By dave | January 2, 2017
Over the past year, I’ve slowly put together a DIY amplifier based on the DIYaudio honeybadger. After a long, on/off process I’ve got both channels working properly with a single large transformer and dual mono PSUs, soft start, overload protection and one side of DC protection working (another seems to have a fault that I’ve not yet had chance to figure out).
My initial plan was that this amplifier would be used in my AV setup to drive my Jensen full size speakers However, it works so well with my Seas Mimir speakers in the office that I’ve never executed the goal of moving it into the AV room.
I’m not one for trying to describe sound but I will say this, this amplifier is clean, in fact I believe it is the best amplifier I’ve ever heard and easily drives either my Jensen or Mimir speakers. In fact along with a little diffraction in front of the grills on my Mimir bookshelf speakers (in the form of some carpet tape), the sound is absolutely fantastic. This amp is very transparent and clean sounding and I’ve never seen anything move bass drivers with such rigor and force.
In fact to digress for a moment. My Mimir speakers occasionally sounded a bit shouty in the mid. I read about the idea of slightly diffracting the centre of the mid-bass speaker in one of the many speaker building books I’ve read, and I have to say it has worked a treat, really taming the speakers, and now sounding much better. It doesn’t fix every song, but what speaker ever does every song well?
Left: speaker with diffraction tape fitted, Right, one channel of amplifier being tested on bench PSU
At the moment, I’m driving the amplifier directly from an Arcam rDac, using a Windows 10 sound stack running at 24bits and 96Khz. This should be good enough for most circumstances, although a volume control in circuit somewhere would probably be useful. Especially given that on one occasion I managed to accidentally select direct mode and disable the volume control; that was a scary moment until I manged to hit pause in Qobuz!
This build is a combination of DIYAudio’s honey badger and the 21st century protection board. These two together provide a way to get up and running with the features of many very expensive commercial offerings, cost effectiveness depends on how much enjoyment you get from building it. For me I’ve really enjoyed building it, and learnt an awful lot along the way.
- 150W power amplifier based on blameless design
- Three pairs of output transistors, thermally stable
- Can drive very low impedance speakers
- Very low noise design (need to put ear right up to tweeter to hear noise)
- Compact Power supply boards for each channel
- Relay boards with soft-start capability
- 12V and 5V start-up options
- DC and overload protection
- Low Rds MOSFET “solid state relays” on the outputs
The Case and power supply
- Both channels are mounted on 300 x 165mm (4U rack) heat-sinks that are 40mm deep, they were manually drilled and tapped to mount the honey badger, (I’ve got really good at tapping recently).
- The bottom is a 3mm thick aluminium sheet
- Fitted with a Canterbury windings 700VA 36-0-36 transformer
- Dual PSU boards with diodes mounted on top (error on original board).
- The raised section has the 21st century protection components on it
- On the rear, there is power ingress - fused and switched at entry and the DC protection boards (one missing)
If you combine these two projects together, it gives you the equivalent of a very high quality commercial amplifier but it does cost quite a bit to build. I’d imagine it cost me the best part of £800-900 to complete the build including wiring and case, but I did go for the best quality components in each position. I’m sure that some savings could be made here and there if you were able to avoid any subjectivity.
Left: safety first, earth to chassis. Right, part of protection and one channel shown.
Left: raised control board with transformer below. Right: Top view of amplifier exposed.
A bit messy inside at the moment I’m the first to admit. At some point I will probably make an attempt to tidy up.
I started by building one board at a time, getting each one working in isolation. To do this I tested each one on a bench top supply. I started with the voltage very low and increased it slowly, in addition I had the current limited to the minimum possible. Many people also suggest a bulb tester; which may well be better in the event there is a short in the circuit somewhere. I’m currently running it “hot”, that is just over 100mA through each pair of output devices, giving a total of 300mA. When I had it running on my bench top supply.
Given this has now become a part of the office furniture, I’ll need to look at other options for the AV room. On thing on my mind is the possibility of using N-Core modules bolted direct to the back of my Jensen units with Sorbothene couplings. Interesting idea, given I’ll need 3 for the front speakers, and a couple of the regular modules for the back and height (atmos) units. But that is another project, for another time..