Balanced F5 question

[ichiban]

For those who had paid for the SumR toroids, have you received any reply upon the receipt of the payment and the estimated delivery time?

I got this email today

Your transformers were shipping today
Canada Post item # CX --- --- --- CA.
Please let me know when you receive them
and how they work in your application.

Thankyou,
Richard
Sum R

 

[pchw]

Thank you, Ichiban. I will be wanting for Richard's email patiently.

 

[fitzfish]

Fred, Patrick, and all of us who participated in the early adopter’s toroid group buy -

Richard at SumR emailed yesterday to let us know they were all complete and would be shipping over the next few days. Each of us should receive a confirmation email with tracking information once yours ship.

I expressed our appreciation to Richard for his help providing custom transformers made to Patrick's specifications.

Dave

 

[EUVL]

Totally agreed.
And many thanks Dave for all your hard work organising for us.


Patrick

 

[dazed2]

Damn where was this group buy? How much was the toroid?

 

[pchw]

Damn where was this group buy? How much was the toroid?

2 transformers x $124 + $59 shipping + $12.40 paypal charge = $322.40 USD total
That is for a GB of 10 toroids. The price may be lowered when the quantity goes up in the future, and ship to Canada is likely lower than to US as well.

 

[lhquam]

I searched this thread carefully, but cannot determine what jfets and output mosfets are to be used in the "final version" of the balanced F5. The original schematic (post #1) shows IRFP240 and IRFP9240 devices for output and 2SK370 and 2SJ108 input JFETs. Is there an adequate supply of matched devices?

 

[EUVL]

2Sk170BL, 2SJ74BL (GR will also do if Idss > 4mA), 2SK1530Y, 2SJ201Y.


Patrick

 

[h_a]

Is there an adequate supply of matched devices?

As always, IRFPs/Toshiba Jfets are offered by Jack (TechDIY) and me, I think Blues has the Toshiba mosfets.

Hannes

 

[EUVL]

For F5X stereo, you need matched quads, not pairs.

Patrick

 

[h_a]

Hi Patrick,

I suppose you mean N-to-P matched fet-pairs with same transconductance matched between legs? In that case only the Toshibas would do, however, as one looses just a few dB in THD if complementarity is not that perfect, so for those wanting to save some money or simply prefering the IRFPs I think the IRFPs would do also pretty well.

Any case, it's a matter of taste

Hannes

 

[BigE]

Is someone putting together a "parts bag" of matched bits for this build?

 

[EUVL]

If you wish to have my advice, don't waste your time getting parts until the prototype build has been reported by AR2 & Fitzfish. Then you will hear detailed descriptions of different configurations being tried out and listened to. Estimated time not before end of March.


Patrick

 

[BigE]

Thanks! I can wait.

 

[BigE]

If I am going to plug this into a 15 amp breaker, is it necessary to use a 600 VA toroid? eg. Won't a 300 VA work if the rail voltages are 20 volts?

Eg. 300 VA toroid, with 2 x 20 volt @ 7.5 amp secondaries.

That's 15 amps worth of current at 20 volts....

Forgive me if this is a silly question, for I am new at this.... the last physics I studied was 25 years ago....

 

[EUVL]

See :

http://www.diyaudio.com/forums/pass-labs/172770-balanced-f5-question-12.html#post2371325

Please take time to go through the thread, and maybe also check some basics on the many internet sites dealing with Class A Amplifier Power Supply.


Patrick

 

[dazed2]

Correct me if I'm wrong but I think on the line side the calculation should be 300VA / 120V = 2.5A draw.

So a 600VA transformer should draw max 5A. Not a problem for a 15A 120V household line.

However, in Nelson's F5 article, he states that the line fuse is 3A slow blow. If you guys using 600VA toroids, do you still use a 3A fuse, or do you upgrade to 5A fuse?

Lastly, Nelson also states that he "believes" the MOSFETs can only take a max load of 10A at 24V with an impedance of 2Ohm. Does this current load change with a lower rail voltage?

 

[qusp]

will there be any problem using 2SK1529/J200 in this amp in place of 2SK1530/J201? I only ask, because I have a small bag of them left from another project and from what I can see at least its close enough to have to ask if there is something i'm not seeing. being that they are of the same family, with the main difference being a slightly smaller package and lower current handling. still within spec for this build I would imagine and the lower capacitance of the smaller pad might be an advantage. I will have ample heatsinks, i'm using keratherm red isolators, so seems it should be alright. perhaps the sonics are not as good Patrick? I have not used its larger brother so dont know.

i'll be driving ~6-8ohms 2 ways

 

[AndrewT]

Dazed and BigE.
Do more research.
I'll start you off.
Vac is not the same as Vdc

If the amplifier is to run on +-20Vdc you do not use a 20+20Vac transformer.
20Vdc/sqrt(2) = 14.14Vac Use a 14Vac or 15Vac transformer.

Power distribution.
The power distributed either from the mains or within your amplifier is governed by the formula Power = Volts * Amperes.
Sometimes Volts and Amperes are not quite in phase. So we use VA = Volts * Amperes.

If you have a 600VA transformer and want to connect it to 110Vac mains then the maximum primary current is defined by the same formula but rearranged.
Max I = Max Power / applied voltage.
Imax = 600VA / 110Vac = 5.45Aac (this calculation assumes transformer is 100% efficient. If we know the 600VA is 93% efficient then actual primary Max I = 5.45 / 0.93 = ~5.9Aac
Use a T5A or T6A fuse to run this transformer up to it's maximum continuous rating.

But, there is a problem.
The fuse will often/sometimes blow when you start up the amplifier.
You need to add a soft start to allow the fuse to pass starting current without nuisance blowing.

This gives you a number of starters for your reading/homework.

 

[AndrewT]

will there be any problem using 2SK1529/J200 in this amp in place of 2SK1530/J201? ................i'll be driving ~6-8ohms 2 ways

the smaller To3p package is not so good at dissipating heat.
If you build using the smaller package and ask it to dissipate the same heat, it will run hotter. This will result in less reliability. I cannot estimate whether it might reduce life from 100years to 50years or from 10years to 1year.

If you reduce the heat by reducing the PSU voltage and/or reducing the bias current so that Tj is the same in both packages, then reliability should be restored.