FEELER : IT'S ALIVE!!!Finally finished 32C project! (SCHEMATIC & BOM)

[tonedude]

+1 on that...

Anybody know where I can get 50k or 47k rev-log pots that aren't OMEG? The Omegs are pretty expensive for us Canadians. Plus I used them for the 500-series Studer 169 EQ and have still not found knobs for them yet. :-\

 

[ForthMonkey]

Anybody know where I can get 50k or 47k rev-log pots that aren't OMEG? The Omegs are pretty expensive for us Canadians. Plus I used them for the 500-series Studer 169 EQ and have still not found knobs for them yet. :-\

Expensive for me,too.I've used linear pots.Not fit OMEG layout but still ok to use.With linear frequency range has lack but not bad.

This one is the best but expensive...I didn't find any rev.log 50K or 47K instead of this one...

http://www.audiomaintenance.com/acatalog/om-01-028_extended_info.html

 

[kante1603]

Same here,so I went for.the OMEGs.
Seems close to impossible to source from other manufacturers or in low counts.
They fit very well.Today I received my switches, so I might work on it next weekend,the rest of populating except of one cap is done so far.


Best and happy hunting,


Udo.

 

[skeeler87]

Thanks guys,

Looks like I'll have to go for the Omeg pots, oh well I'll make it work. Next I have to find knobs that fit 4mm D-shafts... If I locate any I'll drop a link here.

Also, would there be any need/benefit to use input and output transformers with this project? It seems pretty obvious that its not needed because no one has said anything about them but would I gain anything from using them?

 

[kante1603]

Thanks guys,

Looks like I'll have to go for the Omeg pots, oh well I'll make it work. Next I have to find knobs that fit 4mm D-shafts... If I locate any I'll drop a link here.

I'm going for SIFAM.Available for nearly all shaft diametres.
Also if you want to use 6mm types there are adapters to find in the web,both 6 to 4mm or 1/4" to 1/8".


Best,


Udo.

 

[rainton]

I think i will indeed buy some 16mm alpha 50k log stereo pots.

Dissembling them and swapping  front & back wafer will give you a dual 50k reverse log

I'll order some more in case I mess up - but at 1.60 Euros each it's not that big of a deal

 

[skeeler87]

I think i will indeed buy some 16mm alpha 50k log stereo pots.

Dissembling them and swapping  front & back wafer will give you a dual 50k reverse log

I'll order some more in case I mess up - but at 1.60 Euros each it's not that big of a deal

Damn that actually works?

I think I'll try that out just as an experiment.

Thanks guys,

Looks like I'll have to go for the Omeg pots, oh well I'll make it work. Next I have to find knobs that fit 4mm D-shafts... If I locate any I'll drop a link here.

I'm going for SIFAM.Available for nearly all shaft diametres.
Also if you want to use 6mm types there are adapters to find in the web,both 6 to 4mm or 1/4" to 1/8".


Best,


Udo.

Thanks Udo! Can't believe I didn't come across these before.

 

[kante1603]

I think i will indeed buy some 16mm alpha 50k log stereo pots.

Dissembling them and swapping  front & back wafer will give you a dual 50k reverse log

I'll order some more in case I mess up - but at 1.60 Euros each it's not that big of a deal

Have read about it and seen some tutorials for it during the last years,but never done it myself.
Please keep us posted when you do it,maybe some pics might be useful.They're needed on other eq builds too so it could be a very nice option.
Since you're in germany may I ask where you get them from?


Thanks in advance,


Udo.

 

[rainton]

Have read about it and seen some tutorials for it during the last years,but never done it myself.
Please keep us posted when you do it,maybe some pics might be useful.They're needed on other eq builds too so it could be a very nice option.
Since you're in germany may I ask where you get them from?


Thanks in advance,


Udo.

www.banzaimusic.com

They're based in Berlin

 

[kante1603]

O.K.,I´m done technically,and the eq works.Seems to be a nice add to my collection,from what I´ve heard it sounds indeed different but very nice.I like it!

Two things to mention for now:

1.:Gain structure,eq in with all gains to zero (or center) position boosts roughly +6dB compared to bypass mode.

2.:Low Pass potentiometer seems reversed.In fully ccw direction it has no effect,turning cw decreases cut off frequency.Also the pot action happens on the first few millimeters.

Best,Udo.

P.S.:Here´s a pic from my test setup:

Edit:Issues solved.

 

[kante1603]

Addendum:


I removed the LPF potentiometers and wired them reversed-works perfect now!
The filters sound really nice I must say……


Next step:Gain structure,should we change the gain setting resistor in the input receiver?


Thank you,


Udo.

 

[kante1603]

O.K.,


I strapped a 10k parallel over R4 from the bottom side to get 5K.
Works at unity gain level now.
I hope that was correct technically?


Thanks,


Udo.

 

[ForthMonkey]

O.K.,


I strapped a 10k parallel over R4 from the bottom side to get 5K.
Works at unity gain level now.
I hope that was correct technically?


Thanks,


Udo.

I didn't get ny problem like this but if you get 6 dB gain,i believe you must change input resistors.Input resistors are 10K.You can change it to 20K.You will get -6 dB.

 

[kante1603]

I didn't get ny problem like this but if you get 6 dB gain,i believe you must change input resistors.Input resistors are 10K.You can change it to 20K.You will get -6 dB.

So changing R4 to 5k is wrong?
Because it gives -6dB too.
Two times 20k in front is a bit on the high side,no?
I wonder why you haven't had this boost too.......I'm pretty much sure I've built them correct after the info and schematics you've shared here with us.


Thanks again,


Udo.

 

[ForthMonkey]

I'm not sure with R4 but if it's working no problem.I checked my design and i saw that i used 20K input resistors.

As i said,if it's working and result is ok,it' ok.

 

[kante1603]

I'm not sure with R4 but if it's working no problem.I checked my design and i saw that i used 20K input resistors.

As i said,if it's working and result is ok,it' ok.

Yes,hahaha.... ;D
The eq sounds indeed nice,I like the filters a lot.
If you're willing to make another batch I'd be in to buy some more sets if I may.


Have a nice evening,


Udo 

 

[kante1603]

Update:


For those who are interested,the current drawn at 16vdc (4dBu into 100k load) per rail is 55mAs,just for info.


I gave it a try and changed the input resistors to 20k (R4 set back to 10k):The offset between EQ bypassed and EQ in (gains all flat,filters off) is now less than 1/10th dB-perfect for me.


I confirm the EQ is now fully working.


Have fun,


Udo.

 

[Zjcc56]

So, What opamps are you guys using? Im finding the NE5532N hard to find. It looks like NE5532P would be a drop in replacement. Is this correct? Also has anyone ordered the front panel and confirmed that it fits?

 

[kante1603]

So, What opamps are you guys using? Im finding the NE5532N hard to find. It looks like NE5532P would be a drop in replacement. Is this correct? Also has anyone ordered the front panel and confirmed that it fits?

Hello,


personally I used NE5532AP,worked fine.
The differences on the last letter seem to be differents brands and hints on noise figures.
I might try some old Signetics types at a later point,but at least I know the AP types working fine.From what I know the "N" type is the standard type,if you can find any low noise types I'd go for them if I were you.


For the front panel,I haven't ordered it.Seems there's something odd with them because they have double drill markings in several spots.Not sure which ones are correct.I asked but did not get an answer so far.


Best regards,


Udo.

 

[rainton]

Hey guys,

I started building mine and I wanted to add some points.
First off  I like the sound a lot - the filters are crazy and also the eq seems to be extremely versatile with the overlapping bands.
Even with gain all the way up the Q is rather wide but very musical sounding.
I didn't use NE5532s though but HA-4741s made by Harris and also used in the original Harrison console EQ.


Since the footprint of the  4741 ICs is a different one I had to do some extra work. They are 14 pins instead of 8 but it's a quad opamp instead of the 5532 being a dual opamp. So for the entire stereo EQ + filters I only needed 7 HA-4741 ICs.

To compensate for the different footprint I created kind of an "IC-farm" on a dedicated pcb which meant quite some extra wiring on the audio side, but made it easier to supply them with power since I only needed to feed DC to this extra pcb to provide +18V DC to all of the ICs.

So, some extra work, but I really dig the sound of it with the HA-4741s

Anyway here's some points found before I can confirm and also some extras I found while building it:

- as ForthMonkey mentioned in the first post: the gain pot on the band pcbs needs to be wired in reverse (cut the traces on pcbs)

- as kante1603 found out: the LP filter pot also needs to be wired in reverse (cut the traces on pcbs)

- I had the same issue with the unit not being at unity gain with all filters and EQ flat. I tried to parallel R4 with another 10K resistor, but it still was not quite unity gain for me - approx. 1 - 1.5db above unity.
So I soldered in a 10K trimpot instead an dialed in unity gain which worked great and  I recommend it for all builders.

- Now a new one but still very important I think: If the EQ is in bypass you'll end up having the phase of your signal  reversed!!
If the EQ is engaged everything's as it should be.
The problem here is that the "left" input pin on the filter pcb is connected to the front right pin of the push button switch and vice versa. Then from the front right pin of the switch the signal goes to the right output pin -> phase switch

If you test your EQ with a single signal (and not in a mixing situation) you probably might not notice at first if you feed it with a balanced signal.
But I use it on the unbalanced inserts of my console and in this situation that means as soon as you put the EQ in bypass you feed the signal to ground -> SILENCE  ;D

So if you soldered the switch to the pcb you need to cut traces again and rewire - if you use a panel mounted switch like I do just swap the wires

Hope this helps

Thanks again for this project ForthMonkey!