sontec 1 RU build thread

[Trench Recordings]

Double check this with their product specs and measurements but i have a few spare harwin sockets and they fit igors board.

http://www.digikey.ca/product-detail/en/H3167-05/H3167-05-ND/3919400

 

[tonedude]

I did place the Mill-Max sockets on the pins of the DOA and then soldered the sockets in the right position on top of the i/o PCB, worked just fine!

I'm changing out the chips on the I/O board to discrete op amps (APP992), and the mill-max sockets I bought are too large on the solder end. Would anyone happen to have a mouser part number for the correct size?

Thanks,
Paul

 

[pH]

It looks like Igor suggested to solder the bottom of the pin onto the board like you did tonedude. I tried one and it seems to work fine.

 

[tonedude]

Hmmm....?

I wonder if my sontec is working as it should?

When I send in a mono signal (eg white noise...) in to both channels of my Igor Sontec, and try to cancel the signal out through phase shifting one of the returning channel, it doesn't null, not even close (I get about -30 dB or something).

When doing the same with my Behringer T1951, modified to something "close" to BP Net EQ spec, it almost nulls.

How can I understand this? Is there something wrong with my Sontec i/o board?

 

[tonedude]

Fixed....

 

[Siegfried Meier]

Hey guys,

I built up 2 of these over the years - a +/-6dB version a few years back, which sounds excellent and just now finished a +/-12dB version.  However, I have an odd hum with the mains cranked in the top end.  Even with the boost/gain at 0, when the freq is set to the lowest, around 1k, I hear the hum.  The trafo positioning and even one of Don Audio's toroid shields doesn't seem to do anything at all.  I put a ground wire on the back of the freq select pot and connected it to star ground and it got a little better, but still not as good as the other unit.  Could it just be that the different caps used in this unit are more sensitive?  But usually you'd hear a difference in boosting the frequency...in this case I'm not boosting at all, I'm simply selecting the frequency.  That's an odd one...both channels do it as well, which makes it double odd...

Any advice much appreciated.
Thanks!
Sig

 

[Biasrocks]

Hi Sig,

Mark from Sharktank here.

A few things to check.

Make sure the front panel is grounded and the pots are grounded to the panel.

Check with an meter.

You could try scraping away the finish around the pots and where the front panel connects to the enclosure.

Recheck your grounds on all the boards, makes sure you have zero ohms on your ground points to your main audio ground.

Barring that you may want to seperate audio ground and power ground until the last possible point, verify with a scope to make sure there's no hash on your audio ground.

Mark

I built up 2 of these over the years - a +/-6dB version a few years back, which sounds excellent and just now finished a +/-12dB version.  However, I have an odd hum with the mains cranked in the top end.  Even with the boost/gain at 0, when the freq is set to the lowest, around 1k, I hear the hum. 

Any advice much appreciated.
Thanks!
Sig

 

[Siegfried Meier]

Well, the only pots that are actually attached to the panel are the gain pots, and I feel that's the weakest part of this project - the design should have been so that all the pots bolt to the panel.  I took buss bar and attached it from the back of the hi freq pot to my star ground and it's made a significant difference.  Once the 2nd channel went in and the top was attached, it was actually pretty decent.  I'm probably audibly testing this a little bit unrealistic (mains and levels all cranked), but if I put my finger on the back of that pot, and touch that cap directly behind, I can get the hum to disappear 100%.  I'll do a bit more poking around when I get some free time, but for 99% of tracking purposes, it'll probably be just fine.

Thanks!
Sig

 

[jefepeters]

Hello,

Quite a few years back I picked up the I.J. Research PCBs for this project, but never got around to building it. Is it true the Alphastat pots specified in the BOM are no longer available? (Or only as a bulk special order?) If so, are there any other viable alternatives or am I out of luck?

Thanks,
Justin

 

[mrcase]

Hey!

I have the vice versa situation. I missplaced my pcb and can only find the pots I bought for it. I might sell them, if another search doesnt bring out the board.  pm me if you are interested.

 

[Gold]

I want to make a +/- 3dB version of this. To do this the gain set resistors (for example RF2B,RF2C)need to be about 68K Ω. I was wondering if the value of the pot could be lowered to reduce noise? Normally I'd just try it but I don't have center tapped pots in different values. If so is it worth doing?

 

[Harpo]

... To do this the gain set resistors (for example RF2B,RF2C) ...

for usual R18, R19, R20, R21 and R22 are the gain setting resistors ...

I was wondering if the value of the pot could be lowered to reduce noise?

yepp, as long as IC6 and IC8 can drive the then increased load of actually 6K5 (=5 x (50K/2 + 7K5) in parallel)
good luck

 

[Gold]

Thanks Harpo.

I was looking at your spreadsheet. I see you can enter the number of switch positions you want and it will tell you the resistor values for the range you have by evenly dividing the range. I was wondering if there is a way to enter the number of switch positions with the center frequency you want for each position and have it tell you the resistor values? In other words if I want 11 positions with the center frequencies being 20Hz, 40Hz, 75Hz, 100Hz, 125Hz, 150Hz, 175Hz, 200Hz, 250Hz, 300Hz, 350Hz. Can I enter those in to a spreadsheet and have it spit out resistor values?

I plan on figuring it out by measuring. I don't know Excel and I think it will be easier than using anRPN calculator a million times. I have a dual 25K pot. I'll make up the rest of the resistance with resistors. Hopefully that will give me enough resolution to measure.

 

[Harpo]

Paul, yepp, in cell C23 of 'SontecCalc_Igor.xls' you fill in the number of wanted step positions (in your case '11') and simply overwrite the evenly divided calculated frequencies in cells D26 ... H36 with your wanted target frequencies.
Just as a reminder, don't miss the sentence 'Update the cap.values in the red cells with measured real world capacitance of your fitted parts.'

 

[Gold]

Thanks Harpo, it worked! I got scared when I clicked on the cell and saw the equation the first time.

 

[Gold]

Now I'm not so sure it worked. Here is a link to the .xls file I used.  https://we.tl/t-8UnvDpSMlz    I made a rotary switch with 11 positions for the High Mid band using the values in the Series Resistance table.  I’m not using the  High Shelving band in this build. Just four bell bands. My High Mid is the second  0.47uf/330pf band.

Using the values in the table it looks like the center frequency is somewhat close but the available gain in the band is about half as much. With the 100K rev log pot and 68K gain range set resistors I was getting +/-3dBat a given center frequency. Now I'm getting about 1.5dB and the center frequency seems a bit off. The calculated values for 1K Hz seem to be closer to 1k3 Hz.

Shouldn't the overall resistance value from one end of the string to the other end of the string for the rotary switches be 100K? I tried lowering the value of the pot since I have the 68KΩ gain range set resistors. I tried a 10K pot but there was less gain available in the High Mid band I tried.

 

[Gold]

Here is what I got empirically. Way different than the spreadsheet. I must not understand something.

 

[Harpo]

Now I'm not so sure it worked. Here is a link to the .xls file I used.  https://we.tl/t-8UnvDpSMlz    I made a rotary switch with 11 positions for the High Mid band using the values in the Series Resistance table.  I’m not using the  High Shelving band in this build. Just four bell bands. My High Mid is the second  0.47uf/330pf band.

Paul, you seem to have missed adjusting the parts values in rows 8 ... 17 for your desired range.

See attached file with updated parts values for your target frequencies ... http://www.hausverwaltung-heger.de/al_leck_trick/SontecCalc_PaulGold.xls.

 

[Gold]

Harpo,

Thanks for taking the time to do that but I guess I still don't understand. Don't the resistor strings need to add up to 100K? Using the second band labeled Lo Mid in the spreadsheet the total resistance in the Series Resistance table is 11,129Ω. If I subtract 11,129 from 100,000Ω I get 88,871Ω. That's close to the measurement I got for the first switch position which was 88,580Ω.

It still doesn't make sense to me because the last switch position is 0Ω. If I put 88,871Ω before the first switch position then the last switch position can't be right as 0Ω should be the top of the range of the band which is about 8K Hz.

 

[Harpo]

Don't the resistor strings need to add up to 100K?

No. The equation for bandpass center frequency is set by 1/(2PI * SQRT( (RFx.9+pot.value) * Cfb *  (RFx.10+pot.value) * Cshunt) ).
Keeping cap values ratio from Sontec circuit and setting the substituted pot.values to zero ohms (CW end of pot travel) giving the upper end of the bandpass filter.
Your FI wanted 5,500 Hz for the 2nd low mid band requires a RFx of 2,323 Ohms instead of Sontec 7,987 Hz with RFx 1,600 Ohms. Increasing the pot.value to 11,129 Ohms (giving series resistance 2,323+11,129 Ohms) brings the BP center down to your wanted 950 Hz for the substituted potsCCW end instead of Sontec 100,000 Ohms for 126 Hz.

It still doesn't make sense to me because the last switch position is 0Ω.

The CW end of the substituted stereo pot with rev.log taper is zero ohms, setting the upper end of the BP center frequency with the remaining 2,323 ohms series resistors.