Nuuk Buffered Passive Preamp Issue

[filholder]

Hi all,

I have just finished a Pre-amp for my Lm3886 MonoBlock. The Passive preamp was being used before with a 100k motor Pot built using a LiteAudio Input and Motor pot control. I had an issue with this setup sounding a bit dull and so i started a thread about my dissapointment with the passive setup.

People on this forum told me that the pot value was too high and so i tried lowering this value by placing a resistor acroos the input and output of the pot to lower the value, this did seem to help however i wasnt fully satisfied so i order a replacement pot and set about builting a Nuuk Buffer and PSU. Over the weekend both of these went into the setup, I has been a lot of work since i keep insisting on building everthing into way too small enclosures. Still that my problem.

What i wanted to ask people advice about was the results.

Basiclly the issue is that at zero volume on the pot the actual volume is a loud listen level. The pot works but very rapidly so if a turn it even a few degree the neighbours start banging on the floor!!!

Nuuk brought up the isssue of grounding and that maybe the pot isnt grounded properly. I have enclosed a diagram on the current grounding layout. If anyone has any comment as to wether this is wrong please tell me. If not i will take it the pot is defective and stick back in the old 100k one and put resistors across it.

Any comment very gratefully recieved.

Phil

 

[jan.didden]

It could be that by mistake you got a linear taper pot instead of a log (audio) taper pot. If that is the case, you can emulate a quasi-log taper by placing a resistor of 1/5 the pot value from the wiper to ground.

Jan Didden

 

[filholder]

Well i was assured it was log when i bought it and i dont see how at min volume ie 10K it would make any difference wether is was log or lin, since the value should be the same and surely it should be enough to make the amps silent. Also if i put resistors acroos the wipers i will lower the value of the pot and therefore make min volume even higher wont it?

 

[analog_sa]

the neighbours start banging on the floor

Fixing the neighbours may be easier then fixing the pot in this situation - how difficult can be to get 3 wires soldered correctly?

 

[Gcollier]

Are you sure the buffer is set for a gain of 1X or are you amplifying the input signal?

 

[filholder]

how difficult can be to get 3 wires soldered correctly?

well there are 10 pins on the pot plus 2 for power and i got it with no doumentation, and for some stupid reason i thought that the resistance between input and output should vary as opposed to the resistance between input and ground.

Should be 30 minutes work tonight to fixed. Head screwed back on the right way now. Actually to be honest i didnt quite understand how a a pot worked until i thought about it long and hard today. Then after 1 or 2 hours of drawing pictures on paper I worked out the way i had it and the way it should be.

It should be I- G-O and i had is G-O-I if G is ground, I is input and O is ouput.

Live and learn thanks for the help anyway guys.


Phil

 

[filholder]

Ok i have messed up again, can somebody help before i shoot myself.

Which should be wire where please please please.

I have 2 as ground, 1 as in and 3 as out.


please begging help

fil

the two 1's arent join how i have it, still doesnt work

 

[moamps]

..

 

[carlosfm]

well there are 10 pins on the pot plus 2 for power and i got it with no doumentation...

Well, try to get it.
It shouldn't be that hard.
With all those pins it probably has dedicated pins for loudness circuits and all that %$$&%$%&$, so you may be connecting it wrong.
Or use your multimeter.

 

[filholder]

Carlos my poor multimeter is worn out as am I.

Still it works, i cannot believe how many times i have had to re wire the [email protected]?#ing thing. BY the law of averages i should have hit it before now several times and what makes it worse was i was bloody measuring it with a multimeter everytime.

A drunk monkey with a soldering iron would have got it quicker.

Just shows you how dangerous a little knoweldge can be. Almost there now just some LED's to rewire and i can get them wrong twice can I???

Phil

Thanks to everyone especially the man of so few words moamps, your diagram showed me I had the inputs and output backwards.

 

[rabbitz]

Here's some homework for you from Rod's great site.

http://sound.westhost.com/pots.htm

10 pins..... what the... ?????? What's the brand and model?

 

[filholder]

Its an Alps R16 series 10KDX i think they are called, several pins are unused but then you get the issue that the .pdf manual shows connections but does give a very clear idea which way you are viewing it. Also i was reading the diagram wrong and though that the sweep was connected to earth. All told about 7 different wire solutions, all involving desoldering the blooding thing from the board i had it on to re-wire. Total nightmare.


Still all working good now, sounds very clean and punchy, a vast improvement over the passive setup. I am sure i will improve a bit aswell and all the solder joints and caps bedin a bit. Have to say though i thought the preamp project would be after build my gainclones but was a lot of work and pretty frustrating. Thing is with all this you learn each time you do it so the next thing you build get easier.

I do find it funny that i built all of Nuuks PSu, all of his buffer design on board point-to point without a single issue then couldnt wire up the bloody pot. ho-hum

Fil

 

[Nuuk]

I do find it funny that i built all of Nuuks PSu, all of his buffer design on board point-to point without a single issue then couldnt wire up the bloody pot. ho-hum

Yes, and after I wrote this !

 

[filholder]

Hi Nuuk,

Yep silly me, all those pins seems to short cicuit my brain.

Anyway can i just take a moment to thanks you personally for all your help on the project. I has been a real learning experience and like you have said the difference between a Gainclone with and without a buffer is far from subtle. I left mine on today to hopefully let things burn in a bit, and it really is sounding excellent. All the punch and drama i was after is suddenly there, the music just sounds far more alive and exciting which is exactly what i was after.

Once again thanks for all your help, no way i could have done it without your constant guidance, and also the help of other member of this truely excellent website.

FIl

 

[carlosfm]

I has been a real learning experience and like you have said the difference between a Gainclone with and without a buffer is far from subtle. I left mine on today to hopefully let things burn in a bit, and it really is sounding excellent. All the punch and drama i was after is suddenly there, the music just sounds far more alive and exciting which is exactly what i was after.

A buffer or a pre, it needs an active stage.
I'm glad you like the results, because me and Nuuk are recommending this for years and nobody listens.

Oh, you guys have to stop calling this a 'Gainclone'.
It's a chip amp, whatever.
Very far from the Gaincard.

 

[Nuuk]

Anyway can i just take a moment to thanks you personally for all your help on the project.

Thanks Fil. I must point out that the design of the buffer was given to me by Andrew Rothwell who in turn based it on an idea by the late Les Sage. The point being that sharing information and ideas is what has got us from living in caves to where we are now!

Oh, you guys have to stop calling this a 'Gainclone'.

Carlos, we tried to change that two years back but the name stuck. In the UK most of us call vacuum cleaners 'hoovers' although they are made by different manufacturers and have little resemeblance to the original Hoover design!

 

[filholder]

Ok having listened to the machine a lot last night i have to say that there is a slight Buzz or Humm or whatever you want to call it going on. It is not huge but it is there and wasnt before and just wondering if there is a cure. I am guessing it is my grounding layout since it is a bit of a mess

I have done a sketch of the curretn grounding layout and a proposed one i might try and implement. Could anyone comment of wether what I was thinking of doing is correct or wether there is a better solution. The whole star earth thing is made more difficult by the fact the Buffer and passive preamp are in different boxes which i drilled holes into and bolted together so i didnt have to use interconnects which i though would be a bad idea.

The illustration only shows grounding since i guess this is where the issue is

Ok here is the current

 

[filholder]

And heres what i thought might help

Would my new layout constitute a 'Star Ground'?

Any comments gratefully recieved.

Fil

 

[moamps]

....Yes, and after I wrote this...

Hi,

The diode D1 in the negative discrete regulator isn't biased properly.

Regards,
Milan

 

[Nuuk]

Probably not the answer that you wanted to hear Fil, but I would put all the pre-amp stuff in one box (or keep the PSU separate).

Ov from PSU to buffer board.
0V from buffer board to pot.
0V from input socket to buffer board.
0v out from buffer board to ouptput socket.