Hello, I have a problem with my DIY Class-A 2SK1058 MOSFET Amplifier...
I noticed the cones come forward when turning the amp on... and then immediatly go back...but without a sound... no thump or so...
Someone at analog-forum in germany asked me to check the DC Offset...
WOW... I measure no mVs... I measure 11DC Volts on both sides...
How can this be?
Dear friends, does somebody have an idea?
I noticed the cones come forward when turning the amp on... and then immediatly go back...but without a sound... no thump or so...
Someone at analog-forum in germany asked me to check the DC Offset...
WOW... I measure no mVs... I measure 11DC Volts on both sides...
How can this be?
Dear friends, does somebody have an idea?
Pic of the schematic will certainly help.
You mention the cone goes out and then immediately back in, which means the DC goes away. Is that accurate or you mean it only goes back in when you turn the amp off? So turn on cone moves out, then turn off cone goes back to normal?
What voltage rails are you running, which will help determine where the issue might be with 11vDC.
You mention the cone goes out and then immediately back in, which means the DC goes away. Is that accurate or you mean it only goes back in when you turn the amp off? So turn on cone moves out, then turn off cone goes back to normal?
What voltage rails are you running, which will help determine where the issue might be with 11vDC.
You could reduce the "turn on thump" by using a smaller output cap. 4700u seems excessive, to me, for an 8 ohm load. Try 1000u or even 470u. The downside is that this option may hurt bass response some.
Or use a relay with switch on delay on the speaker output. You may need to give the output capacitor a way to initally charge up and bring the output potential to 0v, such as a ~1k resistor to ground where the speaker would be. In normal operation that magnitude of resistance should make little difference. After a delay the relay switches the speaker in and by then the DC offset is gone and the amp has "settled".
Or use a relay with switch on delay on the speaker output. You may need to give the output capacitor a way to initally charge up and bring the output potential to 0v, such as a ~1k resistor to ground where the speaker would be. In normal operation that magnitude of resistance should make little difference. After a delay the relay switches the speaker in and by then the DC offset is gone and the amp has "settled".
I said may need. I meant to say will need.
The rhs of the output cap will sit at the same voltage as the lhs all day long if it has no DC path to ground.
Last edited:
Looks like a nice, simple amp. I bet it sounds great.I didnt think correct about the electrical situation and conclusion in general...
All the best!
What a great little amp! 5 beautifull Watts of delight...
Yes, now I understand your comment Nelson!
It all sucked at the end... what a hassle...
Just so there's no mistake, and at the risk of being tedious, my little joke
was referring to the fact that with the +terminal of the speaker to ground,
the turn-on thump should suck the woofer in.
I was concerned that you might have the + of the speaker attached to
the output. Since the amp inverts phase, we want the + going to ground.
Hi, yes I had counterfiet transisters in my last Rod Elliott 3A... only turned the amp up to 2 oclock...
made the cone stick out 1 inch and with alot of hum...
I was very lucky that my drivers servived... Beyma 15XA38Nd...
When I hooked up the speakers to the small amp I measured 0 Volts output...
At the speaker terminals...
All the best!
made the cone stick out 1 inch and with alot of hum...
I was very lucky that my drivers servived... Beyma 15XA38Nd...
When I hooked up the speakers to the small amp I measured 0 Volts output...
At the speaker terminals...
All the best!
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.