Well, it happened during startup. I had my cd player on and one speaker was powered down..... So 1 side was playing and the other side was quit because of that. Could that be it? It was only for 5 seconds before smoke appeared.
What do I have to replace? The resistors are fried, but could anything else be dead aswell?
What do I have to replace? The resistors are fried, but could anything else be dead aswell?
That mean that amplifier has been oscillate, but why?
Is this amplifier a tested by scope unit?
Are you sure for the input filter and values of compensation capacitors?
Are the output transistors the recomended type and original parts?
Just now i see....electrostatic panels.
Ask Andrew if this is a suitable load.
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No scope tests were done. All parts are original. No ebay stuff. The amp has been playing beautifully for months! Today even. I only powered down, moved it 10 cm and powered up again. Forgot to power up one speaker. Then smoke from zobel resistors on the side were the speaker was turned off.....
Well, ESL's have very high load capacitance - up to 1-2 uF. Both the sx and nx amp should be able to drive this without breaking into oscillation. Can you try it again but with the speakers powered up and connected correctly?
note that the Zobel is is AC coupled - so its only high level HF that can make them smoke and not DC. you can power up without any load connected to the outputs and measure on the output of the amp - should be 0 +_ a few 10's of mV max.
I don't know what the load looks like when its not powered up - might be its not the same.
Another test you can do is to wire a low value (say 1 Ohm 5W or 10W) resistor in series with the speaker to see how it behaves.
note that the Zobel is is AC coupled - so its only high level HF that can make them smoke and not DC. you can power up without any load connected to the outputs and measure on the output of the amp - should be 0 +_ a few 10's of mV max.
I don't know what the load looks like when its not powered up - might be its not the same.
Another test you can do is to wire a low value (say 1 Ohm 5W or 10W) resistor in series with the speaker to see how it behaves.
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Something isn't clear....
Are the fried resistors zobel parts?
What do you mean....repair the psu?
Is the power supply damage?
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Ok,now is clear.
Change these and power amp. again WITHOUT SPEAKERS CONNECTED.
Measure output for d.c presence as Andrew recommended.
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No - this would not fry the Zobel, because then it would be shorted out.
I took a quick look at the circuit diagram of an electrostatic.
If the speaker is not powered up OR there is no load and you had full voltage swing at HF going into the amp, you could get a hot Zobel resistor. The Zobel is ~10 Ohms in series with 0.1uF.
At a rough guess, for the Zobel to smoke, you would have had to have had ~100 kHz or thereabouts swinging almost rail to rail.
1. Check that the Zobel cap is ok and not shorted
2. Try running the amp with an 8 ohm resistive load
3. The OPS of the sx-amp is very rugged, so I doubt it is blown - anyway, even if you did have the full DC on the output because of a blown output transistor, the zobel would not smoke - unless the Zobel cap was short.
Also, see if you can get a scope to check that it is not oscillating. The Final ESL's (600i) are a brutal load - impedance continues dropping all the way up to 30 or 40 kHz. See Keith Howard's article about this in Stereophile here:-
http://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2#JB4eccgsl0o4KBcy.97
I took a quick look at the circuit diagram of an electrostatic.
If the speaker is not powered up OR there is no load and you had full voltage swing at HF going into the amp, you could get a hot Zobel resistor. The Zobel is ~10 Ohms in series with 0.1uF.
At a rough guess, for the Zobel to smoke, you would have had to have had ~100 kHz or thereabouts swinging almost rail to rail.
1. Check that the Zobel cap is ok and not shorted
2. Try running the amp with an 8 ohm resistive load
3. The OPS of the sx-amp is very rugged, so I doubt it is blown - anyway, even if you did have the full DC on the output because of a blown output transistor, the zobel would not smoke - unless the Zobel cap was short.
Also, see if you can get a scope to check that it is not oscillating. The Final ESL's (600i) are a brutal load - impedance continues dropping all the way up to 30 or 40 kHz. See Keith Howard's article about this in Stereophile here:-
http://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2#JB4eccgsl0o4KBcy.97
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Bonsai,
Fantastic job on the design documentation of Ovation SX design (15-25 watts Class A). My speakers are 96 dB efficient (min. of 4.9 ohms and a low capacitative phase angle), so I am particularly interested.
I understand that you have implemented the zobel network on the supply board. However, I do have my own supply boards, and can easily PTP the zobel onto my supply board as detailed in your design doc. My question is, are the main boards available separately?
Thank you,
Anand.
Fantastic job on the design documentation of Ovation SX design (15-25 watts Class A). My speakers are 96 dB efficient (min. of 4.9 ohms and a low capacitative phase angle), so I am particularly interested.
I understand that you have implemented the zobel network on the supply board. However, I do have my own supply boards, and can easily PTP the zobel onto my supply board as detailed in your design doc. My question is, are the main boards available separately?
Thank you,
Anand.
The PSU/protection board location for the Zobel works.
But I think the better location for the stability enhancing amplifier Zobel is at the output devices and connected via very short low area loops into the supply rail decoupling.
Install your Zobel on the amplifier PCB using very short very low loop area wires.
I don't agree. This is one of the topics I wanted to discuss with you way back. You did not take up the invitation.
It was hard enough just to get you to alter your stance on the location of HBRR & HBRL in your diagrams.
BTW,
The added resistor is still not corrected in your amplifier wiring pdf.