question on rolloff below 100Hz

wintermute · 12:56 AM

Hi,

I made a kit soundcard preamp, initially to allow me to do basic cro measurments with my pc. I'm now thinking I'll also use it with speaker workshop, as a safegaurd between the amp and my soundcard.

I measured it's freq response using rmaa 5.2 and it starts to rolloff at about 150Hz and is down about 1db at 30Hz.

http://home.exetel.com.au/wintermute...mp_compare.htm is a comarison between the soundcard in loopback and with the preamp in circuit.

I don't think I can post the circuit diagram, due to copyright but Its using a TL074 and the only cap in the signal path is a 10nf coupling cap on the input, I suspect this is the culprit, but I'm only guessing, so thought I would ask if I should increase the value of this cap, and if so what to?

Regards,

Tony.

sreten · 15th December 2003, 04:57 PM

47nF to 100nF sounds reasonable to me.

sreten.

wintermute · 15th December 2003, 10:57 PM

Thanks Sreten I'll give it a try

Tony.

wintermute · 12:58 AM

I put in a 68nf wima cap (replacing the no brand 10nf) and not only is the freq response now almost identical to what I get doing a loopback test on the soundcard, but the distortion went right down to almost nothing.

I'll put the new graphs up just as soon as my ISP's web server comes back online

It might get slightly better if I put the 100nF caps I bought at the same time, but they are no brand, and I really can't complain about the freq response improvement the 68nF ones made!!! So I think I'll leave it as is. The only thing that bugs me now is the huge spike at 50Hz with the SC preamp. Not sure where that is coming from since it's running off a 12V battery. probably radiated, the kit came with a cheap plastic box, may be necessary to stick it in a metal box.

OK ISP is back on line new url is http://home.exetel.com.au/wintermute...mpare_MKII.htm

Tony.

sreten · 16th December 2003, 04:23 AM

Distortion across capacitors is related to the AC drop across
them (higher=higher) and their voltage rating (higher=lower).

but you seem to be sorted

/sreten.

14th December 2003, 11:07 PM	#1
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	question on rolloff below 100Hz Hi, I made a kit soundcard preamp, initially to allow me to do basic cro measurments with my pc. I'm now thinking I'll also use it with speaker workshop, as a safegaurd between the amp and my soundcard. I measured it's freq response using rmaa 5.2 and it starts to rolloff at about 150Hz and is down about 1db at 30Hz. http://home.exetel.com.au/wintermute...mp_compare.htm is a comarison between the soundcard in loopback and with the preamp in circuit. I don't think I can post the circuit diagram, due to copyright but Its using a TL074 and the only cap in the signal path is a 10nf coupling cap on the input, I suspect this is the culprit, but I'm only guessing, so thought I would ask if I should increase the value of this cap, and if so what to? Regards, Tony. __________________ Any intelligence I may appear to have is purely artificial Some of my photos Last edited by wintermute; 16th July 2011 at 12:56 AM. Reason: updated url to new host.

15th December 2003, 10:57 PM	#3
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	Thanks Sreten I'll give it a try Tony. __________________ Any intelligence I may appear to have is purely artificial Some of my photos

16th December 2003, 03:49 AM	#4
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	Thanks Sreten I put in a 68nf wima cap (replacing the no brand 10nf) and not only is the freq response now almost identical to what I get doing a loopback test on the soundcard, but the distortion went right down to almost nothing. I'll put the new graphs up just as soon as my ISP's web server comes back online It might get slightly better if I put the 100nF caps I bought at the same time, but they are no brand, and I really can't complain about the freq response improvement the 68nF ones made!!! So I think I'll leave it as is. The only thing that bugs me now is the huge spike at 50Hz with the SC preamp. Not sure where that is coming from since it's running off a 12V battery. probably radiated, the kit came with a cheap plastic box, may be necessary to stick it in a metal box. OK ISP is back on line new url is http://home.exetel.com.au/wintermute...mpare_MKII.htm Tony. __________________ Any intelligence I may appear to have is purely artificial Some of my photos Last edited by wintermute; 16th July 2011 at 12:58 AM. Reason: update url to new host.

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
Using SS to augment < 100Hz?	bigwill	Tubes / Valves	3	25th January 2009 06:13 PM
Which Driver to use for 100hz-500hz?	KCCT82	Multi-Way	27	6th January 2008 04:59 PM
How to kill a 100Hz open baffle resonance?	Katapum	Full Range	12	22nd November 2005 04:51 PM
subwoofer/woofer to go up to 80-100hz?	Guijs	Subwoofers	2	24th October 2005 09:23 PM
Aleph 5 100Hz problem	piewie	Pass Labs	14	7th April 2004 02:43 PM


	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

15th December 2003, 04:57 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	47nF to 100nF sounds reasonable to me. sreten.

16th December 2003, 04:23 AM	#5
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Distortion across capacitors is related to the AC drop across them (higher=higher) and their voltage rating (higher=lower). but you seem to be sorted /sreten.

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

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