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Old 25th November 2007, 12:50 PM   #1
Unkle77 is offline Unkle77  England
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Default building a amplifier questions

Over the last couple of months i have built 2 different pre amps and i am very happy with them, now i want to build a amplifier.

Now i understand that you are meant to decided what the end stage is first then work backwards.......

but unfortunately i am not even sure on that side. i think i want two floor standing speakers with hi, mid and low cones. I am not sure if i would need a sub woofer.................. but i do listen to electronica which uses a lot of bass; so what are the pros and cons?

I was looking at the DX HRII which i think will do the job, i will need one for each channel and one for the sub woofer? ( if i decide one is needed)

will 100watts be enough for driving 3 cones or will I be limited?

Im going to go to the wiki and try and work out if i want 4 or 8ohms speakers.....

any input will be greatly appreciated
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Old 25th November 2007, 01:32 PM   #2
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It really depends what speakers you are using, you don't need a sub-woofer if you have decent bass from your main speakers - and if you're adding a subwoofers there's no point wasting money on decent bass units in your mains.

HiFi speakers are 8 ohm - end of story! (pretty well), don't think of anything else. A 'real' 100W per channel, with decent speakers giving decent bass, should be able to easily exceed the threshold of pain in a normal living room!
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Old 25th November 2007, 02:48 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
I agree with Nigel.
100W and 8ohm drivers around 90db/W/m will give very adequate sound levels in a domestic environment.
A good three way should give wideband music reproduction without the need for an extra sub-bass speaker, unless you want true sub-bass for film sound effects.

I would be tempted to suggest
20 to 25mm for treble,
100 to 150mm for mid,
200 to 250mm for bass.

If you can get all the drivers around 92 or 93db/W/m then you could manage with just 50W/channel.
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Old 28th November 2007, 01:03 PM   #4
Unkle77 is offline Unkle77  England
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thanks for the advice on the speakers thats sorted that out, i now know the rough specs to look for now.

Ive deciided that i wont go for a subwoofer, doubt i would use it, i'll just make sure i have compitent main speakers.

now as for the actual amplifier im still not sure which one to build, on the one hand i have the dmx-hrII from this board or i could build one form the elliot sounds site:

http://sound.westhost.com/project3a.htm

but i have no idea which is better? I take it the only way to tell is for me to build and use both?
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Old 29th November 2007, 10:44 AM   #5
Nordic is offline Nordic  South Africa
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I think it will be better to compare the standard original DX (not the HRII) to Rod's amp...

The original version is a little more powerfull, due to not loosing some voltage for regulation..., on the other hand, the HRII is better sounding than the ESP one...

The plain DX has tonnes of bass, I have had 2 people ask me if I was running a subwoofer allready.... and I don't... (with both the DX, and HRII), I think Carlos has measured it to something like 86W into 4 ohms at 10Hz... thats alot of bass power right there, just waiting for a speaker that can handle it.

My boxes only goes down to mid 30Hz range and the bass is all there...
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Old 30th November 2007, 11:50 AM   #6
Unkle77 is offline Unkle77  England
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are you saying your speakers only go down to 30hz or the DMX-HRII........

Doesnt the efficiency of most loudspeakers die off at <30Hz anyway?

I think i will be going down the HRII route.
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Old 30th November 2007, 07:29 PM   #7
Nordic is offline Nordic  South Africa
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my speakers....
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Old 2nd December 2007, 09:43 AM   #8
Unkle77 is offline Unkle77  England
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ah ok cheers for the help!!
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Old 5th December 2007, 08:38 PM   #9
Unkle77 is offline Unkle77  England
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right now that i have decided what circuit i am going to use i need to work out what else i want in the box....

Into this amplifier i am going to have about 6 seperate inputs. I will use a project from esp to switch through the inputs automatically to find which one is being used, at the same time i will have a motorised switch turning round, so that i can switch manually as well.

I am also going to have a preamp inside the same box but i want it to only turn on when it is needed. ie when my mixer is being used i wont need the preamp so there is not point in it being on and wasting energy. But unfortunately the preamp takes +/- 15v and the power supply for it takes 16vac, i was hoping to use the same power supply as the amplifier but i don't think that is possible.

Is there any way i can use another separate switch which mimics the motorised switch for the audio to allow AC to be connected to the preamp? (ie when the audio switch is on "AUX" the second switch allows AC to then flow to the preamps power supply)

I will also use the muting circuit on esp to stop those unwanted sounds.

now on a slightly odder note i am going to have LED's in my amp box, 5 of them in total all at 3.5 volts taking 350mA each. so I will need to some how come up with a circuit taking 240vac down to 3.5v.
Alternatively I could use the AUX circuit of the preamps power supply to power the LED's and have it switch on all the time. Could this introduce any noise into the regulated preamp supply? (it is the 05 project on esp btw).

Sorry about the ramblings...

So to sum it up, i have a power supply for the power amp and preamp wired to the same mains lead. When push the on button both the power amp and preamp's power supply turn on with the LED's. It then switches through the inputs for a bit. If i am using "AUX" the preamp turns on and i have sound, when i turn to another source the preamp turns off. When i then press the on/off button the muting circuit between the amp and speakers then switches in.

Will any of this introduce any noise into the signal? Is it ok using the same power lead to power both power supplies? Can an LED introduce noise?

When i become competent in electronics and a program to put it into i will produce a simplified schematic (with black boxes) for what i am planning.

but if you can point anything out now i would be very grateful.
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