Increase gain on Primare amp, circuit diagram included

[Nick1881]

Hi all,

I wonder if I could once again call on the clever people of pfm.

I have a 7 channel power amp for my home cinema, a Primare A30.7. It has 26dB of gain but I would like to increase it to 29dB. Can anyone help me with the calculation and needed resistor changes please?

Primare sent me this diagram of channel 1, can't make it post for some reason so here is a link.
https://imgur.com/a/FbkgyNn

If anyone could help it would be great @Julf was a lot of help in the past.

Thanks
Nick

 

[Arkless Electronics]

Nearest with standard value resistors would be to replace R123 and 134 with 11K. I'd make C113, 115 about 220pF as well if I were you... It's rolled off pretty early in the treble even as standard and will get much worse when you increase the gain if you do not compensate for this by also changing the caps..

 

[Nick1881]

Nearest with standard value resistors would be to replace R123 and 134 with 11K. I'd make C113, 115 about 220pF as well if I were you... It's rolled off pretty early in the treble even as standard and will get much worse when you increase the gain if you do not compensate for this by also changing the caps..

Thanks so much for the reply. Do you know how the gain is calculated in this circuit? I always like to learn something. I previously replaced the gain caps in my Hypex nc400 modules, that was very easy, just lowered 1 resistor value and there was plenty of info around and help from Julf.

This may be more tricky as I will have to replace them for all 7 channels.

 

[Arkless Electronics]

Just google balanced input op amp stage and you should find all you need to know...

out of curiosity... why do you want to increase the gain?

 

[Nick1881]

Just google balanced input op amp stage and you should find all you need to know...

out of curiosity... why do you want to increase the gain?

My ceiling speakers are very low sensitivity, claimed 86dB. I find that I have to increase the volume levels a lot on my AV Processor to get the same level as my other speakers.

Ideally I would buy another amp with 29dB already but that's a lot of expense. My front L&R speakers are powered by the nc400 modules with a little gain bump and the levels are nicely in the middle of the trim range.

I'm running a 5.1.4 Atmos home cinema.

 

[Arkless Electronics]

Not sure if this applies here but there seems to be a common misconception that if you need to have the volume above say "12 o clock" or whatever that it is a problem.... in most cases it is not a problem and for those with a passive pre it's good if you are using it towards full volume!

 

[Nick1881]

In the processor settings the trim levels for each speaker are like this.

Left Front -6dB
Centre 2dB
Right Front -6dB
Right Surround 4dB
Left Surround 2dB
L Front Height 4.5dB
R Front Height 5.5dB
R Rear Height 11dB
L Rear Height 9.5dB
Subwoofer 4dB

It's those rear heights that are the problem, they aren't positioned great and are behind some Cara fabric and surrounded by Rock wool, maybe that's my issue.
I guess I could actually reduce the gain on my Hypex modules as I'm having to reduce the trim by quite a lot.

 

[Nick1881]

Not sure if this applies here but there seems to be a common misconception that if you need to have the volume above say "12 o clock" or whatever that it is a problem.... in most cases it is not a problem and for those with a passive pre it's good if you are using it towards full volume!

Hey Arkless,

Thanks for questioning me, you made me re-think things and come up with another solution. I did some re-positioning of the rear heights and now they are at a much better angle and I have gained some, well gain.

Now they are like this
R Rear Height 8dB
L Rear Height 7dB

So I have about 3dB extra now.

Easier than changing loads of resistors, though I'm tempted to put my Hypex back to stock spec or close.

Thanks again
Nick

 

[Julf]

If anyone could help it would be great @Julf was a lot of help in the past.

Hi, Nick, and sorry for not responding earlier, but I am in a 3-day "death march" meeting in Los Angeles right now. Sounds like you have found a solution.