F5 Turbo Builders Thread

[Bksabath]

Originally Posted by flg

Find a comfortable quality operating point that does not dissapate more than you can tolerate. I have had a 750W heater in my listening room. I only need to turn it up 1/2 way in the winter to heat the room!

I agree with you I have used much less gas heating than the year before
and the heath output of F5 was certanly part of it.

That is way I was saiing that one shuld find out rougly How much power your speakers need.

The rest is gready BoyZ thing

[AudioSan]

Originally Posted by jacco vermeulen

On the MUR3020W datasheet, the Vf axis is linear, but the vertical axis is logarithmic scale.
10-15 degrees doesn't make a significant difference in Vf, so mounting the diodes on one heatsink or the other doesn't make the diodes kick in a lot sooner.

But a 15 degree jump in diode die temperature does make a difference current wise.
Take the example of my previous post : 40C or 50C diode temperature means ~0.865A or 1.25A diode current at a Vf of 0.6
One MOSFET would do ~2A drain current, the other nearly 2.5A

10C temperature difference between one location of a heatsink and another isn't that round the bend.
(e.g. EUVL's heatsink measurements in the latest LinearAudio fagazine)

so you will recomand having external heatsinks for the diodes? to get the diode heat down 10-15C?

[AudioSan]

Originally Posted by Bksabath

I agree with you I have used much less gas heating than the year before
and the heath output of F5 was certanly part of it.

That is way I was saiing that one shuld find out rougly How much power your speakers need.

The rest is gready BoyZ thing

i cut out the aleph2's for heat reasons 700W was too much in the summer time

[buzzforb]

FLG and BKsabath,
There are many that would say that extra power improves the sound, whether it is used or not. Audiophoolery, dunno. Nelson, either jest-fully or seriously, says the higher power version he built had a more relaxed presentation. I am not ready to write it off yet, but i think we are all looking at the same way. At the end of the day, the diodes do no harm and only add potential, so why not.

[flg]

buzzforb, I beleive the extra pwr thing but my take is a little different. Down in the low wattage area (1W by some standards) is where the 98% of the music is (or some very high %). It is only momentary transients of 10-20db above the average level, that you need all the power for. These momentary transients, in my view, can be of lesser quality amplification. Many people are forcing clipping of these transients and don't even notice! Circuits that have a "soft" clipping response, such as tube circuits, are well known to sound very good. Is missing the transient totally preferable to a slightly more distorted version?
Designing the amp to work in it's own classA, lower power state, amplifies 90+ % of your music. The momentary adventure into high power classAB will not likely be an issue.
The Vf of these diodes and the Vdrop of the Rs needs to be chosen carefully. As is the H.S. discussion currently happenig. Has anyone looked into other diodes? SiC maybe? I saw a comment not responded to regarding a resitor in the diode lead???

[buzzforb]

Sounds wonderful with Salas' 6V6 in front. F5 is the best of the Firstwatt amps for bottom end, no question. I think the BA output stage has more soul, but we are talking sugar vs spice now.

FLG,
I agree. As for other diodes, unless you want to use them more actively in playback, I dont know what is accomplished in trying others, but then again, I dont know squat. I like the idea of a 2 pair V3 biased at 1.5 to 2A across .22 Rs with really well matched ppairs. I really wish i had a couple thousand pieces to sort through.

Excuse the mess in my ever changing test room.

[Bksabath]

@ buzzforb post 244

Yes absolutley current clipping is much worst than voltage clipping I am in favor of using the diodes.

By the way one can easily find ot how bad current clipping sounds just by undersizing the capacitance on the suply and listening to a few traks.

So far we made quite a bit of progress

The way I see it is

Diodes need sinks on way or other

Source resistors can be tweaked (if you got preaty good matched mosfets)to give wanted volt drop for required Idle Bias Current

Keep in mind that Papa said "they sound beter at hi bias"

With diodes we are going in to class AB operation but at the volume level at wich the transition happens we are not going too ear much difference
Speakers distort much more than amplifiers any way.

Same again as current demand goes up suply need to be oversized and PCB traks need to be prety thick.

Same again for trafos a 20 20 V secondary 300VA wuld give F5 7.5 amps
For Turbo (and again way I see it no point going tubo for less than 40 V rails)
so 30 30 V traffo rated 300VA wuld only give 5 amps as we are considering that we may be asking the amplifier to be capable of more than this with the diodes in place Trafo VA need to go up

If you use bigher Traffo CL 60 need to go up as well or soft start is much more atractive.

I am pulling 40W dissipation on TO220 at present, for turbo operation (going in to class AB more often) I will have to reduce that a bit.

I dont know how much especialy as in class AB one of the mosfets will be off
while the other is conducting.

So lets say 4 pairs instead of 2 pairs I am using at the moment PCB got to be longher

If PCB is longher speaker out track got to be thiker + I am using loads of current so a buss bar there make same sense.

Question.

What is track width and PCB cooper veigth on Papa 150 W amplifiers?

[buzzforb]

Originally Posted by Bksabath

@ buzzforb post 244

Diodes need sinks on way or other

I will be doing seperate like Jacco recommended

Originally Posted by Bksabath

Source resistors can be tweaked (if you got preaty good matched mosfets)to give wanted volt drop for required Idle Bias Current

Keep in mind that Papa said "they sound beter at hi bias"

Audio Gospel Truth

Originally Posted by Bksabath

With diodes we are going in to class AB operation but at the volume level at wich the transition happens we are not going too ear much difference
Speakers distort much more than amplifiers any way.

I thkn setup dependent. Some speakers can handle more than others iwthout distorting and if you have smaller F5T vs bigger counterpart, you may hear them more than you think

Originally Posted by Bksabath

Same again as current demand goes up suply need to be oversized and PCB traks need to be prety thick.

Same again for trafos a 20 20 V secondary 300VA wuld give F5 7.5 amps
For Turbo (and again way I see it no point going tubo for less than 40 V rails)
so 30 30 V traffo rated 300VA wuld only give 5 amps as we are considering that we may be asking the amplifier to be capable of more than this with the diodes in place Trafo VA need to go up

If you use bigher Traffo CL 60 need to go up as well or soft start is much more atractive.

Dual 400VA. Final will have dual 600VA.

Originally Posted by Bksabath

I am pulling 40W dissipation on TO220 at present, for turbo operation (going in to class AB more often) I will have to reduce that a bit.

I dont know how much especialy as in class AB one of the mosfets will be off
while the other is conducting.

IS this true with diodes? Perhaps this is where the magic happens

I know this, the F5T likes to be turned up. As my volume knob increased, there was no loss in clarity, but tons extra body. Not like F5 I have built before. Am i lying to myself, perhaps. Maybe Fairchild vs IRF, dunno. Maybe Audiophoolery, dunno. Mind is a deceitful thing.

[a.wayne]

Buzz you have a full f5t up and running ..?

[a.wayne]

Originally Posted by buzzforb

FLG and BKsabath,
There are many that would say that extra power improves the sound, whether it is used or not. Audiophoolery, dunno. Nelson, either jest-fully or seriously, says the higher power version he built had a more relaxed presentation. I am not ready to write it off yet, but i think we are all looking at the same way. At the end of the day, the diodes do no harm and only add potential, so why not.

Big un , beats little un everytime .....