[sts9fan]

So I bought a gainclone kit and I am getting ready to build it I just need to order a transformer. I work with proteins all day so trying to wrap my head around this electrical stuff is driving me crazy. If some one could explain to me why I want each value that would be wonderful as well.
Thanks in advance!

[Occam]

It would be helpful if you could provide some actual information.
What gainclone kit?
What chip?
How much power do you need from that chip?
A link to the kit.
What does the kit provider recommend?
Do you want a single transformer for both channels or dual supplies?

I realize working with e. coli epimerase all day is trying, but if you want help, you've got to meet us half way.....

That being said, gainclones generally run off of 18-24v secondaries with anywhere from 80va-300va toroidal transformers.

apexjr.com carries inexpensive surplus toroids -
http://apexjr.com/miscellaneous.html#Toroids

and ebay -
http://search.ebay.com/toroidal-torroidal-toroid-torroid-transformer_W0QQcatrefZC6QQcoactionZcompareQQcoentrypageZsearchQQcopagenumZ1QQfromZR9QQfromZR9QQfsooZ1QQfsopZ1QQfstypeZ1QQftrtZ1QQftrvZ1QQsacatZQ2d1QQsatitleZQ28toroidalQ2ctorroidalQ2ctoroidQ2ctorroidQ29Q20transformerQQsspagenameZSTRKQ3aMEFSRCHQ3aSRCH

and PartsExpress carries Avel toroids -
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=278&CFID=1317523&CFTOKEN=62613455

[GBB]

So I bought a gainclone kit and I am getting ready to build it I just need to order a transformer.

As Occam points out, transformers in the 18-24 volt range are typically what you want.
If you check the datasheets for the standard gainclone chips such as the LM3885 or the LM3886 it says the maximum supply voltages should be +40v and - 40v while typical operating conditions are +28 and -28.

The supply voltage from a bridge rectifier is typically 1.4 x Vac so that a 20v transformer will give you 28v after rectification.  So transformers that are rated with dual secondaries 18v and 18v will give you around +-25v and transformers with 24v secondaries will give you around 33v.  These are only approximations since the actual voltage will change depending on the load.  For example a transformer that is rated for dual 20v secondaries with a rating of 200VA will put out 20v when you are drawing 5A from each secondary but will actually have a higher voltage when you are not drawing as high a current.

In terms of where to buy transformers, I've had good luck buying toroidal transformers off of ebay.  I've bought from Antek Inc on ebay (seach for user johnango) and been satisfied with the results.  For a stereo gainclone, the following transformer would work well:
http://tinyurl.com/qxpdn


---Gary

[sts9fan]

my bad this is the kit I got
http://audiosector.com/lm3875.shtml

I think I am going to use one for both channels. That means dual secondaries right? What would be the difference in using that one on ebay with 23V secondaries vs another with 16v? How would that effect the final operation of the amp?

Thanks

[sts9fan]

bad

[Occam]

Sts9fan,

If you go to Peter's site that you provided the link for, in the upper right you can click on 'user manual' pdf and on page 15 of that manual you'll find the answers to your questions. It all there, and here -
http://audiosector.com/nigc_kit-users_guide.pdf
It says that anything over 300va is 'frivolous', but then again, a larger transformer will have better regulation. In reality, the Antek transformer that Gary suggested is ideal -
http://cgi.ebay.com/23-23V-400VA-Toroid-Transformer-Stepper-Motor-Driver_W0QQitemZ270030623705QQihZ017QQcategoryZ4660QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
as Antek takes liberties with their specifications and by my reckoning, its a 330va 22v dual secondary transformer, which is spot on with the user manual recommendations.
Just follow the user manual instructions.

When its up and singing, please post your evaluation and comments.

Happy soldering,
-Paul

[sts9fan]

Thanks for your help and being patient with me.

[sts9fan]

oh will the Noobdom ever stop??

So I now have my transformer and I am confused as usual. The thing has four input wires and four output wires. Now I am assuming I connect the input wires together ie reds together and blacks together. Is that correct? All it says on the transformer is input 120v red-black red-black
                                                       output 23v blue-green blue-green
I am having one hell of a time figuring out how to wire these boards together. All the holes are well maked but I am not 100% on the lingo. The manuel for this kit is ok but does not do much once the boards are put together.  ANY help would be MUCH appreciated. Even a good book that I may be able to understand would be great. Thanks.
         
 

[art]

This may sound confusing to you, but here is what I would suggest:

Make a separate rectifier for each secondary winding, and then tie the two leads that you want to make the common ground at the central ground of the amplifier.

A lot of people, including guys who do it for a living, take the easy way out, and tie the proper wire from each secondary together, and make a centre-tapped arrangement. You have to get the phase of the secondaries right to do that.

The easy method saves one bridge, yields a slightly higher output voltage, but does not sound as good. (You are going to have to trust me on this one.) In addition, the chances of making a ground loop, messing up the ground in some other manner, are much more likely if you take the easy way.

Spend a few $ more, buy an extra bridge, and take the positive of one supply and the negative of the other supply, and tie those to the ground point for the entire amp.


Ooops.......just noticed that you have a kit with a PCB...........suggestion may not be feasible.

Pat