Papa mentioned that you may want to add some resistance but did not go into detail. Here is a section from data sheet regarding adding components for added stability:
"The HA-5002 can become unstable with small capacitive loads (50pF) if certain precautions are not taken. Stability is enhanced by any one of the following: a source resistance in series with the input of 50Ω to 1kΩ; increasing capacitive load to 150pF or greater; decreasing CLOAD to 20pF or less; adding an output resistor of 10Ω to 50Ω; or adding feedback capacitance of 50pF or greater. Adding source resistance generally yields the best results."
They also mention adding current limiting resistance on the output stage power supply connections to prevent over current.
Are you powering the 5002 with bipolar supply?
Thanks mikegranger yes the HA5002 is a bit of a challenge to get working properly.
I do indeed have current limiting resistors attached learnt from the Albert built with 22 of the beasties. (They would smoke the current limiting resistors as soon as there was no input connected but placing a 150kOhm across the input to ground resistor prevents this)
The F6 sounds fantastic quiet and stable and has played non stop for 4 days from various sources PC,CD player and phone all sounding magnificent.
I did experiment on the prototype with different load resistors as Nelson suggested but since the paralleled windings of the Jenson are roughly 38 ohms I put a 1 kOhm 470 Ohm and even 1 Ohm and it made no difference in the output waveforms. In the Albert there are typically 1 Ohm resistors in the paralleled devices so one of them does not go into over drive so to speak.
Again the F6 sounds amazing and on the scope clean as a whistle my comment was regarding the windings noise when driven at 3.8KHz one can only here it when you have you ear to the Jensen and it being really driven hard. I was just asking if others have noticed anything like this and what effects it has.
Yes I'm driving the HA5002 from a separate regulated bi polar supply.
Otherwise it really is a Fantastic sounding amp stable and quiet.
I do indeed have current limiting resistors attached learnt from the Albert built with 22 of the beasties. (They would smoke the current limiting resistors as soon as there was no input connected but placing a 150kOhm across the input to ground resistor prevents this)
The F6 sounds fantastic quiet and stable and has played non stop for 4 days from various sources PC,CD player and phone all sounding magnificent.
I did experiment on the prototype with different load resistors as Nelson suggested but since the paralleled windings of the Jenson are roughly 38 ohms I put a 1 kOhm 470 Ohm and even 1 Ohm and it made no difference in the output waveforms. In the Albert there are typically 1 Ohm resistors in the paralleled devices so one of them does not go into over drive so to speak.
Again the F6 sounds amazing and on the scope clean as a whistle my comment was regarding the windings noise when driven at 3.8KHz one can only here it when you have you ear to the Jensen and it being really driven hard. I was just asking if others have noticed anything like this and what effects it has.
Yes I'm driving the HA5002 from a separate regulated bi polar supply.
Otherwise it really is a Fantastic sounding amp stable and quiet.
I just checked the FET's again and the ones I have installed in the F6 are C2M0160120D's my mistake. So my Rds on is 160mOhm.
Perhaps you have mentioned it but any reason why you chose the Cree's over the IRF's?
Did you match them?
Thanks. Nash
I have been inspired to put the F6 with Cree C3M outputs in the project queue...
But, I was wondering if the Jensen transformer is still "the only" choice. It looks like several Lundahl offerings might work, for instance the LL1517. While it is more expensive and its performance is unknown, the Lundahl has the advantage of being easy for me to locate. Has anyone tried alternate transformers?
But, I was wondering if the Jensen transformer is still "the only" choice. It looks like several Lundahl offerings might work, for instance the LL1517. While it is more expensive and its performance is unknown, the Lundahl has the advantage of being easy for me to locate. Has anyone tried alternate transformers?
nashbap I had built the prototype with the IRF's and then when testing the frequency response was a little low or so I thought. Nelson explained and showed the frequency response in his article and it matched perfectly.
Then of course Greedy Boyz always want more so when someone mentioned the Crees had lower input capacitance I had to try them to see if would change things. The frequency response stayed the same so a bit more investigating and it turned out as Nelson again said the transformer is the limiting factor.
The Crees also had a lower Rds ON 130mOhm versus 180mOhm and a slightly high current capability.
At the end of the day is how it sounds and to be quite honest there is not that much and I did compare them side by side my opinion was a bit more punch from the Crees but the IRF's had more gain again not enough to cause me to put them in the final F6, the Crees are here to stay!
Seeing needtubes comment after your post the transformer is definitely the limiting factor for frequency response but the F6 sounds so good I'm not going to bother. I now need to build a phono amp.
Then of course Greedy Boyz always want more so when someone mentioned the Crees had lower input capacitance I had to try them to see if would change things. The frequency response stayed the same so a bit more investigating and it turned out as Nelson again said the transformer is the limiting factor.
The Crees also had a lower Rds ON 130mOhm versus 180mOhm and a slightly high current capability.
At the end of the day is how it sounds and to be quite honest there is not that much and I did compare them side by side my opinion was a bit more punch from the Crees but the IRF's had more gain again not enough to cause me to put them in the final F6, the Crees are here to stay!
Seeing needtubes comment after your post the transformer is definitely the limiting factor for frequency response but the F6 sounds so good I'm not going to bother. I now need to build a phono amp.
just to make shure what ZM meant about setting the trimmers,
-Is it wiper-to-source pin of mosfet?
-i used different directions in installing the trimmers, cause the trim-screw is on the side and not on the top. therefore i installed the trimmers that i can trim from the top of the opened amplifier when finished. i hope i am right that the trimmers are symmetrical and wiper is the middle pin (ahh, me lazy, i can (will) look it up of cause in the datasheet
)tnx, stefan
The frequency response is governed by the transformer not the output devices.
If you want to create something different you'd be better off making a turbo front end. ZenMod and I discussed this already.
If you already have 2sk1530 then use them. Use what you have.
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nashbap here is the response from Nelsons article as 2 picoDumbs mentioned the transformer is the limiting factor.
No I did not match the Crees at over $10.00 USD a pop our Canadian dollar at the time was horrendous I could only afford to buy 6! I bought them from Mouser, they now have some newer ones already mentioned by someone at $60 each not much to gain there as they are even higher input capacitance.
I'm just enjoying the F6 as it meant to be listening to it's glorious sounds.
No I did not match the Crees at over $10.00 USD a pop our Canadian dollar at the time was horrendous I could only afford to buy 6! I bought them from Mouser, they now have some newer ones already mentioned by someone at $60 each not much to gain there as they are even higher input capacitance.
I'm just enjoying the F6 as it meant to be listening to it's glorious sounds.
Hello,
I am trying collect my F6.
Rail voltage 24.5v
Jfets idss 8.2
Zeners 7.2v
R11,12 100ohm
R7,8,9,10 10k
Problems: irfp240s does not get warm but R3 bloody hot at 30 seconds. Bias is look like ok (0.5v) but offset is 24.5 volt around. I cannot change surely.
What are you masters opinions about my problem.
I am trying collect my F6.
Rail voltage 24.5v
Jfets idss 8.2
Zeners 7.2v
R11,12 100ohm
R7,8,9,10 10k
Problems: irfp240s does not get warm but R3 bloody hot at 30 seconds. Bias is look like ok (0.5v) but offset is 24.5 volt around. I cannot change surely.
What are you masters opinions about my problem.