1176 best low noise build

[Spencerleehorton]

I’ve opted to use some 24v bulbs I had I didn’t know how much current to give them but experimented and ended up liking 27ma at around 18v seemed to light them up nicely.
I wanted to use 3 of them, 2 for both VU meters and one for a front panel jewel light.
So using the 180 ohm 10W resistor with 37v off the diode bridge gives me what I want.
I have some 22k switched pots for the attack pot but the switch is disconnected in the CCW position, can’t seem to figure it out with the switch this way??

 

[Spencerleehorton]

Channel 1 isn’t playing ball, for some reason signal is only getting to q1 drain and no further? I’ve put in a brand new 2n5457 and checked the pin out?
Will try another fet but I’ve also changed q2,q3 and q4 and used scope but no signal through?
I’ve checked all resistors and checked all continuity through the first and second stage.
Also checked all voltages and all voltages are fine?

 

[Spencerleehorton]

Also one of the vu meters is sticky?
And since putting in the bulbs ch2 has got noisy so I’m thinking of changing the vu meters.View attachment IMG_0732.jpeg

 

[Spencerleehorton]

Also now thinking of going with a separate psu to feed both channels due to the noise?

 

[Spencerleehorton]

Have changed the Q10 to 2n5458 in channel 1 and now get small signal to q4 and see very low signal on output.
So then changed Q6 and Q7, no change.
Will now change Q8 and Q9 and see if anything changes.

 

[Spencerleehorton]

I’ve built a LTspice model of the 1176 now so this should help me track down the problem.

 

[Spencerleehorton]

Have changed Q8 and Q9 but still no change?
Also changed the NE5532.
so signal still not getting past Q2 collector?
Have tried to input signal further in circuit to see if line amp works but also no signal gets through?
Hope to make a break through today!!

 

[Spencerleehorton]

what i have noticed both on my LTspice model of the 1176 and on my pcbs, if i change r17 from 6.8k to 3k i get much better voltages which align with the G1176 schematic, setting both input and output to middle positions i get clean waveform, 12v positive side and 12v negative side.
there maybe some difference as ive made the meter circuit using the transistors rather than the TL071 IC.
im going to check today.
this is all refernce for me for the future as within the other threads i cant seem to find any answers.

 

[Spencerleehorton]

Well what a frustrating day!
Have got ch1 now to a stage where it is passing audio and signs of compression but the level is quite low and GR has a problem where when I select GR it cuts about 5-6v of voltage on the 30v rail?
It seems to be the meter circuit at fault and I’ve tracked it down to the R58 100k resistor which in circuit measures either 45k or 25k depending on which way you toggle the tracking trimmer?
On channel 2 the tracking trimmer does not change the resistance of R58, it just stays at 100k!!!
I’ve been searching all day for what is causing this and not found it!!
Will continue tomorrow, all voltages are now within what they should be apart from channel 1 meter section.
Pin 2 voltage and pin 6 voltage on the TL071 are off, I don’t have the IC in for this problem to happen?

 

[Spencerleehorton]

found the culpret, now both channels work great, have only setup by ear so next stage is to setup properly.
waiting for a pair of better VU meters as one of these sticks.

 

[Spencerleehorton]

View attachment IMG_0782.jpeg
Ordered some meters which should be the same as the Neve 2254 ones below the 1176 here, too is a API-312 preamp, then 1176, then a pair of Neve 2254 then a pair of Neve 1290 preamps.
View attachment IMG_0780.jpeg
Still not sure what I’m going to go with to feed the bulbs for the VU meter and pilot light, but will figure something out.
Need to put in switch for nuke/slam and stereo connection switch.

 

[Spencerleehorton]

New digital scope arrived today so I can start to go through all my rack gear and tidy everything up.
I’ve started to setup channel 1 on this stereo 1176 but still waiting for replacement VU meters, nuke switches and stereo connect switch are now installed.
I’ve used 2 x 470 ohm 5W resistors for bulb feed of 36vdc to 28v 40ma bulb.
For the 12v bulbs within the VU meters I’ll use the other 36v feed on the other channel or may end up making a dedicated psu for the 3 bulbs? Have to see how it effects the noise?

 

[zzzzz]

This thread is of interest to me. Also, are your 2N5457’s legit? Ton of fakes floating around and real ones are difficult to find nowadays. A bag of fake JFETs were a big head scratcher for me once.

Honestly best bet for genuine 5457 is to get the SMD version from a good retailer (digikey, mouser) and put them on a little SOT-23 to TO-92 adaptor. This DIY guitar pedal site sells them pre-assembled: https://aionfx.com/component/2n5457-jfet/

Also, try nice looking warm white LEDs with a wide viewing angle in place of the incandescent bulbs?