Hi Guys,
I've got a very low-level 50-100 Hz buzz problem in my system, which mainly comprises NAS - USB DAC - passive preamp - Q-Watt amp.
Here's what I know:
1) With NAS paused, connected through USB DAC and passive preamp: Buzz
2) With Q-Watt phono line inputs disconnected, but powered on and speakers connected: NO buzz.
3) With phono inputs reconnected to the amp, and passive preamp, but DAC disconnected: Buzz
4) With NAS replaced by mobile phone playing through USB DAC: Buzz
5) With preamp source switched to TV or another DAC: Buzz
6) With selected source (USB DAC) disconnected from passive preamp: Buzz
7) With ALL selected sources disconnected from passive preamp: Buzz
So it seems the buzz is not coming from the Q-Watt amp or linear power supply (?), but is being picked up by the passive preamp or the cables leading to the amp...
Does this make sense to anybody? The passive preamp is unpowered, and even when disconnected from all sources seems to generate low level buzz like an earth loop. But with no earth connection. Could it be an earth loop from left channel to right channel? Please help!
Pops
I've got a very low-level 50-100 Hz buzz problem in my system, which mainly comprises NAS - USB DAC - passive preamp - Q-Watt amp.
Here's what I know:
1) With NAS paused, connected through USB DAC and passive preamp: Buzz
2) With Q-Watt phono line inputs disconnected, but powered on and speakers connected: NO buzz.
3) With phono inputs reconnected to the amp, and passive preamp, but DAC disconnected: Buzz
4) With NAS replaced by mobile phone playing through USB DAC: Buzz
5) With preamp source switched to TV or another DAC: Buzz
6) With selected source (USB DAC) disconnected from passive preamp: Buzz
7) With ALL selected sources disconnected from passive preamp: Buzz
So it seems the buzz is not coming from the Q-Watt amp or linear power supply (?), but is being picked up by the passive preamp or the cables leading to the amp...
Does this make sense to anybody? The passive preamp is unpowered, and even when disconnected from all sources seems to generate low level buzz like an earth loop. But with no earth connection. Could it be an earth loop from left channel to right channel? Please help!
Pops
Pops, the first thing I would try is to connect GND to the chassis of your Tisbury preamp enclosure. As far as I can see, the chassis is unconnected and that could possibly "capture" hum from its environment.
Note that with GND I mean audio signal ground, not PE which is earth.
I would use the GND connection that is going to the Q-Watt amp to make the connecting with the preamp' enclosure. This way it your Q-Watt who is supplying GND to the enclosure.
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After more than 2 years of daily use, I took the Q-Watt out of service to tackle the bass 'buzz issue'.
I was inspired by Rod Elliott's 10-Ohm ground loop breaker, and I suppose I always intended to include one but never got around to it. I made up one loop breaker using the structure of a 35A bridge rectifier, and placed it between the common power supply ground and the mains earth connection.
I should say straightaway: that did not work. Buzz remained at a very low level, unchanged. This confirmed my suspicion that the earth loop was local to the amp-preamp pair, circuit being formed by the common ground in left and right channels.
So, I made another identical ground loop breaker. This time I placed them between each PS ground and the common star ground such that there is now 20 Ohms isolation between left and right 'ground', and 10 Ohms between each channel and mains safety earth.
In case of a fault drawing high current, the parallel 35A diodes breakdown and allow sufficient current to trip the 2.5A mains fuse.
And... it works!! Now there is absolutely nothing to be heard from the bass driver when source is paused or off.
I listened for a month now, and I think it sounds better now that the empty periods are truly silent, but I'll be honest it's a highly unscientific test.
Anybody struggling with ground loop on a Q-Watt, just remember: 1) use independent power supplies for left and right channel and 2) consider a Rod Elliott 10R loop breaker in the earth connection to each channel.
Pops
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Hi Guys,
Interesting to read the problems of the background hum.
An interesting read in Elektor Q-Watt - Simple Audio Power Amplifier (110656) - Elektor LABS | Elektor Magazine
I'm still running both my Elektor Q-Watt & the Elektor Pre-Amplifier together, superb!
Happy to hear of your solution Pops. Enjoy it hum free!
Interesting to read the problems of the background hum.
An interesting read in Elektor Q-Watt - Simple Audio Power Amplifier (110656) - Elektor LABS | Elektor Magazine
I'm still running both my Elektor Q-Watt & the Elektor Pre-Amplifier together, superb!
Happy to hear of your solution Pops. Enjoy it hum free!
Solving hum problem in stereo amp with one PSU
I have also build a stereo power amplifier with two Q-Watt modules and also have this terrible hum problem due to the ground loop that is very difficult to avoid with this design where the power ground and signal ground are both interconnected on the PCB. I think the PCB should isolate both grounds by inserting a low value resistor (like 10 Ohms or so) on the PCB's between both grounds and connecting both the low level input ground at the RCA inputs and the power output ground with heavy duty stranded cable directly to the star point between both large electrolytic buffer capacitors. This resistor is only needed in case one of the two ground connections to the star point is accidentally broken. This resistor assures that the large PSU and loudspeaker currents flow to ground via the direct galvanic connection and hence stay away from the sensitive input circuitry.
I think Elektor should address this problem, as almost all stereo amplifiers have a single supply and hence have solved this hum problem.
I have solved the hum problem of this amplifier in stereo configuration with one power supply by cutting the earth connection on the PCB next to capacitor C5, between resistors R12 and R13, and grounded the input circuit via a 6 mm2 solid copper wire to the earth connection of the input connectors. The hum in the speakers is now unaffected by the input ground loop.
I have also build a stereo power amplifier with two Q-Watt modules and also have this terrible hum problem due to the ground loop that is very difficult to avoid with this design where the power ground and signal ground are both interconnected on the PCB. I think the PCB should isolate both grounds by inserting a low value resistor (like 10 Ohms or so) on the PCB's between both grounds and connecting both the low level input ground at the RCA inputs and the power output ground with heavy duty stranded cable directly to the star point between both large electrolytic buffer capacitors. This resistor is only needed in case one of the two ground connections to the star point is accidentally broken. This resistor assures that the large PSU and loudspeaker currents flow to ground via the direct galvanic connection and hence stay away from the sensitive input circuitry.
I think Elektor should address this problem, as almost all stereo amplifiers have a single supply and hence have solved this hum problem.
I have solved the hum problem of this amplifier in stereo configuration with one power supply by cutting the earth connection on the PCB next to capacitor C5, between resistors R12 and R13, and grounded the input circuit via a 6 mm2 solid copper wire to the earth connection of the input connectors. The hum in the speakers is now unaffected by the input ground loop.
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Hi Calpe,
Me too! No complaints from me.
Ok just one. I've got a faint mechanical buzz from the 2x 420VA transformers that has worsened over the years. They were bespoke from Canterbury Windings Home but I wish I had gone for the fully potted and encapsulated 'Supreme Audio Grade' from Toroidy.pl. They are bigger though... would not have achieved the same regulation...
Lesson learned. Smother the tranny in epoxy.
Pops.
Me too! No complaints from me.
Ok just one. I've got a faint mechanical buzz from the 2x 420VA transformers that has worsened over the years. They were bespoke from Canterbury Windings Home but I wish I had gone for the fully potted and encapsulated 'Supreme Audio Grade' from Toroidy.pl. They are bigger though... would not have achieved the same regulation...
Lesson learned. Smother the tranny in epoxy.
Pops.
Hi Calpe and Pops, glad to 'hear' from you guys!
My Q-Watts are still running fine too. Although they're no longer in my main stereo setup. Last year I build two PeeCeeBee 4H mono block amplifiers. Not because I was unsatisfied of my Q-Watts but simply because I like amplifiers. I couldn't resist the temptation when I saw the specs of the PeeCeeBee's.
The Q-Watts will replace a small kitchen system. I currently have an aging Squeezebox Boom in the kitchen. From time to time it starts to show its age... The Q-Watts will be driven from a custom Squeezebox that I have yet to build. It's basically an RPI running piCorePlayer. I also have a pair of small speakers that will suite this application nicely.
In the mean time, my love for amplifiers hasn't stopped. A few weeks back I bought a secondhand Yamaha A-S3000 in as new condition. That is my current main system amplifier. Love that retro look of the Yamaha and it sounds great too. Don't you just love this hobby?
My Q-Watts are still running fine too. Although they're no longer in my main stereo setup. Last year I build two PeeCeeBee 4H mono block amplifiers. Not because I was unsatisfied of my Q-Watts but simply because I like amplifiers. I couldn't resist the temptation when I saw the specs of the PeeCeeBee's.
The Q-Watts will replace a small kitchen system. I currently have an aging Squeezebox Boom in the kitchen. From time to time it starts to show its age... The Q-Watts will be driven from a custom Squeezebox that I have yet to build. It's basically an RPI running piCorePlayer. I also have a pair of small speakers that will suite this application nicely.
In the mean time, my love for amplifiers hasn't stopped. A few weeks back I bought a secondhand Yamaha A-S3000 in as new condition. That is my current main system amplifier. Love that retro look of the Yamaha and it sounds great too. Don't you just love this hobby?
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Mosfet
Good to hear from you after so long.
A-S3000 - Features - HiFi Components - Audio & Visual - Products - Yamaha - UK and Ireland
It's a beast!
Good to hear from you after so long.
A-S3000 - Features - HiFi Components - Audio & Visual - Products - Yamaha - UK and Ireland
It's a beast!
Mosfet
Good to hear from you after so long.
A-S3000 - Features - HiFi Components - Audio & Visual - Products - Yamaha - UK and Ireland
It's a beast!
Good to hear from you after so long.
A-S3000 - Features - HiFi Components - Audio & Visual - Products - Yamaha - UK and Ireland
It's a beast!
2000 Euro is certainly not much for this model. It is important to check the condition and age of the amplifier. It the condition is good and the seller has treated the amp well then it is an interesting deal.
delange and calpe, can you give a little more detail on loading the SMPS500R main outputs for testing the aux outputs?
One resistor connected to each + and - main outputs? Then both to GND output?
One resistor connected to each + and - main outputs? Then both to GND output?
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That is correct.
You can remove those resistors when your Q-Watt is connected to the power supply. The Q-Watt will draw enough current.
Thank you! I’m using the Smps500r for a different amp, but need to adjust the aux output down from 16 to 6.3.
Ultra-high performance, yet rather simple - hybrid and more!
Ultra-high performance, yet rather simple - hybrid and more!