F5 power amplifier

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S

slam

Member
Joined 2005
I use my F5 to drive the Mcintosh XRT-22 (87db @ 8 ohm, 2x12" base) and it has authority on base, but my the output votage peaks at around 10 v (around 12W) during the loudest passages.

I use 1 x 400VA + single Cviller's PS board to drive 2 channels so my configuration should be pretty standard.

Did you see rail voltage drops during base passages?

Also you can check basic frequency response with a signal generator (or sound card) + a multimeter just in case.
 
fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
My F5 is short on bass...

tinitus said:
I suppose you had more bottom end before
Which amp did you use then ?

S-8 looks like a 2.5way or 3way
Either way theres 2x woofers in paralel
Maybe thats forcing F5 to deliver less bottom power
Click to expand...

Thanks for your comments.

So far I have used DIY amps (or modified commercial ones) and all with multiple Lateral Mosfet pairs for output stage (except for my modified based JLH amp). Front end is of different configurations. I am mainly inspired by Erno Borbely design.

Is it the single output pair of the F5 or my power supply or else?
 
fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
My F5 is short on bass...

slam said:
I use my F5 to drive the Mcintosh XRT-22 (87db @ 8 ohm, 2x12" base) and it has authority on base, but my the output votage peaks at around 10 v (around 12W) during the loudest passages.

I use 1 x 400VA + single Cviller's PS board to drive 2 channels so my configuration should be pretty standard.

Did you see rail voltage drops during base passages?

Also you can check basic frequency response with a signal generator (or sound card) + a multimeter just in case.
Click to expand...

Thanks for your suggestions.

I can not understand why the frequency response should not be ok with 100kohms input and 10uf MK type. Previously I had 47uf (electrolytic Non-Polarysed) and the bass response was the same.

For the rail voltage drop, I use 0.167 ohm resistor in the C-R-C instead of the suggested 0.12 ohms (of the F4 amp for example), could it have an impact?
Ialso use high ripple Caps for the power supply (I think about 21A per 36000uf)

Anyway, I suppose I will have to bring my F5 amp back on the bench to verify your comments. I have the required equipment.
 
S

slam

Member
Joined 2005
fab said:
Thanks for your suggestions.

I can not understand why the frequency response should not be ok with 100kohms input and 10uf MK type. Previously I had 47uf (electrolytic Non-Polarysed) and the bass response was the same.

For the rail voltage drop, I use 0.167 ohm resistor in the C-R-C instead of the suggested 0.12 ohms (of the F4 amp for example), could it have an impact?
Ialso use high ripple Caps for the power supply (I think about 21A per 36000uf)

Anyway, I suppose I will have to bring my F5 amp back on the bench to verify your comments. I have the required equipment.
Click to expand...

I couldn't see a problem of either as well. It would be good to experiment to make sure the amp behaves as it should.
 
pro

pro

Member
Joined 2004
Hi to everyone.
After three months my F5 played (very well) in these conditions

[img=http://img338.imageshack.us/img338/4687/img0485rid.th.jpg]

last weekend I gave him a home :D

[img=http://img27.imageshack.us/img27/7830/img05011.th.jpg]

Some pictures

[img=http://img338.imageshack.us/img338/6936/img04901.th.jpg] [img=http://img401.imageshack.us/img401/6466/img04911.th.jpg] [img=http://img225.imageshack.us/img225/1036/img04922.th.jpg] [img=http://img67.imageshack.us/img67/5149/img04941.th.jpg]
[img=http://img198.imageshack.us/img198/9173/img04951.th.jpg]
[img=http://img44.imageshack.us/img44/879/img05001.th.jpg]
[img=http://img406.imageshack.us/img406/3498/img05021.th.jpg]


Honestly, going from 250 mA to 1.3 A of bias, I did not find differences in listening. Perhaps there will be with the measure, but listening did not seem to notice improvements.
Regards
 
Last edited:
Melon Head

Melon Head

Banned
Joined 2006
Hi Michele
What are the sensitivity and impedance of your speakers?

Hi FAB
Try getting rid of the resistors in the power supply. Then let me know what you hear. I suspect your operating quite high into class B, so everytime the current draw exceeds the bias current, you are going to get voltage drops.
Also try increasing the bias to 2A (hopefully your heatsinks can handle this).

If I understand correctly you have wired your transformers in series to give 18V AC. One transformer is used fo +18V and 0, and the other for -18v and 0. Is that right?
 
Last edited:
pro

pro

Member
Joined 2004
Hi Thanh
my speakers who play with f5 are Infinity Beta 20, declared 90 bB, but I think that 88 is more realistic.
I have built a Zen V4 and a Pearl phono stage.

Hi Bobo
Looking at the article of Papa "Leaving class A", it seems that the improvement from 0.32 to 1.28 Amp is less then one order (from 0.03 to 0.007 at low frequencies and less at high), but maybe this is not audible.

Hi Nicoch
I don't know
I bought it on Ebay with the 4 Siemens capacitors (trafo is used, caps are new) for 45 €
500VA 17-0-17. Anyway it's a very good trafo, very quiet at +/- 2.6 amps. Better then toroidal, I think.

Regards
 
Last edited:
Melon Head

Melon Head

Banned
Joined 2006
Hi Michele
I have 4 ohm speakers of similar sensitivity.
My experience with the JLH class A, is that increasing bias current does have quite a significant effect.
Well, it is good to hear that you are getting good results at low bias levels.
Hopefully I will have the same experience with this amp (smaller heatsinks).
What are the other amps you have built in the photos?
 
fab

fab

Member
Joined 2004
fabaudio.online
Paid Member
My F5 is short on bass...

thanh1973 said:
....
Hi FAB
Try getting rid of the resistors in the power supply. Then let me know what you hear. I suspect your operating quite high into class B, so everytime the current draw exceeds the bias current, you are going to get voltage drops.
Also try increasing the bias to 2A (hopefully your heatsinks can handle this).

If I understand correctly you have wired your transformers in series to give 18V AC. One transformer is used fo +18V and 0, and the other for -18v and 0. Is that right?
Click to expand...

Hi Thanh

I will try bypassing the series resistors in the PSU. However, I know I get more hum this way...as seen on the scope at least. Thanks for the suggestion.

I operate at 1.3A so I believe that I am always in class A while at low volume. My heatsink temperature is already over 50C at 1.3A.

You understand perfectly my transfos configuration.

Thanks
 
Mooly

Mooly

Administrator
Joined 2007
Paid Member
The closer you run a component to it's absolute limit the shorter it's life. That may be as little as 2000 hours for a capacitor. I would always use the 105C rating as a matter of course.
Think of it this way, a 12 volt bulb is rated for 1000hrs at 12V, at 11 volts it will last 2000hrs, at 10volts it may well last 7 or 8000 hours and so on.
The 105C caps generally have a higher spec when it comes to low E.S.R. compared to cooking grade ones.
 
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