500 series Sontec / GML type eq

Help Support GroupDIY:

saxmonster

Well-known member
Joined
Jan 3, 2012
Messages
525
Well I took a chance and plugged in my IC's.  I was able to test all the filter channels and set them to zero and was able to do all the other calibrations perfectly.  Was pretty easy and was the funniest part.  Everything is working great, no hums, all knobs work as well as switches, etc.  This was my 6th or 7th project I built and I am really having a blast building these projects.  This was a fun one except for the knobs.  These things are a pain in the ass.  I have lifted the little knobs almost to the edge of the bigger knobs cause some of them for what ever reason are rubbing on the larger knobs causing the larger knobs to spin when they are already set,  I think I remember somebody giving some tips on getting the knobs setup properly I will just have to revisit the thread later on. 
 

Attachments

  • 250eq.jpg
    250eq.jpg
    94.7 KB · Views: 212

ncl|usl

New member
Joined
Sep 30, 2012
Messages
4
hello everyone
i would love to build one of this beautiful eq
where can i find the pcb and parts?
thanks
nick
 

EarthTone

Active member
Joined
Mar 1, 2018
Messages
27
If you just build a pair of these in stock form with +/- 12db and normal non-stepped pots, can you get away with using them in your mastering chain? I'm really wanting a pair, but they'll go into my 2-bus chain for mastering... Can you get away with it as-is? I'd rather build a pair without tweaking the design first before changing anything... But should I build them for +/- 6db if I'm planning to use them only on 2-bus? Just looking for opinions from people who have built them here already... Thanks!

ET
 

benewell

Member
Joined
Mar 12, 2017
Messages
6
EarthTone said:
If you just build a pair of these in stock form with +/- 12db and normal non-stepped pots, can you get away with using them in your mastering chain? I'm really wanting a pair, but they'll go into my 2-bus chain for mastering... Can you get away with it as-is? I'd rather build a pair without tweaking the design first before changing anything... But should I build them for +/- 6db if I'm planning to use them only on 2-bus? Just looking for opinions from people who have built them here already... Thanks!

ET

Hi Earthtone,
Currently using mine for mastering with +/-6db, and the non stepped pots. Absolutely love it. You most certainly can get away "as-Is" however, you won't have much wiggle room for minute adjustments. Even when I first tried +/-12 to start I wasn't using more than 4db or so during a mix. A little really went a long way.

I am tempted to try adding stepped pots in a different enclosure... but I'm so happy with the non stepped version that I don't foresee myself investing in that adjustment for a while.

Best,
Brian
 

Rogy

Well-known member
Joined
Jun 3, 2004
Messages
244
Location
Belgium
kante1603 said:
You can make the single bands‘ gain/cut switchable between say +/- 6 or +/- 12dB,it is just one resistor per band.

Udo.

Hello Udo, Could you explain this in a little more detail?

[Ah, found it on Pg14, post 276: @qmp audio - Yes +-6dB is possible..  easiest way on this unit would probably be to swap out all the R69s for 51k..  ]

I have four of these EQ's, and I'm super happy with them (using them for live sound work like you), but would love to limit their gain to +/-6dB per band for finer resolution on the gain pots.

Many thanks!

Best,
Rogy
 

AlexSwan

New member
Joined
Jul 17, 2019
Messages
2
http://www.thedonclassics.com/250eq-diy.html it is still available? I can place ordere? )

Does anyone know maybe there is a rack version?

Is it possible to buy two kit's and make the rack version yourself? Got instructions?

Thank' you very much all, who help )

Sorry for english)
 

AlexSwan

New member
Joined
Jul 17, 2019
Messages
2
I finished my equalizers. Packed in 2u rack case. The sound is amazing, very transparent, tasty, smooth, very happy with the sound. Many thanks to David for making such a project publicly available.

I compared opa134 and DOA. Opa134 is more detailed and crisp, a bit cold. DOA is nicer, warmer, it smooths the sound nicely, but the detail blurs a bit, making the sound more natural. As a result, I left DOA and went along the path C. If you need greater clarity, then it is better to leave opa134. In any case, both options are simply gorgeous.

I wonder if it is possible to replace tl071, and NE5534 with OPA134, and does that make sense? Has anyone already tried it?

Also, my left and right channels are a little out of balance at about 0.4db, is this normal? I can adjust the same balance either on the equalizer or on the bypass.


Ideally, I would like to add an output volume control) Can anyone know where to insert it in the circuit?


And once again many thanks to David) He is a very nice guy, he helped me answer my questions.

In general, the project is not complicated and worth it
 

Attachments

  • IMG_8976.jpeg
    IMG_8976.jpeg
    1.9 MB · Views: 169

saxmonster

Well-known member
Joined
Jan 3, 2012
Messages
525
I have had mine built for a while now, just curious as to how you guys are dealing with the smaller Q knob rubbing against the bigger HZ knob under it.  When they are both in the middle they are good but if I turn the frequency all the way to the left or right and change the Q knob they rub.  How are you guys dealing with this?  Do I sand or cut the Q knob a bit?

Thanks
-Scott
 

PhilipMarlowe

Well-known member
Joined
Nov 28, 2019
Messages
57
Hey guys,
thanks so much for this kit Don, and thanks to this awesome community!

I just finished building my first one. Apart from some minor mistakes it worked well, or so I thought. Unfortunately the high band doesn't seem to do anything. All other bands work fine (and sound amazing!) but for some reason the top band doesn't. 
Edit: found a missing solder point for the gain knobs  ;D
Thanks guys!
 

PhilipMarlowe

Well-known member
Joined
Nov 28, 2019
Messages
57
Another Quick question: what does ccomp4 and ccomp 5 do exactly? Are they needed only with a DOA in place?
Here's my current build. Second one coming soon :)

 

Attachments

  • IMG_9867.JPG
    IMG_9867.JPG
    1.7 MB · Views: 101

Beeswax

Well-known member
Joined
Nov 15, 2011
Messages
57
Location
Taos, NM
Yes, I'm also stumpted about Ccomp 4/5 for "power amp".  Also, why five each of the 75K resistors for R34/R35? 
 

johnsonic

New Member
Joined
Oct 13, 2021
Messages
4
Location
PDX, OR
Hey all! First post!!!

tl;dr - the frequency peak centers don't match the faceplate silkscreen on any pots. Any ideas where to look first?
---
Need some help here and hopefully will be able to offer more in the future.

Got my 1st eq made, and it works! My 2nd EQ is stalled on UPS - managed to lose or wasn't sent one of the mica caps, so waiting on the ups guy for a very expensive mica cap with the shipping. :(

Anyway - it sounds great and it sweeps and am verifying that everything works by sending white noise through it and looking on a spectrum analyzer.

Here's the weirdness - the silkscreen on the faceplate doesn't match the peak centers on any of the channels. Here's where it reads on the silkscreen and what's measured:

silkscreen/measured low to high
48/100hz
70/200hz
550/1000hz
1.9/4khz
6.5/10k

Seems like for all of them to be off there's a single component I should be looking at - any ideas on direction?

Will be able to wire in and test my 2nd unit tomorrow evening.
 

FIX

Paul Wolff
Joined
May 5, 2021
Messages
147
Location
Nashville
The EQ frequency center point of that design is the (referring to the 250EQ DIY schematic) cap across the freq pot pair (refer to the low band section) C27 and the cap going to ground, C28. The tuning of these two caps will determine not only the center frequency, but as you get closer to the optimum center, the band level goes up. As you tune them, you will see the freq shift and the gain go up, and at some point, you will see the gain start to fall down again. That peak is the optimum point with the highest gain and subsequently the end result of the lowest noise. R69 is basically the "summing" resistor into the boost/cut section. When you tune the filters, you can reduce r increase this value to get your correct gain setting.

C27 is the "roll in" frequency and C28 is the "roll-out" frequency. The "bell" switch basically bypasses either the roll in side or the roll out side, creating a shelf. IF the shelf is too broad band, you can also have it switch in a smaller or larger cap into one of the caps.

The basic differenced between the ITI, Sontec and GML is the original ITI, those frequencies weren't optimized as much, then the Sontec used ICs for those amps because Burgess' opinion was that because they were narrow band amps, they didn't need discrete amps. George's opinion was that they did.

The down side of that design is that because you are creating basically an open loop condition for the IC8 and IC7, the noise is quite high. Low noise is best in these positions. When I did the Tonelux EQ, I used this concept (since their are only 5-7 different ways you can do an EQ filter, you have to pick one) but I added 6dB of gain after the boost/cut pot, lowering the EQ noise by 6 dB. It can eat into your headroom a bit, but I never heard a complaint regarding that. Then you can increase the summing resistor R69 and drop the noise the same amount.

Also, if you keep the frequencies of the two low bands at the lowest frequency if not being used and keep the two high bands at the highest frequency when not being used, it tends to minimize the in-band noise.

This is a historical design, and the term "PARAMETRIC" was coined by George in a note to Burgess, left on the door of the lab where they designed it.

referring to this: https://thedonclassics.com/250eq/schematic/250eq-diy-schematic.pdf
 

johnsonic

New Member
Joined
Oct 13, 2021
Messages
4
Location
PDX, OR
For my first few posts I'm certainly adding noise, sorry about that.

I've confirmed that the top and bottom frequencies for each band are accurate on the silkscreen. The intermediary frequencies are off. Will be using my ears regardless, but thought I did something wrong.

Here they are in their natural habitat, just finished them this minute and can't wait to run some audio through!
 

Attachments

  • IMG_9895.jpg
    IMG_9895.jpg
    187.8 KB · Views: 35
Top