sontec 1 RU build thread

cstella · Oct 29, 2012

Hi Group!

I am having a strange problem with my Sontec and hopefully someone here can help. Everything is working ok except the HF band on the second channel. The band works but as the frequency control is turned more counter-clock-wise a hum develops. It's ok until about 6K but any more to the left and it gets bad. Flipping the Shape toggle to 12dB increases the hum even more. The pot is also a little scratchy to. I have checked connections and re-flowed the solder joints in that area but no luck. I have also swapped all the power and signal connectors with the other channel and I still get this problem. So i am pretty sure it is isolated to that board and band. Any help would be greatly appreciated!

Thanks, Charles

Holger · Oct 30, 2012

Try to increase the 5pF CF5.1 to something like 22pF or 27pF

cstella · Oct 30, 2012

Thanks Holger. I put a 22pf in parallel with CF 5.1 and still the same problem. The second channel is fine. I tried swapping out the opamp but that did not help either.

Thanks, Charles

dandeurloo · Nov 9, 2012

buschfsu said:
any chance of ordering the alphastat pots in the us? I need a supplier for...

10 - 50k CTPOT
2207 RD1601-20F4-30R
ALPHASTAT 63250-01610/B50K 50K LIN CENTERTAPCENTERDETENT

10 - 100K RLOG DUAL_ALPHA_2
4196 RD1602-20B4-30R
ALPHASTAT 63256-02600/C100K 100K REV-LOG

Anyone? i will order outside us if i have to.

thanks

Does anyone have a USA source for these?

ptron · Nov 14, 2012

another sontec was born today! flawless (this one was, but the first one gave me some trouble...)
it sounds awsome!!
DOA on output 604 on input.. its a beast!

THANKS A LOT IGOR!

druu · Nov 14, 2012

Nice! No internal shots?

You should trim the pot shafts, will make it look even better!

ptron · Nov 18, 2012

Ill take some porn shots today or tomorow

its really super clean design ... Igor really simplified it i love this eq!
One thing.. With hi Q the eq starts kinda whistling over the noise floor... I asume this is normal
Aah about the shaft trimming, you think a dremel and one of those coarse discs will do the job or i need tungsten carbide tip?

Thanks A lot guys! Your help was priceless

druu · Nov 22, 2012

I've just been testing the right channel on my stepped version and getting some weird measurements. I have +/-12dB selection and testing sweeps through the 1k1 frequency selection from -12 to +12 on the HF band (L/R mode). Any idea what's causing the problem when going into +12db range?

druu · Nov 23, 2012

Seems to be happening on all bands. The above was swept at 96khz, 44.1khz is much more prominent.

Any ideas? Tested same filter board on the left channel of the io board and same problem.

dagoose · Nov 23, 2012

druu said:
Seems to be happening on all bands. The above was swept at 96khz, 44.1khz is much more prominent.

Any ideas? Tested same filter board on the left channel of the io board and same problem.

what about distortion? try it with a lower input and see what happens.

druu · Nov 23, 2012

Hmm that's sorted it! Must be very sensitive to input as I did have the input quite low already, didn't think to lower it as I wasn't monitoring the sweeps. Thanks dagoose!

Meanwhile everything checks out fine now.

On with the other channel..

duantro · Nov 23, 2012

ptron said:
Ill take some porn shots today or tomorow its really super clean design ... Igor really simplified it i love this eq!
One thing.. With hi Q the eq starts kinda whistling over the noise floor... I asume this is normal
Aah about the shaft trimming, you think a dremel and one of those coarse discs will do the job or i need tungsten carbide tip?

Thanks A lot guys! Your help was priceless

Hey Ptron, looks great! I used a thin bladed jewelers saw to cut pot shafts. I think I suggested a dremel and disc previously, but I was referring to doing this to the plastic pots that were use on other builds. I'm still waiting on parts to finish this project. glad to hear that you like it! 8)

druu · Nov 23, 2012

A dremel with cutting disc works well and is quick, but make sure you mask of everything carefully as the shavings can get everywhere. Use some tape to cover the gap so nothing gets inside the pot.

dagoose · Nov 24, 2012

druu said:
Hmm that's sorted it! Must be very sensitive to input as I did have the input quite low already, didn't think to lower it as I wasn't monitoring the sweeps. Thanks dagoose!

Meanwhile everything checks out fine now. On with the other channel..

I think it's the input of your soundcard distorting instead of the EQ itself. You're boosting quite a lot which means more gain = higher output voltage driving the input of your soundcard.

druu · Nov 24, 2012

I think you're right. A bit annoyed I didn't pick that up sooner!

Igor · Nov 24, 2012

Oh, you, soundcard testers!

Take used Boonton 1120, HP8903, and enjoy! Why do you complicate your life?

BTW,
http://www.pmillett.com/hp_8903_software.htm

druu · Nov 24, 2012

I've been considering some proper test equipment but I've only just started DIY gear this year (this project is my second build). Maybe once things become more serious then yes, will definitely invest in something.

Igor · Nov 24, 2012

druu: this is not even a matter of investment, today, just look on surplus stores or ebay,
for $300-500 you can have both used Tectronix scope and HP8903 analyzer, even with dual lab power supply on top.
More matter of space and... been lazy, I'd say

cstella · Nov 25, 2012

cstella said:
Hi Group!

I am having a strange problem with my Sontec and hopefully someone here can help. Everything is working ok except the HF band on the second channel. The band works but as the frequency control is turned more counter-clock-wise a hum develops. It's ok until about 6K but any more to the left and it gets bad. Flipping the Shape toggle to 12dB increases the hum even more. The pot is also a little scratchy to. I have checked connections and re-flowed the solder joints in that area but no luck. I have also swapped all the power and signal connectors with the other channel and I still get this problem. So i am pretty sure it is isolated to that board and band. Any help would be greatly appreciated!

Thanks, Charles

cstella · Nov 25, 2012

I am still trying to sort out the above problem. Any help is greatly appreciated!

sontec 1 RU build thread

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