Beresford Bushmaster DAC

[StanleyB]

I think that the Beresford DAC was the very first of my now infamous "Jerry Hype Forum Fad" threads to appear on the Wigwam. Boy, did that cause a stir!

Those were the days. I remember them well .

I intended to put a simple variable volume control on the Bushmaster, but I soon realized that a simple volume control circuit was out of the question. So that is still under development. Even fitting a volume control to the headphone circuit was not an easy job. The main reason is the DC offset of 1mV. Variable resistors don't like DC. So I am having to use a volume control method that reduces the volume towards infinity, instead of shorting out the signal towards ground. Part of the reason that I use such an arrangement as well is that the headphone output dynamic range is not affected by low volume control settings. This is not always the case with most headphone designs, which then makes the sound so lifeless on lower volume settings in many headamps. I would of course like to use the same principle on the variable output.

[Colin151]

Those were the days. I remember them well .

I intended to put a simple variable volume control on the Bushmaster, but I soon realized that a simple volume control circuit was out of the question. So that is still under development. Even fitting a volume control to the headphone circuit was not an easy job. The main reason is the DC offset of 1mV. Variable resistors don't like DC. So I am having to use a volume control method that reduces the volume towards infinity, instead of shorting out the signal towards ground. Part of the reason that I use such an arrangement as well is that the headphone output dynamic range is not affected by low volume control settings. This is not always the case with most headphone designs, which then makes the sound so lifeless on lower volume settings in many headamps. I would of course like to use the same principle on the variable output.

Cheers for the exaplanation Stan. I kind of understand a little but not fully! My electronics knowledge is not that good! My speciality is to just isten and play with different kit (and do the odd bit of modding if I know pretty much exactly what to do!)

Sounds like you worked very hard to get the headphone section of the Bushmaster with variable volume to work well. I am sure you'll be able to do it with the variable out too. I (for one) would buy that add on as soon as it came as, as I'm sure would many others would on this forum and elsewhere. Remote control with the volume add on would be icing on the cake and also very welcome.

[Ali Tait]

hmmm.......

So it seems some people do rely on the variable output. I guess it's more likely people that use the variable out on this forum than in general though. I am guessing the the majority of people buy Stan's DACs for the good quality headphone amp built in and cheap all in one solution for headphones. The headphone ability was the main reason I bought my Caiman in the first place (to mainly use it with a PC), - then I tried the Caiman on my Cd player/Hifi with speakers.... and didn't look back. So it doubles up for me, it's such a flexible little device.

It is a bit of a shame the Bushmaster does not have variable output right off the bat but I know Stan wanted to price the Bushmaster lower than the Caiman, and something had to give to achieve this. I am glad he choose the variable out rather than the headphone amp ability (for example), and at least there is going to be the add on variable output to come in the future.

Those who rely on the variable output might be a bit stuck on the upgrade path for a while until the add on comes out. I would have suggested a passive preamp or simple attenuator in between DAC and power amp as a potential way around this, but Stan said yesterday that's a no no due to the Bushmasters DC output, - apparently a scratchy sound will result. I am intrigued with his mention of using caps though to sort this out. Where would you put the caps Stan? In between Bushmaster and attenuator?, or in between attenuator and power amp? (I am not that technical!)

A lot of amps/ pres (most?) have caps on their inputs for this very reason.

[Colin151]

A lot of amps/ pres (most?) have caps on their inputs for this very reason.

Yes of course, which is why its therefore a problem with a passive preamp/simple attenuator as there are no caps present. Was just wondering what sort of value cap you would put in series with the DAC and the attenuator in a passive preamp type setup. I would assume the cap value should ideally be quite high, to avoid roll off in the bass.

[Mr.Ian]

Just looked at the circuit diagram of my tube pre and the input goes through a selector switch to a stepped attenuator and then on to an "isolation" transformer (Jensen). Not sure if this will give problems or not but .........

it got me thinking -

would an in line transformer between Bushmaster and pre block the DC and provide a solution ??

[Colin151]

would an in line transformer between Bushmaster and pre block the DC and provide a solution ??

!!

I'm not technical enough to answer for sure, but I know transformers can isolate well so it might be just fine..

[Labarum]

I am having to use a volume control method that reduces the volume towards infinity, instead of shorting out the signal towards ground. Part of the reason that I use such an arrangement as well is that the headphone output dynamic range is not affected by low volume control settings. This is not always the case with most headphone designs, which then makes the sound so lifeless on lower volume settings in many headamps. I would of course like to use the same principle on the variable output.

Confused I am, Stan.

If you have a suitable volume control in the box to control the output for the headphones, can't a variable line out be taken off after that volume control, even if there are some losses? The customer then has more options.

[StanleyB]

Confused I am, Stan.

If you have a suitable volume control in the box to control the output for the headphones, can't a variable line out be taken off after that volume control, even if there are some losses? The customer then has more options.

That would most likely have been the eventual solution that many would have adopted. But the Bushmaster is not a conventional design. You are going to have to trust me on that.

[jandl100]

Stan, you are a tease!

.... I can hardly wait for the Bushmaster to arrive - that's in April, is it?

[MartinT]

Indeed, I think I will then put my Caiman on PC duty, feeding the Mini-T amp.