All things G1176 - the new "repost" thread.

[gswan]

hi, is that possible to use without output transformer?

is there a simple solution?

thank you

Yes you can, as a single ended output from the 470uF cap and GND.

 

[pstcho]

very easy thank you

i hope it will sound diferent than the other with transformers but stay "good"

thank you

 

[gg85]

I've searched the forum plenty but with no luck and i'm starting to lose hope in this build! i'm building a dual unit with mnats rev J boards, no input transformer and lundahl out, signal seems to be good, and the q bias seems to be working well, but when it comes to GR calibration i am having all sorts of problems. firstly, can someone clarify how to bypass the GR circuit so i can calibrate accurately, shorting 22 to ground doesn't seem to have any affect. secondly, i can't seem to get near 0 with my tracking and zero trim pots...on one channel both pots seem to have an affect on the meter but on the other channel, the zero adjust does nothing. and thirdly, no matter what ratio i have the unit on, there seems to be no change at all in compression. when i disconnect pin 18 my level goes really high and the compression ratios seems to work, not sure why this is though.

also i'm using mnats PSU board to power the units, has anyone else found that the regs get very hot...not sure if i should be worrying about this or if its just normal.

any help would be amazing...i've spent hours trying to sort this out and i've had no luck in any way!

 

[gswan]

Be methodical in your test and calibration procedure.

I have built the same (dual unit, active input Lundahl output) with no problems and it is a very useful unit.

Firstly, did you verify the DC bias conditions of the BJT's? This verifies at least that your transistors are inserted correctly and most of the resistors are the correct values.

Once this is verified you can put a sine wave (1kHz) through it with GR disabled and Qbias wound completely out and check the gains of the input stage and output stage as well as checking for any noticeable distortion or artefacts on the output waveform relative to the input waveform. Use test equipment to perform this, not some sort of subjective 'magical ear' test.

If you calibrated Qbias correctly then you have calibrated GR, that's what the Qbias calibration is for.

The calibration of the meter tracking is a separate step that does not have any real bearing on the audio operation of the unit - it is for metering the GR amount (in a fairly crude and inaccurate fashion).

You disable the GR ciruit by disconnecting the input to the GR amp and grounding the input (point 22). This is normally what the switch on the Attack pot does. When calibrating Qbias you are using the meter to measure dB change, and it is connected across the output. Hence it is possible to use an external meter if that is more convenient or if you have a more accurate one handy.

Verify the bias conditions, check the gains and get this adjustment performed correctly and we'll look at the next part - one step at a time.

 

[gg85]

thanks for the help, going crazy here! where exactly do i measure the BJT's and what approximate values should i find? when the output is showing 0 on the VU the level is quite different on the oscilloscope...as if the GR is disabled...not sure how though

 

[gswan]

Here's a table of DC bias conditions and some waveforms through the amplifier stages.
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62

 

[lelabal]

Hi there !
I have just finished my second 1176 unit with Mnats PCBs. The first unit was build one year ago and works great but this one won't work, I need your help !

I've got audio passing trough the unit, IN and OUT pots work but I can't hear no compression ! ...but I can see the compression through the vu meter. So I assume that the GR Meter section is working great. I can see the effect of ratio change on the meter as the signal goes trough it without any problem. Same thing with calibration procedure, it work perfectly on the vu meter and all trimpots are doing cool things.

I can see it... but I can't hear it

When I stuffed the board I've made a stupid mistake, C8 (polarised) was reversed, I powered the unit without seeing it but it didn't see smoke, fire or anything like that. Now I have replaced this capacitor paying attention to the polarity but it still act the same, like I could have let C8 in the wrong way.

Assuming that everything seem to work with the vu meter, my problem must be around the GR AMP section ?

There's another thing which could be part of the issue, C19 and C20, tantalum capacitor are really hard to find so I desoldered it from an old project. Can anybody tell me what voltage you get at C19 and C20 ?

Thank you for your help.

 

[lelabal]

Ok, I've just noticed something weird, in VU mode, the vu meter doesn't move a lot, execpt when I turn the output pot really loud. In GR mode, no problem. Maybe this unit has also an output gain issue ? My other G1176 has more gain and the same rectifier/resistor on the vu meter so maybe the issue is not only in the GR Section...

 

[gyraf]

Ok, I've just noticed something weird, in VU mode, the vu meter doesn't move a lot, execpt when I turn the output pot really loud.

Make sure that you have a genuine VU-meter as described many times before in this thread...

I've got audio passing trough the unit, IN and OUT pots work but I can't hear no compression ! ...but I can see the compression through the vu meter.

GR-meter and actual compression are two separate paths - you can have GR indication without actual GR happening. But if you follow the meter calibration procedure (where you set the -6dB GR so that it shows -6 on the meter), you know that it is actually compressing.

Jakob E.

 

[ilikeit]

hi at all

i have a little problem with my 1176'mnats
everything are ok
no buzz no hum ....
but when i want connect my lamp i have a big humm
i have making a star ground
xlrs,psu,and the rack are connecting
have you got idea??
thx!

 

[gyraf]

use unregulated current for lamps - not the regulated

 

[Kingston]

I'm getting near done with my dual unit, but since I'm not awfully familiar with the details of the design,

what is the original purpose of the optional caps (2X 100uf & 0.1uF) in the output section? (didn't see this discussed earlier in the thread)

Ripple removal? If so, why were they made optional?

 

[gswan]

I'm getting near done with my dual unit, but since I'm not awfully familiar with the details of the design,

what is the original purpose of the optional caps (2X 100uf & 0.1uF) in the output section? (didn't see this discussed earlier in the thread)

Additional bypass capacitors.

Ripple removal? If so, why were they made optional?

They are not on the original 1176 circuit.

 

[Kingston]

Thanks.

I guess it can't hurt to have some extra ripple removal in there, and were not adding any caps on the audio path there either.

 

[onlymeeee]

Hi,

I'm just wondering about some resistor/capactor changes (in the signal line amp) between rev f and g onwards.

As I'm building a mnats 1176 j, with ne5532 input and reissue B11148,
I'm wondering whether I should use the F's values (as it uses the B11148)
or the g/h/k versions.

What were the purposes of the changes?
Because of a different output transformer?
or because of the different input (transformer to ic)?

 

[gg85]

I've just finished checking all the voltages and all sections with a scope and everything is spot on, only i'm still not getting any gain reduction. if i bypass 18 i gain a lot more level and my ratios work and i get compression, but as soon as i connect it back i get a dramatic drop in level and the level remains the same no matter what ratio i have it set on.

 

[gswan]

Sounds like it is mis-calibrated and the GR FET is conducting all the time. Or the ratio resistors are incorrect.

 

[Kingston]

Now this is odd,

I searched 2N5457 from farnell, and got results from "JFET" and "RF JFET" areas.

all the JFET ones are discontinued, but specs of the available ones at RF JFET area look exactly the same. just different manufacturer it seems.

Is there something I should know about, or should I just order the RF JFETs? They are a lot cheaper than the BF245A.

 

[gswan]

There are several manufacturers of the 2N5457. It's usually described as an N-channel General Purpose Amplifier FET. Not sure that it's really an RF FET though, that might be pushing it a bit. They are relatively cheap so you can order a few spares and measure the transfer curves for each to select reasonably matched ones.

 

[Kingston]

Well it says,

N-Channel General Purpose Amplifier
This device is a low level audio amplifier and switching transistors, and can be used for analog switching applications.

technical data is identical on all of them. I'm getting the RF JFET type.