debby

hey everyone  :)

i am noticing when i turn the gain knob, i can hear a thuddy scrapy sound when it reaches zero and i can hear it also when i turn the knob to the end. it has a range of probably 5-10 degrees to zero or to the end of the knob that the thudy scrapy sound can be heard.

i am using the expensive alps pots so i don't think it is the pot or could it?

anyone have the same problem? maybe its a wiring issue? i am still contemplating whether i swap the neon for a zener to stop this low level oscillation that i have.

has anyone ever built a point to point la2a strictly from the bloo or cayacosta diagram and have had no hum or noise issues?

i heard people are modding these to be quiet?


thanks everyone  :-*
tia

debby : )


Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #1 on: September 25, 2009, 01:39:16 PM »
Measure for dc on the connections of the pot, if there is dc somthing is wrong, try als when removing T4. If there is no dc = bad pot or bad tube (least likely)

regularjohn

Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #2 on: September 25, 2009, 07:55:34 PM »
has anyone ever built a point to point la2a strictly from the cayacosta diagram and have had no hum or noise issues?

Yes, I've built several.

reanimatorstudio is right...sounds like DC on your pots

I've built all of mine with neon bulbs and I don't have any noise issues until the gain knob is beyond its useable volume range.  Keep the neon, it's more authentic!

You'll get there, Debby!  ;D
SATANOSCILLATEMYMETALLICSONATAS

debby

Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #3 on: September 25, 2009, 08:36:22 PM »
ohhh........ thanks guys  :)

johnny you are a darl   :-*

i will try to take some time off the next few weeks and try your recommendations. if there are any other recommendations, please feel free to post.
tia

debby : )

spica

Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #4 on: September 25, 2009, 08:59:43 PM »
Hi Debby,

I built mine from the cayosta layout and it is pretty quiet.  It isn't dead quiet, but is very usable and the noise can't really be noticed on vocals.   I did change the first valve to a 12ay7. 

Mine is in a Bloo case as well.  The "kit" I bought turned out to only be the case, turret board, meter and a bit of hardware. 

I have not experienced the same problem you are having -   I used PEC pots.

-Tony

SSLtech

Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #5 on: September 25, 2009, 09:00:11 PM »
DC doesn't come from the source in an LA-2a.... the source is a transformer followed by a resistive attenuation network... no DC is possible.

It can only really 'leak-back' from the tube grid, so I suggest swapping the 12AX7 in the signal path with the 12AX7 in the sidechain and seeing what effect that has.

I've built several Bloos and none have been noisy. I've also built a few other point-to-point LA-2a's and similarly clean and noise-free.

Put a ceramic (or similar) capacitor (80V or better, to be safe) across the neon for low noise, if you haven't already done so... not all the original LA-2a's had them, but some did.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

Re: my bloo la2a makes a little thud on the start and end of the gain knob?
« Reply #6 on: September 25, 2009, 10:08:31 PM »
Quote
DC doesn't come from the source in an LA-2a.... the source is a transformer followed by a resistive attenuation network... no DC is possible.

I know but it is point to point so a mistake could happen


 

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