DIY amp plans is this possible??

Kanifee · 27 Mar 2008 at 22:11

Im after some advice form some serious sound boffs.
I have in the pipeline plans to build a DIY amp and have located the ktis i want to use. the amps are rated at 25watt over 4 ohms and ive been told that with efficient speakers ill achive 90db so pretty loud.
when i build it for a short time it will be used to run some 100w max music power 4-8ohm biwirable speakers. this is were my idea comes i just dont know weather it will be atall possible so ill try to explain and have drawn a diagram to try and better explain my self.
mind the l33t paint skillz

the amps like i say are 25w stereo amps, my plan or thought is to wire each so than deliver only a left or right signal over two channels to feed into the mid and tweeter seperatly, in effect making each amp a mono biwirable amp then using the two to build a single 2 board amp. is this possible and will i gane anything from it ie better performance form the amp, the extra cost of this over using a single amp to govern both channels is £30 so not a massive cost.

badbob · 27 Mar 2008 at 22:17

That's bi-amping (passive) You need speakers with two sets of input terminals (HF & LF)

To go even further, there's active bi-amping. Very similar but there are no crossovers in the speakers themselves, instead the crossover is line level, before the poweramps. Just make sure you wire it up properly, if you connect LF amp feed to HF the treble will be killed instantly.

I'm passive bi-amping some of my speakers. Not worthwhile on lower end gear though. In your diagram you have the wires going to the driver, that's fine if the speakers have crossovers (most bi-wireable speakers do) however some speakers (Linn Aktiv) have HF & LF terminals which bypass the crossover, these are ONLY for when you're active bi-amping (crossover at line level stage)

Kanifee · 27 Mar 2008 at 22:23

so to do this you need more thn jut bi wirale speakers?

badbob · 27 Mar 2008 at 22:29

Depends. If you're passive bi-amping- with no modding, standard speakers with bi-wire terminals are needed. Then 4 channels of amplification, identical. Then a pre-amp with two stereo pairs pre-outs.

If you're experienced/modder for the above you can remove the crossovers, wiring the terminals directly to the drivers. Then you use a crossover at line level- I know it's before the poweramp stage, but not sure if it's between pre-amp/poweramp, or source/pre-amp. Bryston and Linn do crossover boards. Usually if you're doing DIY from ground up with active, you have to find out exact specs of the HF & LF drivers (Bryston crossover has loads of knobs so you match with your speakers) Linn Aktiv are basically ready done for you.

To passive bi-amp, then something like a Audiolab 8000S and two Audiolab 8000SX poweramps will do. Then pair of speakers with bi-wire terminals. Don't forget to remove the bridging link at the back of the speakers, otherwise you'll blow your amps up!

Kanifee · 27 Mar 2008 at 22:37

Yeh i want to passive biamp the speakers with the DIY biamp, is a pre amp needed or is it a case of if you going to the trouble of building the amp id be a fool not to go the extra and build a preamp aswell?

r0undb0y · 28 Mar 2008 at 14:29

That really depends on the design of the kit, pre-amps are just a way of controlling volume when you're using power amps with a fixed gain.

badbob · 28 Mar 2008 at 14:31

You need a pre-amp, otherwise it'll be at 100% volume. A pre-amp reduces the gain, not increases it. Imagine a hose, without a pre-amp there is no restriction. Using a nozzle (pre-amp) you reduce the flow.

Kanifee · 28 Mar 2008 at 17:56

ah i see what you mean, the amps are able to be fitted with a pot meter wich is used as a volume control though i dont know weather this will be viable, can both amps be linked to a single pot meter?