F5X -- the EUVL Approach

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#21
Dual Mono means 2 channels in one case, but with separate transformers and power supplies. So we have not changed the situation since then.

A single channel of F5X consumes 32Vx4A = 128W electrical power, and dissipate all of that into the heat sink when not playing music. So a heat sink for 75W is certainly under-dimensioned. The MF35-151.5 will just take that much power without excessive junction temperature at the MOSFETs. So I am not prepared to advise you to put out more heat into it. Of course I cannot stop you from doing so either.

🙂


Hope this answers your question,
Patrick

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#22
F5 Versions supported by the Main Amplifier PCB

I was asked by PM as to whether one can use our PCB for SE F5, why not bipolar cascode, how about all the other F5 variants, ....., etc.

I try to explain it simply.

The circuitry (independent of component values) of the PCB is identical to the standard F5 as published by Nelson a few year ago, including the over-current protection, but with the following exceptions :

1) It contains 2 Single Ended F5's in (95%) mirror image. The difference to using 2 separate F5 SE PCBs (e.g. from Peter Daniel) is that the left and right halves of our PCB share a common single-point star ground, a common connection to +Vs and another to -Vs in the middle. This is a key layout requirement for the balanced circuit. But still, you may, if you so wish, use one PCB to build 2 channels of SE F5's without problems, even though you might get a bit of power-supply, and to a lesser extent signal, coupling between the left and right channels.

2) It supports both grounded F5X and floating F5X.

3) It supports optional JFET cascode for the first stage (using J111/J174 as per Borberly).

4) It does not include thermistors, but there are enough connection points available if you wish to use a thermistor.

5) It supports the use of 2SK389 / 2SJ109 dual JFETs. This puts quite some constrains on the PCB layout.

You can pretty much use any value of components, and any devices you want, as long as they are TO92/TO247 (TO3P), and pin compatible.
There are provisions to allow the use of MPC74 or TO220 type source resistors.


Patrick

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#23
Cascode using Bipolar Transistors

Another specific question was "Why not bipolar cascode".

This is a good question, and there are indeed some technical merits in using BJT cascodes. BJTs have a higher gm than JFETs like J111/J174 or 2SK246/2SJ103, and hence can reduce Miller effect of the first stage JFETs (2SK170/2SJ74) better, at the expense of 6 more components per channel.

I shall talk to fitzfish about this and see whether we can offer this option on the PCB as well.
Whether we shall also test this particular version will be decide between the test team, as they not only carry the work load, but also the expenses.


Hope I have answered some of your questions sufficiently,
Patrick

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#24
thx

so If I do not get it wrong again, only output devices are on MF35 heatsink and we will have another heatsink for regulator per channel
what Is dissipation for regulator board

EUVL said:
Dual Mono means 2 channels in one case, but with separate transformers and power supplies. So we have not changed the situation since then.

A single channel of F5X consumes 32Vx4A = 128W electrical power, and dissipate all of that into the heat sink when not playing music. So a heat sink for 75W is certainly under-dimensioned. The MF35-151.5 will just take that much power without excessive junction temperature at the MOSFETs. So I am not prepared to advise you to put out more heat into it. Of course I cannot stop you from doing so either.

🙂


Hope this answers your question,
Patrick

.
Click to expand...
 
#25
> only output devices are on MF35 heatsink and we will have another heatsink for regulator per channel

Yes, that is the plan.

Each of the two regulators (one for each channel) sits on a Fischer SK88-125 heat sink, so do the rectifying diodes. Per channel, assuming 16Vac secondaries from your transformer, the dissipating for rectifier and regulator will be 26.5W in total. The SK88 heatsinks sit inside the case, along the centre line and close to the top cover. The top cover has very generous openings protected by a wire mesh for ventilation.


Patrick
 
#26
I hope you would forgive me for breaking my own rules and post one image with non-technical content.

😉


Patrick
 

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#28
#29
#31
I have revisited the cascode options in the last couple of days, and read some of Borbely's paper again. He has abandoned the use of bipolar cascode in favour of JFETs in all his new designs, with reasons.

So I have come up with a new JFET cascode which will give better performance than the J111/J174 and yet not more complex than the bipolar cascode. And we shall include that on the PCB layout, together with the J111/J174 option. The amplifier will then remain an all-FET design.

Again, this is only for experimentation purposes. Only actual test will decide whether it brings anything.


Patrick

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#36
well i have received no reply from fitzfish on the transformer query. perhaps he will see here. perhaps i am not worthy? 😀 anyone else in the build team i can contact who might know?

perhaps the switch to fets also was congruent with his advertising byline creating 'all fet' designs hehe
 
#39
it has come to my attention that my post above if taken seriously could be taken the wrong way. my post

well i have received no reply from fitzfish on the transformer query. perhaps he will see here. perhaps i am not worthy?
Click to expand...
was more me thumbing my nose at the sometimes deserving attitude that seems to be going around lately. it was not meant to be taken seriously thus the smiley, as i know others like myself have their own lives they must get on with. so Dave if you read it like this my apologies, i was not being serious, but i guess its still a bit raw for some people at the moment.

all sorted thanks to pchw anyway, so as you were :cheers:
 
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