SONTEC 432 inspired Equalizer

[Falk]

Good evening,

In this thread I will document the build of an EQ which is based on the Sontec 432. I plan to use Quad Eight AM10 inspired DOAs on +/-28V rails instead of HS2000 / HS6000 DOAS as used originally. For the DC Servo and Filter ICs I will use TL064 and TL074 ICs as used in the original unit.

I will plan the audio board and PSU board entirely in LT Spice. Everything will be laid out on a pcb. Until now I built a spice model of the Quad Eight AM10 and the entire audio path including the three gain stages and the five filter stages (2x shelving, 1x lows, 1x mids, 1x highs ).

Any comment, idea, question and feedback is highly appreciated.
Best,
Falk

 

[shot]

Love it! Good luck!

Do you plan to use switches or pots?
AFAIK peak level can't be handled with a pot since it's grounded at 12 o'clock position. But I need to check on schematic, I vaguely remember that from back when I was studying that schematic.



Luka

 

[gyraf]

Make sure the QE-AM10 opamp is fast enough for this use - iirc, some of the benefits of the sontecs were the very-fast opamps (high gain/bandwidth-product means surplus gain for self-correcting high-frequency misbehavior even at high frequencies and gains). Some of the recent modern off-the-shelf opamps has plenty of this. Here, we do not need the most important benefit of the discrete opamp; the high current drive capability

/Jakob E.

 

[Falk]

Thanks for the super fast feedback. Strongly appreciated.

@luka - I found some center taped potentiometers which I will use for prototyping. Later I will replace them with switches.

@gyraf thank you Jakob. I have never experimenred with OPamps and DOAs. So this is completely new for me. In which positions do you think does the GBWP matter the most? In the filters in the gain stages or in general?

Here is the AM10 vs an OPA604

 

[petermontg]

Hi Falk

If you do a small run of boards I'll definitely take a set off you. God kno s I have that many Sontec parts hanging around I may put them all to use.

best
peter

 

[jensenmann]

It might be a great option to use the 2520-footprint for the HS2030 and HS6000 DOAs, at least additionally to what you´re planning for the AM10 DOA. This gives the freedom of choice of using JLM Audio replacement DOAs since they are available in that format.

 

[steves.mastering]

If you’re going for a 2520 footprint, the APP992 is a brilliant DOA, is nice and fast and is often used in other Sontec projects such as Don250 eq

 

[echoplex]

If you’re going for a 2520 footprint, the APP992 is a brilliant DOA, is nice and fast and is often used in other Sontec projects such as Don250 eq

+1 on this idea

if you want to built a Sontec 432 inspired EQ you should aim for the possiblest cleanest op-amp. The 992 is clean, fast, transparent...!

 

[Falk]

Good evening everybody,

This year came with a couple of changes for me. I have to postpone the plans of making the Sontec Clone to whenever there is time to do it. I dont think it will be before end of 2022.

I found new rooms for my studio and it will take me the next month to build and move into the new studio.

Sorry for the bad good news.

I ll keep you posted.
Best Falk

 

[gyraf]

Good luck with your move..

/Jakob E.

 

[Falk]

Thank you very much. I appreciate it.

Thanks for the advice regarding the APP992. I indeed use this DOA in my Sontec MEP250 Clone. However, your advice didnt let me sleep last night.
So I simulated the APP992 compared it to the QA AM10 and a OPA602 and what shall I say? It clearly succeeds. Much higher GBW. Dont care about the exact GBW - the gain was normalized for comparison. It only proofs Jakobs ( @gyraf ) suggestion to take this into consideration.

Also the simulation works MUCH smoother with the APP992 model. Thank you Pier Paolo for coming op with these great DOAs.

As said. I ll keep you posted but I dont think it will take forever to have a great MES430 clone. If you want let me know which features should be included.

Thank you.
Falk

 

[Falk]

Here is the picture of some mid band EQing and six APP992 models used in the simulation.

 

[Falk]

This story continues 2.5 years later.

I think in March 2022, so not much after my last post here, an original Sontec 432 showed up on Ebay in Germany and it was a colleague selling it. So I bough a train ticket to the south of Germany and picked up the unit.

My plans to clone a Sontec were obsolete.

Some weeks later another colleague called me if I could help him with information to build his very own clone. I provided him with photos and measurements. Much later it turned out he did some basic research for a clone that in near future would be sold by a well known company. Anyways, a pair of his prototype PCBs made their way to me. And meanwhile I found time to make a front panel and order parts.

I will put 6 of Pier Paolos 992 DOAs on each board. Front panel will be purple. I am kinda tired making black front panels. In the meantime the original unit became a crucial tool to craft the sound I always wanted. I am really curious to see if I can substitute the original Sontec and sell it.

I will start to build all the switches first. I think about finishing the unit within the next year. Since I became dad and studio owner time is very very short.

Best,
Falk