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Geeky Hifi Amp Solution


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#21 friendly1_uk

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Posted 11 November 2016 - 06:57 PM

Okay, a little progress. The amp took 8 days to arrive. Running a 4" speaker from one channel, powering the amp from the accessory port, it was not at all bad out the box. Wrong car, but sat on the back seat it was not so loud we had to really shout over it, but was in no way lacking. No electrical noise from the car was present and I had to wonder if further mods were worth it. This using the front channel of a £1000 5.1 theater setup. One known to be very picky. My phone was enough to drive it to distaughtion but the amp gain does need dropping. Out the box it hisses a little if you put your ear to the speaker on full volume. Even with the input grounded.

 

I have most components for the mods but I'm waiting for a tiny drill bit suitable for circuit board use. Any day now..


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#22 friendly1_uk

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Posted 17 December 2016 - 01:37 AM

Well that's one supplier I wouldn't recommend. Then I added a week. Then today notice a youtube where 4 ohms is an issue for him. I'm yet to try but the spec suggests it's fine.

 

First the volume knob comes off.

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Then the 4 Allen Key fastenings come out, and the front lifts away

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Then the fastenings at the rear, including the 5th that holds the input sockets firmly to the rear. This 5th screw may also retain a ground wire inside that could need relocating during reassembly. I'm using a bit of tissue to protect the finish on the screws, although chewed up already during manufacture.

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Now the lid can slide away, and the board slid from the bottom casing so we can have a look at it.

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The heatsink can now be taken off, and a resistor on the board located and removed to reduce the amps gain. As standard full volume is reached very early on the dial, and this excessive gain causes a slight hiss we don't want.

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This resistor between a couple of the audio input caps is a little hard to get at, but will likely stick to your iron and lift away very easily. I used a tinned chisel tip to cover the entire component. Try not to disturb it's neighbour though. You might need some £1 shop reading glasses just to see it. Putting one back can be a mare if your not used to surface mount work.

 

Now lets have a look at the decoupling caps and filter stage. To fit the caps we will be drilling the board and scraping away some of the coating. The tiny filter resistors and associated capacitors just solder on. Here is the board before work starts.

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The next few pictures will hopefully need no introduction. Finding where to drill is best done by looking through the board at a bright light. Or copy closely.

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Somewhere along the way I swapped the led and straightened a smoothing cap, loosing another to make way for the more useful low impedance one right at the chips power input position. This so called decoupling cap. One of which exists for each half of the chip. The positive side being the long bus bar looking part, and the negative the larger mass as usual.

 

Got there in the end. Now watch me loose my post lol


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#23 rustywheels

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Posted 18 December 2016 - 06:26 PM

What sort of heat do these kick out?

 

I'd like to upgrade my speakers and need something to power these, but have really no experience of hifi/audio.  If I placed one of these, plus the 24v step up in the glove box, is that just asking for trouble?  Just want to have some more 'oomph' without going down the sub route or seriously expensive kit.

 

But at same time, I don't particularly wish to set the car on fire  :excl:


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#24 friendly1_uk

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Posted 19 December 2016 - 12:11 AM

It's class D which really came of age right here. With efficiency of perhaps 90% the heat shouldn't be that great. In extreme stress testing the internal heatsink was touching 170c though before it started to click in and out of protection mode.  I haven't felt any heat myself, and have now tried 4 ohms but using 12v.

 

I'm not actually sure that this amp will be happy at 24v using car speakers. It's been said it won't work at 4 ohms at all. It does though and the data sheet says it should. Something is amiss.

 

I will try and give it a workout tomorrow.


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#25 rustywheels

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Posted 19 December 2016 - 04:25 PM

Thanks Friendly. I had assumed I would need the 24v to generate the required output, but if 12v works for a reasonable sound then I'll stick with that (told you I knew nothing about hifi!).

PS I had a colleague when I worked in the early days of Ethernet installs, who always said networks were easy compared to hifi. I am beginning to believe him.
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#26 friendly1_uk

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Posted 20 December 2016 - 12:43 AM

24v will gain you 6db in volume. That's 4 times the power. The amp is nearing the end of it's wick though. These numbers are based in maths, and really 3db is more likely. That's double the power. Which sounds a lot, but a lesser increase would be barely noticeable. 12v would be a perfectly good starting point.

 

Illness put me on baby sitting duties today. I will try to run it up on 4 ohms tomorrow.


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#27 friendly1_uk

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Posted 20 December 2016 - 08:23 PM

4 ohm's seemed no issue. My phones a bit lacking in volume and it was only using 12v, but it didn't change temperature at all. Perhaps my hand warmed it a little from repeated strokes but nothing I considered measuring.

 

You should probably try one without modding it for the car. Leaving the final polishing for indoor use on decent speakers. This will assure you reach full volume and unless your listening with the engine off, you won't hear the subtle differences the mods bring anyway.


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#28 rustywheels

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Posted 20 December 2016 - 08:28 PM

Thanks so much for testing and all the info. As you suggest I'll start standard, which I am sure will be fine. It's not like the MX5 is ever going to be a truly great sound platform so I have no misconceptions there! I'll jump on 'the bay' and order it now.
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#29 HarryB

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Posted 20 December 2016 - 09:45 PM

A+ thread! Just a quick question, I am looking for a similar performance board but supporting Bluetooth, as I want to avoid wired connections. Ideally something that would also support my phone and have a mic input, as well as an FM radio receiver.

 

http://www.ebay.co.u...sd=222035251671

 

Something along the lines of this but without USB or SD card support. Do you have any suggestions?


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#30 friendly1_uk

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Posted 21 December 2016 - 03:43 AM

What you pictured is remarkably cheap and could have an amplifier board added. This £10 board looks like a pair of the amps we have been talking about here, in bridge. http://www.ebay.com/...r-/281712272349

It won't be as good, but is ample for that front end and double the power of the single chip amp I have.


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89 Greddy. FMIC. EMB. LC-1. Gauge linearisation. Walbro+Relay. Racing Mazda ceramic downpipe with split mod. Silenced de-cat. FM duels. FM adjustable roll bars. FM rails. HD engine mounts. 1.8 Brakes with m/c brace. Later gearbox. Torsen LSD. Rokkor Mk2 coilovers. Weapon style bar. White wheels, White car, Black Hardtop. Sunglasses holder, footwell lights.


#31 rustywheels

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Posted 06 January 2017 - 06:22 PM

Everything arrived amazingly quickly from HK.  I've installed some new Alpine speakers, which by themselves made a vast improvement.  I've now knocked up a wiring loom using a spare ISO connector, tapping in the power and speaker outputs for the Fronts.

 

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This is a temporary solution to test it out before I rewire the speakers with some decent cable, rather than the standard loom. Will allow me to plug and play it, which I'll do this weekend. Looking forward to this!


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#32 Quick Silver

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Posted 11 January 2017 - 04:34 PM

Looking forward to this!

 

As am I  :)


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#33 rustywheels

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Posted 11 January 2017 - 05:27 PM

I didn't have much time at the weekend, but I did upgrade my door speakers and then did a quick test fit. Speakers were a big improvement by themeselves plus some Silent Coat. Connecting the amp, then raised the output to a whole new level. However, I had only a temp earth connection which introduced a buzz in the background, so I need to address this. I did test the amp on my home hifi, and no buzz there, and pleasingly a big boost to the output.

I'll have a further go in next couple of days, but I've also got distracted by a Jackson Racing cold air intake that arrived today!
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