F5 power amplifier

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#1,603
Some F5 impression

after one week of listening sessions, the overall sound impression is very nice. The F5 has no hum, no turn on thumb and is dead quite.
I think i like it even more than my tube amps. DC stays at around 5mv and is pretty stable. I can encourage everybody to build this great amp. Thanks to Nelson for bringing again a fantastic design to everybody. This amp will for sure stay a long time.

I have run with a tube pre, with the B1 and with an Aleph P as preamp. I'm a little bis dissapointed with the B1 / F5 combination.
gain is not issue, but the B1 sounds a little bit lean and the voices are not what i like. The Aleph P is clearly better in my setup with the F5 the overall sound is smooth as silk with a better tonal balance.
I still need to try the UGS F5 combination.

some picutures (The Alpeh P case still to build)
 

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#1,610
Nobody reads the article anymore. Like a passing fad.
http://www.firstwatt.com/articles.htm
or more directly
http://www.firstwatt.com/downloads/F5 Power Amplifier for PassDIY.pdf
Then if you want power supply info
http://www.firstwatt.com/downloads/powersupply.pdf
And if you go to the product pages of FirstWatt you can view the info on F5 which has a more complete owners manual that includes the supply schematic.
http://www.firstwatt.com/downloads/F5-om_sm-080527.pdf

Nelson says:

The power supply of the tested amplifier is +/-24 volts and should be rated at 6 amps continuous duty, and more than 10 amps peak per channel. Ordinary unregulated supplies will work fine, and if you need suggestions the Zen Variations #5 (AudioXpress, October 2003) and Zen Variations #3 (AudioXpress, August 2002) both have good
examples of regulators and the raw supplies that feed them. I recommend rail voltages from 23 to 25 volts.
 
#1,611
I know that...I just don't know if mine can run at 6 amps continuously. Probably not, if it need 9 amps peak. The article uses 1 transformer at 6 amps and 9 amps peak. I want to use 2- 6.67 amp tranfos for each channel. I'm not sure if it's cutting it close or not. Peak for how long?

That's all I wanted to know.

BTW- How do you know I didn't read it? Maybe I just didn't understand it.

If this is the way this forum is going to be...maybe you should just call it " Pass DIY for Elite Experts". Maybe I should just take a walk then.

thanks a lot.
 
#1,612
I think using two transformers with your ratings is going to be fine. If you look at the schematic in that last pdf it shows a dual primary dual secondary transformer which is pretty much what you have with your two transformers. Just wire it the same way as shown in the schematic. Your shouldnt have any problems with current and those two transformers seem to match the project very well.
Just my opinion. I have been wrong before, alot, but it makes good sense to me that you have essentially doubled your current capabilities.
Also, I am not trying to offend you. Maybe just moody right now.
Uriah
 
#1,615
It seems a little odd that you are only getting 20V.
Here is the transformer I have in my PS right now
1. Primary I = 0.02A, Secondary V = 18.4VAC at 0.0A, Power = 0 Watt
2. Primary I = 0.65A, Secondary V = 18.1VAC at 3.61A, Power = 65 Watt
3. Primary I = 1.20A, Secondary V = 17.7VAC at 7.08A, Power = 125 Watt
4. Primary I = 2.77A, Secondary V = 16.6VAC at 16.59A, Power = 275 Watt
5. Primary I = 4.00A, Secondary V = 16.4VAC at 24.11A, Power = 400 Watt

Its an Antek 400VA. Not that any of that matters. I get exactly 24V measured at the end of the caps. So what I am saying is that your 20V number seems low for your transformer but that your transformer has different ratings for different current draw and that you might just be testing it at very large draw. I dont know how you are testing it but 20V seems odd.
You should be getting around 23.8 which would be grand for the F5. However if you do some searches or read back through the posts people have tried lower voltages. Probably Zen has a schematic. I think he posted previously a schematic for lower supply voltages.
Uriah
 
#1,617
udailey said:
It seems a little odd that you are only getting 20V.
Here is the transformer I have in my PS right now
1. Primary I = 0.02A, Secondary V = 18.4VAC at 0.0A, Power = 0 Watt
2. Primary I = 0.65A, Secondary V = 18.1VAC at 3.61A, Power = 65 Watt
3. Primary I = 1.20A, Secondary V = 17.7VAC at 7.08A, Power = 125 Watt
4. Primary I = 2.77A, Secondary V = 16.6VAC at 16.59A, Power = 275 Watt
5. Primary I = 4.00A, Secondary V = 16.4VAC at 24.11A, Power = 400 Watt

Its an Antek 400VA. Not that any of that matters. I get exactly 24V measured at the end of the caps. So what I am saying is that your 20V number seems low for your transformer but that your transformer has different ratings for different current draw and that you might just be testing it at very large draw. I dont know how you are testing it but 20V seems odd.
You should be getting around 23.8 which would be grand for the F5. However if you do some searches or read back through the posts people have tried lower voltages. Probably Zen has a schematic. I think he posted previously a schematic for lower supply voltages.
Uriah
Click to expand...

sorry, i forgot to say its 20V under load
i think it should be arround 21V - 22V when no load.

now im using it to power up Pass aleph X.
 
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