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Old 17th June 2012, 09:32 PM   #1
Crumboo is offline Crumboo  Sweden
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Red face Kit recommendations

Hi,

I'm planning to use active (digital) crossover for my DIY 3-way speakers, and is looking for suitable DIY power amps as well.

My speakers:
2x 8" bass in parallel; 4 ohms / 90 dB sensitivity
2x 3" midrange in series; 8 ohms / 89 dB sensitivity
1" tweeter; 6 ohms / 92 dB sensitivity

After some browsing I believe that LM3875:s for mid and tweeter and LM4780 (in parallel configuration) for the bass could be a good choice. Does this seem reasonable?

I don't have much experience of electronics so I'm looking for suitable kit solutions. There are several kits available on the internet, and since I can't judge about the design I'd like some recommendations/options on what to get (both for amps and PSU:s).

Best regards
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Old 17th June 2012, 10:30 PM   #2
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If you want a lm3875 kit then either Peter Daniel or Briangt are good. If you would like to try a Tripath amp then the T2 SE kit looks good at hifimediy.com
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Old 18th June 2012, 06:12 AM   #3
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I'm also looking for 3 amps for my three ways xover. Probably that I'll do this because I already have the LM3876 chips and transfo.

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Old 18th June 2012, 12:09 PM   #4
AndrewT is offline AndrewT  Scotland
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Yes !!!!
One amplifier to one speaker driver.

There is nothing to be gained by paralleling a pair of chipamps to drive a pair of paralleled speaker drivers.

Crumboo,
what are the impedances and sensitivities of the individual speaker drivers?
eg.
Quote:
1" tweeter; 6 ohms / 92 dB sensitivity
Is that 92dB/W @ 1m, or 92dB/2.83Vac @ 1m?
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regards Andrew T.

Last edited by AndrewT; 18th June 2012 at 12:12 PM.
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Old 18th June 2012, 09:07 PM   #5
Crumboo is offline Crumboo  Sweden
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Quote:
Originally Posted by AndrewT View Post
Crumboo,
what are the impedances and sensitivities of the individual speaker drivers?
eg.
Is that 92dB/W @ 1m, or 92dB/2.83Vac @ 1m?
Hi, I rechecked the driver specs:

Tweeter is 94.1 dB/2.83V @ 1m and nominal impedance is 6 Ohm
Midrange is 88 dB/2.83V @ 1m and nominal impedance is 4 Ohm
Woofer is 87 dB/2.83V @ 1m and nominal impedance is 8 Ohm

Measurements that I did actually showed that the sensitivity is actually about 89-90 dB/2.83V for the midranges though...

I obviously connected the woofers in parallel in order to increase the sensitivity, and connected the midranges in series (in parallel the impedance would be too low).

I figured that LM4780 in parallel mode should work fine for the woofers, since it would work with 4 Ohm impedance speakers. Also, I believe that LM4780 would give more power than a LM3875 or LM3886?

Do you think LM3875 would be powerful enough for driving the midranges? I like to play music loud... By the way, the crossover points are at about 400 and 2500 Hz, with very steep filter roll-offs.

I found Peter Daniels page, and this looks good since both LM3875 and LM4780 kits can be ordered there. I suppose he ships overseas?

If i'd use the LM3875 kits for driving tweeter and midranges, would dual-mono (using separate PSU:s) be preferred over the stereo config? Is it wise to use a common transformer for all three channels (tweeter, mid and woofer), of is it better to use separate transformers for each amp?

Any other/more suggestions?

Best regards
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Old 19th June 2012, 03:34 AM   #6
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Quote:
Originally Posted by AndrewT View Post
Yes !!!!
One amplifier to one speaker driver.

There is nothing to be gained by paralleling a pair of chipamps to drive a pair of paralleled speaker drivers.
In reality it's 3 stereo amps with a dual transfo power supply. What's wrong Andrew?

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Old 19th June 2012, 06:35 AM   #7
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Here is a zoom in the XY PCB nearly inspired of Aguilabrava project.

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Old 19th June 2012, 06:48 AM   #8
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Quote:
Originally Posted by Crumboo View Post
I found Peter Daniels page, and this looks good since both LM3875 and LM4780 kits can be ordered there. I suppose he ships overseas?
Peter Daniel makes a top class product and is a great guy to deal with.
I have purchsed several pcb's from him in the past, so yeah he is happy to ship overseas.
Just pay by paypal
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Old 19th June 2012, 06:51 AM   #9
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Quote:
Originally Posted by johnny52 View Post
In reality it's 3 stereo amps with a dual transfo power supply. What's wrong Andrew?

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There is nothing wrong. He is congratulating you on your decision to triamp.
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Old 19th June 2012, 12:42 PM   #10
AndrewT is offline AndrewT  Scotland
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Nothing wrong.
But not about Tri-amp.
It's about one amplifier to drive one speaker.

I see in post5 the same mistake being repeated.
Quote:
I obviously connected the woofers in parallel in order to increase the sensitivity......................I figured that LM4780 in parallel mode should work fine for the woofers, since it would work with 4 Ohm impedance speakers.
There is absolutely nothing to be gained by driving a paralleled pair of speakers with a paralleled pair of chipamps.
Drive each 8ohm bass driver with it's own 8ohms rated chipamp.
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