TDA2030a/LM1875 amp kit retrofit (PC 2.1 speakers) - diyAudio
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Old 5th September 2013, 02:39 PM   #1
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Join Date: Sep 2013
Default TDA2030a/LM1875 amp kit retrofit (PC 2.1 speakers)

Hi, newbie to the site but it seems resourceful, heres a little background on my project
I bought a set of creative gigaworks t3 speakers as an ebay bargain, unfortunately, after a few weeks usage they start to power cycle during usage, they are now unusable, popping on and off after a few minutes of low volume use.
I opened them up to try and diagnose the failure, thinking there would be something obvious, but its beyond my basic electronics.
I am now thinking baout retrofitting a tda2030a or lm1875 ebay amp kit, ive heard the lm1875 is the way forwards so am looking at this:
Assembled 2.1 Channels LM1875 NE5532 Audio Power Amplifier Board 25Wx2+50W(Sub) | eBay
on my reasearching i discovered these kits required an AC input, which i had never considered before, anyway, the standard sub has a nice torroid inside:
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
so my thoughts are, that supply might be usable
i will dig out hte part number in next few days, and test the trasformer output as the speakers pop in and out, to ascertain if its suitable and working.

other thoughts, i would like to retain the factory fittings as much as possible so will mean some modification to the standard PCB
Click the image to open in full size.

as you can see the in/outs are enclosed in the plastic housing at the top right of the picture, power comes in at the top left

do my plans make sense so far? am i missing anything fundamental? all thought welcomed, im not unexperienced with electronics (built and installed megasquirt engine managemnt on my BMW) but i am totally new to HI FI electronics.

Do you think the LM1875 board will be similar sound quality to the factory arrangment?

Thanks for your time, im hoping to keep this thread up to date with pictures and info
Alternatively, if anyone knows how to fix my problem lol
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Old 6th September 2013, 10:33 AM   #2
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Join Date: Sep 2013
ok further research, its not a toroid, its some other sort of PSU and its considered... less than favourable
if i go with the amp kits above, i will be upgrading from class D to AB, and presumably it would be wise to upgrade on the PSU too? although maybe not necessary.. but as stated, the standard amp is failing so it could be PSU related anyhow

now.. i understand i need a 12-0-12 centre tapped torroid ideally, but reading about people have mentioned laptop PSU's
i should have access to somehting along those lines, and i prefer the idea... im not playing with mains power if i use ready built PSU's
so, presumably i need 2 similar PSU's, and reading baout, i want to go higher than 12vdc? ill see what i can find first
how would the dual supplies be wired? +12v from each supply going to the 12v point on the PCB, and the grounds taken to the same 0v point?
sorry for hte newbie question it just shocked me that you can go from an ac input to DC happily

Last edited by alan1977; 6th September 2013 at 10:48 AM.
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Old 6th September 2013, 03:19 PM   #3
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bit the bullet and ordered the assembled kit
i understand it may be a good idea to replace the lm1875's with known genuine items, but ill see how it goes to start off with
been looking aobut for a heatsink, might pull one out of an old server, we'll see..
im planning on going past a recycling centre on the way home to see if i can find an old amp i can steel a transformer from and possibly heat sink
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Old 6th September 2013, 06:30 PM   #4
Mihkus is offline Mihkus  Estonia
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Well, winding your own dual 12V is easy, finding one from random amp: impossible.

You dont need supersized heatsink, depends how hard you will push yo amp...

Toroidal 230V Mains Transformer 80VA 0 12V 0 12V | eBay
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Old 9th September 2013, 08:07 AM   #5
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Havent had a chance to inspect/test the original factory fit transformer as yet
I read threads were people suuggested pentium 3 size heatsinks for 2 LM1875's, i was working on the premise that it wouldbe better to go over the top than undersize, the plan is to have the heatsink in freeair at the back of the assembly, that'll mean that i will have to relocate the pots, no biggy

Thanks for the link to the torroid, Is 12v the max recommended? i've read lots of threads were people are suggesting it is a good idea to aim higher, ie closer to 20?
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Old 9th September 2013, 12:40 PM   #6
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Im now shopping some more
speaker protection and soft start
necessary? on a relatively low output amp? should i worry?

I can see this becoming a hobbie...........
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Old 9th September 2013, 02:08 PM   #7
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I wish i spent osme time on herebefore i purchased ah well
So.. i now know that my stock on board PC soundcard is probably going to be a weak link
and the favoured connection method should be USB via DAC, i toyed with the idea of putting a DAC in the amp/sub assembly, but.... as hobby DJ i have this to hand:
Click the image to open in full size.
Which in the specification states that it has a hi quality DAC built in, specifics of which i cannot find
but i figure it must be better than the output on a budget motherboard
This also gives me scope for hardware volume, bass,treble and mid adjustment, so i can potentially ignore the potentiometers on the amp board, however, is it better to adjust the volume on the amp, or set the volume hi and dial down the source?
Im thinking its always better to keep the source signal hi (less interference?) and adjust hte output volume?
So, i wonder if i can retrofit the stock gigaworks control pod as a volume control
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Old 9th September 2013, 02:49 PM   #8
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Summary questions

1) Do i wish to aim for higher than 12vac for the LM1875?

2) Should i aim to work with the external DAC in my DJ controller (Numark Omni Control) over standard motherboard speaker out (i reckon so) or fit a DAC in the amp?

3)How essential is speaker protection and soft start? my impression is soft start isn't so necessary on lower power systems, and i am 50/50 on speaker protection?

4) I should re engineer the external factory volume control to work with this arrangment, rather than running the amp at high load and altering the input level? (interference, heat, being potential problems). If so, this will allow me to remove the pots (or ignore) fitted to the board, presumably if i jumpered the (bass and treble??) the amp would default to full/min bass/treble so I would need to jumper with a resistor at the mid value of the pot?

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Old 9th September 2013, 07:25 PM   #9
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Ok transformer investigated. I don't know if it'll be any use.. I can't find it online yet, so I'm mostly posting the details here as I do t have any paper to hand lol

It's either tgl/tgi1105 written on the metal work
On the label
Tgl or tgi

Part no tac0170800a10
Model vt-2136-0907
Input 0v-220v-230vac 50/60hz blk-red
Input 0v-240vac 50hz blk-wht
Output ac 20.5v 3600 ma blu
Output ac 8.7v 670 ma yel

So I have 20.5v which I believe the lm1875 can use? There's 2 blue wires so I assume that's good for the 12vac input to the board.
However, I don't have 0 v anywhere it would seem

The white seems to be insualated and tied up

Any way I can utilise this transformer for the amp?
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Old 9th September 2013, 09:34 PM   #10
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22.5 at the blue and 9.5 at yellow
I had them running for 35 mins with the back open and the multimeter watching the supply, not one drop out, closed the back up, another 20 mins and still good
Tried hi and low volume on both the source and volume....
Only difference? Plugged into a socket, not 4 way extension lead, and the source signal was my iPad :/ very confused!
Will set back up on my PC tomorrow and try again... I had written the stock electronics off and almost an hour of usage with no issues
Te pc is fine on other speakers or headphones...
Have gone slightly off topic here...
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