Cloudlifter CL-1Repair

[smilan]

Hi,
I'm trying to repair a Cloudlifter CL-1, on the first LSK389 the are a 33K resistor with a capacitor in parallel that connecting the input signal from the XLR jack to the gates of the LSK389 while the other side of the resistors and capacitors goes to ground.
One of those capacitors measured a short circuit so I tried to de solder the other one to measure it but I destroyed it too...
What would be a reasonable value for C1 and C2?

 

[Khron]

Sub 1nF, most likely.

 

[Whoops]

One of those capacitors measured a short circuit so I tried to de solder the other one to measure it but I destroyed it too...

are there any numbers or letters on the capacitors?

 

[smilan]

are there any numbers or letters on the capacitors?

No, there are no marks on the caps, there are marks on the PCB "C1" and "C2" under the caps.

 

[Khron]

I don't suppose you've bothered to lift the entire schematic, have you?

 

[analogguru]

.....
What would be a reasonable value for C1 and C2?

10pF

 

[smilan]

I don't suppose you've bothered to lift the entire schematic, have you?

If I didn't make too many mistakes it should be look like this:

 

[thenuck]

The original value is 33pF if I remember correctly. Anywhere from 10 - 56pF would be ok.

Those are “frequency limiting” caps. They shunt very high frequency noise to ground so that your FETs aren’t trying to amplify massive EM spikes or radio waves.

 

[smilan]

Those are “frequency limiting” caps. They shunt very high frequency noise to ground so that your FETs aren’t trying to amplify massive EM spikes or radio waves.

This is what I was thinking, what is the benefit of using this method with resistor and capacitor in parallel instead of a classic RC low pass filter (the signal passes thru the resistor and the capacitor filter the desire frequencies to ground)?
Does the two resistors acting as a voltage divider and limiting the current that runs thru the FETs?

 

[Monte McGuire]

R2 and R4 are not part of a lowpass filter, they merely tie the FET gates to ground at DC so the rest of the biasing network (R5, R6, R7) can do its thing. They happen to be next to C1 and C2, but only C1 and C2 are a lowpass filter.

 

[smilan]

R2 and R4 are not part of a lowpass filter, they merely tie the FET gates to ground at DC so the rest of the biasing network (R5, R6, R7) can do its thing. They happen to be next to C1 and C2, but only C1 and C2 are a lowpass filter.

Thank you for the explanation

 

[MidnightArrakis]

If I didn't make too many mistakes it should be look like this:

Other than the XLR connectors, which are self-explanatory.....what are all of the other connectors used for (JP1 - JP7)? Isn't this PCB placed within an XLR-tube?

/

 

[smilan]

Other than the XLR connectors, which are self-explanatory.....what are all of the other connectors used for (JP1 - JP7)? Isn't this PCB placed within an XLR-tube?

Yes, this PCB placed within an XLR-tube. My guess is that the other connectors used to connect this PCB to other circuits in more advanced cloudlifter models like the CL-Zi.

 

[TromNek]

Yes, this PCB placed within an XLR-tube. My guess is that the other connectors used to connect this PCB to other circuits in more advanced cloudlifter models like the CL-Zi.

I have a CL-Z (board# 1914, pretty old) and yes many of those jumpers are for the CL-Z.
JP1- Not Present
JP2- HP Filter switch
JP3- Jumpered
JP4- Variable Impedance Rotary Control (very funky pot with 6 leads, only two are used)
JP5- Jumpered
JP6- Not Present
JP7- Gain switch, two wires

Variable Impedance
there is a blue device (inductor?) installed on the board where you see the "White Box with C3".

Hope I got that mapped out correct? Let me know if you want me to verify anything.

 

[TromNek]

I would love to be able to power my cloudlifter with batteries so I can use it with a portable amp when I 'busk' in the subway.
Ideally, with two or three 9volt batteries.

Given the circuit that smilan provided, is that possible ?
If so, where would I apply the battery power ?

I have a CL2 which has two independent CL1 boards in it.
The boards are an earlier version (4015) than Smilan (4216). But they are identical except for some missing jumpers (jp1 and jp6).
There's lots of room in that CL2 case for batteries.

 

[Tubetec]

Abbey has some comments on his version of the LSK389 fet head amp that might be worth comparing to the cloudlifter , I think theres other threads in here dealing with the subject

 

[TromNek]

Abbey has some comments on his version of the LSK389 fet head amp that might be worth comparing to the cloudlifter , I think theres other threads in here dealing with the subject

thanks, I've read a lot of them. I'll probably build my own at some point.
None of them (as far as I could see) talk about powering the preamp with batteries, they all use the 48v phantom supply.

I guess I'll experiment with batteries using my cloudlifter for now.

I'm guessing I would just duplicate this (205).


If I were to try and use 24v instead, should I half the resistors to something like 3.4K ?
I'm guessing they are limiting resistors and they will drop a voltage because they are in series with the preamp, so I probably want to lower them ?

I'm not up to speed on circuits, so a lot of what I'm doing is guesswork.

thanks again

 

[Tubetec]

Some of the fet based head amps run at anything from 24-48 volts , although the available gain may diminish with lower supply voltages . I cant seem to find any data on what voltages the cloudlifters works off just says 48v but its likely it will work with less . 3x 9 volt cells might be worth a try , probably keep the 6k8 value and try it .

 

[TromNek]

Some of the fet based head amps run at anything from 24-48 volts , although the available gain may diminish with lower supply voltages . I cant seem to find any data on what voltages the cloudlifters works off just says 48v but its likely it will work with less . 3x 9 volt cells might be worth a try , probably keep the 6k8 value and try it .

Will do.

I think headroom diminishes with lower voltage too. But that might only be for certain types of amps. I used to do that to get sweet distortion on my guitar tube amp.

 

[abbey road d enfer]

10pF

For a 160 Mhz LPF?
Typically I put 10nF there, which results in a 50kHz cut-off even with a 600 ohm mic.