yes, it is that sensitive -- and there doesn't seem to be any way around it -- it's only a 200 ohm pot, and 1/16th turn = 1/2 ohm. [Edit] remember it's in parallel with the 10 ohm existing source resistors!
you don't have to make the bias adjustment that "critical" -- and the combined parallel resistances of the thermistor, 2k2 resistors etc also set the gain -- so once you are in the ball park you can adjust P1 and P2 a smidgen (how doe that translate) to effect a bit of a null.
Good mornin'
This is what I did to my board to add a 200 ohm pot for P3 ,most all layouts are the same ,it works ,I don't have a distortion analyzer yet ,but I did notice it tweaks the bias a little bit on those two fets ,I could see it on the output dc with a meter,I have mine set to the middle until I have the necessary equipment to make the adjustment,
NS
This is what I did to my board to add a 200 ohm pot for P3 ,most all layouts are the same ,it works ,I don't have a distortion analyzer yet ,but I did notice it tweaks the bias a little bit on those two fets ,I could see it on the output dc with a meter,I have mine set to the middle until I have the necessary equipment to make the adjustment,
NS
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Nope
I had some boards burned to replace those I'd been using for (I guess) 3 years, but when taking a really hard look at the performance there are a couple more things I would change. I also made a 'boo-boo' in the protection scheme == easily rectified. There's provision for a 100pF cap on the input and a zobel on the output. I also find it helpful to put some some capacitance on the board for local decoupling. You can sub a pair of 2N540's for J74's and get the 1W THD% around 0.003%. Anyone who wants boards they're free ex postage and the PayPal fee.
FWIW, I have never been happy with the foldback overload protection. In fact, I am coming to Peter Daniel's view of just eliminating the protection altogether, although Sister Blanche Marie O.P. would have me assigned to the lowest ring of Dante's Inferno. It just takes more patience to adjust it right.
Said before that i wasn't too happy with the current limiting on the F5 -- so i did some simulations with the original design and the F5-R1. In the latter, the thermistor is connected directly to the source, no longer in parallel with Q5. According to the original article, current limiting was to take place @7A.
The load is a "Voltage Controlled Resistor" which is varied from 0.1R to 10R.
If you did as I have, i.e. change the output MOSFET source resistors, the value of R17 should be changed as well.
The load is a "Voltage Controlled Resistor" which is varied from 0.1R to 10R.
An externally hosted image should be here but it was not working when we last tested it.
If you did as I have, i.e. change the output MOSFET source resistors, the value of R17 should be changed as well.
hi Russelle,
You know I am amazed with this amp,I have some old RS meters for speaker outputs ,I am putting 5 watts out and it's pretty loud,
I use a pair of kustom 200 watt stage monitors,kinda my test speakers,I don't know the spl,but they drive pretty ez,kinda blows you away,,,,GREAT design Nelson,Thank You!
thanks!
NS
It works ,I guess some folks don't like patches,lol What werks is ok for me,lol!
You know I am amazed with this amp,I have some old RS meters for speaker outputs ,I am putting 5 watts out and it's pretty loud,
I use a pair of kustom 200 watt stage monitors,kinda my test speakers,I don't know the spl,but they drive pretty ez,kinda blows you away,,,,GREAT design Nelson,Thank You!
thanks!
NS
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If it folded back, the curve would look something like this (LM723 15V regulator with foldback regulation at 2 amps):
An externally hosted image should be here but it was not working when we last tested it.
4PC 4.7K Thermistor needed
Hello
Do someone has 4PC extra 4.7K thermistor at hand?
I would gladly buy them in case you not planing to use them. To order from Mouser etc the shipping cost more than the parts. From Epay I do not want to buy components, I did learned the hard way.
I have all the parts for the F5 Turbo V1 just I need the thermistors..
My plan to use 3 or 4 pair Toshiba 2SK1529/2SJ200 28-30V rail Voltage with out cascoding..
Also to order I have to know what type feet my need here. Would be better if someone has 4PC and I would take them over.
Please let me know.
gaborzoltan2@gmail.com
Thank you very much
Greetings Gabor
Hello
Do someone has 4PC extra 4.7K thermistor at hand?
I would gladly buy them in case you not planing to use them. To order from Mouser etc the shipping cost more than the parts. From Epay I do not want to buy components, I did learned the hard way.
I have all the parts for the F5 Turbo V1 just I need the thermistors..
My plan to use 3 or 4 pair Toshiba 2SK1529/2SJ200 28-30V rail Voltage with out cascoding..
Also to order I have to know what type feet my need here. Would be better if someone has 4PC and I would take them over.
Please let me know.
gaborzoltan2@gmail.com
Thank you very much
Greetings Gabor
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Ok, I'm not sure if I should open another thread or ask here, but I plan to build two F5 mono blocks and had some questions.
First I would like to keep them small, and was thinking about going with 2x15V 160VA transformers instead of the original 2x18V. Reason would be to need less heat sink area and be able to build them "smaller" so I was hoping to have to loose less power trough the heat sinks. And then : does anybody have a link to a nice calculator for heatsinks ? I once had a link for a very nice calculator that would show the heat on the heat sink depending on positioning and so on - really very nice in order to optimise the placement of the heat sources, but I can not find it anymore.
So, has anybody tried a "undervoltage" F5 ?
Regards, Stefan
First I would like to keep them small, and was thinking about going with 2x15V 160VA transformers instead of the original 2x18V. Reason would be to need less heat sink area and be able to build them "smaller" so I was hoping to have to loose less power trough the heat sinks. And then : does anybody have a link to a nice calculator for heatsinks ? I once had a link for a very nice calculator that would show the heat on the heat sink depending on positioning and so on - really very nice in order to optimise the placement of the heat sources, but I can not find it anymore.
So, has anybody tried a "undervoltage" F5 ?
Regards, Stefan