B1 builders thread

[AndrewT]

Pi not Phi

[Atilla]

For example:

The noise in a 100 kΩ resistor at 25_C (298_K) over the audio frequency range of 20 Hz
to 20 kHz is –104.8 dBV.

Scaling the resistor down to 1 kΩ (a factor of 100) would reduce the thermal noise by 20 dB.

Beware of large resistors used as the input resistor of an op amp gain circuit, their thermal noise will be amplified by the gain in the circuit.

Source: "Op-amps for everyone" Ron Manchini, TI

[valvesound]

I thought so, thanks Atilla

[valvesound]

Originally Posted by AndrewT

Pi not Phi

depends if you greek or english.

what about pie

[RobertHaze]

This is my very humble B1 preamp made mainly from parts I got on Ebay.
The PCB is one I got from China before I knew Mr. Pass sold them too. I have no complaints- it is very well-made and the layout is correct.
I used a Greyhill selector switch and a 25K Ladder attenuator that also came from China.
I went pretty cheap on the Coupling caps- they are Solen metallized polyproplylene bypassed with 0.01uF Dayton polypropylene film/ foil caps. I wish I could afford some fancy teflon caps for it. The coupling caps seem to impart most of the sonic character that this unit has. The Regulator is a LT 1086; the rectifiers are Shottkeys..
Everything is crammed into a 10 inch square cabinet I also found on Ebay. It was the biggest I could find in my price range.
The sound is very detailed, but it sounds a bit on the bright side in the treble to me. I'm used to listening to my 12SX7 mu-follower preamp. It was interesting cascading the tube preamp into the B1. The mu-follower liked the high Zin of the B1, but the redundant coupling caps limited the sound quality.
For my next project, I may try to retrofit a B1 circuit into my preamp or build Erno Borbely's tube/mosfet hybrid op-amp as a line stage. I like that it is DC coupled.

I have to say that the B1 is the most detailed and transparent preamp I've used. It sounds very fast and dynamic. While it sounds a bit bright in the treble to me, it does not cause listener fatigue.
It is smoother yet more detailed than the Adcom unit it is sitting on. I've recapped the Adcom with Panasonic metallized polypropylenes bypassed with some 0.01uF RelCap thetas. The tight layout in the Adcom prohibits adding the preferable axial film capacitors unless I hang them under the PCB.
I'm grateful that Mr.Pass shared this circuit with us. I hope to eventually try building a pair of F5 monoblocks.

[6L6]

Looks great! Congratulations!

[Salas]

Take out the cap bypasses for a test, it may take out the edge.

[AndrewT]

Originally Posted by RobertHaze

.......................
The sound is very detailed, but it sounds a bit on the bright side in the treble to me. ....................
I have to say that the B1 is the most detailed and transparent preamp I've used. It sounds very fast and dynamic. While it sounds a bit bright in the treble to me, it does not cause listener fatigue...............

Originally Posted by Salas

Take out the cap bypasses for a test, it may take out the edge.

Instead I would suggest that you experiment with the RF filter fitted to the Power Amplifier.

I would go further. Keep as much of the audio signal intact and uncorrupted as possible until it reaches the speaker. That means including RF filtering at the input not just at the Power amplifier, but also at the input to every piece of equipment in the audio chain. (except your RF receivers eg TV & Radio although even here appropriate filtering is necessary to limit out of band interference).

As part of my going further, if you don't have RF filtering fitted to your Power Amplifier, then that is your problem !

[voxxonline]

Gents, I want to combine B1 + Uriah's Lighter Note.
I am not very knowledgeable , but hope it will not be too much trouble.
My question is- how to combine power source ?
Can they share the same source ?

[6L6]

You could make a regulator in parallel with the B1's supply to make the 5v required for the LDR volume control. However, it would probably be easier to just have 2 wallwarts powering the one box.