"... high frequency impedance can be important to the stability of the amplifier, particularly with more complex circuits, as the source impedance of the power supply starts figuring into the feedback at frequencies of a mega-Hertz or so. Interestingly, some designers have depended on a particular source impedance of the supply at these frequencies for stability, thus it is possible to destabilize the amplifier circuit by paralleling film capacitors across the electrolytics."
So how do we know when it's okay to use them and when not?
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Some progress today on the fully populated PCB's (except VFETS).
I powered them up and tested/adjusted them fine in the end.
Maybe this useful to some who have the multi-turn 25 trimpot Bourns 3296Y installed:
I figured out they (P3/4) work the same way mechanically as single turns, so I did not bother to check resistance gateQ5-T6; should be 0 ohm before powering up. The note show turn fully counterclockwise, however the 2396Y must be turned clockwise before power up, at least mine!
A fuse blew and somehow the Toshiba mosfets Q5/Q6 survived, I still can't believe it they did. They tested ok after re-adjust.
Just a little glitch that doesn't scare me, but these transistors are scare. The multiturns work just fine with the offset trimming.
Have still work to do on the chassis and PSU, so no sound the next few weeks. Look forward to it.
I powered them up and tested/adjusted them fine in the end.
Maybe this useful to some who have the multi-turn 25 trimpot Bourns 3296Y installed:
I figured out they (P3/4) work the same way mechanically as single turns, so I did not bother to check resistance gateQ5-T6; should be 0 ohm before powering up. The note show turn fully counterclockwise, however the 2396Y must be turned clockwise before power up, at least mine!
A fuse blew and somehow the Toshiba mosfets Q5/Q6 survived, I still can't believe it they did. They tested ok after re-adjust.
Just a little glitch that doesn't scare me, but these transistors are scare. The multiturns work just fine with the offset trimming.
Have still work to do on the chassis and PSU, so no sound the next few weeks. Look forward to it.
Just ordered one of these: Schiit Audio, Headphone amps and DACs made in USA.
And a whole lot of this: Mouser
I really love the F4+BA3FE. The combo keeps me happy. Daily. It'll be moving over for a DCB1+VFET. According to the Pano speaker efficiency test my 4ohm speakers need from 2-5 volts ( 3 volts being really loud ), so I'm thinking I'll still get plenty of volume in the 800ish sq ft space the speakers are currently parked in. Hopefully. The one stereo is frequently used to fill the whole house ( more than 800sf ). My BA3 is built exactly to the schematic, and fed with a DAC with 1.5V output. The Modi Multibit that'll feed the DCB1 and VFET amp does 2 volts out.
And a whole lot of this: Mouser
I really love the F4+BA3FE. The combo keeps me happy. Daily. It'll be moving over for a DCB1+VFET. According to the Pano speaker efficiency test my 4ohm speakers need from 2-5 volts ( 3 volts being really loud ), so I'm thinking I'll still get plenty of volume in the 800ish sq ft space the speakers are currently parked in. Hopefully. The one stereo is frequently used to fill the whole house ( more than 800sf ). My BA3 is built exactly to the schematic, and fed with a DAC with 1.5V output. The Modi Multibit that'll feed the DCB1 and VFET amp does 2 volts out.
I've populated PCBs with resistors and measured resistance between test points,
as described in Nelsons PDF.
One board with Bourns Pots is 100% on spot.
For the other board I had only Spectrol 64Y Pots, and have different values. Here I measured:
T12-T13: 260 Ohms (instead of 250)
T6-T10: 480 Ohms (instead of 430)
Resistance through 500Ohm Bourns is: 460 Ohms
Resitance through 500Ohm Spectrol is: 510 Ohms
I guess that isn't an issue, if I had used eiter Bourns or Spectrol on both channels.
Having such different pot resistances on Left and Right channel is it a problem ?
On the other hand:
Current through Q1 (2sk170) and Q2 (2sj74) would be:
I = U/R = 28V / (R35+P3+P4+R34) = 20mA, if the transistors wouldn't limit the current to about 7-8mA.
With Bourns I get theoretical 20.5mA, with Spectrol: 19.1 mA.
However, since the frontend transistors limit that to 7-8mA, it isn't any issue,
and both channels will sound the same.
Experts, is my thinking correct ?
as described in Nelsons PDF.
One board with Bourns Pots is 100% on spot.
For the other board I had only Spectrol 64Y Pots, and have different values. Here I measured:
T12-T13: 260 Ohms (instead of 250)
T6-T10: 480 Ohms (instead of 430)
Resistance through 500Ohm Bourns is: 460 Ohms
Resitance through 500Ohm Spectrol is: 510 Ohms
I guess that isn't an issue, if I had used eiter Bourns or Spectrol on both channels.
Having such different pot resistances on Left and Right channel is it a problem ?
On the other hand:
Current through Q1 (2sk170) and Q2 (2sj74) would be:
I = U/R = 28V / (R35+P3+P4+R34) = 20mA, if the transistors wouldn't limit the current to about 7-8mA.
With Bourns I get theoretical 20.5mA, with Spectrol: 19.1 mA.
However, since the frontend transistors limit that to 7-8mA, it isn't any issue,
and both channels will sound the same.
Experts, is my thinking correct ?
Why worry about pot R when it can be adjusted
Hi,
the two 500Ohm pots are in the path of the transistors.
Not sure if 2x460 Ohm on left channel PCB makes a difference vs. 2x510 ohm pots on right channel here:
