B1 Buffer Preamp

[chrismercurio]

I was mostly curious about the current...

It was my experience that it sounded (much) better at 18v than at 9v, 12V, or 15v. Though there is something REALLY special going on in the mids and soundstage at 9v, but the bass sucks.

Chris

p.s. I'm using a 2w PEC stereo pot in mine though. I am curious to try the Lightspeed one of these days though.

 

[udailey]

The 7805 will take a 18V input. This should be fine.
Uriah

 

[udailey]

Remove the LED's current limiting resistor from the B1 if you tap off of this.
You would put a jumper inplace of the resistor.

 

[jleaman]

Ive opted out for the lightspeed, instead a nice BRAND NEW 25k Noble pot. Just like Nelson say's, KISS method

 

[erpiii]

Since my post was missed the first time I asked these questions, I'll try again...

Hello...

I have ordered the B1 boards from Mr. Pass and I also have ordered the surplus chassis listed in post #2056 (thanks Lee35210)... it comes with a transformer which outputs two voltages +5v and +18v.

The site info for the chassis states "Filter capacitors are 22,000mF at 16 volts and 470mF at 50 volts. The end result is a linear DC +5 volts @ 1.0 amps and +18 volts @ 1.0 amps supply" The transformer output goes to what look like 2 transistors that are heatsinked on the back.

First question: Does "linear" mean regulated... is that what the transistors do?

Second question: Can the outputs of both be combined to total 23 volts?
I know I can run it at the minimum of 18 but I would like to try both voltages if it is possible to combine them.

Last question: If I use this PS do I need filtering caps as Mr. Pass has suggested when using an SMPS?

Eddie

I have the chassis in hand and I have checked the voltages of both of the output devices 17.8v / 4.8v. The numbers on the 18 volt device say 342 SFC with 2818RC below the 342 number. I haven't been able to find anything on that device. The 5 volt device says L7805SCT. I found that at Digi-key and it says it's output is 5 volts... http://www.datasheetcatalog.org/datasheet/stmicroelectronics/2143.pdf

The power supply has 2 caps and what look like 4 diodes.

The chassis is very nice and will make a great place for my B1.

Can or should I use this PS???

Thanks in advance for any help!

eddie

 

[Magura]

Sounds like you got yourself a regulated 18V supply. Why not use it?


Magura

 

[chrismercurio]

like Magura says



then try a battery!

 

[Zen Mod]

battery is for girliez

 

[chrismercurio]

Can you make out from under the "Iron Curtain" for the next Burning Amp Girlie Man???

 

[Lee35210]

I pulled all the power supply past the transformer and used a 18v regulator board from Welborne. Be careful about which leads you use if doing similiar. I ended up using the leads that went to the +5v circuit. The +18 v leads were too high for the filter caps (35v) on the board. The orange wire needs to be insulated and tucked aside with the other unused secondaries. Also added IEC connector/line filter and line fuse holder on back panel.

 

[erpiii]

Combine the voltages?

Sounds like you got yourself a regulated 18V supply. Why not use it?


Magura

So, can I combine the voltages from both outputs to give me ~23 volts? Do I need any other caps with this arrangement?

eddie

 

[erpiii]

I pulled all the power supply past the transformer and used a 18v regulator board from Welborne. Be careful about which leads you use if doing similiar. I ended up using the leads that went to the +5v circuit. The +18 v leads were too high for the filter caps (35v) on the board. The orange wire needs to be insulated and tucked aside with the other unused secondaries. Also added IEC connector/line filter and line fuse holder on back panel.

So you didn't use the output from the board in the chassis... but you did use the transformer. What was the reason you didn't use PS as it was?

eddie

 

[chrismercurio]

So, can I combine the voltages from both outputs to give me ~23 volts? Do I need any other caps with this arrangement?

eddie

It's sounds best at 18V, why do you want 23?

 

[Magura]

It's sounds best at 18V, why do you want 23?

Exactly my thought.



Magura

 

[chrismercurio]

He COULD use the 5V supply for the lightspeed if he bought one of those.

 

[Lee35210]

I din't use original PS board because was concerned about 30yr old caps,etc plus better parts on Reg board did use

 

[lae2]

I was mostly curious about the current...

It was my experience that it sounded (much) better at 18v than at 9v, 12V, or 15v. Though there is something REALLY special going on in the mids and soundstage at 9v, but the bass sucks.

I have been trying to figure out a basis for tweaking the VCC. The input of my as yet unplugged B-1 will see a max of 2 VRMS. This suggests that as much as 6 V peak-to-peak can be expected. A quiescent Source voltage of 1/2 VCC with a 9V supply suggests that the follower has to swing from 1.5 to 7.5 volts. That may be tight. If I understand correctly (an unlikely possibility) the pinch off voltage has to be subtracted from the VCC and still leave headroom. At 9 Volts it seems to me that the circuit has to be dead nuts tweaked.

I rapidly become lost when it comes to calculating a supply voltage that minimizes noise, maximizes linearity, and accommodates the peak-to-peak voltage applied to the gate.

 

[erpiii]

Shorting unused input on the B1

Since I only plan to use one of the inputs on the Pass B1 circuit board, should I, or do I need to, short the unused input to ground?

Thanks for any help.

 

[AndrewT]

Hi,
you could leave out the switch and take the input straight to the switch output pad.
Or, just leave the switch in the always 1 position and then anything on the 2 position never affects the B1.

 

[LucasAdamson]

I think if you take your inputs straight to the switch output pads, you bypass a resistor.

Perhaps best is hardwiring the switch pad with a tiny length of solid core wire, to make a permanent link to input A's "on" position, and ignoring input B, which will then be isolated.