wizardofoz wrote:That makes a lot more sense now. I'm not sure about the R3&4 (after the input cd blocking cap) how much gain would that give on its own with them as links (0ohm).
Gives a extra 12dB of gain. We found this to be the best way to get the extra gain before making the 1k R11 smaller in value as it keep the noise floor much lower.
This how the new 12PAKAMP PCB works. The trim pot on it is the R11 resistor not a input pad.
What impact does the 10K pot have if its close to max? I would only use that to balance the channels as its an active system that expects everything the same gain. You mentioned using a 10 fixed resistor in place of the pot.
It will help keep the amp gain balanced and stable when unplugged when used with the RCA wiring I showed in the last post. Just needs to be a 10k fixed resistor or the pot left open at full 10k as it will only lower the input resistance not the level if you turn it down.
We are using huge dipole system with 20 of those woofers with 12 x one metre ribbons for 1000 seater theater here at the moment using our new 12PAKAMP PCB that plugs direct into a Hypex DLCP DSP Card to do all the correction. This makes a minimal wiring solution. Uses 60 Amps to make 30 bridged 140W amps. See our jlmaudio instagram photos and facebook pages for images.
Sorry for asking more questions but I hope it makes things clearer too for others building this fine kit...it really is a nice compact design and seems to be pretty robust despite the trails I have had with this build...its still all working. Credit to the quality of the board as it has had several cable changes and surviving quite well with desoldering etc.
Link out the 2 resistors as the previous post mentioned and you should only at worst case need to make R11 470R. But always it is preferable to have a preamp that can output a better level from in to out to keep signal to noise at it best. We found we had heaps of level with on the 2 resistor linked out. With pro level systems putting out +24dBM easy we usually have to attenuate the input signal which is why the 8PAKAMP is setup with a variable input pad. The new 12PAKAMP is feed by the 2.3v output of the DLCP so needed to be able gain the amp so it clipped at the same point. We found if the amp was kept fully balanced in it with our unique circuit it could be run at less than the minimum 10x gain needed for stability and be perfectly stable with no bandwidth caps needed at all.
Really should be looking at why the preamp/xover design cannot put out enough level into the amp set with R11 as 1k to be able to drive it into clipping. Any good preamp should be able to do this easy.