Quad 405 with AudioPower SMPS in original case

[sousoux]

Hi,

My first post on diyaudio although I've been lurking for some time.

I wanted to share a little project I've been working on for some time to change the power supply of a Quad 405 to SMPS but within the old case.

The objective of using an SMPS was to ensure very solid voltage stability. I'd already seen other people who had successfully used SMPS's with Quad 405 type boards although in separate or very large cases. They all were very positive about the results but I like the compact 405 case.

IMG_20110630_204716.jpg

The photo above shows the limited amount of space available. I had a few concerns:

- Heat - The 405 case is a sealed box so I had to be able to get heat out via the front heat sink. This meant that the chosen SMPS had to have an appropriate heat sink/slug arrangement that allowed me to attach it to the front panel.

- Noise - I needed to select an SMPS that would generate a minimum of noise since it was going to be very close to cabling and amplifier boards.

- Space - The SMPS had to deliver at least 800W but fit into the small space available. I also wanted to add a Velemans speaker protection kit to protect my B&W 603 s3's.

After a lot of looking around I decided on the DPS-500/S-D from AudioPower.



The DPS-500/S-D fitted all my requirements plus (and it's a big plus when going into uncharted territory) John, the technical support person, was very quick to answer my emails and was always willing to help.

I discovered a few issues along the way. I wanted to make use of the standby function on the SMPS so that I could use a microswitch on the back panel to turn the amp on and off. I opto isolated the LED output (it's in the non ISO area) of the SMPS and ran that to the Velemans board to open the relays (this is on the small board piggybacked on the Velemans board where its PSU used to be). Since I only had a quad opto isolator available I also opto isolated the front panel power LED. The Velemans board is powered from the +/- 6V secondary output of the SMPS.

I also discovered some coupling between one of the amplifier boards and the non ISO area of the SMPS. This was resolved by simply reversing the right hand amplifier board! The wonders of analogue electronics.

I also added two small aluminum slugs between the case and the front heatsinks to improve heat transfer between the SMPS and the heatsink. Normally the heatsink only touches the case at the amplifier brackets and around where the original rectifier was placed.

I decided to mount the SMPS upside down since it better used the available space and provided a good area for cable routing above.

IMG_20110708_142926.jpg

UP or DOWN?

IMG_20110708_150643.jpg

I also constructed a smaller aluminium L to mount the Velemans board.

The result is stunning. The 405, already great with modestly upgraded boards (caps changed, op amp changed and the classic small sensitivity mods via upgrade kit from Dada Electronics), has far more depth to vocals and fantastically rich, tight bass. There is no detectable noise from the amplifier when connected to the speakers. In fact you can't hear anything ... at first I thought it wasn't working.

This is all subjective I know but I'm very pleased with it!

All this was done making only 2 extra holes in the case (for mounting the SMPS).

The final result ...

IMG_20110914_080035.jpg

I'd really recommend the mod and I'd really recommend AudioPower for their excellent SMPS and customer service.

[AP2]

AudioPower thanks the customer for the item offered post.

Regards
Roberto P.

[Nico Ras]

Nice job. Most important is you are pleased with the modification.