Mezmerize DCB1 Building Thread

[Salas]

I wish I had seen this earlier. I ordered mine from am guy in Israel. Who know when I will get them of if they are fake. This is probably a dumb question but it appears that those Jfets are maybe being fazed out. What is it about them that makes them so much better than BJT? I have tons of BJT devices and they are readily available. Can't these circuits be tweaked to work just as well with those?

Thanks, Terry

JFETS are square law devices, where either current or voltage depends on the square of the other.
BJTS are exponential devices. JFETS are simpler monopolar devices. You can even picture them as heater-less pentodes if you prefer.
Of course most circuits can be transformed to full BJT but they won't sound the same. I am not saying worse or better, I am saying surely different.

What makes JFETS chosen for B1 is the self biasing & simplicity plus linearity they offer with just 2 devices. The high transconductance and low noise of the particular type especially. There are newer interesting SMT ones around, but they will be cooking for dissipation as we bias them here at IDSS. There are ways but not that handy to measure & match, cool, and solder by the normally equipped diyer.

 

[HiFi Rookie]

Re: fuses.
I have a couple "through hole" style fuses (slow blow). I have a IEC terminal at the back of my chassis.
Would you solder one end of each respective fuses to the appropriate IEC terminal and the other end of the fuses to the respective primaries of the trafo? So in other words fuses in between IEC and primaries. Anybody not use fuses on their DCB1?

 

[Salas]

Wire like this from the mains inlet to the transformer primary terminal:

 

[AndrewT]

Re: fuses. ................. Anybody not use fuses on their DCB1?

I don't use nor add fuses to my DCB1.
I do fuse the primary feed to the transformer.
Being in the UK, my plug top is also fused and the distribution board has MCBs and RCCBs.
I don't consider that the DCB1 can gain any safety benefit by adding in some LV fuses.

Salas' reply is also to fuse the primary feed to the transformer.

 

[KatieandDad]

I did try higher currents but eventually opted for 200mA to keep everything cool. At higher currents the MOSFETs started to get very warm, and if you remember, mine have reasonable heatsinks.

I didn't like the B1 running at 60-70 degrees.

 

[Marra]

I wish I had seen this earlier. I ordered mine from am guy in Israel. Who know when I will get them of if they are fake. This is probably a dumb question but it appears that those Jfets are maybe being fazed out. What is it about them that makes them so much better than BJT? I have tons of BJT devices and they are readily available. Can't these circuits be tweaked to work just as well with those?

Thanks, Terry

Terry I seem to remember someone on the forum saying they had bought there 170's from an Israeli guy on ebay but cannot recall their name so all being well they'll be genuine.

 

[Corpius]

Terry I seem to remember someone on the forum saying they had bought there 170's from an Israeli guy on ebay but cannot recall their name so all being well they'll be genuine.

I think that you're referring to Alweit. He sells genuine products. I just ordered some matched 2SJ74GR/2SK170GR fets and some macthed IRFP240/IRFP9240's from him for another project.

 

[still4given]

Hi Corpius,

Yes, that is who I bought them from. I wish I had known he was a member here. I wouldn't have worried. His prices are much lower than Spencer.

Thanks

 

[Audio Zen]

I 2nd Alweit.....genuine product and shipping arrived from Israel to US in a timely fashion.

 

[Stixx]

sorry, wrong post...

 

[HiFi Rookie]

Where do you guys buy shafts to extend your potentiometers and switches?

 

[emyeuoi]

I get mine from hificollective.

 

[Rush]

I get mine from hificollective.

Me too!

Rush

 

[Renron]

All thread rod and small gas line hose. DIY baby, Yeah!

 

[AndrewT]

The case from a discarded ball point pen.
A couple of short bits of flexible (but stiff) tube to make the connections at either end.
No metal to minimise interference.

 

[Marra]

Stainless steel; aluminium or brass tube/rod from the local diy store and remove the brass connector and screws from large strip connectors.

 

[McQuaide]

Flexible plastic hose over the splined shaft on the pot, a piece of wood dowel glued into the knob and stuck into the other end of the hose. It's flexy but works and looks fine.

My source selector came with an extended shaft, so no need to improvise.

An externally hosted image should be here but it was not working when we last tested it.

 

[still4given]

I know I saw it somewhere but can't find it. Which four Jfets are the ones that need matching? I finally got mine but need to know before I can start soldering.

Thanks, Terry

 

[Salas]

Those near the output relay arranged in a horizontal row.

 

[still4given]

Thanks!