Author Topic: Cheap LM1875 thread - who wants one? All gone! (Read 34454 times)

syndromet · « **Reply #30 on:** July 08, 2006, 03:44:33 PM »

Man, that was fast shipping. The parts arrived to day, all in perfect order.

However, I was wondering if you hava a part-layout for this amp? Or do I have to understand what goes where by myself?

Guess I'm not bright enogh for that.

Anyway, Thank you!!!

joecool85 · « **Reply #31 on:** July 08, 2006, 04:03:53 PM »

Yup, its listed in the first post on this thread.

syndromet · « **Reply #32 on:** July 08, 2006, 04:37:12 PM »

Thanks. Guess I was a little to hasty there.. I'll get this started, as soon as I figure out what the secondary voltages on my transformer is, and wich side of the transformer that is primary..

joecool85 · « **Reply #33 on:** July 08, 2006, 04:39:07 PM »

In general the larger wires are the primaries, but its good to double check. What are the colors of the wires?

trevize · « **Reply #34 on:** July 11, 2006, 06:52:17 AM »

thank you very much Joe! I received the kit today!

steve_m · « **Reply #35 on:** July 11, 2006, 09:56:24 AM »

Joe,

Sorry, forgot my manners. I got my kit last week, thanks for getting it out to me so fast. I appreciate it.

regards,

steve

trevize · « **Reply #36 on:** July 11, 2006, 10:00:09 AM »

Ok i received today the lm1875 kit from Joe. I'm thinking about building a stereo guitar amp
(does someone remebers the jazz-chorus with two speakers and two power amps?).

I got a jensen p10r cone for 20 euros from ebay and another one is on the way.

now i need to buy the transformer.

can you tell me the specs for the right transformer?
should i go for a toroidal or not?

syndromet · « **Reply #37 on:** July 11, 2006, 10:18:31 AM »

Quote from: trevize on July 11, 2006, 10:00:09 AM

Ok i received today the lm1875 kit from Joe. I'm thinking about building a stereo guitar amp
(does someone remebers the jazz-chorus with two speakers and two power amps?).

I got a jensen p10r cone for 20 euros from ebay and another one is on the way.

now i need to buy the transformer.

can you tell me the specs for the right transformer?
should i go for a toroidal or not?

That is exactly what I'm planning to do with mine. I will build a stereo top with the two lm1875's and use my digitech multieffect prosessor as a preamp. I will hook this up to two single 1x12" cabbinets, equipped with HH vintage 60's I bought for 30$.
20W should be enough for gigging if you mic it, right? I also wander what kind of transformer I need for this, and if anyone know any shops in Europe with cheap transformers.

trevize · « **Reply #38 on:** July 11, 2006, 11:55:17 AM »

yes if you mic it. 20 w per channel if you have very sensitive speakers can be enough for small clubs / pubs live situation. consider also the fact that is probably possible to have 25W per channel with this ic.

joecool85 · « **Reply #39 on:** July 11, 2006, 12:58:17 PM »

Its possible to hit 30w RMS with these chips, but only at their very max limit. You will want a 18v+18v with 100VA or better transformer. 18v+18v will give you a solid 25w of output. If you are curious, you should really look at the datasheet. It's in the wiki on the contents page.

trevize · « **Reply #40 on:** July 11, 2006, 01:27:14 PM »

this is the cheapest i can find here in italy.
but it's probably highly over rated isn't it? would this be ok?

it's a
240 ac 340 VA
24v+24v 12A and 17v+17v 1A

http://cgi.ebay.it/Trasformatore-toroidale-220V-AC-340VA-24V-17-17V_W0QQitemZ300006383070QQihZ020QQcategoryZ88758QQtcZphotoQQcmdZViewItem

joecool85 · « **Reply #41 on:** July 11, 2006, 03:13:11 PM »

I'm confused I guess. If it is 24v+24v then it will put out too much power (24x1.4 = 33.6v), but if its 17v+17v @ 1amp, the voltage would be fine and the amperage too small.

Bob N · « **Reply #42 on:** July 19, 2006, 12:28:27 PM »

Ok... Got my kit about a week or two ago and had other things that needed to be addressed.... I put it together over the weekend and am having an issue.... with a 12.6 - 0 - 12.6v transformer I'm getting +- 8v... Is this correct?

Another problem... I'm smoking transformers... The first went up in a puff of smoke and andcetthe second smells like it's burning up after about 15 seconds or so... I am getting sound out of it however and it sounds good.... Just wondering about the voltage and where to look for the transformer issue....

The transformer is hooked up 12.6v on the +... center tap 0 as the ground and the other 12.6v on the negative side of the circuit....

RDV · « **Reply #43 on:** July 19, 2006, 01:17:38 PM »

Check the polarity of the big caps on the power supply. Something's not right there somewhere. You may be shorting out the chips also if the heatsink(s) is(are) charged and making contact with ground.

RDV

joecool85 · « **Reply #44 on:** July 19, 2006, 02:16:19 PM »

You shouldn't be going through transformers like that, and a 12.6 - 0 12.6 should give you about +/-17.5v

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