Hello. I just finished building a phono pre based on this schematic:
I already built one and it sounds great. When I assembled my second one tonight, the sound is distorted after a few seconds. A little experimenting revealed that if you turn it off and back on again, the sound is great and then it gets distorted and stays that way after a few seconds. Turning it off and on restores the quality temporarily. Here's a video I took:
Phono stage sound fine for a few seconds and then distorts
If anyone knows what would cause this, I'd really appreciate the help!
Thanks!
I already built one and it sounds great. When I assembled my second one tonight, the sound is distorted after a few seconds. A little experimenting revealed that if you turn it off and back on again, the sound is great and then it gets distorted and stays that way after a few seconds. Turning it off and on restores the quality temporarily. Here's a video I took:
Phono stage sound fine for a few seconds and then distorts
If anyone knows what would cause this, I'd really appreciate the help!
Thanks!
Whomever drew that schematic missed the ground. I'm also not a fan of the floating output caps. Connect the ground and add 470 kΩ on the "outside" of the output caps, and I bet your amp will work just fine. I bet the reason it isn't working is that the ground is floating.
You're using a dual or split supply with this, right? I.e. ±15 V or something.
Tom
You're using a dual or split supply with this, right? I.e. ±15 V or something.
Tom
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Any of the opamps getting hot?Hello. I just finished building a phono pre based on this schematic:
I already built one and it sounds great. When I assembled my second one tonight, the sound is distorted after a few seconds. A little experimenting revealed that if you turn it off and back on again, the sound is great and then it gets distorted and stays that way after a few seconds. Turning it off and on restores the quality temporarily. Here's a video I took:
Phono stage sound fine for a few seconds and then distorts
If anyone knows what would cause this, I'd really appreciate the help!
Thanks!
Hello and thank you for trying to help me! I'm using 2 9 Volt batteries. You can see the power supply setup and hear the problem here: YouTube
I don't know anything about circuit design and I'm new to DIY, but I built this same circuit a week ago and housed it in the same enclosure and didn't have any trouble with it. If it's not a grounding issue, do you know what else could be causing the distortion in the video? Thank you.
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Can you measure the voltage between V+ and ground (e.g. outer contact of any RCA connector)? What's the value imediately after switch on and the value when distorsion starts?
It has huge DC gain (about x600) so any offset gets magnified. Offset varies from chip to chip so one might work and another not work. Poor design.
Then putting 220uF cap in series with the 100R resistors should help.
Or even better, 1uF in series with the 27k resistors.
Or even better, 1uF in series with the 27k resistors.
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The centre point of the two 9 V batteries in series will need to go to the connection I marked PSU GND in the schematic.
I don't know if this is how you've connected it already as your schematic does not show the battery connections. I don't have the patience to try to tease this out from a video. Please post a schematic.
Tom
Hello again and thank you. Here's how the batteries are connected to the circuit:
An externally hosted image should be here but it was not working when we last tested it.
And the schematic of the actual board:
resistor to ground needed on input at all times. Easiest to connect 150k to gnd by shorting its switch contact
Can you measure the DC voltage at the output of each op amp after the problem happens?
The second op amp may be saturating from DC offset.
The schematic you posted doesn't include the power supply decoupling capacitors that are used on the Muffsy PCB at the op-amps. Did you not install them? If you did, is the polarity of the electrolytics correct?
Thank you everyone for trying to help! Absolon helped me to realize that the problem was with my power supply being wired incorrectly. I think this was (as Rayma suggested), this was making an opamp clip from a large DC offset.
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