B1 Buffer Preamp

[jleaman]

ANy one selling boards ? Id like one..

 

[Beftus]

budget restraints...

a budget restraints question... where do spend the largest part of my limited capacitor budget on: the 1uF caps (C100 & C200) or on the 10uF caps (C101 and C201).

I'm thinking of using Clarity Cap SA series for the 1uF and Clarity Cap PX series for the 10uF.

 

[peranders]

ANy one selling boards ? Id like one..

Nelson Pass has boards...

 

[udailey]

Over at the DCB1 thread I think they are working on a second buy for the boards.
Uriah

 

[jleaman]

Nelson Pass has boards...

Thanks, Pm'd him

 

[Arick]

You might want to go to this link bellow to order.
Regards Eric

Pass DIY: Store

 

[Floric]

Figured it out, crossover resistor values were too low compared to the input 'stopper'... less than 1dB loss now.

O.k. I had the filter in an environment where I could omit the input stopper.

 

[jleaman]

You might want to go to this link bellow to order.
Regards Eric

Pass DIY: Store

Thank you, does any one currently have a BOM?

 

[peranders]

You can find it at Nelson's website.

 

[LucasAdamson]

I'm sorry if this has ben covered before, but I just wanted to clarify. In the construction notes, Nelson states:

The best performance generally comes from matching the Idss of Q100
and Q101, and also Q200 and Q201. The Idss is simply the current that
flows through the JFET when the Gate and Source are grounded and +10
volts or so is applied to the Drain. Often when you buy JFETs you can get
them in Idss grades. I use GR or BL grades for this project.

Is that right? I would have thought that matching Q100 with Q200 and then Q101 with Q201 would provide better channel matching. Or am I missing something? Probably...but I thought I'd just check. I ask because I have 2x matching pairs, rather than a matched quad. They are all fairly close, but clearly 2x pairs.

Many thanks
Lucas

 

[LucasAdamson]

I'm sorry if this has ben covered before, but I just wanted to clarify. In the construction notes, Nelson states:

The best performance generally comes from matching the Idss of Q100
and Q101, and also Q200 and Q201. The Idss is simply the current that
flows through the JFET when the Gate and Source are grounded and +10
volts or so is applied to the Drain. Often when you buy JFETs you can get
them in Idss grades. I use GR or BL grades for this project.

Is that right? I would have thought that matching Q100 with Q200 and then Q101 with Q201 would provide better channel matching. Or am I missing something? Probably...but I thought I'd just check.

Many thanks
Lucas

 

[jleaman]

You can find it at Nelson's website.

Done, now to find the psu board if one has been made.

Thank's Par
J'

 

[udailey]

Q100 and Q200 are on one channel so if the combination of these two gives you a power of Y out of the B1 and the combination of Q101 and Q201 give you a power of Y+1 out of the other channel... then you have two channels that are not balanced perfectly.
If out of one channel you have Q100 giving X and Q200 giving Y and out of the other channel you have Q101 also giving X and Q201 also giving Y then both channels give you X+Y and they are balanced.
Uriah

 

[jleaman]

Q100 and Q200 are on one channel so if the combination of these two gives you a power of Y out of the B1 and the combination of Q101 and Q201 give you a power of Y+1 out of the other channel... then you have two channels that are not balanced perfectly.
If out of one channel you have Q100 giving X and Q200 giving Y and out of the other channel you have Q101 also giving X and Q201 also giving Y then both channels give you X+Y and they are balanced.
Uriah

well said

However if one doesn't want to match them, they are for sale with aboard for 40$ matched from passdiy

J'

 

[LucasAdamson]

Q100 and Q200 are on one channel so if the combination of these two gives you a power of Y out of the B1 and the combination of Q101 and Q201 give you a power of Y+1 out of the other channel... then you have two channels that are not balanced perfectly.
If out of one channel you have Q100 giving X and Q200 giving Y and out of the other channel you have Q101 also giving X and Q201 also giving Y then both channels give you X+Y and they are balanced.
Uriah

Of course. Duh! Obvious.

 

[Jacques Merde]

Q100 and Q200 are on one channel so if the combination of these two gives you a power of Y out of the B1 and the combination of Q101 and Q201 give you a power of Y+1 out of the other channel... then you have two channels that are not balanced perfectly.
If out of one channel you have Q100 giving X and Q200 giving Y and out of the other channel you have Q101 also giving X and Q201 also giving Y then both channels give you X+Y and they are balanced.
Uriah

Except that according to Nelson's schematic Q100 and Q101 are on the right channel and Q200 and Q201 are on the left channel. The matching (of Q100 with Q101 and Q200 with Q201) ensures that the upper and lower JFETs in each channel are biased with very close Vgs and Vds.

Since these operate as constant current source loaded source followers with a gain of 1, it is not necessary to match devices between channels, though it won't hurt anything if you do.

Cheers,

 

[wintermute]

The B1 buffer is essentially a voltage follower.
A voltage follower is also an essential part of a Linkwitz-Riley filter.
See this: Active Filters

Has anyone tried the B1 voltage follower as a component in a Linkwitz-Riley filter?

Rob is working on it at the moment http://www.diyaudio.com/forums/blogs/relder/142-b1-active-xos.html And I've been thinking about it but didn't have enough knowledge to realise that the B1 was suitable, as I thought you needed gain to do an active filter.

Tony.

 

[LucasAdamson]

Except that according to Nelson's schematic Q100 and Q101 are on the right channel and Q200 and Q201 are on the left channel. The matching (of Q100 with Q101 and Q200 with Q201) ensures that the upper and lower JFETs in each channel are biased with very close Vgs and Vds.

Since these operate as constant current source loaded source followers with a gain of 1, it is not necessary to match devices between channels, though it won't hurt anything if you do.

Cheers,

Yeah, that's what I was getting at. So I am right then, according to the schematic Qxxx references.

 

[udailey]

Lucas,
Sorry, I got the part numbers switched around when I read that and was thinking exactly what you were thinking. Apparently we are both wrong, or maybe not that wrong, just overly concerned? I have read a few people saying that there is no reason to match the devices in the B1.
Uriah

 

[Jacques Merde]

I have read a few people saying that there is no reason to match the devices in the B1.
Uriah

True, it is not necessary to match Vgs or transconductance. Still, I would match (or select, if you will) for Idss as Nelson suggested. In the Building a symmetrical psu B1 buffer thread good results are reported when the device with the slightly higher Idss is used in the lower position. See post #487 in that thread, and the various follow ups.