Hi All
Phono assembled
I realize that I have low AC Voltage at home (216-220) so low AC out (~34.8AC) and low DC raw output
One channel seems alright but not sure
DC Raw 45-46
Rail + 34,3V Max out, 33.140V for TP1-TP2=3.60V, VR1x=1.582V ~ 105ma CCS
R3x=6k2 Q3x, Q5x ~ 5mA
The others seems to have a little problem
DC Raw 45-46
Rail + 26.8 - 28,9V Max out, TP1-TP2=7.68V, VR1x=1.61V ~ 107.3ma CCS
R3x=6k2 Q3x, Q5x ~ 5mA
what should I look for?
Phono assembled
I realize that I have low AC Voltage at home (216-220) so low AC out (~34.8AC) and low DC raw output
One channel seems alright but not sure
DC Raw 45-46
Rail + 34,3V Max out, 33.140V for TP1-TP2=3.60V, VR1x=1.582V ~ 105ma CCS
R3x=6k2 Q3x, Q5x ~ 5mA
The others seems to have a little problem
DC Raw 45-46
Rail + 26.8 - 28,9V Max out, TP1-TP2=7.68V, VR1x=1.61V ~ 107.3ma CCS
R3x=6k2 Q3x, Q5x ~ 5mA
what should I look for?
Thanks Nick
Replaced R3x with 9k1 and fixed
I have two more questions
1. Do I need to raise Raw DC for better CCS, if I can do it?
2. I see that Tp1-TP2 voltage has a lot of flactuation (i.e from 3.570-3.630) is that normal?
Thanks
Replaced R3x with 9k1 and fixed
I have two more questions
1. Do I need to raise Raw DC for better CCS, if I can do it?
2. I see that Tp1-TP2 voltage has a lot of flactuation (i.e from 3.570-3.630) is that normal?
Thanks
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1. No because you have more than 10V vin-vout already which is good enough and the CCS sink heat will be alright also.
2. Its normal in MC builds due to the K369s thermal behavior when there isn't high Rs to provide much local feedback like in MM builds. That thermal sensitivity will be much more evident in TP voltage shift if you will blow air over them. You can try enclose them in a a mini box of thick paper with foam in it so they will be in a steadier temperature local environment.
2. Its normal in MC builds due to the K369s thermal behavior when there isn't high Rs to provide much local feedback like in MM builds. That thermal sensitivity will be much more evident in TP voltage shift if you will blow air over them. You can try enclose them in a a mini box of thick paper with foam in it so they will be in a steadier temperature local environment.
48db gain
Salas
I have been using the phono pre for a couple of years now with great results. The only issue I have is that the output is a bit low at 42db and a bit high at 57db. Can I wire this to hit a mid point, say 50db?
John
Salas
I have been using the phono pre for a couple of years now with great results. The only issue I have is that the output is a bit low at 42db and a bit high at 57db. Can I wire this to hit a mid point, say 50db?
John
Nick
What problem may occur, if any, if the 7.75V reference is as low as 7.67 or little lower due to lower Rail Voltage I have?
Thanks
What problem may occur, if any, if the 7.75V reference is as low as 7.67 or little lower due to lower Rail Voltage I have?
Thanks
Posting some images of the Phono build
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Has not to do with rail voltage, its just the total VF of your four LEDS. The ones I used in my prototype where kinda strong generics hence the 7.75V listed. Its not a problem.
Interesting signal capacitors. Are the little black ones in the RIAA circuit NOS film & foils? Are the SUFLEX interstage couplers NOS polysterene?
There can be some adjustment of resistor values to recommend for your intermediate target gain. But first I need to know your cartridge model and the IDSS of the K369 you have installed.
I build a small circuit on a pre-board that is part of the bias of the phono circuit as shown in the photo below to adjust the correct bias Voltage (7.75V) before installation. I did apply 35-36V on top and I replace the Fet so I can take exactly 7.75V. Now with lower Rail (~33V) IDSS is lower so the VF from leds (a little lower but at the lower end of 1%, as required)
An externally hosted image should be here but it was not working when we last tested it.
RIAA caps are MKP1837 I bought from Farnel, I just had 10 of them to match them better.
Suflex are NOS Polysterene, yes!
I think there is no difference, at DC at least. You are right on the Ib current. Do you think to replace the fet with a stronger one? Is any reason ?
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Also the cascode transistor steals Ib current. So its normal to lose little VF when in the full circuit.
