MEQ mid-range EQ pultec style (was meq500)

[emrr]

Excellent idea.  We have to see what the bell shapes actually look like.   

Was looking at the PEQ versus the MEQ shapes, and the MEQ stock top boosts are skinnier than the skinniest PEQ bandwidth.  Good set of curves from available Manley covering both of their versions.  Seem to match what I've plotted so far. 

Somebody with some sim experience hack this in and see what's up, or Benchy Fast-fast solder it all together.  Those actual numbers bang out real close with the stock values. 

 

[lassoharp]

That's interesting the difference between the PEQ and MEQ curves.  Seems the lower 1 - 3K or so would benefit from a narrower curve.

My thoughts after using my DIY PEQ are that the 12Khz doesn't really sub for the 16Khz in any desired way on even with the widest Q settings whereas 8K, 10K, 12K have a more exchangeable overlap. But there is 4Khz difference. I may experiment with a ~14K tap and see if that complements the 16K without having to think about Q control mods.

Hopefully I will have some curve shots by early Sept. if none show up.

 

[emrr]

I couldn't stand it, so I moved some wires and tested the mid cut inductor as the high boost inductor with the caps I had.  

You are definitely this week's genius.   Of course my faceplates arrived yesterday.   :

Here's some charts.  First is the mid cut moved to the high boost position, second shows same plus standard high boost inductor (white plots), plus added 7K and 10K using 477mH on that standard inductor.  The curves with the alternate inductor land close to the middle of the EQP-1 bandwidth range, which seems much more useful to me.  I smell a hybrid coming.  

Some experiments with altering the shunt values in the filter section, the 1K and the 5.1K.  

changing 1K shunt to 363 ohms increases overall loss another -6dB, 3.75 dB sharper boost at 300, 0.25 dB sharper at 4K.
changing 1K shunt to 13 ohms increases overall loss another -32dB, 11 dB sharper boost at 300, 0.5 dB sharper at 4K.

changing 5.1K shunt to 2025 ohms increases overall loss another -6dB, no sharper boost at 300,  4.5 dB sharper at 4K.
changing 5.1K shunt to 69 ohms increases overall loss another -33.5dB, no sharper boost at 300,  12.75 dB sharper at 4K.

for 1K cut, almost identical comparison between 1K and 5.1K changes; 3.25 dB deeper and slightly wider shape at max change.

Existing max deviation selections appear best compromise for action versus noise.  These plots are leveled for identical flat response, you should be able to figure out which curve is which.  For each freq, standard/1st opt/2nd opt.  Blue plots are the individual stock 300 and 4K for comparison.

 

[lassoharp]

Nice work!    That's quite a difference!  I look forward to hearing these in action.

Those extra dbs of boost get real expensive really quick - I suppose it could have worked out worse.

Do you have any figures for total passive loss with the new arrangement?  Same as original?

 

[emrr]

Loss with the alternate inductor is exactly the same; dictated by the padding nature of the resistances.  Different pot values would affect this too; beyond my experimental capacity for now. 

 

[emrr]

Got all but my 4K cut caps loaded, here are the compiled curves.
Still planning to trim in some of the wayward values, and probably swap 3K boost taps for the slightly broader width. 
New drawing with actual measured frequencies of two units soon. 

 

[emrr]

Lassoharp's EQP-1A clone visited the studio, and we compared the Q of the high band LC filter with the MEQ type.  I had been wondering about this for awhile.  Will post some plots soon.  Short story is the EQP type is much broader at the narrowest setting, and has much more available boost range.  For example, if you set an EQP for the same max boost as the MEQ, for both narrowest and broadest settings, the shape of the EQP broad extreme is nearly the same as the narrow extreme.  Key parameter being "for same gain setting".  There is no verifiable calibration here, since varying the bandwidth control varies the filter gain separately from the boost control. 

 

[dmp]

4K cut position is still not stuffed or documented.

I just tried this and the suggested value (.047uf) looks perfect. Great work on this project guys.I'm really glad to have been able to get a pair of these.
I followed Doug's recommendation to move the 5k & 7k and can confirm that as well.
I switched the 3k to a .047||.033 instead of .068 to move that closer to 3kHz. 

 

[Denyle Guitars]

4K cut position is still not stuffed or documented.

I just tried this and the suggested value (.047uf) looks perfect. Great work on this project guys.I'm really glad to have been able to get a pair of these.
I followed Doug's recommendation to move the 5k & 7k and can confirm that as well.
I switched the 3k to a .047||.033 instead of .068 to move that closer to 3kHz. 

Hey Dan, If these are the ones I built, be aware that I used 1k for the LF pots (unless you changed them). I thought it might be worth mentioning since you're plotting curves now.

 

[dmp]

Yes, thanks - these are the ones you built (well done, btw). When I measured the LF boost, it goes up to maybe 4-6dB with the 1k pots (instead of to the full 10dB).
I'm going to try them for awhile before deciding to change anything though.

 

[dmp]

Did you guys end up getting your input transformers fixed? I'd guess this is the culprit for the low end rolloff, -6dB @30Hz.
Otherwise, suitable replacements? (600:600/HS-56... maybe Sowter 3603 style f would fit?)

 

[dmp]

I replaced the input transformer with a Sowter 3603f and it improved the low frequency response. It is an easy fit as well, just drill to allow the screws to mount the Sowter.
Still, great project!
Dan

 

[lassoharp]

That looks substantial.  Should be a welcome improvement.  Getting ready to start mine pretty soon. 

 

[emrr]

Coupla pics of mine.  Still haven't tweaked the frequencies tighter, probably will sometime.  I did tweak the FB R to get closer to unity throughput in my system. 

full frontal

front angle

guts

 

[3nity]

Whats the purpose of the 1246/1646?
Thanks

 

[emrr]

input debal and network driver

http://www.groupdiy.com/index.php?topic=26790.msg508063#msg508063

 

[dmp]

Your build looks great Doug!

 

[emrr]

Thanks!  They are cool units to have, and I'm happy with the additional frequencies. 

 

[lassoharp]

Doug,

When you swapped the mid-cut coil into the hi-boost position -  Do you have a tap/cap key used for this particular chart?:


http://farm5.static.flickr.com/4143/4863988577_74392120fa_o.png

I'm really looking to see where the calculated R values fall for this set - and esp the combo that generated the green curve. 

 

[emrr]

Sorry, no data collected.  That was a super fast experiment that I had to blaze through and reverse immediately, or it still wouldn't have happened.