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Preamp/crossover DIY

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[Djo] View Drop Down
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    Posted: 14 April 2015 at 10:12am
Hi!

I'm very proud to share with you a nice preamp/EQ/crossover that I made. The purpose was to have a compact board with everything fixed onto it ; the accusafe, maxamp and velleman vu-meter k4304.
It simplifies a lot the assembly in my boombox. (a classic 2-way reflex box)

There's a 6db gain, mono input buffer (I use a passive stereo to mono cable merger for mp3 player, so you loose about 6db), it is helpful when I plug in my electro-acoustic guitar or my old mono analog drum box which don't have a very hot signal output.

Audio is then processed by a five band, pseudo two octave, graphic equalizer, (+/-12db @ 100Hz, 300Hz, 1k, 3k, 10k) that allowed me to compensate for my enclosure design flaws without any problems. Big smile
It's really a set it and forget it adjustment with trimpots.
Schematics where found on a Texas Instruments note by
Bruce Carter.
http://www.ti.com/lit/an/slyt134/slyt134.pdf

Next, there's a one knob wide range tone control to let the user adjust the frequency response smoothly for different sources.
This is a great design explained by Roy Mallory here :
http://roymal.tripod.com/ReverbTone.htm

Finally, the 12db / octave Linkwitz Riley Crossover is based on Rod Eliot work, I just adapted it to a single power supply.
http://sound.westhost.com/project81.htm

I made the assembly on a perforated board, but I used good quality polypropylene caps, and nice OP amp. (OPA2132 for input buffer, NE5532 EQ/Xover, TL072 gyrators)
I measured about 35mA power consumption for the whole processor, which seems to be great since those AOPs are a little power ungry.
There's not a lot of headroom because of the 12V power supply, but it sounds excellent and there's clearly no noise at all!

I need some time to clean my notes and I'll post my schematics. I hope this design will be a nice inspiration for DIYers.

Cheers!












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bitSmasher View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2015 at 10:28am
Beautiful work! Clap
I would love to DIY similar, but instead take the lazy way out with premade parts
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amlu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amlu Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2015 at 11:14am
Nice one. How did you adapt the circuits for 12v use?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesleyK Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2015 at 11:17am
Very coool! Hope you like the combination ^^!

Looks like you have a extra set of holes under the accusafe, would the maxamp fit that pattern? If so, it should be able to fit the new AccuSafe i'm working on at the moment :).

Edited by WesleyK - 14 April 2015 at 11:18am
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[Djo] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote [Djo] Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2015 at 12:08pm
@bitSmasher : Premade parts are necessary with crucial designs like the maxamp and other SMD boards. But DIY is great because you can do something that fits perfectly your needs/projects.

@amlu : With a single power supply, you need to bias all your AOP to Vcc/2. Look at the other parts of the texas instruments documents, if memory serves me well, there's an example of a classical way to do it properly by using an AOP to buffer the bias voltage.
Main drawback is that you'll need to add some coupling cap on the audio path. Here, I used Nichicon bi-polarised electrolytic caps, they are really great!

@WesleyK : The accusafe/maxamp combination is awesome, clearly the way to go, and those boards are very well made!
There is some room around the accusafe, it should be possible to drill some holes for the same pattern as the maxamp.
The v3.5 is very great, simple, ultra small, working perfect! Have you got some informations about the feature of the new accusafe?

Edited by [Djo] - 14 April 2015 at 12:14pm
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lutkeveld View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lutkeveld Quote  Post ReplyReply Direct Link To This Post Posted: 14 April 2015 at 12:17pm
Awesome work. Looks very clean!
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[Djo] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote [Djo] Quote  Post ReplyReply Direct Link To This Post Posted: 20 April 2015 at 9:13am
Thank you lutkeveld!

I made a quick video test so you can see the action of the processor. Hi and low outputs of the crossover are merged passively, and you can see that there's no dip at the X frequency.



Schematics will follow very soon.


Edited by [Djo] - 20 April 2015 at 9:14am
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[Djo] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote [Djo] Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2015 at 11:22am
Hi!

Here's my schematics :



If you want to follow my layout, be careful to the size and footprint of the components, capacitors especially. A good solder skill is required.



5 band EQ and crossover – BOM
Name Value Quantity Notes
R29, R32 33Ω 250mW 2 5%
R23, R27 330Ω 250mW 2 5%
R4, R6, R8, R10, R12 470Ω 250mW 4 1%
R16, R17 2,2K 250mW 2 1%
R3, R14 3,3K 250mW 2 1%
R21, R22, R25, R26 7,15K 250mW 4 0,10%
R15, R18, R19, R20 10K 250mW 4 1%
R1 33K 250mW 1 5%
R2 68K 250mW 1 5%
R5, R9, R13, R24, R28, R30, R31 100K 250mW 7 1%
R7, R11 113K 250mW 2 0,10%
RV1, RV2, RV3, RV4, RV5, RV6 10K Lin 6 multi turn
C2, C13, C18 47pF 1000V 3 WIMA – FKP2 – Polypropylene Film Capacitors
C4 150pF 1000V 1 WIMA – FKP2 – Polypropylene Film Capacitors
C6 470pF 100V 1 WIMA – FKP2 – Polypropylene Film Capacitors
C8 1,5nF 100V 1 WIMA – FKP2 – Polypropylene Film Capacitors
C10 4,7nF 63V 1 WIMA – FKP2 – Polypropylene Film Capacitors
C19, C20, C21, C22 10nF 160V 4 Vishay – MKP 1837 – Metallized Polypropylene Film Capacitor
C12 15nF 160V 1 Vishay – MKP 1837 – Metallized Polypropylene Film Capacitor
C14, C16 22nF 160V 2 Vishay – MKP 1837 – Metallized Polypropylene Film Capacitor
C3 33nF 160V 1 Vishay – MKP 1837 – Metallized Polypropylene Film Capacitor
C5 100nF 160V 1 Vishay – MKP 1837 – Metallized Polypropylene Film Capacitor
C1 150nF 250V 1 Panasonic – Type ECWF(A) – Metallized Polypropylene Film Capacitors
C7 330nF 250V 1 Panasonic – Type ECWF(A) – Metallized Polypropylene Film Capacitors
C9 1uF 250V 1 Panasonic – Type ECWF(A) – Metallized Polypropylene Film Capacitors
C11 3,3uF 100V 1 Vishay – MKT 468 – Metallized Polyester Film Capacitors
C17 1uF 50V 1 Nichicon – Series ES – Bi-Polarized Aluminum Electrolytic Capacitors
C15, C23, C24 10uF 35V 3 Nichicon – Series ES – Bi-Polarized Aluminum Electrolytic Capacitors
C34 47uF 50V 1 Panasonic – Series FC – Aluminum Electrolytic Capacitors
C26 100uF 50V 1 Panasonic – Series FC – Aluminum Electrolytic Capacitors
C25 2200uF 35V 1 Panasonic – Series FC – Aluminum Electrolytic Capacitors
C27, C28, C29, C30, C31, C32, C33, C35 100nF 50V 8 Vishay – Series K – Multilayer Ceramic Capacitors
IC1, IC2, IC3 TL072 3
IC4 OPA2132 1
IC5, IC6 NE5532 2

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jerronimo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jerronimo Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2015 at 1:23pm
Awesome work Clap

Edited by jerronimo - 05 May 2015 at 1:23pm
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audiomik View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote audiomik Quote  Post ReplyReply Direct Link To This Post Posted: 05 May 2015 at 1:52pm
Good work!
You might find advantages in coating your Vero Board and others with lacquer - Specific types available from RS, etc - Conformal coating is one good one to cover component side as well as the vero board itself is prone to moisture absorption - voice of experience!

You will be exposing your system to condensation using it outdoors.

hope this assists

Mik

Edited by audiomik - 05 May 2015 at 1:54pm
Warning! May contain Nuts
plus springs, washers, screws, etc, etc.
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[Djo] View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote [Djo] Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 2015 at 10:37am
Thanks!
Great advice, I hadn't thought about the moisture/condensation issues. Thumbs Up
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slaz View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 06 May 2015 at 11:27am
Top job that man !!

Very close to something I would love to have actually (been muttering/murmuring about it for a whle, never done anything).

Ideally I would have  an additional HP filter (switchable) at about 55-60Hz or so - 12dB/octave should do..... and possibly bring the EQ pots out to proper external ones with knobs.


REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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