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Old 3rd January 2008, 10:29 PM   #11
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As it can be seen, the equalizer adds about .0077% THD with all of the sliders at 0db. Cutting by 2db worsens the distortion by only another .0001%, and a 2db boost will increase THD by .0002%. This is not too bad, if you are starting out with a low THD amp to begin with.

That's THD. What do the frequency responses look like?
Here's the first two: the sound cards natural frequency response and beneath that, the equalizer a 0db boost/cut.
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Old 3rd January 2008, 10:38 PM   #12
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And this is the frequency response of the last 2 tests, cut 2db and boost 2db.

It's not very linear. More boost or cut in the mid bands with the same slider travel. BUT, no big drops or peaks, so not that bad.

My conclusion is that I'll use this equalizer and be satisfied with it's very good performance...for now
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Old 3rd January 2008, 11:26 PM   #13
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Default Re phase shifts

Hi,

A filter with a cap alter phase shift as frequency change..... as well as a filter with an inductor....... as well as a gyrator (usually as inverted cap filter > inductor), useful in order to make a more ideal inductor. An uneven frequency response from a speaker also means phase shifts. If an EQ is set flat there should be no phase shifts regardless if gyrators or inductors are used.

If one uses an equaliser to smooth speaker response (if succeeded), phase performance should improve. Problem is that with a graphic EQ, Q and centre freq seldom corresponds with the needed correction points of a speaker. And as usual, more electronics in the audio path should be weighted against the response improvement.
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Old 4th January 2008, 01:17 AM   #14
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Default Re: Re phase shifts

Quote:
Originally posted by 4fun

Problem is that with a graphic EQ, Q and centre freq seldom corresponds with the needed correction points of a speaker. And as usual, more electronics in the audio path should be weighted against the response improvement.
Hi 4fun,
That's very true, a parametric eq would be better. If I need to cut only 3 or 4 bands to get the sound I like, maybe I should build one. In the meantime, I'm happy with this one.

A few more components in the signal path doesn't trouble me, as long as they are not degrading performance.

I'm thinking about making a few improvements to this one. Just to see if it's performance would increase measurably.
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Old 4th January 2008, 02:47 AM   #15
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SEXY DESIGN
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Old 4th January 2008, 02:58 AM   #16
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I got one of those. A/B comparison between bypassed and all faders to 0 is intriguing in how much the sound is affected (possibly due to age, for all I know). As a budget eq for processing though, not bad. The upgrades should help at least a little
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Old 4th January 2008, 03:18 AM   #17
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Quote:
Originally posted by DJ Exprice
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Why, thank you!

Quote:
Originally posted by defect9
I got one of those. A/B comparison between bypassed and all faders to 0 is intriguing in how much the sound is affected (possibly due to age, for all I know). As a budget eq for processing though, not bad. The upgrades should help at least a little
Mine sounds different too (not worse, just different). Even with the sliders set to 0, the signal is still going through the filters. This is why I was pleasantly surprised when I looked at the frequency response and it's nearly identical to the sound cards response. There's a slight drop near the bottom (see post #11 pic).
I'm going to upgrade the power supply first, with new smoothing caps and twice the capacitance. If that makes an improvement, I'll do more.
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Old 4th January 2008, 08:35 PM   #18
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Default Re: Re: Re phase shifts

Quote:
Originally posted by MJL21193


Hi 4fun,
That's very true, a parametric eq would be better. If I need to cut only 3 or 4 bands to get the sound I like, maybe I should build one. In the meantime, I'm happy with this one.

A few more components in the signal path doesn't trouble me, as long as they are not degrading performance.

I'm thinking about making a few improvements to this one. Just to see if it's performance would increase measurably.
Hi John,

If you don't plan to keep it in original shape for any original restore plans there is quite easy to alter centre frequencies and Q values to ones desire. You could even make one or two sections parametric.
This site has some info, sparse of math but maybe interesting:
http://www.geofex.com/Article_Folders/EQs/paramet.htm
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Old 5th January 2008, 12:40 AM   #19
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Default Re: Re: Re: Re phase shifts

Quote:
Originally posted by 4fun


This site has some info, sparse of math but maybe interesting:
http://www.geofex.com/Article_Folders/EQs/paramet.htm

Thanks for that, a lot of useful info there. I'll be taking a closer look.

I got ambitious last night and did some power supply work on it.

This unit has a small transformer, maybe 25VA, with two secondary windings. The first winding provides for the op amp supply (+/-15V), the second is for the discrete section of the board, and provides +56V.
They have a 330uF/80V Elna for smoothing on this supply and have split it from there to two rails (I assume one for left, one for right). These rails are decoupled with a pair of 220uF/63V caps.

I changed the 330uf for a 6800uf/100V and the 2 220uf I changed for 2 new Panasonic 220uf/100V.

I then did the sliders flat test with RMAA. There was a slight improvement in THD, but hardly enough to justify the changes. I removed the 6800uf and put in a new Elna 330uf/100v.

Pic shows the original. The three caps are visible in the centre and near the bottom.
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Old 5th January 2008, 12:57 AM   #20
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Changing the smoothing cap from 330uF to 6800uF was good for a .0005% decrease in THD, with no other visible performance increase on the tests. No, I didn't take it and listen to the results. I wouldn't hear a difference anyway (I think it sounds fine as is).

Part of the reason for this exercise is to prove to myself how much of a difference these "tweaks" make. You read a lot here about how different power supply caps sound this way or that way. I've always believed that to be nonsense.

Here it is with the caps changed, with the large 6800uF sitting in a chair that's too small for him. As I mentioned above, I changed that for a new 330uF and left the 220uFs alone.
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