Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Amplifier Discussion => Topic started by: joecool85 on June 22, 2006, 09:21:52 AM

Title: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on June 22, 2006, 09:21:52 AM
Alright, I have  kits that will be complete in a couple weeks.  The pricing is $14, this includes the boards, chips, resistors and caps for a stereo LM1875 along with First Class shipping.  If you want priority shipping it will be $17.  The reason they are more expensive is because Brian didn't have everything so I had to order a good amount of parts from digikey which upped the price a bunch.

If you are interested, post here because its first come first serve.

Paypal payment to joseph.raymond@umit.maine.edu

If paypal is a problem for you, PM me to work something out with check or money order.

Here are some PDFs that will help you out:

http://cordova.asap.um.maine.edu/~raymondj/imagehost/lm1875.pdf

http://cordova.asap.um.maine.edu/~raymondj/imagehost/lm1875-manual.pdf

The manual is unfinished, but it has everything you will need to know.
Title: Re: Cheap LM1875 thread - who wants one?
Post by: Bob N on June 22, 2006, 09:39:03 AM
Absolutely interested! Just let me know when they're ready and how to pay for it....
Title: Re: Cheap LM1875 thread - who wants one?
Post by: trevize on June 25, 2006, 04:21:00 AM
i would be interested! But i live in italy how much would be the surface parcel shipping?

Marco
marco_andreettaATyahoo.it
Title: Re: Cheap LM1875 thread - who wants one?
Post by: joecool85 on June 25, 2006, 07:48:12 AM
^ PM Sent
Title: Re: Cheap LM1875 thread - who wants one?
Post by: steve_m on June 25, 2006, 10:36:40 AM
I'll take one as well. Just let me know when to send payment.

steve
Title: Re: Cheap LM1875 thread - who wants one?
Post by: joecool85 on June 25, 2006, 11:13:58 AM
Ok, so we have:

Bob N - paid (taking transformer as well)
trevize - paid
steve_m - paid
syndromet - paid
DreamSeller

That want kits.  That leaves 1 more stereo LM1875 kit up for grabs.
Title: Re: Cheap LM1875 thread - who wants one?
Post by: syndromet on June 27, 2006, 11:02:20 AM
Depending on the price of shipping to norway, I'd deffenitivly want one.
Title: Re: Cheap LM1875 thread - who wants one?
Post by: joecool85 on June 27, 2006, 01:03:23 PM
If anyone needs a transformer for this I have one for sale:

http://www.ssguitar.com/index.php?topic=170.0

It'd be better for single LM1875 use, but you could probably use it for stereo anyway.
Title: Re: Cheap LM1875 thread - who wants one?
Post by: Bob N on June 27, 2006, 09:07:13 PM
My PayPal is coming Sat morning....
Title: Re: Cheap LM1875 thread - who wants one?
Post by: joecool85 on June 28, 2006, 07:30:18 AM
That's fine, the parts to finish the kits should be in by friday so that works out great.
Title: Re: Cheap LM1875 thread - who wants one?
Post by: DreamSeller on June 28, 2006, 06:36:47 PM
I will take one depending on my payment options.

PM sent.

-Dream
Title: Re: Cheap LM1875 thread - who wants one?
Post by: joecool85 on June 28, 2006, 08:41:03 PM
Sold, no more kits left.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV on June 28, 2006, 08:54:54 PM
Got mine. How did you separate your boards Joe?

RDV
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on June 28, 2006, 09:03:52 PM
I used a ruler to cut against, and then cut about 30 times with a utility knife.  15 times "up" 15 times "down" on BOTH sides of the board, then broke the boards.  The best way to break them is to flex them back a forth several times, that way it slowly/evenly breaks.  You do have to make sure that the lines match within 1mm or less of each other on both sides, or you'll get a pretty shitty break.  All in all it takes me about 2 minutes to break one apart.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on June 29, 2006, 11:40:14 AM
If anyone is interested, I will let the transformer go with a kit for $25 including shipping/handling.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on June 30, 2006, 07:36:35 AM
I'm interested.... PayPal is on the way.... Forgot about my VA check....

Modified***********************************

Ok... payment made.... Be sure to check the email directly from my email account. I had my old shipping address in paypal and didn't see it until after i clicked the submit button. The second email has the right shipping addy. I've since fixed it and deleted my old address...
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: steve_m on June 30, 2006, 08:53:32 AM
Payment sent via PayPal this morning.

Thanks!

steve_m
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on June 30, 2006, 09:52:38 AM
Payment recieved.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet on July 01, 2006, 11:37:39 AM
Have you recived my payment too?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 01, 2006, 01:06:40 PM
Yeah, its listed as paid in a previous post I had.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 01, 2006, 01:40:54 PM
I just recieved the parts I needed.  All the kits are complete now and ready to go.  Unfortunetly, my post office closes at noon on saturdays, so they will be shipped first thing monday morning.

**edit**
This is for:

Bob N - paid (taking transformer as well)
trevize - paid
steve_m - paid
syndromet - paid

Dreamseller, I'm waiting payment, as soon as it comes in I will ship.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: DreamSeller on July 01, 2006, 09:32:02 PM
Dont worry I havent forgotten.

-Dream
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: trevize on July 02, 2006, 06:00:51 AM
thank you very much Joe.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV on July 02, 2006, 01:38:41 PM
Joe:

I just went through my parts and discovered I dont have a 1meg and I got 4ea 22k rather than 2ea 20k & 22k. Is this right? I wonder if that is supposed to be the values. I can get them myself but I want to make sure this is not what I should have received.

RDV
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 02, 2006, 02:12:49 PM
Yup, should have mentioned that.  Sorry.  The 1 meg isn't necessary, it is suppose to prevent popping.  I did it on the left channel and not on the right in my computer amp, and it made almost no difference at all.  The 20k can be subbed for a 22k, thats how I built mine and its fine.  Brian told me to actually, but just because thats what he had to give me.  If you have a 20k, feel free to try it, but 22k will be fine.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV on July 02, 2006, 07:53:15 PM
Cool. I just wanted to be sure. I figured the 22k would be fine for the feedback resistor and all, probably adds a touch more gain.

I've got three amp projects going at once. The LM1875, a stereo LM4780, and another LM3886 guitar amp.

RDV
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 02, 2006, 09:12:22 PM
Wow, way to keep busy!
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 03, 2006, 10:25:47 AM
Bob N - shipped
trevize - shipped
steve_m - shipped
syndromet - shipped

Everyone should get their packages in 4-6 days according to the USPS.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on July 03, 2006, 11:11:59 AM
Thanks Joe!

Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: steve_m on July 03, 2006, 11:52:55 AM
Thanks, Joe.

steve
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet 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?  :o Guess I'm not bright enogh for that.

Anyway, Thank you!!!
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 08, 2006, 04:03:53 PM
Yup, its listed in the first post on this thread.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet 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.. :P
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 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?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: trevize on July 11, 2006, 06:52:17 AM
thank you very much Joe! I received the kit today!
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: steve_m 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
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: 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?

Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet on July 11, 2006, 10:18:31 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.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: trevize 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.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 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.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: trevize 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

Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 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.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N 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....
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV 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
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 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
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on July 19, 2006, 03:21:01 PM
ok.... I went back through everything.... 12.6 out of both sides of the transformer.... 8.1 volts out of the diodes... That's where I'm losing the voltage.... This is without the amp circuit connected and just the power supply and transformer... I've been through everything 10 times at least checking for errors.... I haven't found any bone-headed mistakes anywhere... polarity on the caps is right as well.... Any other suggestions to look at?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 19, 2006, 03:44:09 PM
Are the diodes put in the right direction?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on July 19, 2006, 04:32:46 PM
They're installed exactly the way it shows in the instructions.... I'm gonna put it away for a bit to clear my head.... If you guys think of anything, go ahead and post it.... I'll come back to it after the storms come through.....
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV on July 19, 2006, 04:53:37 PM
All the diodes are facing the same direction with the metal sides towards the big caps?

RDV
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on July 19, 2006, 09:42:39 PM
sure are
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 20, 2006, 06:57:36 AM
I would double check all the solder connections are solid.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: Bob N on July 21, 2006, 02:30:28 PM
I already double checked it and touched all solder connections with the iron again.... Still the same result..... I'm wondering if a diode or two are shot.... I've seen stranger things happen.... I'm gonna get this damn thing if it kills me.... I hate these flaky things that go wrong... LOL All In Alll though, it was a very easy build outside of this .....
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 21, 2006, 03:28:38 PM
I'm guessing that must be it.  Did you check out the pictures I did in the documentation?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: trevize on July 21, 2006, 05:53:44 PM
ok i was able to find the transformer (it a 200va from ebay but it was cheaper than the 70va in the electronic store near house). And this weekend I'm going to build the amp.

Just one question: what kind of fuse should i use (value, slow blow or not...)?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 21, 2006, 06:20:50 PM
2amp slowblow.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet on July 22, 2006, 06:14:07 AM
I found a ransformer with  18V, but it only has 2 wires on the secondary side. Vould that work, or do I need one with 4 wires?
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on July 22, 2006, 07:08:28 AM
I don't think you can use that...on that same note, I don't think I've ever seen a transformer with only two secondary wires.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet on July 22, 2006, 07:24:05 AM
what would happen i I bridged the + sides and - sides? like this:
(http://www.syndromet.com/bilder/ps.jpg)

This is the Transformer:
Transformer 1 (http://www.syndromet.com/bilder/ps1.jpg)
Transformer 2 (http://www.syndromet.com/bilder/ps2.jpg)
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: steve_m on July 22, 2006, 10:20:59 AM
Joe,

I believe a transformer can only have two wires on the secondary, i.e. no center tap. You have to use a full wave diode bridge instead of the instead of the more common full wave diode rectifier setup.

Hammond has a good .pdf file you can download which shows the various setups:

http://www.hammondmfg.com/pdf/5c007.pdf

steve

I don't think you can use that...on that same note, I don't think I've ever seen a transformer with only two secondary wires.
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: RDV on July 22, 2006, 10:26:01 AM
For the PS you're working with:

You'll need either 2 transformers like the one you have, or a center tapped, or a dual secondary transformer. A single un-tapped secondary transformer will not give you two seperate AC voltages no matter how you wire it. You need to do a bit more research on power supplies before you proceed. I'd recommend ESP(Rod Elliott's website). http://sound.westhost.com/index.html

RDV
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: syndromet on July 31, 2006, 02:54:54 AM
I've spent the weekend reading about transformers, and I must say things are a little clearer now. Thanx for the link, RDV!

I also ripped apart another non-working HI-FI amp, and found a 12V center tapped transformer. The amp was actually pretty simular to the 1875, so I guess this will be a good transformer for this purpose.

I also measured the transformer I had lying around from my old Pioneer amp. It gave 20V center tapped. Any idea what I can use this for?

Now I'm waiting for my custom made enclosure (It's nice to have friens working in the alu-industry ;)).
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: DreamSeller on August 20, 2006, 09:16:09 AM
Ive been given a nice set of speakers, Its two 6x9 4 ohms speakers individually boxed but the boxes join together into a nice little case.

-Dream
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on August 20, 2006, 10:18:52 AM
I've heard that while 6x9 (and other car speakers, and hifi speakers) sound great for listening to music, they are rather lack luster with guitar.  Please tell us how it turns out if you use them though!
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: DreamSeller on September 18, 2006, 08:17:00 PM
They sound fine with hifi, Havent finished my LM1875 yet so I cant really tell you. I also get a speaker box with a random 12 inch speaker, I will probly use that with the LM3886 kit.

In term of a replacement speaker, Is there any harm in using an acoustic speaker with electric guitar? I only ask because the specs seem the same and they are a dam site cheaper.

Also I think I have asked this before but is there any harm in plugging a bass into an electric guitar amp?

Thanks

-Dream
Title: Re: Cheap LM1875 thread - who wants one? **All gone!**
Post by: joecool85 on September 18, 2006, 08:38:20 PM
An acoustic speaker should work so long as it has the right wattage ratings, but the sound might not be quite "right."  Also with the bass in an electric guitar amp, it should be ok here and there, but some have said that, especially at loud levels, it is a lot of stress on the amp.