Building a high gain amplifier part 2: The poweramp

Hey guys. I haven't been keeping up with this as well as I had hoped to but life gets in the way you know?

Today i'll give a brief overview of the poweramp. If you are using PCBs from C3amps or SmashGuitars this is all silkscreened so is an absolute breeze.

As usual I always start with the smallest components as it makes it far easier to keep things flush against the board as you build it up.

The smallest parts on the poweramp PCB are the balancing resistors for the filter caps which make sure that the caps see an even voltage. They also perform an additional function of bleeding away any voltage once the amp is powered off making it safer to work on which is a nice bonus. It does take a few minutes though so always check the voltages before working on the amp.

From here we move onto the diodes that form the rectifier for the AC input and also the bias supply. These have a polarity so make sure to check the circuit and silkscreen matches up with the way you insert them.

Also notice in this picture there is a jumper. This is one of the capacitor legs that I saved whilst doing the preamp. 

Next I install the axial capacitors for the bias and filtering. Again these are polarised so be mindful of this when soldering.

And finally moving onto the main filter caps. The F&T caps are truly fantastic for this application and they are what I will be using.

And that is all! Nice and simple just so long as you keep track of the polarities. The next post that I do will actually be wiring the preamp into the amp as I got my chassis predrilled and prepped from C3amps to save some time and work. I'm not going to say when the post will be up as everytime I do that something gets in the way so just keep checking back!

TK

Building a high gain amplifier part 1.5: The preamp continued.

I didn't get much time to take photos during this part as I was rushing somewhat as I had other things on later in the evening.

In this post you will see the board populated with the coupling & bypass caps. Some people will swear by one brand and type of cap whilst others will say that it doesn't make a blind bit of difference. In my experience it does but not as much as some would have you believe.

I have chosen Sprague 716p Orange Drops for the majority of the preamp because they have a certain hifi vibe to them that I like and seem well balanced tonally. For the 1uf bypass caps I have gone for Vishay MKT's, these are polyester caps and have more of a gritty feel to them. Another reason that I chose these for these positions is purely based on the physical size as a 225p orange drop is a really tight squeeze and  I like thing to look nice and clean in my builds so these are not an option.

Below is a quick comparison shot of the 225p and the MKT as you can see the 225p is gigantic!

In this next shot you can see the preamp fully populated with 716ps and the MKTs

And here is the lone Mallory 150 2.2nf cap as I forgot to order the 716p in this value. Luckily I had this kicking about.

And finally we have a bunch of leg cut offs from the caps. I'm going to save a couple of these as they will come in handy for the next post

In a few days I should have part 2 of this log up which is the power amp.

Thanks for reading

TK

InMadOut Transformers - Soldano Replacements.

This post is a follow on from the heavily modded SLO post which can be found here.

I had a few reasons for choosing these transformers. The main one being that I am building this amp around a dual KT88 Power section and these transformers are perfectly specced for the application.

These were made to order and had a very short lead time of around 10 days which is another fantastic reason to use these.

There was a bit of the impregnation resin on one of the endbells which I cleaned off but it also took a bit of the black paint off too so i'm possibly going to dissasemble these and spray them matte black.

The power transformer is an absolute beast!

So now all that i'm waiting on for this build is the chassis & a headshell that I am getting custom made.

Hopefully there will be more posts soon.