All things G1176 - the new "repost" thread.

[rbaker]

I just "fired" up my 1176 for the first time. I didn't connect the lamp yet, and the 220ohm resistor right after the lamp connection started smoking a tiny bit and turned partially black.

I ASSume that the issue is related, or would it be something else causing this?

 

[bradb]

The 100k pot works well and allows you to completely change your threshold, its a very nice fix... thanks jakob. I recommend that you guys try it out.

I may have spoken too soon on my ratios and changing the 56k resistor... When I turn the 100K pot such that it is essentially out of the circut (0 ohms between input and wiper) I'm notice that my ratios are still reversed!

I checked all the resistors on the ratio board and they are correct.

Maybe I have my stops reversed in my lorlin switch, is there a common stupid mistake that I've made?

thanks everyone

 

[rbaker]

[quote author="rbaker"]I just "fired" up my 1176 for the first time. I didn't connect the lamp yet, and the 220ohm resistor right after the lamp connection started smoking a tiny bit and turned partially black.

[/quote]

Update:

I connected the vu lamp, replaced the 220 ohm resistor (tested the one I took out and it was the right impedance) and triple checked for solder blobs.

Fired it up again and the same 220 ohm resistor (a new one) started smoking and turned black. The light on the vu meter does work now.

I quickly turned it off---where should I start? Replacing the 7824? Is it possible I wired the torroid incorrectly?

 

[mnats]

Since mnat's boards have the two optional inputs

Don't know how many times I've said it but my boards are based substantially on Jakob's original design. He originally designed them with both electronically balanced and transformer inputs.

When I did my redesign I added footprints for the optional OEP transformer. Hope that clears things up. Credit where credit is due!

...is it possible to install a switch that toggles the input from the transformer input to the electronically balanced input?
...not sure if that makes any sense...but I'm curious if anyone has done something like this.

There isn't much that hasn't been tried:

http://www.groupdiy.com/index.php?topic=646&start=765

If you wanted to go further and use the same XLR input jacks for both transfomer and transformerless you would need to switch before the input circuit as well. Might be worth using some relays if you wanted to make this a permanent part of your build.

 

[bradb]

I just did a page by page search about the ratios and found that the solution to my problem, the ratio switch also changes the threshold.

edit: see here..

so looks like I'm set... imo and Al, try the 100K pot, its totally legit.

 

[rbaker]

[quote author="rbaker"]I'm building my unit without the input transformer---(I might add it in later)

I thought I read that the parts with a * on them should be left out if building it this way...I just want to be sure I'm correct and also that I'm finding all of the parts.

the ones circled in red?

[/img][/quote]

I think I found the problem...I had posted a similar picture a while back, asking if I had all of the ** parts to remove for electronically balanced input. I missed the the 1000u cap to the right. Someone posted saying I had them all, and I moved on.

Anyway I updated the picture, so that if anyone else sees it, it's now correct.

I'm going to remove it right now, replace the charred resistor, and give it another go.

 

[rbaker]

ok well, I got that cap out and replaced it but the resistor is still smoking. I have triple checked for solder mistakes, cap orientation, wrong placement etc.

I tested the voltage off the torroid and between the two it's 48 vac

Any other things I can check?

 

[sintech]

Maybe post some Hi resolution pics of your Pcb/unit, see if someone can spot what's going on.

 

[rbaker]

I'm making some progress. I had a feeling it had to do with th 1watt 1k1 resistor. I knew I had tried verifying them but they weren't really reading an impedance (it was coming out at like 2 ohms) I figured it just had to do with my cheap dmm and it being a heavier resistor.

Anyway I bought some new 1k1 1 watt resistors that I was able to test and verify.

I put it in and the 220r resistor no longer burns.

BUT now the 100r resistor right next to q7 burns. I was able to take some measurements by turning it on and off quickly. It seems that anywhere I'm supposed to have 30 volts, I have about 26.

for example, the 7824 has 28v/5/26

I tried to buy a new 7824 but I'm having trouble finding them locally. I have replacement bd517/bd518's available.

Aside fromt that I don't know where to start, I guess I'll just start replacing resistors on their way down to that. Any ideas, especially what could be throwing off my voltages?

 

[imo]

Brad,
Congrats! I will check it out as soon as i have a few moments home, out on a short tour-
I didn't totally understand your comment about the ratios? Was the changing of the 56K messing with them or did you not know that the threshold changed with ratios?
BTW, i just completed a stereo balanced input. I have a lot more room on that unit than on the input transformer model. They both sound amazing though

 

[bradb]

imo,

basically when you input a fixed tone and cycle thru the ratios switch you instantly think that your unit is screwy because you get higher GR at lower ratios... but the threshold is actually moving too.

I think changing the 56k resistor will change your ratio, but honestly the 100k pot is really nice and adjustable.

 

[Dr nEon]

Hi!

Question regearding G1176 power transformer that I cant find answered anywhere else:

The original gyraf parts list calls for a 2x24v 500mA tx. (24VA) , but I have seen that people are using 30VA for dual G1176 builds.

I can obtain 2x25v tx rated at either 15VA or 30VA .

I read in another thread that the G1176 current draw is 37.4mA

My additional items are:
vu illuminaton leds = 20mA
and "power on" led = 17mA

so, if my total current is around 75mA , does this mean I can use the 15VA transformer to power a single unit?

Or am I undersizing?

Cheers nEon.

 

[sintech]

Hi nEon, I'm using 2x25v 30VA in my G1176 units, Farnell part number :9531750

If I was making a Dual I'd pop two of these in... eleven quid! you can't go wrong!

 

[gyraf]

bradb,

Thanks for the feedback! I'll try to include this potential fix in a future upgrade!

rbaker,

Seems that something is drawing tooo much current from the supply rails.

You probably have a pcb trace short or a wrongly-mounted or burnt-out transistor somewhere.

Make sure that you have the bd517/bd518's in the right way around!

The only way I can think of to find errors like this is trying to cut (and later resolder!) the +30V supply trace at various locations to try to isolate where the over-current is taken..

Jakob E.

 

[Dr nEon]

Cheers Sintech .

Thanks for the info.

I am still keen to know if anyone has used a 15VA without problems .

If my above calculation is correct , 15VA should be fine , but I fear(as usual!) I may be missing something.

One of the advantages of a 15VA tx would be the smaller diameter . I am mounting it vertically at the back of a 2u case , and i'd like as much clearance as possible , for safety's sake .

Thanx again,

nEon.

 

[gyraf]

Neon,

A 15VA power transformer should be alright for the G1176..

 

[Dr nEon]

Thanks Jakob. :thumb:

 

[bradb]

The 100k pot adjustable threshold is really cool because now I have tons of usable gain in the G1176.

a great deal more gain staging can be performed. Thanks Jakob

 

[rbaker]

[quote author="gyraf"]
rbaker,

Seems that something is drawing tooo much current from the supply rails.

You probably have a pcb trace short or a wrongly-mounted or burnt-out transistor somewhere.

Make sure that you have the bd517/bd518's in the right way around!

The only way I can think of to find errors like this is trying to cut (and later resolder!) the +30V supply trace at various locations to try to isolate where the over-current is taken..

Jakob E.[/quote]
Yeah I figured a large part of it out--- I had bent the pins of the bd135/bd136 but somehow in the last step I put them in backwards. I ordered an extra pair, put them in right and things were working. Then I was measuring voltages on one of them and the probe accidently shorted 2 of the pins---it seems to be dead now so I ordered some more.

Anyway nothing was burning and most of my voltages appeared to be correct. Even though I was tearing my hair out, I learned a lot about following schematics and tracing back why things weren't working, so I'm glad I had all these issues.

 

[astrovic]

[quote author="rbaker"]I'm building my unit without the input transformer---(I might add it in later)

I thought I read that the parts with a * on them should be left out if building it this way...I just want to be sure I'm correct and also that I'm finding all of the parts.

the ones circled in red?

[/img][/quote]

Hi all,

I've spent the weekend building my G1176 (using the Mnats board). It's my first serious project, and I think I've got most of the way there in one hit.

I'm using the OEP 262A2E for both input and output. I've got some issues/questions that I could do with some help on, so I'll describe what I've got so far:

1. The unit passes audio quite nicely. The input and output pots work.
2. I've checked the voltages at each transistor, and they were roughly as posted on the schematic. So far, so good.
3. I haven't calibrated the unit yet. Do I need an oscilloscope to do this, or is there a workaround that will get me there?
4. I when I put a signal through, and put the meter in Vu mode, the meter generally follows the strength of the signal, but never gets very "high" (i.e close to 0Vu)
5. I can't tell, aurally, whether I'm getting any compression. I can't discern a difference between the bypassed signal, 4:1 or 20:1. This has been the case putting in guitar, bass, or vocals (I haven't been able to trial it with anything else yet).
6. My doubts about compression are amplified by the fact that I can't discern the attack and release pots affecting the sound at all.
7. I just thought of this - my wires connecting 18 & 21 from the main board to the ratio board are the same colour. I've shrink wrapped those wires together, and foolishly didn't mark which was which before doing so. So now there is no way of telling which is which. When I was wiring up the board I checked for resistance at both ends of both wires, to identify which was which, and was pretty confident I had it right. If I have them the wrong way around (i.e 18 on the main board is connected to 21 on the ratio board and vice versa), would it give me the symptoms referred to above (sound ok but no compression)?
8. I've installed the two 10k resistors circled in red in the above picture, but not the other parts circled in red. Do I take it I should I should install them?

I'm hoping that all I need to complete the job is calibration, but the lack of discernable compression makes me doubt that. Something is not quite right, and it might be 7 or 8 above.

Any thoughts?

BTW, a big thankyou or Jakob for making this available. Finding his site has given my interest in music (which was waning) a jump start. Thanks also to Mnats for the boards, and to all those guys who have posted in this thread, asking the questions I undoubtedly would have along the way

PS Sorry for the long post. I thought I get it all out there in one hit!