B1 Buffer Preamp

[chrismercurio]

I have all carbon resistors in my unit from Koa Speer (Kiwame) and it's not dark in my system or anyone else's that I have tried it in. What are the caps?

 

[Nick77]

Sonicraft mentions the Takmans are very warm, i am using sonicap 1uf and dayton1% 10uf. For me having just the carbon on the output is a real good balance.

 

[Arick]

Following my last post, finally got the time to draw the way I want to connect my balanced version of the B1. What is not shown on the drawing is the switch to change the input from balanced to RCA and the 4 gang potentiometer. Any suggestions?
Eric

Bump, Any comment?

 

[hayenc]

Not sure about the question, but it would seem that a 4PDT switch with two poles on each board and two of the four gangs of the potentiometer on each board just like they would normally be hooked up is all you have to do.

 

[rgheck]

Bump, Any comment?

That's more or less how I've planned mine, but without the RCAs. That said, for input 2, you will need to arrange to connect the unused channel to ground, which you will want to do at the selector switch. Maybe an easier way to go, actually, and what would give you the most flexibility, would be to parallel RCAs and XLRs on the inputs, too, as on Pass's own preamps. Then you put a shorting plug into the XLR across pins 1 and 3 when you are using the RCA input.

 

[Arick]

That's more or less how I've planned mine, but without the RCAs. That said, for input 2, you will need to arrange to connect the unused channel to ground, which you will want to do at the selector switch. Maybe an easier way to go, actually, and what would give you the most flexibility, would be to parallel RCAs and XLRs on the inputs, too, as on Pass's own preamps. Then you put a shorting plug into the XLR across pins 1 and 3 when you are using the RCA input.

Hi rgheck, I do not understand why I should ground the unused channel of input 2 when using the RCA. I would appreciate an explanation if you can (thank you). As far as paralleling the RCA and XLR on the input, It would prevent me from having 2 sources connected (one with XLR one with RCA) from witch I could switch from.
Eric

 

[rgheck]

Hi rgheck, I do not understand why I should ground the unused channel of input 2 when using the RCA. I would appreciate an explanation if you can (thank you).

I don't fully understand why this is necessary, but I believe the answer is that you will get noise back through the grounds. In any event, this is what Kent English of Pass Labs has to say in a recent article on troubleshooting:

The second issue is an apparent lack of performance when using single ended (un-balanced) interconnects. When using single-ended interconnects on inputs that additionally have associated XLR inputs it is necessary to install the supplied jumpers between pins one and three on the input XLR. The pre-amplifier will function sans jumpers, but performance will be notably diminished. Neglecting to install the jumpers will not harm the pre-amplifier. Never apply jumpers to the output connectors.​

The presence or absence of the XLR connector is not the point. When there's no XLR plug, then they have already grounded it for you and you don't have to do anything.

As far as paralleling the RCA and XLR on the input, It would prevent me from having 2 sources connected (one with XLR one with RCA) from witch I could switch from.

That's not what I meant. On the Pass pre-amps, many inputs have BOTH an RCA plug AND an XLR plug. (The Aleph P has this on all inputs.) That's what I was suggesting you do, just as you are doing for the outputs. You would only use one at a time, for each of the two inputs. As here:

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

 

[Arick]

Thank you Rgheck for the explanation, it is clear. I will still remain with plan 1 as it minimizes the amount of XLR plugs and space required. I will ground the R input 2 on both PCB's and have a 4 contact switch (4 gangs?) to swich from input 1 to input 2 on both PCB at the same time. Regards,
Eric

 

[chrismercurio]

Are you serious that Vitamin Q caps are toxic ( at the outside ) or are you joking ?! As I have small stock of Vitamin Q caps left I am curious. I don't like toxic stuff except for tin/lead solder that is...

I am glad I built a DC coupled B1 "Mezmerize". Cheaper and less mental noise which flavor cap to pick etc.

Sorry I missed this.

PCB's of course! (on the inside) From a bygone era in American manufacturing...

 

[daniloreyes]

quick question.
Mine sounds very good, how ever on the LED I have no voltage, and the led does not lit (yeah measured both ways, and the led was tested out side, before and after).
What could be wrong?

 

[mjf]

hello.
some reasons..........
wrong res r4
bad soldering point
led built in reverted
led bad/shorted
greetings

 

[daniloreyes]

hello.
some reasons..........
wrong res r4
bad soldering point
led built in reverted
led bad/shorted
greetings

Hi,
resistor is the correct one, and there is no voltage across the pads of diode. LED has been tested before and after the fact.

 

[mjf]

can you measure the voltage drop across the resistor (15k in the original schematic)?

 

[daniloreyes]

Hi,

Across R4 is 23.8 volts.

I decided to finish the project and took another 15k to + and added the led.

So I'm done.
This will be the reference. I'm doing another with better components to compare differences.
It actually sounds pretty good indeed.

 

[mjf]

can you try out an another res with 3.3k or so (instead of 15k)?
probably the current is to low with this led.
greetings

 

[daniloreyes]

I suspect that the R$ was bad, because like I said, the LED was good. so since the board was installed already I bypassed the resistor with another 15k and now I'm good.

 

[exojam]

I have quick question (probably very basic) but since I am not sure I will ask.

I am interested in building this unit but here is my concern. Right now I am going from my TT -> Cambridge Audio 640P -> Onkyo PR-885 -> Crown XTi100

The Crown only has XLR inputs for that I could use. Would I lose anything by using the B1 if I either go like this:

TT -> Cambridge Audio 640P -> B1 -> Onkyo PR-885 -> Crown XTi100 or

TT -> Cambridge Audio 640P -> B1 -> RCA to XLR adaptor -> Crown XTi100

Thank you in advance.

James

 

[AndrewT]

I suspect your Crown XTi is designed to accept both balanced and unbalanced signals.
The user's manual should detail what needs to be done to accept the unbalanced signal. It may simply be a switch or a jumper plug or a separate input socket.

 

[exojam]

The manual does say it can take unbalanced connections but there are only XLR input on the amp itself (also seen in the manual).

James

 

[AndrewT]

does the manual tell you how to connect an unbalanced signal?

If not then go read Rane and Jensen for good advice on converting a balanced input to unbalanced input.
It is very easy and very cheap. Not quite reversible but you can return the input to standard specification for resale.

The modification can be done inside the XLR plug. That involves no modification to the Crown, but I would rather do a Crown mod.