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DIY PRE AMP / SOURCE SLECTOR

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ashar

Member
Joined
Sep 2, 2018
Messages
50
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Location
amravati
So this started as a need for running a lot of sources to multiple amps , which is always a trouble when u dont have a lot of inputs on your power amp. Also a preamp is usefull for phonostage application.
I searched youtube and google for inspiration.
Then i checked what i have in inventory to be used as donor parts for my preamp.
Most of the parts are scavanged from my stockpile of used amps/decks/electronic gadgets found at flea markets etc.

My idea of preamp and its purpose
: pre amplifier for turntable and old type decks
: multiple source selection to run on any amp without touching or changing the rca chords
:Vu display to complement a rack system
:a bridge between all my rack system

Donor cabinet came off as a bus bar box which is heavily build and suits my purpose this ll have machined alluminium front panel which i ll make later IMG-20180910-WA0011.jpg IMG-20180910-WA0013.jpg IMG-20180910-WA0018.jpg IMG-20180910-WA0009.jpg

Inspired by the design of a DUAL amp as i have same set of vu meters

dual-cv-1260.jpg



These vu meters are a piece of art , they look so similar to DUAL amps vus
luckily i have the vu driver board aswell
IMG-20180910-WA0010.jpg IMG-20180910-WA0016.jpg

Another beautifull find from a closing recording shop a hand assembled source/amp selector

IMG-20180910-WA0020.jpg IMG-20180910-WA0015.jpg

A very nice client of mine after knowing my build send me some goodies
: eight audio preamp
: akai vu with driver board (to be used in some other project)
: 4 way splitter IMG-20180910-WA0014.jpg
IMG-20180910-WA0012.jpg

Next
Add a hidden bluetooth reciever that will go on when u select bluetooth switch .
Got a car bluetooth reciever aswell for same. I ll power it with a cell charger for 5v output . and will draw the aux out to the selector board.

will post the progress as and when i get more time. Waiting for your valueable inputs.
Regards.
 

haisaikat

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Dec 12, 2010
Messages
2,962
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Kolkata
Do you plan to run the preamp board and the input switching section from same power source? They can be separated to minimize distortion, calls for two transformers.

But I agree that having multiple inputs on preamp is a must and good to see your project progress
 

ashar

Member
Joined
Sep 2, 2018
Messages
50
Points
18
Location
amravati
@haisaikat , i now get what you mean.
so i ll do following
use individual transformer for vu setup, do u think tats needed ?

i m already using a mobile charger for the usb powered bluetooth card.

so i ll have three power supplies in total.
 

haisaikat

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Joined
Dec 12, 2010
Messages
2,962
Points
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Location
Kolkata
@haisaikat , i now get what you mean.
so i ll do following
use individual transformer for vu setup, do u think tats needed ?

i m already using a mobile charger for the usb powered bluetooth card.

so i ll have three power supplies in total.

If this is a diy and you have different power supplies from main for different modules, it's still fine, saves you cost of buying separate transformer
 

ashar

Member
Joined
Sep 2, 2018
Messages
50
Points
18
Location
amravati
If this is a diy and you have different power supplies from main for different modules, it's still fine, saves you cost of buying separate transformer


ok understood , isolating power supplies for each module will lead to least distortion.
 

ashar

Member
Joined
Sep 2, 2018
Messages
50
Points
18
Location
amravati
another goodie coming in from a dear friend.
Preamp board IMG-20180910-WA0099.jpg

slector switches (they are all JAPAN make realised today while working with them)
have been mounted on the chasis.

1536612831272447.jpg 1536612831815576.jpg

next is rear panel rca jack boards
1536612829987294.jpg
 

avesbilal

Active Member
Joined
Jun 23, 2014
Messages
164
Points
43
Location
Hyderabad
Nice project...

You will have to isolate the RCA Negative from the chassis as it might cause hum, I am not sure if you are already doing it.

Regards
Bilal
 

ashar

Member
Joined
Sep 2, 2018
Messages
50
Points
18
Location
amravati
Nice project...

You will have to isolate the RCA Negative from the chassis as it might cause hum, I am not sure if you are already doing it.

Regards
Bilal


thankyou , i ll keep that in mind.
I have planned to use shielded wires for rca

@avesbilal your pointers on shielding would be helpfull , if you can take out some of your time ans guide on the same

another issue is wether i should use a traditional transformer with bridge and filter caps or simply buy a 12v smps
 

avesbilal

Active Member
Joined
Jun 23, 2014
Messages
164
Points
43
Location
Hyderabad
Linear power supply will be better then SMPS (Except In cases SMPS are specifically designed for Audio use). if you are using linear power supply you might have to use a regulated one.

below are some points I remember might be helpful

1. Use star grounding.

2. Ground the shielding of RCA at the connector end.

3. Try to avoid any PCB/connectors/Potentiometer shaft which has signal negative touching cabinet.
 
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