The Bushmaster strikes back

[StanleyB]

Just got the blank boards from the PCB factory. After a quick QC check with some of the components that the holes and solder pads are in the right place, it is now off to the surface mounting plant for the next stage.

[Rowlf]

Looks like it is progressing really well, Stan! Congrats. And really looking forward to seeing it all come together.

[Val33]

Hi Stan

So what are the differences? I see larger toslink sockets and a trim pot to the side of the volume control and red led's.

Val

[StanleyB]

I did a bit of rethinking and redesigning of every part of the Bushmaster. Some are in response to requests, whilst others are solutions to technical challenges. I don't want to go into deep technical details for now, but a quick breakdown should be the least that I can do.

Internal power supply section:
A lot of people who bought the Bushmaster MK1 factored into the price the additional cost of a noise filter such as the sBooster, and a linear power supply. I have been working and perfecting my Virtual DC power supply circuit since the TC-7510 so that it would be possible to use an external SMPS, without having to fit noise muting relays in the audio output stage. But the sBooster showed that there was still some way to go as far as filtering out the SMPS noise was concerned. So I designed a DC linearizing circuit inside the DAC's power supply circuit in order to tackle the SMPS noise with a lot more rigour. I posted some pics of the before and after results taken from one of the prototypes of the MK2. I shall take some pics from the final PCB and post them here in order to keep things together in one thread. Once you see those pictures the performance improvements in the power supply section of the MK2 will become a lot clearer.

Headphone section:
I changed the volume control to an even more pronounced logarithmic one so that it is now possible to make very fine adjustment of the volume level at up to 50% of the headphone gain output. For the hard of hearing and people who like to listen to music loud, you'll have to go past the 1PM setting if you want your music very loud.
I increased the available headroom in the headphone amp so that music with a very large dynamic range does not get compressed as the music level increases. It's difficult to explain the effect that this added headroom is having without first listening to it with a track that has a wide decibel span.
I also added a balance control to the headphone output that operates over a very small range. It's not designed to cut the sound out when turned fully one way or the other. It's purpose is to make it possible for people with a slight difference in hearing to be able to adjust the headphone output levels so that both left and right output sound about identical.

Toslink input circuit:
I am now using a pair of 25MHz optical sockets instead of the 15MHz ones that were previously the highest rated bandwith type available. This gives even better jitter response from the optical input.

Because of the lower noise floor from the power supply section the line output signal has an even better signal separation with vocals and instruments. This is actually very clear to hear with headphones, which produces a superior 3D output.

[Val33]

Thanks for the info Stan, sounds like you better put me on the list for one as soon as they are available

Val

[reddave]

I'll take my place on the list, too. Albeit way behind many afficianados aficianados aficienados music lovers on here.

[Xapito]

Also interested, will wait for further dev updates / news.

[StanleyB]

Also interested, will wait for further dev updates / news.

Developments and updates are completed . See first picture in this thread. What you see there is one of the boards. But in those boxes behind and underneath the PCB is the first batch of PCBs awaiting insertion of the components in the SMD assembly factory. Then they are off to the case assembly factory, etc.

[StanleyB]

The average SMPS would have a noise figure of about 300mV.
The original Bushmaster power supply is a specially low noise SMPS design. Typical noise figure is around 50mV.

Screenshot of the Bushmaster PSU at 20mV



The Lurcher PSU (better known as the MCRU PSU) is a linear design with a far lower noise figure.

The following screen shot is of the LPSU at 20mV



As can be seen, the LSPSU is far less noisy at 20mV. To get an idea of how quiet it is you have to go all the way down to 1mV.

The following screen shot is of the LPSU at 1mV

[StanleyB]

And now for the performance of the two power supplies after passing through the DC Linearizer filter.

The following screenshot is of the Bushmaster SMPS at 1mV after passing through the DC Linearizer.



As can be seen, the Bushmaster PSU noise after passing through the DC Linearizer outperforms the noise figure of the Lurcher linear PSU at 1mV.

The Lurcher PSU will also work with the DC Linearizer however.

The following screen shot is of the LPSU output at 1mV after passing through the DC Linearizer



As can be seen,the Lurcher PSU initial low noise performance is further enhanced by the DC Linearizer. But the performance difference between the original SMPS and the Lurcher linear PSU is now substantially smaller after processing by the DC Linearizer.