500 series Sontec / GML type eq

[Quantum J Audio]

I've emailed Don Classics twice in the last few months as wanted two of these kits plus an extra Omeg pot as one of the pots has failed on one I have already. Have never received a reply, are they still in business?

Did the pot fail mechanically? If it is not working that is really strange and I'd say very unlikely to be the pot. Have you measured the resistances to see if it functions as expected.

Is Don still in business? I tried contacting him twice regarding shipping and vat costs from the UK ( after brexit) and he hasn't responded

Yes he is still in business. He has been away after getting married and finishing a degree. I spoke to him today I'll get him to check his junk mail!

 

[saxmonster]

Anyone know why I am getting two different sweeps on the left and right units when they both are in bypass? Phase should not be and issue as the sound is coming out of the same channel on my interface I just patch it to the left unit or to the right unit. Should all frequency’s be turned fully to the left even in bypass? Really don’t like that 5db drop over the course of the spectrum either. Would work on getting them calibrated to the same curve first then hopefully figure out the 5db drop. I have my calibrated sound card file also loaded in REW and that was pretty flat untill 15k or so.

 

[abbey road d enfer]

Anyone know why I am getting two different sweeps on the left and right units when they both are in bypass?

No, we don't but it sure is not normal. Actually both channels seem defective.

Should all frequency’s be turned fully to the left even in bypass?

No, their position should be undetermined. The role of the bypass switch is to compare any combination with flat signal.

Really don’t like that 5db drop over the course of the spectrum either.

I wouldn't either.

Would work on getting them calibrated to the same curve first then hopefully figure out the 5db drop.

This kind of anomaly goes further than calibration. there is something definitely wrong in this unit (both channels).

 

[saxmonster]

No, we don't but it sure is not normal. Actually both channels seem defective.

That’s what I was thinking too. Well at least I am consistsnt at messing up my builds, lol.

No, their position should be undetermined. The role of the bypass switch is to compare any combination with flat signal.

ok just wanted to double check, if it’s in bypass there should be no effect on the signal at all Passing through it.

I wouldn't either.

This kind of anomaly goes further than calibration. there is something definitely wrong in this unit (both channels).

Thanks for verification abbey on my thinkings, it was late at night and I thought I was seeing things, lol. Will try to investigate more and possibly email Don and see if he has any ideas.

 

[Forcemusicgroup]

Resistor Wrong somewhere... btw if you have anymore of those boards... I'll grab a pair..

 

[saxmonster]

Hello,
Sorry about all the confusion but I did some more frequency sweeps today and everything looks great now. Not sure what I was doing wrong (was probably up Too late) but when bypassed and when on both units are functioning great and no issues with the frequency response today.

 

[abbey road d enfer]

It happens quite often.
Objects and appliances are facetious. Like tools - you put them there, and 5 seconds later they are not in sight. Only once you have ceased looking for them, they suddenly reappear.
Your build has played tricks on you.
Fortunately they seldom do it while you're recoring a million-dollar session.

 

[PhilipMarlowe]

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

This looks so cool- how did you build the PCBs into a rack? Did you do the front plate and silk screen yourself? And how did you manage the power supply? I would like to build this EQ again like you did, with a fatter power supply like on the 5x1 series, only without a 500 series rack.

 

[Jeff5]

This looks so cool- how did you build the PCBs into a rack? Did you do the front plate and silk screen yourself? And how did you manage the power supply? I would like to build this EQ again like you did, with a fatter power supply like on the 5x1 series, only without a 500 series rack.

I'm planning to put mine into a 24v case too. If you get yours working, can you share what psu you used?

 

[PhilipMarlowe]

I'm planning to put mine into a 24v case too. If you get yours working, can you share what psu you used?

Did you manage to figure this out?

 

[Jeff5]

Did you manage to figure this out?

Short answer: the following links are for kits/pcbs that will work. You'll need +- voltage for op amps, which was something I had to learn about.

https://www.fivefishstudios.com/diy/psu2448plus/
https://glass-ware.stores.turbify.net/dulv.html
https://www.jlmaudio.com/shop/ac/dc-kit.html?display_tax_prices=1
https://proaudiogc.com/en/3-rails-adjustable-power-supply-pcb-

Long answer: When I learned about op amps and the +- voltage thing, and got comfortable reading the schematics for these power supplies, I realized the circuits are so small they can easily be made on a turret board (perf boards are typically not rated for that). Although pcb is way better if space is an issue.

Toroidal transformers such as this one are good for these types of PSU.
https://www.parts-express.com/Avel-Y236103-30VA-15V15V-Toroidal-Transformer-122-605?quantity=1
You should know what the "30va" and "15v+15v" mean, then you'll be in good shape.

Just research anything you don't know on the schematics then you can make your own PSU for most projects.

Also check out the pcb Gerber files for the MEP250A on this site:
https://hiegdk.com/spe/

 

[Quantum J Audio]

Toroidal transformers such as this one are good for these types of PSU.
https://www.parts-express.com/Avel-Y236103-30VA-15V15V-Toroidal-Transformer-122-605?quantity=1
You should know what the "30va" and "15v+15v" mean, then you'll be in good shape.

You could also run this off a decent switched mode PSU with some filtering.

 

[Quantum J Audio]

How would you describe the sound of Don's version of the 250eq? Is it more transparent? Are there options for it, like transformers?

As this is a faithful reproduction no TX's were considered in the design. In my workflow a pair of 250's will go across the mix buss. My chain is normally Don Classics 500 G-BUS (prototype) THE 250EQ and then a pair of Don Classics NV73 for some Neve/Carnhill qualities.

This is the product description from the new store coming soon.

Transparent and Musical Sound​

• Transparency: The EQ is known for being extremely transparent. It allows engineers to shape the tone without significantly altering the character of the source material.
• Musicality: Its equalization curves are smooth and natural, making it a favorite for both subtle tone-shaping and aggressive EQ moves.

---

Exceptional Flexibility​

• Frequency Range: The EQ covers an exceptionally wide range of frequencies, which allows it to be useful for a variety of applications, from mastering to mixing.
• Bands: Each band is highly adjustable, providing precise control over frequency, gain, and bandwidth (Q-factor).

---

Clean Gain and Sweet Harmonics​

• Phase Accuracy: The EQ is prized for maintaining phase integrity even with drastic adjustments.
• Sonic Sweetness: Though technically “clean,” with a subtle sweetness in its tone, especially at high frequencies.

 

[abbey road d enfer]

Transparent and Musical Sound​

• Transparency: The EQ is known for being extremely transparent. It allows engineers to shape the tone without significantly altering the character of the source material.
• Musicality: Its equalization curves are smooth and natural, making it a favorite for both subtle tone-shaping and aggressive EQ moves.

---

Exceptional Flexibility​

• Frequency Range: The EQ covers an exceptionally wide range of frequencies, which allows it to be useful for a variety of applications, from mastering to mixing.
• Bands: Each band is highly adjustable, providing precise control over frequency, gain, and bandwidth (Q-factor).

---

Clean Gain and Sweet Harmonics​

• Phase Accuracy: The EQ is prized for maintaining phase integrity even with drastic adjustments.
• Sonic Sweetness: Though technically “clean,” with a subtle sweetness in its tone, especially at high frequencies.

Perfect example of total BS. Any half-decently designed EQ should at least tick all the points.

 

[DB_]

Perfect example of total BS. Any half-decently designed EQ should at least tick all the points.

I'd say the marketing BS was spat out by an LLM and give @Quantum J Audio some slack for taking on a web store and marketing.

The best news I've heard all year is I might get to acquire a pair of Don Classics 250s.

 

[abbey road d enfer]

LLM: Latin Legum Magister, Lymphoma-Leukemia-Myeloma, or...

 

[zamproject]

...large language model ?
Now human talk like IA to describe the world...

 

[Quantum J Audio]

Perfect example of total BS. Any half-decently designed EQ should at least tick all the points.

I disagree, a sontec is transparent and musical, a neve 1073 is not, it is coloured and musical, both EQ’s sound great and are well designed, but the later is much more coloured.

it’s pretty hard to describe how an EQ sounds and feels without listening and using it.

Instead of just calling it out as BS you could offer some constructive alternatives. That would actually be helpful and appreciated.

It was these kind of comments that contributed to Dave giving up on the forum, which is pretty sad for this community.

I don’t need the income from selling these kits, it’s a lot of work to get this together and it won’t make me rich. So I’d really appreciate constructive feedback.

 

[abbey road d enfer]

% of EQ's with identical I disagree, a sontec is transparent and musical, a neve 1073 is not, it is coloured and musical, both EQ’s sound great and are well designed, but the later is much more coloured.

That means distortion and/or frequency response quirks.
What I meant is that producing a transparent EQ is the easiest thing in the world for any decent designer. There's nothing to brag about.
Producing a "coloured" piece of equipment that sounds good is a challenge. Not all types of distortion are pleasant.
Transparency comes with a simple set of rules.
As to sounding musical, it's just a matter of properly adjusting the dominant parameters, Boost/Cut, BW (which some call improperly Q), and choice of frequency.
99% of EQ's with same B/C, BW and frequency have absolutely identical response.
If a difference is audible it comes from other parameters.

Instead of just calling it out as BS you could offer some constructive alternatives. That would actually be helpful and appreciated.

Did I make myself clear?