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Old 19th February 2011, 08:53 AM   #21
EUVL is offline EUVL  Europe
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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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Last edited by EUVL; 19th February 2011 at 09:17 AM.
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Old 19th February 2011, 09:09 AM   #22
EUVL is offline EUVL  Europe
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Default 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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Last edited by EUVL; 19th February 2011 at 09:21 AM.
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Old 19th February 2011, 09:14 AM   #23
EUVL is offline EUVL  Europe
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Default 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

.

Last edited by EUVL; 19th February 2011 at 09:22 AM.
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Old 19th February 2011, 09:36 AM   #24
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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

Quote:
Originally Posted by EUVL View Post
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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Old 19th February 2011, 09:43 AM   #25
EUVL is offline EUVL  Europe
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> 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
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Old 19th February 2011, 10:01 AM   #26
EUVL is offline EUVL  Europe
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I hope you would forgive me for breaking my own rules and post one image with non-technical content.




Patrick
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Old 19th February 2011, 10:13 AM   #27
reytnz is offline reytnz  New Zealand
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You are Forgiven...
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Old 20th February 2011, 08:15 AM   #28
EUVL is offline EUVL  Europe
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Those who are interested in the discussion why to have 16V 2A per FET for the 4-MOSFET balanced circuit can have a look at :

Balanced F5 question
Balanced F5 question
Balanced F5 question


Hope it helps to clear rather than to confuse,
Patrick
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Old 20th February 2011, 08:54 AM   #29
EUVL is offline EUVL  Europe
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Default Is 16V rail voltage too low ?

See :

F5 For Low Z Loads ?
F5 For Low Z Loads ?

I find that I do most of the listening at no more than 4V pk-pk, which means in the F5X (balanced) the Vds across each FET is no less than (Rail Voltage - 2.5V). The extra 0.5V deduction comes from the source resistors of the MOSFETs.


Patrick
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Old 20th February 2011, 02:57 PM   #30
EUVL is offline EUVL  Europe
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Default Comments about paralleling output devices

F5 For Low Z Loads ?

Patrick
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