Stereo 1176 support - Mnats/Hairball

[Stagefright13]

Just look at schematic all mine will go into slam mode. By buttons or switches. Same thing. http://www.stagefrightrecords.com/P1020378.JPG

 

[Spencerleehorton]

hi stagefright,

i dont think its as easy as looking at the schematic dude!!! lol

regards

Spence.

 

[Spencerleehorton]

hi all,

have tried the setup procedure and cant get VU mode meter anywhere? so its definitely nothing i'm doing wrong in the setup.
both channels will calibrate in GR mode but nothing in VU mode?
anyone got any ideas?

regards

Spence.

 

[Spencerleehorton]

Hi all,

As always a couple of wrong resistors and a bad chip in the balancing board so far on one channel. That channel sets up fine now, just got try and figure out  what's happening with this other channel.

Regards

Spence.

 

[velo-hobo]

I did keep the 1:2 myself...

You just need to split the resistors on the 4:1 ration on each of the series and wire the intermediate position to the additional switch position=> substitute the 150 for a 68then 82 ohm and the 47k in 20K then 27K

Thanks for that info dmnieto - I knew it must be relatively simple, and looking at the schematic that makes a lot of sense.  You are referring to the Rev D schematic, yes?  In the Rev A schematic, the first resistor on one side of the series is 120ohms rather than 150.  I would guess that a 56 and a 62 would be appropriate substitutions in this case.

How did you wire your SLAM! mode then?  From reading elsewhere (and looking at the schematic) it seems it's really just the 4:1 and 20:1 buttons that are creating the effect.  Did you just wire it the same, 4:1 and 20:1 switches closed in that mode?

Also, the rotary switch ratio boards that mnats provides are designed for the 5-way switches.  I think there will have to be some clever wiring going on in order to make the 6-way work with the existing boards and the 2:1 ratio.  I assume since you designed your own board that this wasn't an issue for you.

Almost makes me want to give in and order the 5-way switches, but I'm still populating the PCBs so have some time to ponder it...

 

[Bobby Baird]

I am also very curious as to how to have 2:1 and all those ratios including slam on a 6-way switch with the ratio switch board supplied by mnats?
I have bought Dan's case, boards, and a 2-1176 hairball kit. I just need mouser supplies. Is anyone implementing a passive switchable high-pass filter in their builds? Would this be inserted after the ratio switch, but before c17 with a simple spdt toggle switch incorporating a cap, resistor, and ground wire?

I will be installing bypass relays and super slo-mode on the attack switches.

I would like to here from others about where in the circuit to implement a switchable high-pass filter and what values work well for certain cut-off frequencies? I am thinking 120hz.

How to implement 2:1 4:1 8:1 12:1 20:1 and slam with 6-way switch on mnats 5-way switch board if it's possible?

Thanks in advance for anyone willing to shed some light on these mods.

 

[velo-hobo]

Yesterday evening on my way home from the shop I think I figured out a way to add the 2:1 ratio and use a 6-way switch with the mnats ratio board and still use slam mode.

Still need to prove it in practice, though basically you stuff the board and wire up the switch as shown on the mnats pages, BUT replace the 47k and 150 resistors that are associated with the 4:1 position with two resistors in series for each that add up to those values (or close) as mentioned in the above post by dmnieto and the other thread I referenced about 2:1 4:1 8:1 20:1 mod.

Physically, each of those resistors will have one leg in the pcb thru-hole and the other floating free.  The free ends would be tied together and this junction is the location to tie in the 2:1 switch.  The ratio board traces need to be studied to determine which pad goes to which resistor since they are not of equal value.

Using Dan's case, the 2:1 switch position would be at the extreme counter-clockwise end of rotation.  All the leads from the switch terminals go to the ratio board as shown by mnats except leads from the 2:1 terminals go to the aforementioned resistor junction.

Slam mode is still wired up as shown in the mnats pics, essentially closing the 4:1 and the 20:1 switches simultaneously, and the pairs of resistors in the 2:1 mod mimic the stock arrangement.  Thus Slam mode should work as though the 2:1 mod doesn't exist.

Again, this is my hypothetical solution - still populating the main PCBs (just finished all those resistors!), but I think this is the method I will attempt unless someone can find fault with it.

 

[Bobby Baird]

Yes, I was figuring resistors would have to be soldered directly to the switch for the 2:1 position, and keep the 2:1 position out of the 4:1 thru 20:1 slam loop. Sounds about right. I just don't know without tinkering as I haven't got my build under way just yet. So, the extra 2:1 resistors will be piggy backing on the 4:1 resistor location on the board, but the 2:1 resistors legs will only be soldered on one leg of the 4:1 resistor board location. With the other 2:1 resistor legs soldered directly to switch?

 

[velo-hobo]

So, the extra 2:1 resistors will be piggy backing on the 4:1 resistor location on the board, but the 2:1 resistors legs will only be soldered on one leg of the 4:1 resistor board location. With the other 2:1 resistor legs soldered directly to switch?

The two stock 4:1 resistors are split into the four news ones.  2:1 switch connects to half of each pair, 4:1 runs through both pairs.  If you look at the schematic, imagine R22 and R58 are each split into two resistors in series that add up to their original values.  The 2:1 switches connect at the junctions between these new pairs.

Physically the series pairs of replacement resistors need to connect to the same spots on the ratio board as the stock 4:1 resistors do, and the 2:1 switch terminals connect to the junction between those.  That way, 2:1 switch closure sees only the first half of each pair, 4:1 sees both.  Whatever physical implementation makes most sense to you is the way to go.  I'll probably post a picture once I get one put together.

 

[Bobby Baird]

So the 2:1 switch position will be right in between the new r22 r58 series pair of resistors. So r22 is 47k, r58 is 150.
Example: r22 in series
23.5k < 2:1 ratio switch position < 23.5k < 4:1 = 47k

Same for r58

75r < 2:1 ratio switch position < 75r < 4:1 = 150r

I need pictures.

 

[velo-hobo]

Right, except good luck finding two 23.5k resistors!  If you take a look at the thread I mention in post #166 (http://groupdiy.com/index.php?topic=47196.0) you'll see that they've come up with some new resistor values to get the ratio boards to function like the 1176ae (2:1 4:1 8:1 20:1)

Seems like success was reported by some folks on that thread using that scheme to achieve 2:1 (or something close to it), and as well by dmnieto here on this thread.  Both instances report using a 20k and 27k in place of R22 and a 68ohm and 82 ohm in place of R58, although user Kingston suggests using a 100ohm in place of the 68ohm (at least I think that is what they are suggesting - hard to tell) to keep 2:1 from being louder than the other ratios.

R58 and the associated chain of resistors apparently control make-up gain after compression?  You can see on the schematic that this half of the ratio circuit interacts with the GR Control Amp, which seems to jive with that concept.  If you were to use a 100ohm for 2:1, then I would think a 47ohm would be a good one to put after it to get 4:1 to work normally.  Might try that out myself.

Disclaimer, I am not an electrical engineer, just familiar enough with this sort of thing to muddle my way through it and possible come up with some bad ideas.

Also, I realize this is sort of getting away from stereo-specific build issues, but there's already a ton of info in this thread on the ratio mod topic.  Moderator's call as to whether it all belongs elsewhere...

 

[Bobby Baird]

Right on ya those resistor values were arbitrary. Have a look at igor's 1176 schematic http://groupdiy.com/index.php?topic=43338.0 it shows 2:1 and how to implement the 100hz high-pass filter before the side chain. I will have to tweak the auto gain resistor by ear with a hand full of different resistor values to get a approximation.

 

[velo-hobo]

Thanks for pointing out that thread, I hadn't seen it yet.  Can you point to the specific post #'s that reference the 2:1 ratio?  It's a huge thread, I'll read the whole thing at some point but for posterity it would be nice to have a direct link here in this thread.

 

[Bobby Baird]

At the beginning of the tread click http://twin-x.com/groupdiy/thumbnails.php?album=417 and view docs download zip and look at the schematic.

 

[velo-hobo]

Ah it's in an attachment, that explains why search didn't find it.  Thanks for the heads up.  Good luck with your build, I'll post photos of my ratio assembly once I get it together.

 

[velo-hobo]

Looking at the schematic and build thread on Igor's 51x-F76, it would seem the sidechain HPF is an RC scheme using a 56k resistor to ground and a .022uF cap in series between the ratio and the output.

Igor's schematic says 10nF/.01uF but it and the BOM are marked TBD, photos of actual builds show he has supplied a 22n/.022uF cap with the kits.  Using this calculator (http://sim.okawa-denshi.jp/en/CRhikeisan.htm) it sets the cutoff at about 130Hz. Seems like I see people aiming for the 80-100Hz range, which would indicate a .027uF or .033uF cap (larger cap value=lower cutoff frequency)

Can anyone who's done a HPF mod on the hairball 1176 report on how they achieved it and at what cutoff frequency for the sweet spot?  dmnieto?  I suppose I could just try when I get to that point since it is a very simple mod to experiment with, but reports from someone who's already done it would be helpful.

[Edit - I did some more reading and I'm realizing that the desirable cutoff frequency is heavily dependent on program material - but for a single frequency option, maybe something between 100-200Hz is best? Thus .018 or .022uF might be the way to go.  Will have to experiment!]

I think I will use the bypass switch location on Dan's case to implement the HPF since I don't plan on putting together a relay-based true bypass for my current builds.  I already stuffed the faceplate with a DPDT switch too so it is ready to go.

 

[Bobby Baird]

I wouldn't go any lower than 120hz on the high-pass filter because you want the kick and bass to bloom, but below 200hz because you will still want to compress the low-mids and snare. I might socket those and play with the values when I get my build going. It will probably be another month before I can purchase the mouser bits. I will use the capi 24 volt relays which worked well in my last build they are cheap you ought to implement them in your build. It's a great way to a-b your signal to make sure you are actually making an improvement and to check gain staging. Here is the link to the relays I use. http://classicapi.com/catalog/product_info.php?cPath=102&products_id=389
Thanks for the info on the hpf calculator.

 

[velo-hobo]

Yep, I realized that about the HPF after reading some more and seeing what was typical out in the world.  Makes sense to me.

Thanks for the heads up about those relay kits, I didn't realize anyone was doing a kit that is that small, simple and cheap.  Might actually go for that and add another switch hole for the HPF.

 

[dmnieto]

I did keep the 1:2 myself...

You just need to split the resistors on the 4:1 ration on each of the series and wire the intermediate position to the additional switch position=> substitute the 150 for a 68then 82 ohm and the 47k in 20K then 27K

Thanks for that info dmnieto - I knew it must be relatively simple, and looking at the schematic that makes a lot of sense.  You are referring to the Rev D schematic, yes?  In the Rev A schematic, the first resistor on one side of the series is 120ohms rather than 150.  I would guess that a 56 and a 62 would be appropriate substitutions in this case.

How did you wire your SLAM! mode then?  From reading elsewhere (and looking at the schematic) it seems it's really just the 4:1 and 20:1 buttons that are creating the effect.  Did you just wire it the same, 4:1 and 20:1 switches closed in that mode?

Also, the rotary switch ratio boards that mnats provides are designed for the 5-way switches.  I think there will have to be some clever wiring going on in order to make the 6-way work with the existing boards and the 2:1 ratio.  I assume since you designed your own board that this wasn't an issue for you.

Almost makes me want to give in and order the 5-way switches, but I'm still populating the PCBs so have some time to ponder it...

You can use the same 6 position rotary switch (instead of the 5 position one) from mouser. They are almost the same.

I used the same rotary pcbs as everybody else... I just cut the trace that joins the pad 7 with 24 (If I remember properly) because it predates one of the holes for the rotary switch. Then in the pad for the 150 and 47K resistors I put two series resistors (80+60), (20K+27K) and i wired the middle point to the free holes of the rotary switch pcb.

Other than the fact that the positions are 4:1 8:1 12:1 20:1 SLAM and 2:1, it works very well.

Something else is that because of its configuration the 2:1 threshold is much lower than 4:1, almost 12 db lower... so you need to control the input properly

 

[dmnieto]

Can anyone who's done a HPF mod on the hairball 1176 report on how they achieved it and at what cutoff frequency for the sweet spot?  dmnieto?  I suppose I could just try when I get to that point since it is a very simple mod to experiment with, but reports from someone who's already done it would be helpful.

[Edit - I did some more reading and I'm realizing that the desirable cutoff frequency is heavily dependent on program material - but for a single frequency option, maybe something between 100-200Hz is best? Thus .018 or .022uF might be the way to go.  Will have to experiment!]

I think I will use the bypass switch location on Dan's case to implement the HPF since I don't plan on putting together a relay-based true bypass for my current builds.  I already stuffed the faceplate with a DPDT switch too so it is ready to go.

I used a two pole active sallen-key in my design... at 120Hz if I remember, my wife sometimes swap the capacitor to get it from 120Hz to 160Hz