Strange vol. pot behaviour ?!

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Hi!


I'm in the final stages of putting together my DIY "boomblaster", consisting of 4 GC circuits (with MFB topology filters), 2 bass drivers, 2 coax mid-high-drivers, and a subwoofer equalizer (Thomesen).

Upon connecting the signal cables to the (cheap) 100k linear pot and testing (this being the second tests, inside the final enclosure, on workbench everything worked before), the sound was not as expected.

First of all, sound is OK (without volume regulation, that is) when I connect the cd player directly to the amps.

But when using the pot, sound becomes very quiet, and lacks any highs. Upon slowly turning up the volume, at about 80% max volume, the sound level "jumps" up to what it should be like, and the highs and everything else is there, like it should.

Is maybe the pot broken (too long soldering or something)? I exchanged it for another 100k pot (old, used, could also be broken), and it was the same.

I am going nuts over this! Any suggestions?

Thanks,

Arndt
 
Because that's what most people used in their GCs...

On the other hand, I do not have any resistors from input to ground (other than the connection through the pot, that is)

But I always thought that using a linear one instead of a log pot would not result in the sound "jumping" up at one special position of the pot? :confused: :confused: :confused:


Thanks so far. I will take a look if I have a log pot lying around (I doubt it).

Otherwise, would a 15k resistor to ground after the pot help?

Bye,

Arndt
 
If the pot is wired corectly I can't see how it would make the sound jump, regardless off liner/log ore resistor or not after the pot.
Are you sure you have wired it correctly? loking at the pot from the front you have gnd(left)-out(middel)-in(right)? If you swaped in and out I supose somthing like this could happen.
 
Hi!


If I'd swapped (mirrored) (I did that one before) cables, it should still function normal, but with anti-clowise rotation for making the volume louder.

It is connected the way you described it...

I haven't found time to do the reistor to ground, in two hours or so...


Bye,

Arndt
 
mskeete said:
Do you have a buffer after the volume control ?


Nope, directly connected to high power OP-Amps (OPA541 and OPA548), with MFB-circuits in order to implement high/low-pass filters, gain 22,...


... like I always did when implementing gainclones

But I never used a vol pot before (all my other DIY-amps are directly connected to DSP with digital volume control)...

Bye,

Arndt
 
Thanks for the input.

I could also rewire the signals. right now (because of shorter cables) the input signal goes to the bass processor (which should have input and output buffers), from there to the pot, from the pot to the mid/high GCs, from there to the low pass GC.

I think by installing the pot before the processor I could make use of its input and output buffers, therefore improving stability.

But this will have to wait for tomorrow (it's dark outside, and my head's already spinning because of soldering fumes :cannotbe: :cannotbe: ).


Bye,

Arndt
 
Hi!

Couldn't wait until tomorrow...

I did all the above mentioned changes (resistor, position of bass processor in signal chain), and now it works (somewhat) fine.

Volume pot works alright, but the coax chassis play way louder than the bass chassis (although being from the same series / manufacturer). So I will have to adjust the balance between those a little bit...
And some humming issues (no wonder, crazy layout)

And the coax drivers (13 cm) have not the same value-for-buck ratio like the bass drivers (16 cm)... They produce distorted noises pretty fast.

After all I can say that it is not that easy to produce something as nice as the JVC BoomBlaster with DIY stuff... at least not for the intended purpose (somewhat portable party machine)...

Bye,

Arndt
 
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