Strange vol. pot behaviour ?!

Cradle22 · 28th January 2004, 04:41 PM

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

SY · 28th January 2004, 04:50 PM

Why are you using linear taper?

Cradle22 · 28th January 2004, 04:56 PM

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?

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

Kermit · 28th January 2004, 05:09 PM

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.

mskeete · 28th January 2004, 05:10 PM

Yes. A 15k - 25K resistor will help

Cradle22 · 28th January 2004, 05:12 PM

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 · 28th January 2004, 05:26 PM

Do you have a buffer after the volume control ?

Cradle22 · 28th January 2004, 05:30 PM

Quote:

Originally posted by mskeete
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

mskeete · 28th January 2004, 05:38 PM

I think you'll find that your filter response will vary depending on the volume control setting unless the resistor values in your filters are really high compared to the value of the pot

Frank Berry · 28th January 2004, 05:44 PM

What you are experiencing is high frequency oscillation due to the wide bandwidth of the IC.

Install the volume control external to the amplifier and enjoy the sound.

28th January 2004, 04:41 PM	#1
Cradle22 diyAudio Member Join Date: Jan 2003 Location: Dortmund, Germany	Strange vol. pot behaviour ?! 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 __________________ ************************ A Sacrifice For Freedom

28th January 2004, 04:50 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Why are you using linear taper? __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

28th January 2004, 04:56 PM	#3
Cradle22 diyAudio Member Join Date: Jan 2003 Location: Dortmund, Germany	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? 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 __________________ ************************ A Sacrifice For Freedom

28th January 2004, 05:09 PM	#4
Kermit diyAudio Member Join Date: Jun 2002 Location: Oslo - Norway	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. __________________ Sven Sødem

28th January 2004, 05:12 PM	#6
Cradle22 diyAudio Member Join Date: Jan 2003 Location: Dortmund, Germany	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 __________________ ************************ A Sacrifice For Freedom


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

28th January 2004, 05:10 PM	#5
mskeete diyAudio Member Join Date: Oct 2003 Location: London	Yes. A 15k - 25K resistor will help

28th January 2004, 05:26 PM	#7
mskeete diyAudio Member Join Date: Oct 2003 Location: London	Do you have a buffer after the volume control ?

28th January 2004, 05:38 PM	#9
mskeete diyAudio Member Join Date: Oct 2003 Location: London	I think you'll find that your filter response will vary depending on the volume control setting unless the resistor values in your filters are really high compared to the value of the pot

28th January 2004, 05:44 PM	#10
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	What you are experiencing is high frequency oscillation due to the wide bandwidth of the IC. Install the volume control external to the amplifier and enjoy the sound. __________________ Frank

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Strange XO behaviour	tinitus	Multi-Way	10	7th March 2009 02:50 AM
Aleph X strange behaviour	JBL4435	Pass Labs	26	25th May 2008 10:28 PM
Strange 45 behaviour - help	hal3101	Tubes / Valves	2	9th November 2007 08:38 AM
Strange behaviour of DIR1703	ptraj	Digital Source	0	16th June 2004 02:54 PM
Strange amp behaviour....	5th element	Solid State	13	6th July 2003 04:54 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read