Testing outside the box


Space is a bit tight inside the box, so I’m just testing the RIAA amplifier on a few records before I install it permanently inside.  So far, I’ve got through these but the queue is growing!

  • Cowboy Junkies – Trinity Sessions
  • The Pogues – If I should fall from grace with God
  • Lou Reed – Transformer
  • Fat Boy Slim – You’ve come a long way baby
  • various Jazz
  • Radiohead – the Bends
  • vaious Sinead O’Connor

There is something about listening to vinyl that’s lost on CD’s.  It’s making me very happy to hear the difference again!

We built this city,

We built this city on silicon!

Silicon City

Silicon City

Just thought this board looked a bit like a city with towers, houses and roads.  In fact it’s a very-low-noise balanced-input audio amplifier with active ground-control (to Major Tom?) and RIAA filters for playing vinyl records.  Records are not cut with a flat frequency response; the bass is reduced as is the treble so that the cutting / etching of the track stays within physical bounds.  Playing a record requires the reverse filter at 3180us (50Hz low pass), 318us (500Hz high pass) and 50us (2120Hz low pass).

And yes, there was a deliberate decision to colour coordinate the components as long as quality wasn’t compromised – much like what I’ve done to Phoebe and Chloe recently.  In fact, for Phoebe, Chloe and this PCB, colour choice has forced higher quality components to be used.

I call it creative OCD art and it gives me great satisfaction!  Horowitz and Hill were not wrong with the name of their classic book.

Thanks again to the fab folk at Ragworm for producing the PCBs.

A long time ago in a galaxy far, far away….

i.e. about 25 years ago, while at uni, I got into Hi-Fi, and built my own speakers and amplifier.  I can’t remember much about them as I sold them to a friend, and went on to purchase off the shelf kit.

At the turn of the millennium when I was still single, without kids but with time and cash to burn, I picked up my audio electronics hobby with an aim to build the best pre-amp, including the best RIAA photo preamp I could:

My OTT preamp

My OTT preamp

It had (has)

  • balanced input for the phono
  • balanced output to feed my Chord power amp
  • self-designed RIAA filter
  • top quality components
  • OFC wiring throughout
  • completely independent left and right channel power / circuitry
  • a PIC16F84 controlling buttons (3 – source, mute and tape!), relays switching the inputs and a 20 x 2 LCD display showing what was playing (eg “phono (muted) -> tape” – and to avoid noise, it shut down after each button press has been handled – all written in assembler.
OTT preamp internals

OTT preamp internals

It was completely designed by me including schematics, layouts and I made the PCBs.

It was completely OTT, but it worked like a dream (and still does); I took it and my Wilson Benesch Full-Circle record player to Doug Brady in Warrington when shopping for some speakers, and they were amazed at the clarity and accuracy of the sound it produced.  Sadly the speakers are long gone, ebayed to pay for Phoebe’s tuition, but the preamp lives on.

But what’s always let me down was the case: just a big black box completely out of keeping with the rest of my (now aging) HiFi kit.

I’ve always wanted to tart up the preeamp, but never got round to it – until now.

What’s this got to do with the Raspberry Pi, you may ask?  Virtually nothing – except for one little detail: I was on a hunt for a more snug Raspberry Pi case for Chloe and google images threw up this link!

The moss dropped off and the stone started rolling…

This is just a rehoming project and won’t be related to the Raspberry Pi in any way, but I thought I’d post in case anyone out there is interested!