One of the prototypes.
Group Buy is underway!
Working from home all day today has given me the chance to really crank this amp up for extended periods of time. I love it. I think you'll love it. No more messing around, let's start this GB properly!
As usual, it's payment in advance for the PCBs plus postage. Each board is $5 plus P&P at the following cost:
USA: $5
World: $9
That'll cover materials and actual postage costs. Any leftover cents will go to the pfm coffers.
To figure out how much to pay:
- Take the number of boards you'd like and multiply by $5. Eg. 4 PCBs = $20
- Add postage for your order. Eg. $9 to the UK + $20 = $29 for 4 boards posted to the UK.
- Send payment via PayPal.
- If you can't do a gift, please calculate the PayPal fees yourself (i'm too old and lazy for that!!)
- Please please please put your REAL NAME and PFM alias somewhere in the payment subject or message. If you don't tell me your name and alias, you'll hold things up.
- Make sure you provide a postal address!
- As each pfm member pays, I'll put a check next to your name (not your real name, your pfm alias) on the first page of this thread.
- Once either (a) everyone has paid, or (b) we get to Friday 30th of April, I'll close the group buy and place the order.
Schematic
The latest schematic can be downloaded here. Like I said earlier it's a mix of NCC, Acoustica, and PD.
BOM
The latest BOM can be downloaded here.
Connection diagram
A diagram of how to wire this thing up to two separate power supplies can be found here. Note: the diagram assumes you're using HackerCAP PSU boards. If you're using anything else, I assume you know enough about what you're doing to not need a diagram.
Some background
My current power amp is made up of a dual-mono configuration consisting of heavily modified NCC clones off eBay, separate front-end and output stage transformers, separate VBEs for the front end, etc etc.
It was a pain in the arse to build and wire up. It also takes up too much space in the case.
I wanted to simplify things and, to that end, came up with a new layout for NAP-style power amp PCBs. They're the same size as Naim NAP boards (5" x 3.5") and borrow from the NCC circuit, the eBay clone circuit, Acoustica mods, and PD's FET-based VBE.
The PCB incorporates:
1. Pretty much the same audio circuit as the NCC200/eBay clones
2. TO-247 output transistors
3. Acoustica-style output transistor decoupling with on-board 470uF caps
3. Magic pixie dust
4. Well-sorted grounding
5. Big spaces for feedback caps (will accommodate MMKs and even 68uF Wima MKS4)
6. Big spaces for input coupling caps
7. Separate power inputs for front-end and output stage supplies
8. On-board FET-based VBE front-end power circuitry ala PigletsDad
9. Each of these amp boards is designed to be used with two of my poweramp rectifier PCBs, one for the front-end one for the output stage. The front-end requires 5 dedicated 0V returns, the output stage requires 4.
Grounding is carefully arranged so that the on-board 0V star is where all of the different 0V points meet, and is therefore the only common point for:
1. Audio 0V
2. Front-end supply 0V
3. Output stage supply 0V
The rest of the 0V points are labelled FE (front-end) or OP (output stage) to make it clear where each 0V return should be wired to.
Here's the board layout as it stands just now. It's pretty much done (although I'm considering a dedicated 0V return for the feedback cap to return to the front-end PSU board's 0V star), I'm just tidying up the BOM:
I was just going to have a handful made for my own personal use but figured I'd throw it out there: anyone else interested in some of these? Clearly they're only really of use to people building NAP-style amps with separate front-end regulation so I imagine there's a limited audience, but we'll see how much interest there is.
Cheers,
Carl
Pricing
They're $5 per PCB plus postage and packing.
Paid
Everyone.
HackerCAP (haha, couldn't resist!) interest so far
You need 2 PSU boards per amplifier board. In other words, 4 PSU boards and 2 amplifier boards for a stereo power amp. See this thread for the power amp PSU PCB group buy.