Mnats rev J stereo 1176 with Balancing board and adjustable PSU build

HI Guys,

thought i would document my build of this unit as the balancing board option doesn't seem to have been documented.
I have built a G1176 with adjustable psu and a balancing board and it works nice.

I have a 24vac toroidal which will feed both the +30v/-10v and the +18v/-18v psu (+30v/-10v for the main pcb and +18v/-18v for the balancing board)

The balancing board is from the the GSSL 9k preamp and you can either use SSM2142 or DRV134. i've used the SSM2142 but will also put in the DRV134 to compare.

I have left out the following off the main pcb as im using adjustable psu:

CR6, CR7, CR8, CR9, CR10, C24, C25, C26, R85, R86, 7824 regulator.

I put 2 jumpers in to connect from where the diodes were to get the +30/-10v into the main pcb.
Looking at the component side the 2 diodes to the left are the the + side and the two diodes to the right are the negative side, so connect the 2 diodes to the left to the bottom connection of where the 7824 would have gone.
The 2 diodes to the left need to connect to left hand R85 side, that gets the power in.

Everything else is fairly straight forward, check all resistors before you put in, saves a lot of mucking around after!! and also make sure you get all components the right way round, worth taking your time to save time later.

For all the off board connections i suggest putting wire or header pins in so you solder to the pins rather than the pcb, as you can over heat these pcbs if your not careful and also if you make a few mistakes with connections this helps.

It states the only gnd connection to the chassis from the main pcb is on the input XLR and you can also connect the mains power ground from the IEC power connector to this point and I have XLR Pins 1 connected together In a star ground config.

I have also used OPA2604 instead of 5532, as it says these are direct replacements and I have loads.

regards

Spence.

Hi All,

the it seems was from the meter pcb where a wire was either loose or had come off, i changed all the points to the meter and ratio board by having header pins on the back to solder to, 0v from the DC side of the psu pcbs and both linked on the 0v and connected to chassis. I also took off the screen from output of balancing board, so only screen connection is on the input header to XLR.
Plugged it back in and hey presto no hum!! so it must have the correct grounding scheme now.
Will put together some photos of the various bits now, i also have a stereo unit which i can document.

regards

Spence.

ground from mains lead should have a dedicated/not shared and robust connection/bond to chassis

HI Shabtek,

could you be more specific within this scenario please?

regards

Spence.

open up some gear and look.
usually green wire inside goes immediately to the metal shell/chassis connected with a ring terminal, conductive screw/locknut.

i don't like (regulating bodies don't either) the xlr doubling as the connection for safety ground--that should be its own thing

hi shabtek,

sorry don't mean to be rude but what you have said does not explain at all, if you could be specific this could help a lot, as in this setup it is needed to be specific as using two different psu for power and i have some valid questions.
I do understand about star earth it just sounded as though you knew something i didn't, which wouldn't be the first time!!

regards

Spence.

on further investigation the hum was coming from my gyraf g9 which was plugged in line with the 1176!!!
i now have correct grounding scheme, just need to fault find the gyraf g9 as it seems there is a ground loop.

regard

Spence.

doing final prep of all connections and then will try and power up and setup, then i need to sort out the hairball stereo link.

Spence.

What shabtek is saying, is that where your 240vAC mains enters the box, the mains earth "safety ground" wire should immediately be mechanically secured to the chassis close to where it entered using a sole dedicated fixture such as a nut and bolt and star washers. A ring terminal on the mains earth wire makes this easy. No other "grounds" should be tied in to this point.

Double check with your meter in continuity mode or ohms mode that you have a very low impedence path path between chassis and the mains earth ("safety ground") wire of the incoming mains wiring. Plugging an IEC cable into the unit (but not into the wall/mains!) makes this a very easy test to perform. If you show more than an ohm, something is wrong.

XLRs, etc, "shields" should tied to chassis somewhere else, preferrable very close to where they come in, using a very short wire, so as to avoid injecting incoming RF into the chassis. They should not share a common point with the mains earth "safety ground".

Pertaining to your noisy G9: One of the most common causes of a "ground loop" Is tying the incoming shield on the audio input to circuit ground instead of chassis. Make sure shield (pin 1, or "sleeve") goes immediately to chassis, NOT to circuit ground.

Hope this helps.

Hi guys,

Hit a few problems with building this stereo unit, I'm getting distortion, quite a lot of it on the right hand channel and when the dist trim is turned the distortion gets much worse, doesn't sound good?
Bias control doesn't seem to do anything?
My left hand channel doesn't seem to pass audio yet? Need to investigate further why the left channel not passing audio.
Will post some pictures to show progress.

Regards

Spence.

Got some pics yet? High res with good lighting preferred.

Still having problems with the dual 1176?

hi,

yes still having problems, a friend is taking a look and i hope to have the prognosis soon.
will update then.

regards

Spence.

hi all,

I've made a schematic which i hope to update once you guys can let me know my errors!!
i need +30v, -10, +18 and -18v.
i need to use a voltage doubler as the transformer is 19v/0/19v, if anyone can help please.

regards

Spence.

Spencerleehorton said:

I've made a schematic which i hope to update once you guys can let me know my errors!!
i need +30v, -10, +18 and -18v.
i need to use a voltage doubler as the transformer is 19v/0/19v, if anyone can help please.

Click to expand...

Not knowing your transformer rating, some edits to make it at least work for the usual suspects...

hi harpo,

i have a 15/0/15 at 30vac which i think could work?
the 19/0/19 i think is 15vac.

thanks for the changes, i have updated, hopefully this is workable?

regards

spence.

Ok.

ive now sorted the psu side of things to get +30v, -10v, -18v and +18v, when i plugin one pcb my voltage stays at 30v and -10v, but when i plug the other in as well it drops to 27v and -10v.

Im using the attached psu setup. the only change i have done is C8 which ive changed to 2200uf/63v as that is all i had close to 1000uf/63v.

regards

Spence.

Spencerleehorton said:

I have also used OPA2604 instead of 5532, as it says these are direct replacements and I have loads.

Click to expand...

Just wanted to point, that OPA2604 and 5532 are completely different animals (OPA2604 is FET-based, and significantly noisier).
Though, this will not make much difference in this application, IMHO.


Regards,
Andrey

Spencerleehorton said:

ive now sorted the psu side of things to get +30v, -10v, -18v and +18v, when i plugin one pcb my voltage stays at 30v and -10v, but when i plug the other in as well it drops to 27v and -10v.

Im using the attached psu setup. the only change i have done is C8 which ive changed to 2200uf/63v as that is all i had close to 1000uf/63v.

Click to expand...

Whatever 'one pcb' and 'the other' might be ...
assuming at least one of these secret pcbs is a G1176, you left out the no more needed voltage setting network R87 and R89 at the LM7824 as well?
In the PSU C9 and C10 will better be 1000uF caps as well to deliver the current demand of connected load, assuming this load might be 2x G1176.
Measure the DC voltage across C8 to see if a 63V cap rating is realy needed (in your previous post this was a center tapped 38VAC transformer that would call for at least this caps voltage rating).

AFAIK there is NO direct replacement of ANY different type of opamp (if this would be true, only one type of opamp would be needed to cover all requirements for impedances, I or V noise data, current drive ability, supply voltages, GBW, ...) . Sometimes it might work (for better or worse) but I wouldn't count on it.

HI Harpo,

yes sorry, what i meant was one Mnats G1176 pcb is connected with 30v and -10v i get correct voltage on the two rails on the G1176 board which bridge across where the onboard power would have been, when two Mnats G1176 coonected the volatge gets pulled down on each to 27v.
R89 (200R) is getting very hot and is not needed so i will remove, along with R87 is still in there and should i also remove C23?
I have some 5532 on order so will replace the OPA2604 which i have in there, i had read that these work work in replacement but obviously this information was wrong.
thanks again for all your help, much appreciated.

regards

Spence.

right, ive taken out R87, R89 and seem to have no smoke for the moment!
R16 which in previous build of 1176 didn't seem to do a great deal, in this build seem to unleash massive distortion? could this be the fact that im using OPA2604 rather than the NE5532?
also i have found i have a dodgy lorlin pot on the left hand channel ratio control, pushing or pulling the control seem to sort it out but this will have to be changed.
both channels pass audio now but no compression seems to be happening, i will see if i can check all voltages first.

regards

spence.