All things G1176 - the new "repost" thread.

[dirtyhanfri]

Hi

I'm building my first 1176, and think I screwed up choosing the output transformer... I'm using Mnats version of Gyraf board and got 5002 output transformer from Hairball

Is there any way to use the 5002 output transformer on the Mnats board?

I'm building this layout http://mnats.net/files/1176Flayout.pdf

I could get a cheap OEP and go on, but I'd like to use the 5002 (I won't build any other 1176 soon I think)

Any ideas?

 

[dirtyhanfri]

Well, Hairball support (very gently keeping in mind the time difference, they're great) recommend me to keep out the tertiary winding in the 5002, I didn't try it yet, but looking at  OEP A262A2e datasheet (http://sound.westhost.com/articles/a262a2e-transformer.pdf which is used in the board I'm building, with both primaries and secondaries in series, looks like I need a 600Ohms primary and 2x 600Ohms windings in series for the secondary, right?

Looking at 5002 datasheet (http://library.hairballaudio.com/datasheets/5002.pdf) I think I could connect RED secondary wire to GREY and have two 600Ohms Windings in series, as in OEP transformer, but I'm not sure if unused primary winding (WHITE/RED & WHITE/BLACK wires) will give any trouble.

Yes, it's easy to try by myself, and I will do it, but I'd like to get a bit of knowledge on what's going on, because I'm a bit missing when it comes to transformers.

Thanks

 

[knight84]

Hi,

My unit works great  and I already liked the sound very much. Now only issue left is low-gain. I saw some pages but couldnt be sure which to follow. Could someone guide me to the link for highest gain settings or If possible give the instructions for it?

 

[hymentoptera]

There should be tons of gain available. Have you completed the calibration process?

Which output transformer and did you install it "reversed"?

 

[knight84]

No I installed as it is in the project documents.  I calibrated but couldnt do it properly cause my Voltmeter wasnt that precise so had to do it at farely high voltage values. Now I have around 4-5 dB gain which is very very low. As I read on the forum people get around 30-35 db gain after switching the tranny which will give 12 dB. So maybe I also made a mistake somewhere or due to the calibration I get something wrong.
Thats another issue but there should be a way of reversing the tranny without taking it out from the pcb right?

 

[hymentoptera]

Pretty sure you'd have to desolder it to flip it around. I think it's the Lundahl that get's flipped, but I'm not sure what other transformers fit that pinout, so I could be wrong. If you're using the Lundahls and the mnats PCB see these instructions http://mnats.net/1176_revision_j.html

If you're using another board or different transformers, then disregard.

Hopefully someone who's built a few and experienced the low volume problem will chime in.

 

[knight84]

Yes I have the Lundahl. But I have seen a swedish chief mod and a mod which incorporates cutting the traces on pcb, but didnt get that I need to flip the tranny around with these mods. I couldnt be sure which way to go so I asked here again.

 

[FrankoPanko]

I'm asking for some advice. I finished Gyraf 1176 compressor PCB # 8 of PCB Grinder and I have an unusual problem. So far I have already made more than ten of its 1176 PCB by MNat "rev H" design and everything worked okay, but this 1176 compressor at point 19, where they are connected diodes FDH 333, when I turn up the signal from the input level voltmeter reading of -1, 9V no signal and -0,2V with input level pot in full. I know that the value should fall to a maximum of approximately -1,5V and gain reduction meter turned left long before even crossed the threshold of compression. I reviewed several times all connections and components, everything looks ok, only the values of voltage on Q4 and Q15 are 1V lower than normal. When I turn release pot, gain reduction meter also responds to several millimeters. I tried disconnect points 7, 20 and 21, but still at a point 19 there is a difference of about 2V, and it should be less than 0.5V.
Do you have any idea of where to start searching for error?
Thank you!

Alan

 

[hymentoptera]

I'm asking for some advice. I finished Gyraf 1176 compressor PCB # 8 of PCB Grinder and I have an unusual problem. So far I have already made more than ten of its 1176 PCB by MNat "rev H" design and everything worked okay, but this 1176 compressor at point 19, where they are connected diodes FDH 333, when I turn up the signal from the input level voltmeter reading of -1, 9V no signal and -0,2V with input level pot in full. I know that the value should fall to a maximum of approximately -1,5V and gain reduction meter turned left long before even crossed the threshold of compression. I reviewed several times all connections and components, everything looks ok, only the values of voltage on Q4 and Q15 are 1V lower than normal. When I turn release pot, gain reduction meter also responds to several millimeters. I tried disconnect points 7, 20 and 21, but still at a point 19 there is a difference of about 2V, and it should be less than 0.5V.
Do you have any idea of where to start searching for error?
Thank you!

Alan

Diodes installed correctly? Release is 5Meg pot? Check all resistors are correct around Qbias adjust? Qbias calibration has been attempted? Checked all other voltages, especially in the GR amp?

 

[knight84]

Hi again, I need to reverse the 5402 on the pcb. But I use Gyraf's pcb that I etched by myself. How shall I reverse the tranny?
Shall I drill a hole for the 5th pin as well on the other side than connect it to the ground from closest place?
Is this all that I should do to get 1:2 ratio ?

 

[gyraf]

IF you really need the extra gain (which is rare), just cut the copper traces and solder on wire connections..

 

[knight84]

IF you really need the extra gain (which is rare), just cut the copper traces and solder on wire connections..

Thanks Jacob, I have the same idea. For a clean comp. like this around 10-15 db compression would be maximum for me.  Dont need 35 db.
But I think I have a problem on calibration or some other part. I have around 3-4 dB now on full open settings.
Can you guess or advise what to do first ?

 

[dirtyhanfri]

Hi

I'm building a G1176 and when I power it R36 gets burn. I tried flipping Q8-9 and now Q7 gets hot also.

Should I stay looking them and trying different positions or should I just replace Q7, 8 &9 and check the whole board for shorts? I checked datasheet of Q8&9 so I'm pretty sure they were installed correctly, but also spent some time yesterday looking for shorts (it was my first milled PCB and got some copper chips around).

I'm a bit confused, yesterday I readed R36 burns due to Q8&9 installed un the wrong way, but also seen a post from Jakob saying R36 is like a fuse, designed to burn if something else fails.

Any ideas to where start to look?

 

[dirtyhanfri]

Finally I could find a pair of little copper threads shorting traces to ground. I just learned to check every board I mill before soldering (those copper chips are really small and hard to see)

Now everything looks fine, I have  correct voltage readings in every transistor (except Q1&Q10, not especified in the schematic I found in gyraf's web) they're actually like 0.4V high, but I'm almost sure that's due to DMM battery about to die.

The problem is in GR mode, the meter needle goes all the way up and stays stuck on the right, doesn't look so good for the meter... In +4 or +8 mode it goes to 0 normally, I didn't passed audio yet.

Measuring V going to the VU I found there's like 10VDC in the signal going to the meter, that looks bad...

In Q10 I have the same 10VDC in every leg, with a 0.6V drop in one of them. In Q1 I have 0V in every leg.

In the resistor coming from Q1 to Q10 (R48) I have 1V on the leg near Q1 and 10V in the other side, that doesn't look right either...

That leads me to think I have reversed my fets, they're according to mnats layout but following the schematic and datasheet I think they're flipped, but tried yesterday to flip them and nothing changed.

My bet is I fried the TL071 when I powered it up with Q1&10 reversed and when flipped them I didn't notice a change because the fried TL071, thought the TL071 didn't get hot.

I have to say in some moments the needle went to 0 for a second or two, and them went again all the way to the right.

I really suspect on the FETs, any ideas? Maybe new FETs and new TL071?

 

[dirtyhanfri]

Well, I tried another pair of FETs (2n5457 flipped 180º)and this looks better, but not good still...

I now have more usual voltages (in R48 , Q10 & tl071) but when I put the 071 it's output (pin6) stays at +12V, and positive supply (+25V at pin7) falls to +13V, tried with new IC's, no change.

I suppose you all noticed the 12V drop in the supply and 12V in the output of the IC, looked for shorts again with no luck...

When I take the Tl071 out, pin6 in the socket stays at 0V...

Every transistor looks ok according to a schematic with voltages noted I got from gyraf site .

Disconnecting diode after pin6 of TL071 doesn't make any change either...

I got my FETs from evilbay... Fakes? Does somebody bother to fake a few transisors for audio freaks? Don't think so...

So, any clue about what's going on here?

Of course I double checked IC orientation...

 

[dirtyhanfri]

I realized Pin5 (Offset null 2) in Tl071 is not connected anywhere (I'm using mnats RevF layout) while Pin1 (Offset null1) is connected to pin 8 (NC )through a 100nF cap.

I tried to connect pin5 to pin8 with no results, connecting pin5 to ground didn't change anything either.

Maybe I should remove the cap between pin1 & 8?

Also I realized there's no local decoupling in the opamp, maybe it's oscillating or something? I didn't scope the output...

Any ideas?

 

[dirtyhanfri]

Maybe I could DC couple the signal going to the meter with a cap? Or do I need DC in the meter?

I also thought to try something with Offset pins in TL071, I could take out the cap between pin 1&8 or maybe I could try something like this

Any advice?

 

[dirtyhanfri]

Solved.

Pin2 on TL071 was bent and not touching the copper track, I don't understand how couldn't notice it when soldering...

 

[mihailojocic]

VU METER question.

I found some old school TEAC VU meters (from Tascam portastudio). After some time I realised that there is no rectifier inside, so I build few pieces.

Do I need 3,6k resistor in the VU Meter circuit or Jakob include that one on the meter board?

 

[Spencerleehorton]

Hi,

hit a bit of a stumbling brick, i have just wound a 1176 output txf, all checks out ok, ive taken out the line bal pcb and put in the txf.
I get no compression now?
Ive got it wired as Gyraf schematic, there still seems to be some considerable distortion when turning the input gain up.
any ideas?

regards

Spence.