Microphone boosters?

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Tubetec

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Theres quite a few designs to digest there . I note you also add a couple of extra transistors at the output Abbey , does this mean extra gain or better drive into low loads ? Could op amps be added to make the device line level output ?
 

abbey road d enfer

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Theres quite a few designs to digest there . I note you also add a couple of extra transistors at the output Abbey , does this mean extra gain or better drive into low loads ? Could op amps be added to make the device line level output ?
The transistors are there to provide low output impedance, so the gain does not vary with the impedance of the mic preamp. They also reduce the DC voltage reaching the FET's.
 

Tubetec

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The cathederal pipes design admits gain varies to some extent depending load /phantom supply .
Is there other benefits to using the LSK389 compared to single jfets like in some of the others or is it just a matter of convienience ?
 

moamps

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This one has the FET's in parallels, which solves both issues and improves noise.
But the schematic is faulty and although in JFET's drain and source are interchangeable, this should not be done. The symbol for JFET 2SK209 is wrong, so it turns out that the lower part does not work at all.
 

abbey road d enfer

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The cathederal pipes design admits gain varies to some extent depending load /phantom supply .
Is there other benefits to using the LSK389 compared to single jfets like in some of the others or is it just a matter of convienience ?
The idea is that the offset is reduced because the matching between monolithic FET's is very good. It would matter when connected to a transformer-based preamp, not so much with a xfmr-less.
 

abbey road d enfer

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But the schematic is faulty and although in JFET's drain and source are interchangeable, this should not be done. The symbol for JFET 2SK209 is wrong, so it turns out that the lower part does not work at all.
Yes, the schemo is definitely wrong. I don't think that 2SK209 has built-in reverse protection diodes, so it may work more or less. I don't know what diodes D1 & D2 are supposed to do...
And I think the absence of separate source resistors is detrimental to THD. I haven't simmed the circuit so I may be wrong...
 

mrbutterskin

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FWIW the owner of cloudlifter told me the high price is due to the use of USA mfg for everything, including the steel, pcb, and assembly. They're frequently on ebay for $100 used
 

Walrus

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Looks like the cascode circuit. The separate source resistors are there, and capacitors everywhere they're needed.
Also it seems there are a few through-hole components; what are they? Inductors?
You confirm it's the Cloudlifter?
Yes definitely a Cloudlifter.
The through hole components are pin headers for jumpers, can’t remember what they did now as it’s a good few years ago when i opened it up.
 

abbey road d enfer

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Yes definitely a Cloudlifter.
The through hole components are pin headers for jumpers, can’t remember what they did now as it’s a good few years ago when i opened it up.
Aah, OK. I remember having seen a schemo somewhere with jumpers for input attenuation and unbalanced input.
 

amplexus

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So basically the Cloudlifter and the Cathedral pipes are practically the same circuit, certainly the same active devices and both SMC.... and yet the CL is 3 times the price... ouf.
 

MidnightArrakis

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The many areas and/or pieces of "floating and isolated copper" on this PCB don't "float my boat"!!! But, that's just me. Proper PCB layout technique requires that you either somehow connect these "isolated copper" areas to GND or you delete them from the layout. While perhaps not as critical here in an audio circuit, "floating isolated copper" can certainly cause all manner of issues at higher "RF" frequencies!!! I have had to pay specific attention to this exact issue when I was designing "RF" PCBs for radio communications equipment for defense contractors. But.....HEY!!! IT'S ONLY ROCK'N'ROLL AND I LIKE IT!!!
 

moamps

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The many areas and/or pieces of "floating and isolated copper" on this PCB don't "float my boat"!!! But, that's just me. Proper PCB layout technique requires that you either somehow connect these "isolated copper" areas to GND or you delete them from the layout. While perhaps not as critical here in an audio circuit, "floating isolated copper" can certainly cause all manner of issues at higher "RF" frequencies!!!

You noticed that very well. You can often see poorly made PCBs on this forum and elsewhere, with ground planes included. Ground plane can sometimes significantly degrade the characteristics of a circuit that has high-impedance parts, which is often the case with audio circuits.

1637914546108.png

In RF circuits the situation is different where the circuits are low impedance mostly 50, 75 ohms or even lower and the properly designed ground plane improves stability. But so it is nowadays, anyone can be an influencer or PCB designer.:(
 

Newmarket

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The many areas and/or pieces of "floating and isolated copper" on this PCB don't "float my boat"!!! But, that's just me. Proper PCB layout technique requires that you either somehow connect these "isolated copper" areas to GND or you delete them from the layout. While perhaps not as critical here in an audio circuit, "floating isolated copper" can certainly cause all manner of issues at higher "RF" frequencies!!! I have had to pay specific attention to this exact issue when I was designing "RF" PCBs for radio communications equipment for defense contractors. But.....HEY!!! IT'S ONLY ROCK'N'ROLL AND I LIKE IT!!!

Yes - looks like someone hit the "Copper Pour" button without having ticked the "Remove Isolated Copper" box.
 

MidnightArrakis

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You noticed that very well. You can often see poorly made PCBs on this forum and elsewhere, with ground planes included. Ground plane can sometimes significantly degrade the characteristics of a circuit that has high-impedance parts, which is often the case with audio circuits.

View attachment 86679

In RF circuits the situation is different where the circuits are low impedance mostly 50, 75 ohms or even lower and the properly designed ground plane improves stability. But so it is nowadays, anyone can be an influencer or PCB designer.:(
THANK YOU!! I appreciate your comment and compliment!!! In addition to what you have highlighted, take a look at the larger "floating copper" to the upper-left of the piece you pointed out and the other larger area over by Pins 2 & 3 of the XLR connector on the right-side of this PCB.

What I was referring to concerning the "RF" PCB layouts is that these "isolated floating copper" areas can resonant at frequencies either above or below the circuitry's main frequency. This then causes issues with the circuit operation, despite whatever low-impedance the routing track is operating at.

I suppose these types of things were going to become inevitable due to the proliferation of all of the - FREE - PCB design software available these days!!! I was recently reviewing 2 PCB layouts that a member of this forum had sent to me in order to find out why his layout didn't work after he had had several PCB's fabricated. I basically determined that his circuitry couldn't/didn't work because he had specified that his vias were to have 6-mil drills while the minimum drill-size of his fabricator is only 10-mils!!! So, I am guessing that his vias ended up being "non-plated" because the drill-size hole was smaller than what the fabricator could effectively plate-thru. "Live & Learn".....huh???

The PCB design software that I use costs $3,700 and therefore has "just a tad bit more" capability, especially in the area of DRC checking and routing, than what a FREE software program offers. My program also offers me having up to 16 different types of vias with fully configurable parameters on each layer. The - FREE - software that this guy used allows you one single via and even then you are restricted on how you can have it set up!!! NO THANKS!!! But still, I get the allure of having and using -- FREE -- PCB design software to those on this forum. And, I myself have had to download and install two different FREE PCB design programs just so I could load-in, review and work on the PCB layouts that members of this forum have sent to me so I could find out what it is that they have done incorrectly. You know....."When in Roman....."!!!

TAKE CARE!!!

/
 

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