for ClassA it does matter. The supply rails will vary in current demand from 0.002Amperes to 2.598Amperes when driving 27W into an 8r0 resistive load.
Oh, we still have to account for the current flowing in the NFB loop.
What is predicted for the ripple voltage on that final 15400uF when the current rises to 2.6Aperes?
Would one expect the ripple voltage to be halved when the smoothing capacitance is doubled?
This does not consider the peak transient currents that real speakers will demand from the supply rails. 4ohms speakers will make this case even more difficult to satisfy.
How can you expect the amplifier to do it's job well if the PSU cannot meet expected current demand?
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Probably not. I glue mine right to the case of the Mosfet,
which minimizes the open case effect.
I thought the "open case effect" was my imagination. I'd like to try this, what type of glue is used for this fairly high heat application?
Russellc
Here are the pics I promised earlier in the thread.
I have a problem though...... something is going on with Q4 when I connect up the speaker (just one channel, left side in the pics) for some reason when I connect the speaker the 0.47R resistor for Q4 smokes. It does this whether the inputs are shorted or not.
Could this be oscillation? I did use a gate stopper - its on the board, (PDs F5 boards) but I haven't seen anyone else report problems even though it could be mounted right on the leg.
Fran
I have a problem though...... something is going on with Q4 when I connect up the speaker (just one channel, left side in the pics) for some reason when I connect the speaker the 0.47R resistor for Q4 smokes. It does this whether the inputs are shorted or not.
Could this be oscillation? I did use a gate stopper - its on the board, (PDs F5 boards) but I haven't seen anyone else report problems even though it could be mounted right on the leg.
Fran
Attachments
No, they're in fully - well tightened down.
I went back and added in the temp compensation stuff - thing is, when I tried back out in my workshop, it all powered up fine. I had these hooked up to my stacked quads when the resistor smoked. I wonder if thats something to do with it. They would present a pretty bad load. No problems when hooked up to the test speakers.
I'm doing some more investigating.... can't see anything wrong in my wiring etc....
Fran
I went back and added in the temp compensation stuff - thing is, when I tried back out in my workshop, it all powered up fine. I had these hooked up to my stacked quads when the resistor smoked. I wonder if thats something to do with it. They would present a pretty bad load. No problems when hooked up to the test speakers.
I'm doing some more investigating.... can't see anything wrong in my wiring etc....
Fran
Nice... a high rewing 16V - F5 !
Did you check the isolation for the MosFet?
Arne K
From the manual!
"A caveat is in order here – this is a very wide band amplifier with a high input
impedance. In order to prevent the output voltage from bleeding back to the
input at very high frequencies (thus making a fine power oscillator), keep the
input and output cables separate, and don’t externally connect the speaker
ground to the input ground. Good ground shielding on the input cables is
important, and caution is called for in using Litz and other specially low
inductance / high capacitance cables. I have not seen a specific example of a
problem, but historically it is to be expected when an amplifier’s bandwidth
exceeds 200 KHz. If the amp makes funny noises, runs extra hot, or blows
fuses, this might be an indicator of such an issue."
Your pictures missing rca ground!!!!
No, RCA ground is there alright - its kinda tucked around the RCA jack and runs along the piece of alu angle to the star ground on each PS.
The amp plays perfectly with my horns.... so I'm starting to think that this may be an issue with the other speakers I hooked it up to.... stacked quads. I reckon it doesn't like the impedance presented by them.
Anyway, I haven;t actually made up my mind on this..... need more time. I was blaming my valve pre but now I don't think it was the issue.
Fran
The amp plays perfectly with my horns.... so I'm starting to think that this may be an issue with the other speakers I hooked it up to.... stacked quads. I reckon it doesn't like the impedance presented by them.
Anyway, I haven;t actually made up my mind on this..... need more time. I was blaming my valve pre but now I don't think it was the issue.
Fran
Think I finally found a configuration I am happy with.
CRC PSU 3 x 18,000 uF - 4 x 1R0 - 4 x 18,000 uF, one for each channel
F5 cascoded input with 3 x output pairs.
38 Volts supply, around 70W/8 ohm.
Now I just need to get PCBs made, unless I have a few last minute changes.
CRC PSU 3 x 18,000 uF - 4 x 1R0 - 4 x 18,000 uF, one for each channel
F5 cascoded input with 3 x output pairs.
38 Volts supply, around 70W/8 ohm.
Now I just need to get PCBs made, unless I have a few last minute changes.
