Lightspeed Attenuator volume problem

Sancho49 · 2017-09-13 11:56 am

Hi everyone !

I've build a Lightspeed attenuator, designed by George Stantscheff (Thank you !)

DIY Lightspeed Attenuator - Passive LDR Volume Control (optocouplers)

Same componant, LDR matched with LED Tester and DMM.

My power amplifier : DIY Firstwatt F5
My Source : Musical Fidelity VDAC2, Output Imp : 47Ohm / VOut : 2,2V
My Speaker : Fullrange Fostex FE166EN Backloadhorn

PC --> V-DAC2 --> B1 with Ladder pot --> F5 -- > Speaker Fostex : OK

PC --> V-DAC2 --> Lightspeed Attenuator --> F5 --> Speaker Fostex : Volume Too high, with no control !!

But ... problem with the volume control.

100k pot not affect the volume level

Low or high position of the pot, always at full power ... No difference.

I've control my solder joint, wiring etc.

Are you any idea ?

Thank you very much for your precious help !

Sancho

MAAC0 · 2017-09-13 11:48 pm

Have You feed 5V to max pin of the pot ? Is it correctly wired ? Substitute on of the optocoupler with a standard led, check if it fades when you operate the potentiometer.

georgehifi · 2017-09-16 2:43 am

Here's the circuit diagram, double check make sure it's the same, you only need one trimpot on the louder of the two channels to do the final channel calibration with.

Cheers George

Sancho49 · 2017-09-16 4:44 pm

Hi MAAC0 & George

)

George, it's exactly the same circuit, I add some pictures.
The soldering is dirty, but no short circuit and solid connection.

Thank you

georgehifi · 2017-09-17 12:39 am

"100k pot not affect the volume level
Low or high position of the pot, always at full power ... No difference."

You obviously have some thing wired wrong.

To hard to tell from these pics, better off tracing and drawing yours, then we may see where you've gone wrong.

BTW way mods!!! I'm not getting email notifications when a post is made, yet my instant email notification box is checked?

Cheers George

PRR · 2017-09-17 3:56 am

georgehifi said:
BTW way mods!!! I'm not getting email notifications when a post is made, yet my instant email notification box is checked?

See Forum Problems Thread.

Mark Whitney · 2017-09-17 9:12 am

Check the NSL. Does the cathode lead (coloured dot) connect to the 0V?

Measure the DC voltage along the control circuit. Start at the regulator, then the pot, then the NSL. Rotate the pots to see if the voltages change.

Measure the resistance over the NSL at different pot positions.

Please fix the audio wiring, that is not the way to do it.

georgehifi · 2017-09-18 12:14 am

As mark said make sure about the dot (cathode) on the NSL's goes to negative of the supply, if not you would have blown the leds in all the NSL (now junk)
If it does go to negative of the supply, then look to make sure the the negative has nothing to do with the rca/chassis earth. See my circuit above the negative of the supply is NOT together with the chassis earth/rca.

Cheers George

Sancho49 · 2017-09-18 5:12 pm

Hi Everyone and thank you for your many response !

Cathode of the NSL (Dot side) is on the negative side of the PSU.

And yes, the RCA (-In & -Out) aren't wiring on the negative side of the power supply.

I use the same typon, like this
With
Mesure

Resistor in the 4xNSL varying between 0Ohm and +/- 11KOhm

georgehifi · 2017-09-18 9:45 pm

Your going to have to go over it again, as there is a mistake somewhere, as there are thousands of these circuits working out all round the world.
I suggest to trace and draw your circuit out with pen and paper and you will find the mistake.

Cheers George

Mark Whitney · 2017-09-18 11:09 pm

So the control circuit and the resistance of each of the NSL devices is correct.

That only leaves a mistake in the how the RCA's are connected to the board.

georgehifi · 2017-09-19 1:04 am

What you can do is to have all 4 nsl's unhooked (cell side) and put an ohm meter on each one, rotate your vc and two should go from <100ohms to a few kohms, the other two will be the opposite. This will tell you if it's your output hookup section or the led power side that has the problem.

Cheers George

georgehifi · 2017-09-19 2:30 am

BTW this is why I always recommend that you should use 8 pin dip gold sockets as the nsl's fit into them perfectly, and once your happy with the complete build, then they can be solder into the socket, and then do your final calibration.

Cheers George

Sancho49 · 2017-09-19 6:31 pm

Use a 8 pin dip gold sockets is a great idea !

I finaly found the mistake on my build of the Lightspeed attenuator ! Trank you

Label "In" and "GND" are reverse on one of the side, on the typon.

0% of pot = No sound
5% = Loud
10% = Very loud

@ 2,5% of the pot ... :spin:

VERY Very great with my Firstwatt F5 vs Buffer B1 !

But, I've a second "problem" .....
Are you any idea to increase the "smooth" of the volume control ?

Thank you

georgehifi · 2017-09-20 9:03 am

Sancho49 said:
But, I've a second "problem" .....
Are you any idea to increase the "smooth" of the volume control ?

Thank you

Your speakers are very efficient 96dB you need to either reduce the source output or the gain of the amps.

BTW did you use a 100kohm logarithmic pot for the led volume control? If you used a linear this is your problem.

Cheers George

georgehifi · 2017-09-21 11:40 pm

Just looked at your pot in the pics, it says 100k this usually means linear, it should read 100kA this is a logarithmic pot which you should be using.

Cheers George

Sancho49 · 2017-09-23 7:12 pm

Hi,

I already use a 100K log pot.
If i use a different pot value (Like a 250k or other), the volume controle will be more smooth and progressif

Thank you very much :up:

georgehifi · 2017-09-23 11:48 pm

Never tried it, but good luck trying to find a good 250k log pot.

Cheers George

Sancho49 · 2017-10-25 1:37 pm

Hi Everyone,

I've finaly finish the built of the Lightspeed.
Replace the 100K with 250KOhm, work perfectly.

Thank you again for your help, this is a very very good volume control :yes:

AndrewT · 2017-10-26 9:34 am

georgehifi said:
................

BTW way mods!!! I'm not getting email notifications when a post is made, yet my instant email notification box is checked?

Cheers George

I have reported a similar problem over the last couple of years.
I don't have email notification turned on. Instead I use the search function built into "User CP - Subscribed Threads"
This search misses out some of my subscriptions and does not return them in the search.
It appears to be subscriptions in very old Threads that is causing the problem. It's as if the Forum software turns OFF the subscription when it becomes very old.
So far they have refused to correct the problem.

Lightspeed Attenuator volume problem

Member

Member

Member

Attachments

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

Member

R.I.P.