[BUILD] 1176LN Rev D DIY

[allfreak]

Obviously I'm way to nooby to get something like fet matching...  read 1000 web entries about that issue to match Q12/Q13.
I have to call it a day before I throw something at the wall...
there are so many different schematics. Some of which don't use ECB to label... maybe don't label at all. I wish someone could draw a picture of a foolproof fet-tester for 3708s. 
I liked this one:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=46:1176lnfets&catid=34:1176ln&Itemid=62
but I'm still to stupid to make sense of the schematic.
Don't know how many I've already killed....
Going for an Ardbeg now.

 

[Echo North]

Obviously I'm way to nooby to get something like fet matching...  read 1000 web entries about that issue to match Q12/Q13.
I have to call it a day before I throw something at the wall...
there are so many different schematics. Some of which don't use ECB to label... maybe don't label at all. I wish someone could draw a picture of a foolproof fet-tester for 3708s. 
I liked this one:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=46:1176lnfets&catid=34:1176ln&Itemid=62
but I'm still to stupid to make sense of the schematic.
Don't know how many I've already killed....
Going for an Ardbeg now.

Q12/13 just need to be HFE matched.  Most cheap DMM's have an HFE tester on board.  Should take you 10 seconds.

 

[jplebre]

As mike said it, just grab a £5 Digital multimeter with a HFE tester.

If you think you might want to do more stuff there's the atlas peak but it's expensive (about £70).

I've built a little circuit with a 9v battery and a few resistors and a socket, but I was told HFE should be matched within the current range needed so I didn't use it for long.

 

[jplebre]

@Mike that might hint at my problem then. I can see the sine wave at the junction R7 and Q1. Different amplitude but it's there.
It just seem that it's a negative feedback from Q2 or Q14 so I didn't care much at the time.

same issue on both units. Swapped C22, attack assembly and ratio board. All else works fine (bit of a drift on the threshold but ok).

Also,  should Q4 run almost too hot to the touch with a heathsink?

 

[allfreak]

I actually have a DMM with hfe testing. It gives out numbers in a Range between 890 and 897.
what am I supposed to do with that crappy info?

 

[allfreak]

Can someone please explain where the two 9v batteries in this schematic go (esp. the -9V???)
http://www.axtsystems.com/index.php?option=com_content&view=article&id=46:1176lnfets&catid=34:1176ln&Itemid=62

What DMM (brand, model) gives decent hfe readings? (And is available in Germany...?)

 

[jplebre]

That's too high for 3708. IIRC their maximums are 600-800 hfe even at 1mA from some datasheets I read.

are you using the right pinout (ECB) and section of the HFE? (NPN vs PNP?)

 

[jplebre]

a lot of ppl from the forum and some techs here in london recommended this: http://www.peakelec.co.uk/acatalog/jz_dca55.html

I own it, and I use it pretty much on every build so I feel it's worth the extra £££

 

[Echo North]

Can someone please explain where the two 9v batteries in this schematic go (esp. the -9V???)
http://www.axtsystems.com/index.php?option=com_content&view=article&id=46:1176lnfets&catid=34:1176ln&Itemid=62

What DMM (brand, model) gives decent hfe readings? (And is available in Germany...?)

+10 and -10.

The + from one 9V goes to +10 and the - to common.  Opposite for the -10.

 

[allfreak]

Thanks for the answers. The pinout should be correct. It's labeled well. I've read many threads on this topic and I've got the feeling that FET testing is one of the biggest issues. At least for beginners. With DMM readings starting at 40-something up to 1000 and depending on the DMM probably everything in between it is very confusing. And if I understood correctly, this causes problems with the VU readings later on.
I'll go for the Atlas Peak and hope for the best.

 

[Echo North]

Thanks for the answers. The pinout should be correct. It's labeled well. I've read many threads on this topic and I've got the feeling that FET testing is one of the biggest issues. At least for beginners. With DMM readings starting at 40-something up to 1000 and depending on the DMM probably everything in between it is very confusing. And if I understood correctly, this causes problems with the VU readings later on.
I'll go for the Atlas Peak and hope for the best.

You're mistaken, those are not FETs (2N3707/8).  The Q12/Q13 are NPN BJT's (can't believe I didn't notice this error earlier).  The only FETs in the D are Q1/Q10.  They come matched in the kit.

You just have a sh*tty HFE tester or your using the wrong pinout.  I have one I bought for $30 and it works great.  If you don't match them for HFE it's not the end of the world.  The Q1/10 curve matching (which is done for you) is way more important.

Mike

 

[allfreak]

Whoopsy. Didn't See that. Thanks. Can't believe the hours wasted.

 

[allfreak]

I believe the problem is mostly between my ears.  :-\  Only did some guitar effects so far - but I'm determined to learn.

I couldn't find documentation on the DMM (Uni-T UT61A) and the manual isn't helping. I figured if they are serious about NPN and the 3708 is ECB, then I have to get the Base into the middle hole. Is that correct?

Now I get readings around 277-283 which sounds more like it. But they seam to be suspiciously close. Is that normal or am I still do something wrong? Does "matching" mean that they should have the same ß or is a +/- 5 ß ok?

Thanks again.

 

[jplebre]

I can't find a good picture online of the HFE adapter. Sometimes they are inline or circular, but they have a repeated lug so you can either rotate it or just move the BJT left/right and that should fit most combinations of pinout.

that seems about right for the 3708. They won't be too far off the high values will be exception rather than average on the batches I got.

+-5 at 280 is 2% tolerance. Pretty close already.

 

[allfreak]

So, within 2% is sufficient?

 

[Echo North]

So, within 2% is sufficient?

Definitely.

 

[allfreak]

Almost finished now. But...

At the end of mnats guide soldering the meter circuit (male xlr, output transformer,...) I have soldered that green wire to the negative pad of C25 and attached it to the chassis of the output transformer as shown.

Then I tested for continuity with my DMM and noticed that I not only have continuity to the negative pad but also to the positive... how can that be - or is it supposed to be? I tested the power section before stuffing the board and it was fine.

 

[Echo North]

Almost finished now. But...

At the end of mnats guide soldering the meter circuit (male xlr, output transformer,...) I have soldered that green wire to the negative pad of C25 and attached it to the chassis of the output transformer as shown.

Then I tested for continuity with my DMM and noticed that I not only have continuity to the negative pad but also to the positive... how can that be - or is it supposed to be? I tested the power section before stuffing the board and it was fine.

Hard to measure that in circuit.  That cap can take a long time to charge and it depends what's in parallel with it.  The reading you're taking isn't very meaningful.

 

[allfreak]

with other words: Don't worry. Yet?

 

[Echo North]

with other words: Don't worry. Yet?

If you have the correct fuse in your unit it will pop if you have anything really wrong.  Stand back when you turn the unit on (this is generally a good idea for first time startup on a circuit...exploding caps and all).