500 series Sontec / GML type eq

[tomheavybeats]

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?

 

[johnsonic]

Pretty sure they're still kickin' - he answered my questions about the silkscreen.

The omeg pots for me measured within tolerance at both sides of the range, and are consistent between my two units for any point within the sweep. However, the resistance when turning the pots is inconsistent. Not a huge deal, but one of the frequency and one of the Q knobs has zero drag. Hoping it improves or I don't notice over time?

Here's David's response for future folks regarding the silkscreen markings. I think it makes total sense:

```
Yes, different pot makers do non-linear wafers slightly differently, and so you get slight deviation from what the pot manufacturers did on the original 250s. The main thing is they’re consistent within the manufacturer however.

It was one of those decisions I had to make, whether to leave it as original, or do it tailored to Omeg pots. At that early stage, I didn’t want to limit myself to a specific pot, so decided to stick with the original silkscreen, just in case, I changed pots down the line, and then the silkscreen would be neither original nor correct to the pot. So, I stuck with the only constant, ie. The original.
```

Overall, I'm LOVING these EQs. Dropped some app992s in them and it's true - stick with the ICs - they are better.

 

[tomheavybeats]

Pretty sure they're still kickin' - he answered my questions about the silkscreen.

The omeg pots for me measured within tolerance at both sides of the range, and are consistent between my two units for any point within the sweep. However, the resistance when turning the pots is inconsistent. Not a huge deal, but one of the frequency and one of the Q knobs has zero drag. Hoping it improves or I don't notice over time?

Here's David's response for future folks regarding the silkscreen markings. I think it makes total sense:

```
Yes, different pot makers do non-linear wafers slightly differently, and so you get slight deviation from what the pot manufacturers did on the original 250s. The main thing is they’re consistent within the manufacturer however.

It was one of those decisions I had to make, whether to leave it as original, or do it tailored to Omeg pots. At that early stage, I didn’t want to limit myself to a specific pot, so decided to stick with the original silkscreen, just in case, I changed pots down the line, and then the silkscreen would be neither original nor correct to the pot. So, I stuck with the only constant, ie. The original.
```

Overall, I'm LOVING these EQs. Dropped some app992s in them and it's true - stick with the ICs - they are better.

Thanks for letting me know and the extra details, I will just keep trying him I guess.

Good tip about the APP992s, I was going to buy them also but may stick ICs I have one unit currently with IC and sounds great, but I think I'm better off buying 2 new units so I can match components better for a stereo pair for the mix buss. I have read this whole thread and really want to try stepped pots but not enough info unfortunately for me to be confident to try

 

[Zim]

I made mine with a couple of headers so I could swap between either IC’s or DOAs - APP992’s here also. (IC’s running on 16V, DOAs on the 24V rails).

Personally I stuck with the DOA’s. For me, while the IC’s gave a ‘more accurate‘ representation of the signal going in, the DOA’s seeme pd to make it a little more ‘3D’. It’s annecdotal but, as an experiment After I’d built mine I tried eq matching with Fabfilter’s Pro Q3. With the IC’s installed Pro Q3 nailed the eq match, but it couldn’t eq match with the DOA’s.

I’m not saying one way is better than the other, just that there is a difference and, if you can, it’s worth trying both to see which you prefer. I love these things - frankly can’t see anyone being disappointed whichever way they go!

 

[tomheavybeats]

I made mine with a couple of headers so I could swap between either IC’s or DOAs - APP992’s here also. (IC’s running on 16V, DOAs on the 24V rails).

Personally I stuck with the DOA’s. For me, while the IC’s gave a ‘more accurate‘ representation of the signal going in, the DOA’s seeme pd to make it a little more ‘3D’. It’s annecdotal but, as an experiment After I’d built mine I tried eq matching with Fabfilter’s Pro Q3. With the IC’s installed Pro Q3 nailed the eq match, but it couldn’t eq match with the DOA’s.

I’m not saying one way is better than the other, just that there is a difference and, if you can, it’s worth trying both to see which you prefer. I love these things - frankly can’t see anyone being disappointed whichever way they go!

Thanks and will try both I think. Is there an issue with stereo matching on the mix buss though with these? Haven’t really read much on here about component matching or how people go about compensating. Also aren’t tolerances on Omeg pots quite high? Seems like there would be quite a mismatch between left and right

 

[Zim]

I haven’t used mine on mix bus yet. I asked David about component matching before I built mine and His advice thatthe biggest variance would be in the pots. He recommended measuring the values of all the pots and then using the pots of closest values in the same position on each unit - prioritising closest matches in the frequency band that you think is of most importance to you.

(So if you think you’ll be using the low mids least, the pots with the biggest discrepancy would go there. Best would go e.g on highs).

To get it perfect for a mix, I believe the recommendation is to run tones to get the two channels matched up perfectly, but I haven’t been able to find anywhere that explains how to best do that in practice. If anyone can explain the process I’d be grateful...

 

[grid_stopper]

To get it perfect for a mix, I believe the recommendation is to run tones to get the two channels matched up perfectly, but I haven’t been able to find anywhere that explains how to best do that in practice. If anyone can explain the process I’d be grateful...

I dont have these units, but i would guess that you could run white noise at equal amplitude through both, and monitor the return with a frequency analyzer, then adjust until you obtain a reasonable match between the two channels

 

[tomheavybeats]

I haven’t used mine on mix bus yet. I asked David about component matching before I built mine and His advice thatthe biggest variance would be in the pots. He recommended measuring the values of all the pots and then using the pots of closest values in the same position on each unit - prioritising closest matches in the frequency band that you think is of most importance to you.

(So if you think you’ll be using the low mids least, the pots with the biggest discrepancy would go there. Best would go e.g on highs).

To get it perfect for a mix, I believe the recommendation is to run tones to get the two channels matched up perfectly, but I haven’t been able to find anywhere that explains how to best do that in practice. If anyone can explain the process I’d be grateful...

Oh what great advice, thank you. Will totally do that and yes running tones as well

EDIT: got through to David and ordered a pair of these plus an extra Omeg pot to fix my other one. Great service!

 

[johnsonic]

Just wanted to report back here - I'm two months in on using these and LOVE THEM. They sound super natural, and are great on 2buss duties but am loving them most as part of my channel strip, especially with how it handles the high/mid frequencies. It's hard to make them sound unnatural and they usually get the job done. Would recommend.

 

[Quantum J Audio]

Just wanted to report back here - I'm two months in on using these and LOVE THEM. They sound super natural, and are great on 2buss duties but am loving them most as part of my channel strip, especially with how it handles the high/mid frequencies. It's hard to make them sound unnatural and they usually get the job done. Would recommend.

There is not an EQ I've ever used that can add HF gain so naturally in the way these do. I would choose a pair of these over a GML on the mix buss any day.

 

[ltn.koerschgen]

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.

Hi Guys,
just finished my 250EQ.
Works on the 16v and 18v Rails with stock ICs.
Everything calibrated.

But I have the same issues as Johnsonic.
The frequencies are way off, basically the same amount as Johnsonic mentioned.
I also can get max +/-3db gain/attenuation on each band.

Did I made some mistake somewhere?
strange that its the same thing on two different eqs from two different people...
Any hints where to look?
Its too far away to use it...

Thanks!

Best,
koerschgen

 

[abbey road d enfer]

I dont have these units, but i would guess that you could run white noise at equal amplitude through both, and monitor the return with a frequency analyzer, then adjust until you obtain a reasonable match between the two channels

White (or actually pink) noise in conjunction with an analyzer is one of the most inaccurate ways of evaluating frequency response.
It is much more accurate, and not more difficult, to use a soundcard and one of the usual free measurement softwares, such as REW, RTAA, Audiotest...

 

[johnsonic]

Hi Guys,
just finished my 250EQ.
Works on the 16v and 18v Rails with stock ICs.
Everything calibrated.

But I have the same issues as Johnsonic.
The frequencies are way off, basically the same amount as Johnsonic mentioned.
I also can get max +/-3db gain/attenuation on each band.

Did I made some mistake somewhere?
strange that its the same thing on two different eqs from two different people...
Any hints where to look?
Its too far away to use it...

Thanks!

Best,
koerschgen

Hello! Look up to post #402 regarding the silkscreen - makes sense to me. I've just been using my ears and not relying on the silkscreen and it's been working out great. Also, a tiny little turn on some of the pots moves the band quite a bit, so the silkscreen would just be an approximation anyway.

I have the correct +/- db though - assuming you followed the calibration steps to a T?

 

[ltn.koerschgen]

Hello! Look up to post #402 regarding the silkscreen - makes sense to me. I've just been using my ears and not relying on the silkscreen and it's been working out great. Also, a tiny little turn on some of the pots moves the band quite a bit, so the silkscreen would just be an approximation anyway.

I have the correct +/- db though - assuming you followed the calibration steps to a T?

Thanks Johnsonic!
Yes, I read the whole thread, but didn't expected the silk screen that far away from the measured Frequency.
Any way, there seems to be no problem at this side.
I did all the calibration steps, but still can get only 3 db gain/attenuation.
It seems to be a general thing wich affects all 5 bands...
any ideas?

Thanks.K

 

[ltn.koerschgen]

Ok, I measured it properly, looks interesting...
The Levels are around 12-13db boost/cut except the LF band (105Hz +/-9db)
All measurements were made with the most narrow q setting.
The LF shelf is actually a very wide Bell curve (peak at 17hz)
The HF shelf could be the same, but my measurements stopped at 24Khz.
TH HF Shelf gives a overall 2db cut/boost over the whole frequency Band (maybe its only mine...)
There is no difference between the stock ICs and my own OA10 DOAs (DOA THD is roughly 0.0001% better over the whole Freq Band)
Anyone experienced the same issue with the LF Band?

Thanks,
K

 

[ltn.koerschgen]

And here measurements with the widest Q, same frequencies as above.
I think the LD Gain issue is just analog variation and depends on the Q.
Its roughly +/-15db in shelf and wide Q...
Looks promising, can't wait to finish the second one and put it on the 2Bus against the BT50!

Best,
koerschgen

 

[ltn.koerschgen]

It should be noted, that all of the Frequency Pots should be fully ccw when trimming for lowest noise... (stated in the original schematic)

 

[abbey road d enfer]

Anyone experienced the same issue with the LF Band?

A look at the schemo should bring a non-ambiguous answer...

 

[robinhuntmusic]

had the same experience with those doa's on 24v, just felt a bit more lively. Great stuff this

 

[PhilipMarlowe]

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