you can keep the balance all the way - and if you only need SE-output you can just fix that with the output transformer.
This will of course be more expensive, but at the same time probably alot better!
 

mars2

Member
2003-12-19 2:45 pm
Basel
Listening how it sounds is the best idea!

You could also experiment with the voltage divider ratio - the bigger the amount of the cathode coupled voltage, the lesser distortions (but also less 2nd-order).

You can`t keep it balanced all the way with parafeed output.
You would have a balanced to single ended conversion at the input due to the SE nature of the stage and then a conversion back again via the transformer out.
With this configuration also, you will loose the advantages of balanced stages!
 

mars2

Member
2003-12-19 2:45 pm
Basel
That`s what I mentioned in a previous post - with the lampizator circuit, you`ll never get an exact conversion as for example the broskie circuit with a long tailed pair differential amplifier, followed by his cathode follower.
This configuration should definitifely give top conversion and sound quality!
 
Hello,
A better tube output stage is the Broskie unbalancer, gives you high gain and low output impedance.
Scroll down to "Unbalancer as I-to-V Converter"

Here's a thread about it.

Regards,
Danny

That is a much better circuit.

However, if you want the ES9018 to act as a current source, you want your I/V stage to present mOhm-level input impedance.