Best I can tell, the noise problem has not yet been resolved. My best guess is the 250 volt supply as another poster suggested. You can easily test this by temporally shorting out the gate of one of the mosfets to ground. If it’s coming from the supply, then the noise on the shorted channel will significantly decrease. I would pull the tubes as you have done previously. The mosfet can be ruled out by shorting drain to source. The noise will persist if it’s coming from the supply. It will go away if from the mosfet.
Good luck.
Good luck.
Potentiallyincorrect
Thanks for the trouble shooting tips.
I will try both those tests. They are easy enough to do.
Just to clarify, each channel has 2 mosfets. Are you saying to only short one mosfet not both?
Thanks for the trouble shooting tips.
I will try both those tests. They are easy enough to do.
Just to clarify, each channel has 2 mosfets. Are you saying to only short one mosfet not both?
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Aren't you only testing outputs single-ended presently? Fit it on the signal path that you're monitoring.
Also, shorting Gate-ground and/or Source-Drain can produce new failures when you have a 250V supply. Please be careful. At the very least, the shorting jumper should be soldered in place with the power off -- not simply applied with a hookup wire *freehand* with the power applied. Did the newly-fitted 0,1uF bypass capacitors have absolutely no effect?
Your last Vero-strip image still shows some unnecessary parasitic capacitances. In general, if two components are connected in series, the strip used to connect them SHOULD NOT extend several centimeters in both directions from the junction. For example, trim the strip that is the junction between the 100k and 25k Source resistors.
In future designs, I recommend leaving out the gain-matching Plate resistor trim. Just fit one percent resistors -- they match closer than the valve sections will. The current method adds so much stray capacitance that it won't be balanced at higher frequencies anyway. If you feel you absolutely can't do without it, fit a trimpot between the Cathodes; the drawback is that altering signal balance will also alter DC balance, but to a lesser degree.
As unnecessarily high-impedance as all the nodes are after the gain pot, I'm kinda surprised you aren't picking up some AM radio.😉
Regards
Also, shorting Gate-ground and/or Source-Drain can produce new failures when you have a 250V supply. Please be careful. At the very least, the shorting jumper should be soldered in place with the power off -- not simply applied with a hookup wire *freehand* with the power applied. Did the newly-fitted 0,1uF bypass capacitors have absolutely no effect?
Your last Vero-strip image still shows some unnecessary parasitic capacitances. In general, if two components are connected in series, the strip used to connect them SHOULD NOT extend several centimeters in both directions from the junction. For example, trim the strip that is the junction between the 100k and 25k Source resistors.
In future designs, I recommend leaving out the gain-matching Plate resistor trim. Just fit one percent resistors -- they match closer than the valve sections will. The current method adds so much stray capacitance that it won't be balanced at higher frequencies anyway. If you feel you absolutely can't do without it, fit a trimpot between the Cathodes; the drawback is that altering signal balance will also alter DC balance, but to a lesser degree.
As unnecessarily high-impedance as all the nodes are after the gain pot, I'm kinda surprised you aren't picking up some AM radio.😉
Regards
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Rick,
I'm testing it by hooking up the rcas outs, and listening. So I'll short the fet that goes to one of the rcas and pin 2 of the xlr
When I do the test i will use a short piece of wire soldered in. I do not want to create more problems. I have enough already!
Thank you for looking at the Veroboard image. I'm sure it's not easy to make heads or tails of it. I have to update the image to show the that i trimmed all the traces on the one channel. I did that on one channel to see if it would help. It made not difference at all.
I haven't added the 0.1uf caps yet. I don't have any and will put in an order. I'm in the process of choosing parts. I need some help choosing the parts for the muting relay components.
My friend thinks it may be the wires exiting the strip boards that could be causing the noise.
I'm testing it by hooking up the rcas outs, and listening. So I'll short the fet that goes to one of the rcas and pin 2 of the xlr
When I do the test i will use a short piece of wire soldered in. I do not want to create more problems. I have enough already!
Thank you for looking at the Veroboard image. I'm sure it's not easy to make heads or tails of it. I have to update the image to show the that i trimmed all the traces on the one channel. I did that on one channel to see if it would help. It made not difference at all.
I haven't added the 0.1uf caps yet. I don't have any and will put in an order. I'm in the process of choosing parts. I need some help choosing the parts for the muting relay components.
My friend thinks it may be the wires exiting the strip boards that could be causing the noise.
When shorting the get gate to ground, power in R12, or R16, depending on which get gate you are shorting will be about 2.6 watts. That’s a bit above the 2 watt rating you have on the schematic. This will be ok for short duration, just long enough to hear a difference, then shut things down. Sorry, I did not catch this in my first reply.
PotentiallyIncorrect,
Is the get gate the same as the gate ? I don't understand your comment about powering in R12 or R16. I haven't done this test yet.
Post 42 should have schematic for the 250v.
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It was supposed to be FET not get! Damm autocorrect.
Those resistors will have 250 volts across them while the FET gate is grounded. Power is (250)^2/24k. Or 2.6 watts. That’s a bit much for 2 watt rated resistors. Can be done momentarily without problem. They will get hot and eventually overheat and fail if left with that much voltage on them for long.
Those resistors will have 250 volts across them while the FET gate is grounded. Power is (250)^2/24k. Or 2.6 watts. That’s a bit much for 2 watt rated resistors. Can be done momentarily without problem. They will get hot and eventually overheat and fail if left with that much voltage on them for long.
Also the resistor #’s I have called out came from your first post, looks like they have been renumbered since then.
I don't think the shorting should be done. Please decouple with the 0.1 uf and use the 2.2k stopper resistors first.
Jean-Paul, I understand your concern. The second diagnostic that shorts drain to source does not carry the same hazard. Would you be opposed to it also? There are 2 schools of thought, both are valid. When possible I like to do diagnostics to rule out/in specific possibilities. The other is to apply standard accepted practices in hope it solves a problem. Neither is wrong.
Jean-Paul
I'm getting my order ready. I will order all items at once.
Once received i will start by installingthe 0.1 uf and use the 2.2k stopper resistors first.
Is this relay appropriate for the muting relay?
https://www.mouser.ca/ProductDetail...evices/TQ2SA-5V-Z?qs=HLLy2pIPwusDvK2M74sAxg==
why does it need to be double throw?
I would need 2 of these for the channels Left and Right?
DPDT as you normally want to mute L and R with just 1 relay. I would keep it simple by only muting the asymmetric outputs and when the device functions as it should then also add muting of the symmetric outputs.
The relay you choose is OK but it is small so hard wiring/soldering is not that easy for a beginner.
The relay you choose is OK but it is small so hard wiring/soldering is not that easy for a beginner.
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My plan is to build tube power amps that will use xlr inputs and they would be fed by this preamp. So the rcas won't get much use if all works to plan.
I will first try to deal with the noise as suggested. Then i will try to add the muting relay and other suggestions you made.
My understanding of the DPDT must not be correct. I would of though double poles or more would be required , but only single throw. When you have a double throw isn't the opposite contact not engaged when one is engaged? how is that beneficial here?
Looks like this relay would fit on a piece of strip board. My soldering skills are not so bad for a beginner. If the relay is up for the task, then i may go for it.
how about this for the transistor in the circuit?https://www.mouser.ca/ProductDetail/ON-Semiconductor-Fairchild/BC547ATA?qs=%2Fha2pyFadui9ynJ0cFt9ZDiJil%2FeZmRxmK%252B4hbcf7KQ%3D
is it ok?
I will first try to deal with the noise as suggested. Then i will try to add the muting relay and other suggestions you made.
My understanding of the DPDT must not be correct. I would of though double poles or more would be required , but only single throw. When you have a double throw isn't the opposite contact not engaged when one is engaged? how is that beneficial here?
Looks like this relay would fit on a piece of strip board. My soldering skills are not so bad for a beginner. If the relay is up for the task, then i may go for it.
how about this for the transistor in the circuit?https://www.mouser.ca/ProductDetail/ON-Semiconductor-Fairchild/BC547ATA?qs=%2Fha2pyFadui9ynJ0cFt9ZDiJil%2FeZmRxmK%252B4hbcf7KQ%3D
is it ok?
I read your link. I don't believe the heaters are dc lifted.
The heater circuit is dcne of the , and one heater wires is grounded also.
Perhaps you can use fine multi-strand wire and solder the wire and pin at once, then shrink wrap the connection.
you can float the heaters, that is, remove one side from ground then dc lift them, even if you may be using dc to power those filaments...you will be surprised to find another kind of noise is cured by doing so....
the author of that book, Merlin Blencowe is a member here, merlinb......
the author of that book, Merlin Blencowe is a member here, merlinb......
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I found another relay that has 6 poles and single throw.
it's 15v so I can use the 15v from my bipolar power supply that is used for
the volume control. Do you think it would work for the muting circuit?
https://www.mouser.ca/ProductDetail/TE-Connectivity-Axicom/5-1393808-7?qs=FT0qJ7ezHL89AuHVuFl4Vw==