I remember the amp and the post. However, his is a sample of one. PL appears to use the common mode feedback resistors in all of their SuSy designs. This may be due to the fact that they are producing many amps a month and need some way of insuring a consistent and achievable result.
Graeme
Graeme
Could be, we shall see...
While I have your attention, have you any idea on the bootstrapping idea or thermal compensation that you would be willing to share? The bootstrap in particular is an interesting topic if it has the capacity to improve performance and eliminate a seperate supply for the front end. Not that I am convinced but I would like to understand more.
Ian.
While I have your attention, have you any idea on the bootstrapping idea or thermal compensation that you would be willing to share? The bootstrap in particular is an interesting topic if it has the capacity to improve performance and eliminate a seperate supply for the front end. Not that I am convinced but I would like to understand more.
Ian.
Ian,
In general I don't think that either of these issues is important to the quality of the sound of the amplifier. The thermal compensation is just good engineering on Nelsons part. There definitely is a thermistor in the photo and the circuit is probably very similar to what Nelson did in the old Threshold amps.
I think the front end has it's own supply. Look at all the wires coming from power transformer plus you can see what appear to be regulators on the power supply board down below.
The bootstrapping is probably something to do with running the bias 20% below what would be required for full class A. Sort of feels like a reprise of the old Threshold sliding bias idea but in a much more modest form. So this looks like a heat reduction idea.
All in all I don't think any of these things are present to improve the sound. Once again though, I have say that these are only guesses on my part.
Graeme
Steen - thank you for the link.
In general I don't think that either of these issues is important to the quality of the sound of the amplifier. The thermal compensation is just good engineering on Nelsons part. There definitely is a thermistor in the photo and the circuit is probably very similar to what Nelson did in the old Threshold amps.
I think the front end has it's own supply. Look at all the wires coming from power transformer plus you can see what appear to be regulators on the power supply board down below.
The bootstrapping is probably something to do with running the bias 20% below what would be required for full class A. Sort of feels like a reprise of the old Threshold sliding bias idea but in a much more modest form. So this looks like a heat reduction idea.
All in all I don't think any of these things are present to improve the sound. Once again though, I have say that these are only guesses on my part.
Graeme
Steen - thank you for the link.
Ian Macmillan said:
The older X amps wich featured an UGS module had the bias generator between the drains of the voltage gainstage.
I would think the new XA.5 uses a variation of that UGS circuit but coupled as it is in the preamps (drains tied togheter) driving the outputstage via two capacitors as the Jfets are driving the output fets in the F4.
Maybe this would not exactly fall under the term bootstrapping but it would make the stage capable of swinging clooser to the rails by half the bias voltage.
Ok thanks, I will take a look at it.
I am not sure if the "old" XA100 had an UGS of sorts or not, of hand I think it did. The biggest difference is probably that the .5 sports a PP output. Seriously overkilled, with a load of output fet's, 48 as far as recall.
Answering Ians post further upstream. Several posts slipped in between
I am not sure if the "old" XA100 had an UGS of sorts or not, of hand I think it did. The biggest difference is probably that the .5 sports a PP output. Seriously overkilled, with a load of output fet's, 48 as far as recall.
Answering Ians post further upstream. Several posts slipped in between
steenoe said:Ok thanks, I will take a look at it.
I am not sure if the "old" XA100 had an UGS of sorts or not, of hand I think it did. The biggest difference is probably that the .5 sports a PP output. Seriously overkilled, with a load of output fet's, 48 as far as recall.
It is something more like the XA100.5 that I am trying to build, complete with UGS, PP output and a small amount of SE bias
Ian.
gl said:
Ok, thanks Graeme.
Ian Macmillan said:
It is something more like the XA100.5 that I am trying to build, complete with UGS, PP output and a small amount of SE bias
Ian.
Looking forward to see how it goes
For now, I am working on Le Cheff's circuit and I will report back on the sound, ofcourse Hi guys,
you are communicating very fast..................
three hours absent and a lot of new replies.
Seems that there is interest...
Well, there is always some interpretation when you try to reconstruct such an amp with pictures.
But I am quite sure that I know the new UGS, the outputboard and the supply.
I can see most of the paths to the two connectors of the UGS modul. And when you are also knowing the basic circuit, it is no problem to interprete the rest. I can see all values of the taken resistors and not every value makes sence on every place in a circuit - so the possibilities are very, very small. Because there is no paths from the J-Fet sources to a connector pin to find and all pins are reserved, I explained that there is no Mcmillan feedback applied.
Please forgive me but I will not public my "interpretation?" of the modul for not running in trouble with our master...
Have ordered the cascode transistors and some other parts today...
The next step will be to etch the boards, which takes some time for me, because I have no experience in doing it. Also it is a problem to get photo?-positiv?-coated? boards in my needed size.
When this is managed the only real secret will be the bias circuit and perhaps the bootstrapping.
In the meantime I will brood about it and hope to find new ideas...
Greatings
Dirk
you are communicating very fast..................
three hours absent and a lot of new replies.
Seems that there is interest...
Well, there is always some interpretation when you try to reconstruct such an amp with pictures.
But I am quite sure that I know the new UGS, the outputboard and the supply.
I can see most of the paths to the two connectors of the UGS modul. And when you are also knowing the basic circuit, it is no problem to interprete the rest. I can see all values of the taken resistors and not every value makes sence on every place in a circuit - so the possibilities are very, very small. Because there is no paths from the J-Fet sources to a connector pin to find and all pins are reserved, I explained that there is no Mcmillan feedback applied.
Please forgive me but I will not public my "interpretation?" of the modul for not running in trouble with our master...
Have ordered the cascode transistors and some other parts today...
The next step will be to etch the boards, which takes some time for me, because I have no experience in doing it. Also it is a problem to get photo?-positiv?-coated? boards in my needed size.
When this is managed the only real secret will be the bias circuit and perhaps the bootstrapping.
In the meantime I will brood about it and hope to find new ideas...
Greatings
Dirk