sontec 1 RU build thread

[mikeyB]

@ mikeyB: I like this. Hope this EQ will help to make more good music.
@ slowbass: these are 50k lin centertap centerdetent pots from Alphastat, not 5k.
Please see BOM, for cat. Nr's.

Nearly finished 2nd unit(mine) - me mate at pobaudio.com mastering can't praise it enough - "incredibly versatile, powerful top end" You really have to get silly with the q to make it scratch - ps how about some vactrol elements in place of the pots for a mutron filter flavour? - hehe

 

[Igor]

I have voltage-controlled second order THAT2180-based VCF for this purpose

 

[rrs]

Woo -Hoo my Sontec fired up perfectly first go.

thanks Igor.  ;D

 

[Igor]

Happy about this. Have a fun!

 

[kambo]

are we using shorting or none_shorting switches for gain, frequency and Q

 

[Igor]

For mastering variant you mean? Shorting Elma's

 

[kambo]

thanks Igor,
mastering variant

 

[Kingston]

I have quite a few questions about the output stage and the weird grounding scheme.

1. Why is output XLR connector chassis combined to pin1 with a 10R resistor? seems a bit pointless.
2. Why is chassis ground combined to GND2 in the I/O section with the 0,1+22R filter?

I removed the 0,1+22R filter, used a jumper instead of the 10R resistor, and connected to chassis in PSU only, and on XLR's separately (pin1 never touches GND2). About 10dB less hum.

Same as I do in all my gear.

But most importantly, I don't quite understand the output section.

3. Why is GND2 connected to pin2 using a 68r resistor? What does this achieve? Isn't the output still basically unbalanced?

Might someone shed a bit light on the output topology?

 

[Kingston]

I just want to relay some information. It has been said in the thread before but maybe it needs to be said again, and maybe it needs to be updated in the schematic.

The 12pF compensation caps in the feedback loops of both the input and output section are, shall we say, optimistic, and maybe even a bit pointless. If we one wants to more freely swap opamps and especially different types of discrete opamps, there is a real danger of oscillation.

Use a 47-100pF. Still very wide bandwidth, but far less danger of oscillation.

 

[RightOnMusic]

where can i find the BOM for this?  the link on the OP is dead.  i'm considering buying a pcb set, but i'm certainly not going to if i cant get a darn parts list...  any help???

 

[slowbass]

I asked Igor and he sent me this bom (bom_sontec.doc) I've just changed the quantity of the pots from digikey : 1 x 5K lin potsw and 3 x 5k lin pot instead of the contrary. There maybe a resistor missing for the amp pcb. I hope it's ok to copy it here.

BOM  for 1 channel!

CONNECTORS

2 MOLEX 3 PIN (NOT USED WITH NEUTRIK CONNECTORS)
2 MOLEX 5 PIN
3 MOLEX 4 PIN 3.81 PITCH
1 OUT CON-NEUTRIK_AG_NC3.
1 IN CON-NEUTRIK_AG_NC3

FARNELL CODES FOR NEUTRIK'S:

Order Code: 724518
Manufacturer Part No: NC3FAH1

Order Code: 724543
Manufacturer Part No: NC3MAH


POTENTIOMETERS

1 5K LIN POTSW  (instead of 3)
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=CT2204-ND

3 5K LIN POT (instead of 1)
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=CT2226-ND

5 50k CTPOT
2207 RD1601-20F4-30R
ALPHASTAT 63250-01610/B50K 50K LIN CENTERTAPCENTERDETENT

5 100K RLOG DUAL_ALPHA_2
4196 RD1602-20B4-30R
ALPHASTAT 63256-02600/C100K 100K REV-LOG

WWW.ALPHASTAT.DE

SWITCH

2 SWITCH TOGGLE 2PDT RA PCB

FARNELL Order Code: 9473319



OP-AMP

1 ad706 OR OPA2604(24V PS) 'CAN BE OTHER LOW OFFSET DUAL OPAMP
2 OPA604 OR JE990 ETC 'CAN BE OTHER LOW DIST FAST HIGH CURRENT OPAMP (Forssell 993?)
5 OPA2604 OR OP275 ETC 'CAN BE OTHER LOW DIST FAST DUAL OPAMP


RESISTORS

5 22R R-EU_0207/10
2 68R R-EU_0204/7
2 100R R-EU_0204/7
2 100R R-EU_0207/15
4 392R R-EU_0204/7
8 1k6 R-EU_0204/7
2 3k R-EU_0204/7
1 4k7 R-EU_0204/7
1 8K2 R-EU_0204/7
1 10k R-EU_0204/7
1 10k REU_0207/12
1 11k R-EU_0204/7
4 11k5 R-EU_0204/7
1 17k4 R-EU_0204/7
10 20k R-EU_0204/7
4 20k R-EU_0207/12
4 30k9 R-EU_0204/7
4 36k5 R-EU_0204/7
4 55k R-EU_0204/7
10 1m R-EU_0204/7
1 2m R-EU_0204/7
1 3m9 R-EU_0204/7
1 510k R-EU_0204/7

8 7k5 R-EU_0204/7
'USE 4K7 FOR MORE BOOST/CUT; INSTALL ON BOTTOM SIDE OF FILTERS PCB


CAPACITORS-ELECTROLYTHIC
2 100U CPOL-EUE5-10.5
2 100U CPOL-EUE5-13
CAN BE 100-470 UF 35-50V, POWER SUPPLY BYPASS CAPS

4 33U CPOL-EUE5-6
USE 33U 25-50V HIGH QUALITY TANTALLUM OR AUDIO GRADE ELECTRILYTHICS


CAPACITORS-CERAMIC

17 0.1U 5MM PITCH CERAMIC POWER SUPPLY BYPASS
' VALUE CAN BE 0.047-0.33 UF 50V


CAPACITORS-POLY ETC.

1 0.15U C-10-15/6
2 0.47U C-10-15/6
8 1U C-10-15/6
1 2U2 C-10-15/6
1 1U C-10-15/6
2 2u2 C-10-15/6

1 4u7 C-10-15/6 (PITCH UP TO 35MM, POSSIBLE TO USE 2 CAPS IN PARALLEL)
1 ** C-10-15/6


CAPACITORS-SILVER MICA OR POLY

1 3n3 C-7-10/5
2 2n70 C-7-10/5
1 100P C7.5/3
1 150P C5/2.5 NOT NECESSARY WITH OPA604
2 330P C7.5/3


CAPACITORS-SILVER MICA OR COG
5 5p C2.5/2
2 12p C7.5/3


MISC
1 LED3MM

C2.5/2 MEANS PITCH 2.5MM, 2MM WIDTH
C-10-15/6 MEANS PITCH 10 OR 15MM, 6MM WIDTH
CPOL-EUE5-10.5 MEANS POLAR LYTHIC CAP EUROPEAN SYMBOL 5MM PITCH 10.5MM DIAMETER
R-EU_0204/7 MEANS R EUROPEAN SYMBOL 0.25WATT 7.5MM PITCH

Power supply BOM:

DIODES
4 1N4004 D20, D21, D22, D23
4 1N5400 D16, D17, D18, D19

RESISTORS 1/4W
1 10k R24
2 200R 2% R4, R5
1 rx+ 3k6 2% for 24v R1
1 rx- 3k6 2% for 24v R7

(200R/1.25V)=(Rx/(Ux-1.25V))
Rx in Ohms

IC'S
1 317 LM317 IC1
1 337 LM337 IC3

4 CERAMIC CAPS 0.1UX50V PITCH 2.5MM C9, C10, C11, C12

ELECTROLYTHIC CAPS 50V
4 100u CPOL-EUE3.5-8 PITCH 3.5MM
2 3300u CPOL-EUE7.5-18 PITCH 7.5 OR 10MM

2 HEATSINK FARNELL 1313891 , 1315516 , ETC


!!!!CHECK ALL RESISTORS BEFORE INSTALLING TO PCB.
BE PATIENT AND CAREFULL.
UNIT DONE WITHOUT MISTAKES
WORKING FROM FIRST FIREUP,
ONE WRONG ******* LIKE
33K INSTEAD OF 33R
OR REVERSED 'LYTHIC POWER SUPPLY BYPASS CAP
CAN ADD SOME HOURS OF HEADACHE.

 

[Igor]

I removed the 0,1+22R filter, used a jumper instead of the 10R resistor, and connected to chassis in
PSU only, and on XLR's separately (pin1 never touches GND2). About 10dB less hum.

Hi Kingston! Very ineresting about 10 db hum. I just did same experiment with Sontec which I had on my table.
Same -89 db unweighted noise level when EQ in, filters at 0.
No hum, hiss only.

Anyway. All these are OPTIONS. In many real life situations you will get less ground noise when pin 1 IS connected to
ground thru small resistor, 1...10 Ohm. Etc etc. Regarding the feedback capacitors, 12pF is quite enough with MOST opamps.
47-100 pf will make this EQ sounding bit phase-shifty on highs.

Regarding the 68R resistor, imagine the situation when eq out goes into electronically balanced line receiver. CMRR.
Take handbook for sound engineers, etc, this is so-called "ground compensated" unbalanced out.
I prefer high voltage opamp, ground compensated out to electronically balanced.
Anyway, you can throw here THAT1646.

BTW. If you don't like the way pcb's design done, make your own. Etc etc

 

[Kingston]

I had -95 unweighted noise level with EQ in with the RF filters and 10ohm resistor. -104 now that they're gone and pin1 never touches GND2 (only case). Quite impressive for unbalanced equipment. Decent PCB layout I'd say.

About the pin1 to ground through 10ohm resistor... That seems to be somewhat against most pin1 related guidelines I've seen. But this doesn't really matter because you made it optional anyway.

47-100 pf will make this EQ sounding bit phase-shifty on highs.

How can you hear that?!

LPF -3dB @ 1/(2*PI()*11000*47*10^-12)=300kHz

Great to know we have a dolphin doing the listening tests.  

BTW. If you don't like the way pcb's design done, make your own. Etc etc.

I'll admit it, this certainly crossed my mind when I realised how the pot placement had been implemented...

Only one third of them are physically attachable to the front panel, and this is the only support holding the PCB in place.

It will break. The tiny Q-pots will break first.

What's most strange about this is that the PCB is dual layer and the alphastat/digikey pots are recommended to be used here. It would have been trivial to move all the pots to the "front row" in your PCB design software so that they can be all attached to the front panel...

Just mild criticism for better future projects.

 

[Igor]

I like _constructive_ kind of criticism.
Regarding the cap, I said what I said. It came from testing not one circuit in several mastering studios.
You can call me audiofoolish as well as some of my customers. I will aggree. It will noty give any satisfaction to both sides

I can measure on my Sontec with: 20-20k filter, 0dbV in, 0dbV out _only_ 96db S/N  with EQ IN, all gains at 0.
Tell me where came -104 from. I feel something new here.

Regarding the pots etc. I used skirted Elma knobs for gains and knobs with pointers for the rest.
If the pots will be placed on front pannel with nuts, it will look really weird.

Let's do an experiment and try to brake freq and Q pots.

Next. I'd like to see your Sontec PCB and front design. Can promiss only _constructive_ criticism.

 

[Sarcastic Sound]

if you feel like you need to have ALL of the pots on the pcb attached to the front panel get out your lathe and make some hollow shaft extensions that are threaded internally on the pot end, and externally threaded on the face plate end. precision mill them to reach the faceplate and be nutted on with the rest of the pots.  this will give you the mechanical strength that you seem to need.

personally I feel them not necessary at all. if the front panel is made to a high tolerance the shaft should just fit threw the hole with 1.5mm clearance around the diameter of the shaft and the knob should be 2mm off the face plate (just enough space to not touch the faceplate when in rotation). this high tolerance does not allow enough stress to be put on the pot to even have a chance to break. if you push the pot the knob will hit the face plate and stop. if you move the knob horizontal or vertical (or anywhere in between) the face plate will hole will stop movement.

I thank Igor for contributing to the DIY community and feel it not necessary to scrutinize him on design choices. Especially when he is SOOOOO helpful in giving support to builders. Like said before, if you don't like the design then design your own!

Now go have a smoke and drink of choice.

Cheers Igor and THANKS!!!  ;D

 

[Kingston]

Guys what the heck!  

Since when has it not been ok to discuss design choices? I thought that's what prodigy pro is all about.

I had no idea this was such a touchy subject for some. This is DIY, and it's all about modifications and making things work better.

Igor, if you don't want people to comment on your design, don't publish anything. Did you really think you had made some kind of perfect PCB with absolutely no errors? Come on, we know better not to argue about something like that.

Like said before, if you don't like the design then design your own!

Seriously now. That's just a plain stupid thing to say. In fact, it's logical fallacy in our context of discussion. http://en.wikipedia.org/wiki/Straw_man

This forum is all about discussing design - at best anyway. We're not all painting by the numbers here. How else are you going to learn design, other than discussing, testing and building?

Ps. I don't have a lathe nor access to one. I would have simply liked to used the existing threads of the pots. Much easier than having to make a highly specialised custom part because of a bad choice in PCB design.

I can measure on my Sontec with: 20-20k filter, 0dbV in, 0dbV out _only_ 96db S/N  with EQ IN, all gains at 0.
Tell me where came -104 from. I feel something new here.

Nothing new here that you wouldn't already know.

1. Well shielded PSU transformer.
2. Schottky diodes.
3. Big high quality PSU caps and lots of them.
4. great opamps.

These are Pier Pablo's (ppa here at the forum) FET opamps. They have exceptional specs by any standards.

 

[Igor]

Since when has it not been ok to discuss design choices?

Any prob here except the name of thread:

Topic: sontec 1 RU build thread

and it is good to have clean thread with high concentration of usefull information.

Did you really think you had made some kind of perfect PCB with absolutely no errors?

Never pretended to be errorless.
But...you know, if someone come and pissing off something you put a lot of time....etc etc.

Ps. I don't have a lathe nor access to one. I would have simply liked to used the existing threads
of the pots. Much easier than having to make a highly specialised custom part because of a bad choice in PCB design.

If I need to make my own good choice, I do my own pcb's

Nothing new here that you wouldn't already know.

1. Well shielded PSU transformer.
2. Schottky diodes.
3. Big high quality PSU caps and lots of them.
4. great opamps.

There can be microne difference (like -95 or -94.5 db) difference between mumetal shielded toroidal trafo or not shielded but quiet toroidal trafo
(2x25V 30VA from Farnell for xample) because there no high gain high impedance path. Etc etc.

Same about difference between say MBR360 and 1n5400.

Fully aggree about PS caps quality. Again, no need huge (10000u) values, low ESR is what really matter, and tones of bypass ceramics.

Yap. Forssell's are my discrete favorites. OPA(2)604 are my chip favorites.

If you want to promo opamps, please not here. Again, concentrated useful info for building this EQ.

If you so good in numbers, please calculate the noise of ideal opamp in inverting connection, feedback resistor 20k, input resistor 3.3k.
This is the noise of summing amp without filters and input bal. line receiver.
Add noise of input balanced line receiver. Than add noise from filter's opamps. Add some dB for "noise figure".
Etc. My friend simulated this EQ about 3 years ago and helped me with calculation of resistors for stepped EQ.
IIRC we got approx. -93db in theory. Sorry, I am very bad in mathematics.

BTW. It can be nice to have simulation graphs of freqresp and phase shift for opamp in connection mentioned above with Cfb 47-100pF.
Than, simulate hi freq filter and cut 3db. I'd really like to see the simulation plots

This is constructive part.

OOPS. Missed one little thing.

Quite impressive for unbalanced equipment.

Ahem...a....Why unbalanced????

 

[Igor]

Bump. No answer. Anyway, have a good day.

 

[Kingston]

Why are you so hostile? I suspect we have a classic case of language boundary here. You somehow think I'm making fun of your design.

Or maybe you really can't take mild criticism? Oddness.

Anyway, what do you need an answer for? You don't really want me to discuss anything at all and seem to be mad at me for some reason. I think it's best if I just leave the thread so you can police it as you see fit.

But this is what really ticks me off:

If you want to promo opamps, please not here. Again, concentrated useful info for building this EQ.

You are happy to relay your own experiences and that you love Forsells and whatever, but then when someone else has anything to say, alternative solutions etc, it's somehow not "concentrated useful info".

Someone already asked me in private about using alternative opamps. Probably because he was afraid you would be angered if he asked here. I think it's a testament of the "concentrated useful info" of this thread.

I have seen it more than once in the past, but when a developer throws a hissy fit in front of his customers or acts like a princess, it's instantly bad for business.

Here, you can have "your" thread back. Anywhere else seems better at prodigy pro.

Mike

 

[Igor]

Regarding hissy fits, you were first.

Cool. I can aggree with everything. But where -104dB came from?

Can you please specify measurement setup?

Regarding the language boundary's, I understood fine everything you wrote.
I droped some lines about noise and frequency responce, seems my english was wrong,
or you prefer take electonics discussion aside and move into psychology?
BTW. Mild critisism imho like "dude, why can't we take the pots to front?" etc.