G1176 - too much input level with opamp input...

hello,

while i was calibrating and testing my new G1176s I found a big difference compared to a original 1176 unit.

the behaviour of the input pot is quite different..

in the g1176 the level at the "test point" is too high
compared to the rev.f 1176. (when both input pots are full cw)



so I'm looking for a simple mod to decrease the max. level after the 10k input pot and match it to the max level of the orig. 1176.

so does anyone have an approach??

thank you,
mat

I already tried to increase R6 (27k) which seemed to work, but when I re-calibrated the unit the behaviour is the same, as before..

here is the schematic of both input sections:

I've noticed this with my 1176 build as well. While I don't have an answer I'm also very interested in a fix :grin:

Steve

I also tried to tame down the input signal before the pot with a resistor to ground, but that results in a filter with c35

...

[quote author="matthias"]...so I'm looking for a simple mod to decrease the max. level after the 10k input pot and match it to the max level of the orig. 1176.
[/quote]
Hi,
Place a trimmer (47 or 100k) parallel on R1a, and set them to get the same gain.

Regards,
Milan

thank you...

3k7 is the correct value !!

Is this trimmer used as a variable resistor in parallel with R1a OR a voltage divider with one side to ground and the wiper in parallel? If 3k7 is the correct value will a simple 3k7 resistor in parallel with R1a do the trick?

Cheers,
Ray

replace R1a with 3k7

only on the electronic balanced input.

ah, interesting ..

I'm having this same issue (on just one of my two RevJ completed builds), with the IC 5532 input stage.

On my first completed unit I would normally get a good working level at around the halfway point on the input pot, whereas on the second build I'm getting the same amount of level with the input pot right down at 1/4 or less on the input dial.  Compression threshold seems to work in the same way, at the same operating point, but there's just significantly more level coming in on the second unit.

Not sure why it's happening on one and not the other, because I've double/triple checked all board components and wiring, and I can't find any differences between the two builds, but maybe presume a transistor somewhere may have a different characteristic, or something..

Anyway, is this resistor substitute known to solve the problem?

..please use the dedicated 1176 help thread...

Jakob E.

matthias said:

while i was calibrating and testing my new G1176s I found a big difference compared to a original 1176 unit. 

Click to expand...

The G1176 has a different circuit than the any of the originals 1176

Same circuit as rev. F, but different transformers, giving less gain, but IMO close to the same sonic imprint.

Jakob E.