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Old 16th January 2015, 03:12   #1
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Talking DIY: Pre-Amp to pump up the bass!

I recently bought a Redmi Note 3G phone, and since then I started using it via Aux Cable in my Santro...reason being it was sounding much better than my JVC HU. I was wondering why it is so, why my 128 kbps or 320 kbps files aren't giving me that Solid Bass through the Head-Unit.

I remember when I got the Head Unit in 2012, the dealer said you would get more bass if you buy the next model, but I was not in a mood to spend more, as I don't spend a lot of time in the car. I also recalled he said the Sub-woofer out on that next headunit is more powerful.

Since the last couple of days, I wanted to experiment and build a pre-amp to boost it up. Google uncle helped me a bit, but all solutions I found were either too complex to start with, or weren't specifically for CAR ICE.

Finalized a circuit, and being an old Electronics hobbyist, I was able to find each and every part in my cupboard itself!!

Assembled it, installed temporarily and it was not giving any output; just some pulsating sound from the car's sub-woofer. Removed and brought it back to the work table. I tested it using a Laptop with output to an old Aiwa Home Audio System. In AUX, realized the gain was too high. Circuit includes a preset, thus lowering it sounded the home system well. Bypassed it and the level dropped drastically.

System was working!

It was midnight by then. Went back to the garage, reconnected all the wires and BOOM, I'm loving the system. The Bass Thump is SOLID now.

I would say that, since 3 years of having a SUB in the car, I never experienced this bass. Now I can show off the power of a sealed box which throws the bass, without that BOOM BOOM echo leading to headache (as in other not-so-custom systems that people have).

A water bottle on the gear console-based holder was showing the effect. In 10 minutes of tuning, my pulse was HIGH. Turned it off as neighbours would mind and its chilling cold too.

System needs to be properly installed this Sunday. Will post those pics once done. For the time being, enjoy the assembly pics.

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Last edited by GTO : 16th January 2015 at 14:28. Reason: As per PM :)
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Old 17th January 2015, 09:44   #2
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Default Re: DIY: Pre-Amp to pump up the bass!

Hi ghpk,

The assembly looks neat, if you could share parts details and circuit diagram, it would benefit other users as well, as on face of it the cost doesn't seem to exceed Rs.100/-
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Old 17th January 2015, 10:14   #3
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Default Re: DIY: Pre-Amp to pump up the bass!

Hey ghpk, awesome work! keep it up! I'm also a fellow audiophile and DIY enthusiast.
here are some tips for you.

1. For your application, actually what you need is a passive impedance convertor. an active pre-amp like the one you have built will also do the job, but sometimes simplicity has it's own rewards.

2. In this case, most headphone out sockets have an output impedance of 32 ohms, and most line level inputs have an input impedance of either 10k, 47k or 100k ohms.

3. The simplest way to achieve impedance equalisation for this application requires just two resistors in a ladder config and for this set up, the ideal values would be 2.2k ohms and 1k ohms. Use 1/4W metal film resistors. One can play around with the ratio until you get optimum results for your case.

4. Next is improving reliability & quality of implementation - for this I recommend soldering the two resistors directly into a 3.5mm headphone male plug on one end, and a good quality shielded line level cable and good quality RCA male socket(s) on the other end of the cable.

5. Lastly, use telescopic shielding for this implementation, i.e. connect the shield to ground, only on headphone end.

Have fun!
cheers!
-ootb
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Old 17th January 2015, 13:29   #4
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Default Re: DIY: Pre-Amp to pump up the bass!

mishraak : this is the initial version but the output is mind blowing.
once tuned there's no distortion or irritating bass, the deep bass is making me love the car ICE all over again.

Yes the parts costed around 50 Rupees or so.
I'll be building another version of this tonight itself.

only to differentiate between transistor based and IC based output quality, if any hear able changes exists.

Circuit diagram is included below, I built the right side one.
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outofthebox you seem to have good knowledge about this, thanks for your expert comments, but un-fortunately my car head unit doesn't has a headphone out so this was the only possible solution I could think of.
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Old 17th January 2015, 21:02   #5
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Default Re: DIY: Pre-Amp to pump up the bass!

have you tried installing viper4fx on the phone?
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Old 17th January 2015, 21:35   #6
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Default Re: DIY: Pre-Amp to pump up the bass!

No I have not tried that, but I do plan to try "Xperia_Z3_WALKMAN_v2.0_By_ibanez7"
in a day.

It might add little more quality to modification I've done already.
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Old 17th January 2015, 23:23   #7
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Default Re: DIY: Pre-Amp to pump up the bass!

Hi ghpk, eagerly waiting for your V2.0 on this pre amp. I am experiencing a similar dissatisfaction with my 8 year old sony headunit and 3 year old sony amp + JBL bass tube setup in my Chevy Spark. A friend who is an avid ICE enthusiast(considering he runs pio+audison+focal setup in his VW polo) suggested me to remove the sub from the tube and install it in a sealed box.

Maybe i should try this jugaad before stripping apart my sub as i am afraid that once removed from original tube , it wont fit into an aftermarket box with such precision and neatness as there are no good ICE installers in Allahabad.
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Old 17th January 2015, 23:57   #8
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Default Re: DIY: Pre-Amp to pump up the bass!

Starting assembling the V2 in a hour. got all spares.
but would be testing it tomorrow afternoon, else my neighbors are going to start a fight now.

I know Allahabad is messy for techy stuff.
To tease I went to a car accessories shop/ICE installer in civil lines, and asked him how much bass he can pump thru I purchased from him few yrs back, he said 10% more than what I had in it, and then I walked him to my car and gave him a short audition, he kept on insisting to show him the device but I was in a hurry so drove away. LOL

coming back to your query, it depends how carefully you dis-mantle the bass tube, and I am not sure what size woofer is inside so can't tell what exactly would be the outcome.

To my personal taste, Sealed box sounds much better and those with vent give lots of echo and I get headache in initial 5 minutes.
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Old 18th January 2015, 05:07   #9
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Default Re: DIY: Pre-Amp to pump up the bass!

assembled Version 2, it failed on me for some reason.

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Not going to spend more time on this, time for a version 3 later today.
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Old 18th January 2015, 06:52   #10
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Default Re: DIY: Pre-Amp to pump up the bass!

gphk, I see only one input and output am guessing the circuit is mono - the pre out of a car HU is stereo, and the input of your amp also should ideally be stereo (from the photo it appears you are driving the sub in bridged mode)

do you have any noise or hum from the sub? it wouldn't hurt to add a voltage regulator, especially for discrete circuits.

can you share the circuit diagram of your v2/v3 boards?
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Old 18th January 2015, 23:15   #11
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Default Re: DIY: Pre-Amp to pump up the bass!

JL audio CL-RLC does the same thing.
Its costly but gives you peace of mind.

It gives you 2 x 8volts preouts with volume control from a single preout.
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Old 21st January 2015, 21:50   #12
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Default Re: DIY: Pre-Amp to pump up the bass!

greenhorn : yes its a mono system currently, I use amp for sub only in bridged mode so that should work fine i think.

was not able to make the v2 circuit work, so postponed this till next weekend but v1 is already making people call me and ask for a demo, friends who have experienced it are spreading the fire like anything.

I plan to complete this with "fit it forget it" in 1 or max 2 weeks time and post a completed Video for this DIY Project too, however I am planning to Add 2 necessary things every sub-woofer owner would want to have. will include details for it once its working.

SolidSnake: you can consider mine one as a "Low Cost Solution" or a DIY Project, there are expensive and quality products which would do this but I love doing DIY stuff and that's why i shared the details here.

Edit: v3 circuit will come here soon after testing as its custom mod.

Last edited by ghpk : 21st January 2015 at 21:53.
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Old 22nd January 2015, 15:10   #13
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Default Re: DIY: Pre-Amp to pump up the bass!

even though the sub works in bridge mode
1. it needs input to both its channels, else you are running at 1/4 power.
2. I don't see a summer circuit anywhere to add the L&R signals
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