[dlowman]

I am looking for a good diy transformer for the gainclone I am making.  It's going to be 5 channels.  This is the one I am currently looking at:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=122-675

Do you guys have any other recommendations?

Dan

[JoshK]

If there is one take-away from my experiences with Occam and the development of the Felicia it is that toroids (without interwinding shields, which 99% of toriods lack) are crap.  

Think of it this way.  Toroids do their job very efficiently, they are wide bandwidth, efficient and pass lots of current.  Exactly what we don't want in a transformer....at least partially.  The AC lines that feed the toroid have tons of crap on them.  Due in part to Fridges, AC's, blow dryers, etc, and not just your own but all of the grid, hence all of the US if you are American.  

Why is this the case, well Occam (Paul) explains it better than I, but simplistically it boils down to "capacitive coupling" which means more "crap" is contaminating your ground, which means your ground is no longer zero and the circuit that is operating above ground is no longer operating optimally.  Good ol fashion EI cores, R-cores, etc are much better than Toroids in that they lower capacitive coupling so they pass less crap to ground.  BUT...they have the dissadvantage of being larger, heavier, more expensive and emanate a magnetic field that you need to account for; i.e. you should place it far away from components that are succeptible to EMI.

Engineering and design considerations rear their ugly heads yet again.

[dlowman]

So if I plug the amp into the felicia will that illimate that?  

ALso how far away do these other transformers have to be to elliminate the field?

Dan

[Occam]

So if I plug the amp into the felicia will that illimate that?  

ALso how far away do these other transformers have to be to elliminate the field?

Dan

Well, is your amps powersupply is drawing less than 35-50 watts, a Felicia will do an excellent job in filtering out mains bourne noise, as well as 'cancelling' reactive leakage to the chassis. Realistically, its not appropriate for even a 2 channel linear powersupply powered chip amp under many typical loads,

As far as spacing an EI core transformer, as far as possible. But there are steps that can be taken, such as shielding with mu-metal (expensive) or low carbon cold rolled steel. Some vendors have been quite successful in eschewing the typical toroid, and incorporating EI transformers, notably Steve McCormack in his lovely DNA amps.

[Occam]

Dan,

And from a practical perspective, the Avel toroid transformer will make an excellent powersupply. I use 2 in my own mono Aksa amps. I'd love to use r-cores, split bobbin or sheilded EI core transformers, but we simply don't live 'in the best of all possible worlds', and facing reality, we make compromises.

If you're feeling masochistic, I could ship you 10 56va split bobbin, dual 12volt secondary transformers. You'd need 10 bridges and configure it as 1 transformer/rail/amplifier. Yours for $20 + shipping. But you'd probably need to put the ps in a separate steel chassis, and frankly it would be a royal pain in the arse. Feed that with a 3kw distribution transformer configured as a 1.5kw balancing transformer, and Bob's yer uncle! This would give you a distributed Felicia, with low noise and balanced power. But if I ever tried to do it in my home, SWMBO (she who must be obeyed) would kill me.

As I said, we all have to make compromises.......

I've actually got this massive, nekk'd 2kw shielded EI core transformer sitting on the floor of our 'family' room, that I'll configure to feed balanced power to my Aksa amp, and SWMBO is not pleased.