F5 For Low Z Loads ?

[flg]

Originally Posted by eyoung

could you not add a serial R or RC to the speaker or OP to give the amp a more hospitable load to drive...???

Just a thought, EL

Well, No, would be my easy answer. That would change Qts, I guess, and muck up the bass responce.
But, let's explain it this way. I have 16 8 ohm speakers in 8strings of series pairs. 2 ohms. Because, it is said that even more than 1 speaker in series will cause one to suffer ill effects from the back emf of the others. I personally could not explain or understand that concept except to say that I find it less important of a problem if there are only 2 in series. I believe the paralell inductance of the group will also be lower making for an eaiser load on the amp. Additionally, less voltage gain is needed due to the lower output Z Speakers allowing less chance for the signal to be hosed up...

[Melon Head]

Originally Posted by Zen Mod

just an idea - there was similar or exactly same idea recently - why not combine F5 and F4 ?

something as mini F5 - same front end , but with nice 2SJ76/2SK213 "outputs" ..... say 100mA of Iq ...... driving multiple Toshiba final outputs in common source ;

so - count it as 2,5 stages ........

Originally Posted by Melon Head

Speaking of different.
How about this one?

Edit: I was too lazy to add the gate resistors

I would go with your original idea first. As Nelson says two pair is enough.
I built up three a pair version a long time ago now, so it can be done, no problem.

Go for it

[flg]

So, where was I... A few pics are in order. I actually thought I would be raising more questions too? Once I decided to change the output configuration, I'm opening somewhat of a can of worms with the sound and the original design. It's difficult to judge How much things will change the sound or where I should be correcting for the changes. So far my changes are: 19V rails rather than the stock 24V, Dual output Toshiba FETs with .27 ohm Source Rs. in the output. And, the low Vgsth of the Toshiba's will require a smaller Drain R in the input stage to maintain the correct bias, I'll go with 620 ohms for now and stay with the 5k pot. With the lower Vds on the output transistors, I should be able to up the bias beyond the 1.3A stock value (2x of coarse) maybe as high as 1.6A/FET.
Lets see, 1st pic is a H.S. from HeatSink USA. 10.08" x 8" (200mm) section. This should be good for around .35C/W but we'll see. Bias is adjustable to optimize for available dissapation.
Second pic is the back of the H.S. with the mostly stuffed CViller board set up for dual outputs. FET holes are drilled and tapped, just gotta do some board mounting and H.S. mounting holes.
Last pic is 1 of the Antek 400VA 2X15 transformer(1/ch).

[flg]

And...

[a.wayne]

Originally Posted by Nelson Pass

Of course the problem is not driving, say 100 watts into
1 ohm, which implies 12 watts into 8 ohms. The problem
is that people with 1 ohm loads want a couple hundred
watts into 8 and over a kilowatt into 1. Even that's
do-able, but they want it to sound good also.

Since meeting demands like this requires a lot of hardware,
it's prudent to define what you actually want in advance.

50Watt @ 8 ohm with good sound will do ...

Originally Posted by Nelson Pass

I recall that the ill fated Pass Monster project died out
just after I delivered a preliminary schematic.

Hmmm... the revival time might be upon us .........

Originally Posted by Melon Head

I would go with your original idea first. As Nelson says two pair is enough.
I built up three a pair version a long time ago now, so it can be done, no problem.
Go for it

3 pr's with the standard front end or with cascoded front end ? ..

[flg]

Well, because of the loss of gain by a factor of 4 in the output stage, when driving 2 ohms, 2 pair is necessary. Smaller Source Rs will help to a small degree. But, 3 pair would probably regain a similar gain figure to the stock F5. I'm willing to go the easy route for now. The CViller board is set-up for 2 pair of outputs.
As far as power, my goal was to drive 2 ohms relatively well. At 1.3A/FET, I should be getting over 25Wrms max output into 2 ohms. At 1.6A/FET, I'm doing over 40Wrms. On a speaker with over 100db efficiency that's more than I'll need.

[Melon Head]

Originally Posted by a.wayne

3 pr's with the standard front end or with cascoded front end ? ..

Both standard and cascoded. However I used IRFP devices.

[woodturner-fran]

I tried both of my f5 amps with my stacked quads - they didn't play nice together.......

the highs had a touch of harshness that isn't in the amp with other "normal" speakers. But the main thing was that every now and then the source resistors would smoke on the f5. 9 times out of 10 it would be fine then on the 10th they would go.

I couldn't figure it out - not usual stuff like plugging cables when powered etc.


Fran

[a.wayne]

Originally Posted by woodturner-fran

I tried both of my f5 amps with my stacked quads - they didn't play nice together.......

the highs had a touch of harshness that isn't in the amp with other "normal" speakers. But the main thing was that every now and then the source resistors would smoke on the f5. 9 times out of 10 it would be fine then on the 10th they would go.

I couldn't figure it out - not usual stuff like plugging cables when powered etc.


Fran

Instability ?

[woodturner-fran]

Could be....... any suggestions for checking this out?