Korg Nutube preamp noise issue.

[Lloyd_]

Hi all, I’m new here to please be gentle.



Wondering if someone could help me,
my lovely partner bought me a Korg Nutube pre amp but unfortunately I’m having a problem with it.

I followed the diy guide and it works and plays but there is quite a lot of hiss coming through both speakers when it’s turned on, it also gets louder when the volume is increased.

Is there a check list I can run through to try and eliminate it?
Many thanks.

Lloyd.

 

[Osvaldo de Banfield]

With a schematic will be easier to us help you.

 

[6L6]

Hiss and not hum?

How much hiss... can you hear it with music playing quietly?

please post a series of well-lit, in-focus photos to help the troubleshooting.

 

[6L6]

@Osvaldo de Banfield

 

[Osvaldo de Banfield]

Try removing (temporarily) the 10uF at the triode's grid to isolate both stages and see if the issue continues or not.

Thanks to 6L6 for the circuit.

 

[Lloyd_]

Hiss and not hum?

How much hiss... can you hear it with music playing quietly?

please post a series of well-lit, in-focus photos to help the troubleshooting.

Hi. Yes I can hear it with music playing.

 

[Lloyd_]

Try removing (temporarily) the 10uF at the triode's grid to isolate both stages and see if the issue continues or not.

Thanks to 6L6 for the circuit.

Thanks, One before the jfets?

 

[Lloyd_]

Hiss and not hum?

How much hiss... can you hear it with music playing quietly?

please post a series of well-lit, in-focus photos to help the troubleshooting.

Will have to put it re assemble it again, wiring was as per diy guide, i do have a pic of the board.

 

[Osvaldo de Banfield]

This one. If the noise is still present, we can suppose the culprit is the tube or the JFET follower.

But IMO this design can be enhanced notoriously. Why use a JFET follower (high input impedance, desirable) and using only 1600ohm gate resistor (3300 paralleled)? (Less than a germanium transistor).

 

[Lloyd_]

This one. If the noise is still present, we can suppose the culprit is the tube or the JFET follower.

But IMO this design can be enhanced notoriously. Why use a JFET follower (high input impedance, desirable) and using only 1600ohm gate resistor (3300 paralleled)? (Less than a germanium transistor).

Hi. I removed the 10uf capacitor and the noise is still present. But obviously now doesn’t get louder with volume.
So what’s the next step get a replacement Nutube?

Many thanks.

 

[DNic]

Hi, what P/S are you using

Cheers

 

[Lloyd_]

Hi, what P/S are you using

Cheers

The one that came with the kit, Triad24v switch mode.

 

[Osvaldo de Banfield]

Try adding a large (100uF 16V) capacitance from 10K at the grid of tube wiper to ground. Perhaps the pot is noiser. Or try replacing the pot itself.

 

[Lloyd_]

Try adding a large (100uF 16V) capacitance from 10K at the grid of tube wiper to ground. Perhaps the pot is noiser. Or try replacing the pot itself.

Thought I had isolated the noise to the Jfet or nutube, the noise was still there with the input signal cut off.

 

[Osvaldo de Banfield]

Yes, we reduced the part list of possible culprits, but still we don't know who is/are.

 

[DNic]

I have you tried using a different P/S. I use this one, Both my B1-K are is dead quite.
They are not that expensive & give quite an upgrade over the standard switch mode P/S
https://www.ebay.com/itm/2728100244...RlydkSMRQ5oyHKa19xskvupg==|tkp:Bk9SR7ja2pC6YQ
https://www.ebay.com/itm/1256437778...HeGUjUcQnqeU3UNMH0vKCl+A==|tkp:Bk9SR7Ta2pC6YQ

Cheers

 

[Lloyd_]

Try adding a large (100uF 16V) capacitance from 10K at the grid of tube wiper to ground. Perhaps the pot is noiser. Or try replacing the pot itself.

So I’ve ordered a 100uf 16v.
Can you please explain where should be connected on the board.

Sorry new to all this.

 

[Osvaldo de Banfield]

Between the wiper or cursor of the preset, geneally the center terminal) and ground or cathode.

 

[Lloyd_]

Between the wiper or cursor of the preset, geneally the center terminal) and ground or cathode.

Sorry I understand ground, I have no idea where wiper or cursor is. Is that a terminal on the Nutube?

 

[Osvaldo de Banfield]

With my apologies of the ugly drawing, this is the wiring. Positive terminal of capacitor to the right.