converting BGW 750C to BGW 750B VU meter PSU hock up

[bonesbiggis]

hello

I am rebuilding my 750C into a 750B.

I have rebuilt the vu meter in kicad but am a little confused about
the hock up of the LM324 ?

from what I can understand it is the LM324 ic pin 4 to +15V and pin 11 between R527 and D507 ?

would be really happy if some one can confirm i am on the right way.

 

[Audio1Man]

250 series runs +/- 55 volts, where 750 series run +/- 75 volts.
Duke

 

[ralphs99]

Hi BB, Nice work, looks great! Love the copper handles

Yes, the -Ve rail for the meters is derived from the amplifier -Ve rail as there's no separate low voltage negative supply

And as Duke has pointed out, the voltages of the 750 are higher requiring a higher value 5.1k 2W resistor for R527 to drop more volts

Also, suggest raising R527 from the PCB by 1-2mm, if you have space under the front panel, to avoid scorching the PCB in the longer term due to heat from the resistor

Cheers, Ralph

 

[bonesbiggis]

Tnx Ralphs always nice with good locking handles.

So the ic will have -10V on the negative side and +15 on the positive?

Tnx for the advice, it will be space to rice the resistor the led's is going to sit on the other side of the pcb later. there was not possible to do that on the 3D picture.
Maby it will be a 3W Resistor then its quite a big drop from -75V

 

[ralphs99]

Sounds good to me. The different +/- supplies for the opamps are no issue

I'm sure some of the BGW experts can confirm

 

[Audio1Man]

Hi ralphs99
We never had a problem with the heat on the display. I guess you might see my name on the schematic?
Duke Aguiar 8 years @ BGW

 

[ralphs99]

👍

 

[bonesbiggis]

its cool to talk with somebody how really knows tanks again Ralph an Duke !
I will update this tread with some pictures when i received the VU pcb.

Have switched to mjl15024/25 do i aim for same bias as usual?