Using the slightly lower rated jFET as the sink means that the upper amplifying jFET is running at just below 100% of Idss. This ensures that the upper jFET has a -ve Vgs and that appears as a small negative output offset at the output terminals.
A 1mA difference in jFET Idss will result in a big output offset.
Read D.Feucht on how to remove that output offset.
Add Rsu into the source leadout of the upper jFET.
A 1mA difference in jFET Idss will result in a big output offset.
Read D.Feucht on how to remove that output offset.
Add Rsu into the source leadout of the upper jFET.
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B1+ Copland CTA505 power amp
Hello all,
I am considering buying a Copland CTA505 amplifier.
Since I already have a built B1 preamp I was wondering:
- how will the B1 pre work with such an amplifier?
Hifiengine ( specs ) : Copland CTA505 - Manual - Valve Power Amplifier - HiFi Engine
Hello all,
I am considering buying a Copland CTA505 amplifier.
Since I already have a built B1 preamp I was wondering:
- how will the B1 pre work with such an amplifier?
Hifiengine ( specs ) : Copland CTA505 - Manual - Valve Power Amplifier - HiFi Engine
woody,
Don't worry about the slight deviation from 2/V, it's unimportant as this is a B1 and not a DCB1.
Don't worry about the slight deviation from 2/V, it's unimportant as this is a B1 and not a DCB1.
I just got my B1 Buffer board with matching JFETs.
Question: Can this be modified to eliminate the extra input (really only need one input) and avoid the selector switch and extra wiring? Is it a simple matter of a few jumper wires or something? Just wondered if someone has done this as a simplification.
Thanks!
Question: Can this be modified to eliminate the extra input (really only need one input) and avoid the selector switch and extra wiring? Is it a simple matter of a few jumper wires or something? Just wondered if someone has done this as a simplification.
Thanks!
I just soldered a permanent jumper wire to input 1 where the selector switch would go -- others have done the same.
Single input
Would you happen to have a pic of your board with the jumper? Just one wire is all that's necessary?
Thanks!
Would you happen to have a pic of your board with the jumper? Just one wire is all that's necessary?
Thanks!
Odd question: But why delete what you don't need... Today?
Could be clever and simpler to build it and simply not use it..
until you need to 😉
Could be clever and simpler to build it and simply not use it..
until you need to 😉
Disabling the external switch actually requires adding 2 small jumpers. So nothing is being deleted... 😀
Sorry for the tiny photos, it's all I can find...
The jumpers are the bare wire bridges in the middle, from R2 and L2 to the unlabeled pads in the middle. Mostly obscured by blue wire... :/
And you can see where the inputs attach, above those pads coming from the rotary switch.
EDIT - here's a bigger photo -
The jumpers are the bare wire bridges in the middle, from R2 and L2 to the unlabeled pads in the middle. Mostly obscured by blue wire... :/
And you can see where the inputs attach, above those pads coming from the rotary switch.
EDIT - here's a bigger photo -
An externally hosted image should be here but it was not working when we last tested it.
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A3 attenuator wiring
Would anyone be so kind to draw where the connections should be? I'm left 😕 since there are six volume connectors on the B1 however eight on the A3 attenuator.
Thanks
Would anyone be so kind to draw where the connections should be? I'm left 😕 since there are six volume connectors on the B1 however eight on the A3 attenuator.
Thanks
1) Please look at the traces on the a3 and see if each channel's G are connected.
2) b1 W and a3 OUT are connections. That I'm sure of.
3) b1 CW is most likely a3 IN
4) b1 CCW is most likely a3 G
Do this on both channels.
the worst that will happen is the pot will act backwards, if so, swap CW with CCW
2) b1 W and a3 OUT are connections. That I'm sure of.
3) b1 CW is most likely a3 IN
4) b1 CCW is most likely a3 G
Do this on both channels.
the worst that will happen is the pot will act backwards, if so, swap CW with CCW
The G are not connected? Strange.
Can you post the schematic? I'd like to see how it's made. I suspect it may not work properly with one set open...
In the time being, use the G near the output.
Can you post the schematic? I'd like to see how it's made. I suspect it may not work properly with one set open...
In the time being, use the G near the output.
6L6's wiring directions were spot on for the A3 attenuator. I'm powering mine with two 9v batteries wired in series and it sounds phenomenal. I only have 9400uf and will have 30,000uf when my Digi-Key order gets here. Much better than my old Denon 2808CI running as a preamp which died.
So far what I noticed immediately:
- The B1 just gets out of the way
- Sounds more dynamic when the movies/music calls for it.
- Chimes, bells, buzzes, swooshing of a coat. They all sound more noticeable and distinct.
Using a Luxman M-02 as the amp and Pioneer BS22 speakers. Must say I am impressed as I know these are not the best speakers yet I was able to notice the difference quite easily. Curious just how great it would be if I finished my DIY speakers or still owned my Energy Reference RC70 speakers.
Must admit though I think I am the first to use a cardboard box...
So far what I noticed immediately:
- The B1 just gets out of the way
- Sounds more dynamic when the movies/music calls for it.
- Chimes, bells, buzzes, swooshing of a coat. They all sound more noticeable and distinct.
Using a Luxman M-02 as the amp and Pioneer BS22 speakers. Must say I am impressed as I know these are not the best speakers yet I was able to notice the difference quite easily. Curious just how great it would be if I finished my DIY speakers or still owned my Energy Reference RC70 speakers.
Must admit though I think I am the first to use a cardboard box...
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Just thought I would add that I would not recommend 9v batteries wired in series. It sounds phenomenal but not for long. The batteries will only last 1-2 days if not disconnected at night. Also, common sense for most but turn off the amp first or experience a large pop...So easy to accidentally forget that lol
Pros
- Sounds phenomenal at first
- Easy and safe
Cons
- Sound quality begins to diminish after only a few hours. I assume from the voltage dropping
- Only powers the B1 Buffer for 24-36 hours continuously
- It will last longer than 36 hours but will lose volume. Sooner or later volume is at max and sounds very flat. Eventually it will start crackling.
- 9v batteries are expensive when they only last a day or two
I would recommend two SLA 12v batteries wired in series instead. Upgrade the 25v filter caps to 35v first though.
- SLA batteries are rechargeable unlike most 9v batteries
- Outputs 24v in series and a voltage drop will not matter as much at all since 18v is the minimum.
- SLA batteries have 5-12 Amps while 9v batteries only have 500 mah
Pros
- Sounds phenomenal at first
- Easy and safe
Cons
- Sound quality begins to diminish after only a few hours. I assume from the voltage dropping
- Only powers the B1 Buffer for 24-36 hours continuously
- It will last longer than 36 hours but will lose volume. Sooner or later volume is at max and sounds very flat. Eventually it will start crackling.
- 9v batteries are expensive when they only last a day or two
I would recommend two SLA 12v batteries wired in series instead. Upgrade the 25v filter caps to 35v first though.
- SLA batteries are rechargeable unlike most 9v batteries
- Outputs 24v in series and a voltage drop will not matter as much at all since 18v is the minimum.
- SLA batteries have 5-12 Amps while 9v batteries only have 500 mah
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