500 series Sontec / GML type eq

Put me down for a pair. Which option will depend on the cost.

I would love a pair of these!

Put me down for two please.

Jack

Wow, that is amazing work!! Definitely interested in a pair

Wow...definitely interested in a pair

Wow, great project. Congrats, onlymeeee

Since I´m servicing and keeping a bunch of Sontecs in mastering rooms in my area alive I have an opinion on these. While repairing  250s we did a bit of experimentation with caps an chips. There´s a lot of blahblah about swapping chips which in this case is not recommended. We found that sticking with TL071 and 5534 is the way to go. Having said that I had a 250 on the bench which was stuffed with a few LF356 instead of TL071 and  the owner did not notice a difference between channels.
He did complain, though, when I replaced the tantalum caps in the filter section with electrolytics. He said that it sounded cleaner than he wanted it to be. So stick with tants in the original spots if you want it to sound like a Sontec 250.
The original in/out circuit is DC coupled. I´d go for a precision chip in these spots. I found the OPA (2)132 series in my measurements to have at least double the DC precision of the OPA(2)134 series, which means less DC offset, but without any difference in sound. I tried hard to find a sonic difference in many circuits but I did not. Double the price, though. Anyway, just to throw another chip into the game.

I'll take a pair of PCBs.

Interesting about the TL0 chips, that has been my experience in many EQs. Seems in an EQ a nice slow chip sounds so much better than a fast chip.
Of course GML used their own op amp, but I have no idea how fast that is...
Is the schematic for the original that indicates component types posted here somewhere?

Have a search for Igors or fabios old boards should be schematic around somewhere.

Here's the original schematic, courtesy of Gyraf:

http://gyraf.dk/schematics/Sontec_MEP250a.GIF

@jensenmann - Awesome. Thanks for the info.  So it seems like your findings echo my own..  which is always good! 
Yes, I believe the OPA132 is made identically and labelled either 134 or 132 depending on how they test in regard to DC offset..  Lots of options in regards to great sounding fast FET input opamps these days!


PS. The PCBs arrived! But the most innocuous of parts, the lowly screws, got themselves into trouble at customs having come from US.  However I've received a card saying they'll be with me on Tuesday!  So everything will be ready on Tuesday finally!

PayPal at the ready

Do we have a price yet ?

The screws arrived, so all is here finally! 

Yes no worries, now everything's in my hand I can confirm price on everything... 

It's  £165 for a raw kit with all the hard to get parts...
ie. PCBs, front panel, L-bracket, hardware, centre tap pots, polystyrene caps, knobs & coloured caps.. 

Then for anyone that wants something else, just PCBs etc, just email..  as it's easier than doing different paypal buttons for each combination of items.. 

Pricewise for that.. it's : 
£30 off for knobs & coloured caps.. so, £139 without knobs. 
£60 off for metal.. so £79 without knobs or metal.
£5 off for polystyrene caps
£10 for hardware
£10 for centre tap pots

Full details at:  www.thedonclassics.com/250eq_diy.html


Any questions or broken links etc let me know..  you may have to refresh browsers etc to see the new website addition... 

I noticed the first item in the mouser cart, 12v relay, is out of stock. Is there anything special about that relay, or will any relay that meets the specs work?

Have a look in the General BOM, there's an alternative under column K

Yep, as things go on backorder I'll add alternatives to the general BOM.. 

The Omron alternative works great...
653-G6K-2P-DC12

Can you tell me what the row to row spacing is on the dual concentric pots? Ive contacted the US distributor for these items and they say there are 2 choices, 7.5mm or 10mm.

guilds100 said:

Can you tell me what the row to row spacing is on the dual concentric pots? Ive contacted the US distributor for these items and they say there are 2 choices, 7.5mm or 10mm.

Click to expand...

I've uploaded the footprint with a 2mm grid...  So between rows there's 10mm...



I've told Omeg to expect diyers to order these so they gave me a part number to always quote, so they should know the exact way to make it.. Perhaps the distributor is just being extra thorough
 

guilds100 said:

Can you tell me what the row to row spacing is on the dual concentric pots? Ive contacted the US distributor for these items and they say there are 2 choices, 7.5mm or 10mm.

Click to expand...

Great!  Will you let us know the results of your work?
Thanks!
Best,
Bruno2000

I'm currently working on this as well with the US dist.  Simple part # prompted some questions back so they may not be familiar with these. If I find something out before the other fella I will post.

Cheers.