Hi Salas / All,
I removed the SSHV2 out of the equation, fitted diodes to V1 cathodes and did a rewire. Used a proper copper ground bus and following Frans grounding scheme minus the chassis ground resistor & diode bit.
Straight CRC passive PSU 294VDC B+ and the copper ground to the negative side of the PSU.
Much better, I have to turn the volume up to the point I hear valve hiss, and some hum, but the music would be very loud.
The next stage would be to reintroduce the SSHV2, I am a little confused with connecting FOS & S+F.
Do I connect S+F to V4 pins 2&5, and the copper ground bus to FOS with a link wire.
A couple of noob questions:
How do I check the 1.36mA and 3.5mA biasing of the valves?
How do I check channel balance?
It is sounding very good so far, cant wait to have it fully sorted
Many Thanks
Ian
Ian hi, now this rework looks much better. Congrats.
As Massimo wrote you could check any resistor in series to a valve in each stage totem. Using Ohm's law you can divide the voltage drop across a resistor by its value. That is the current.
For gain you would need some 1kHz test signal in the low mV range as Massimo also wrote, although having near current values between channels stages is a first ballpark step.
After you will fit a proper for dimensions cap in the reg (even of typical industrial quality) and you will recheck on dummy load its working good, you will apply Force plus and Sense plus to a central B+ node common and equidistant between channels towards the output stages. You will apply Force 0 and sense 0 to a ground node common and equidistant between channels towards the output stages. Without local shorting links hopefully this time.
I use a DIY SUT based on 1: 10 OEM JT-115EPC Jensen microphone transformers .
http://i.ebayimg.com/00/s/NjY3WDg1NQ==/z/p3AAAMXQlgtS6Rxg/$_57.JPG
The cartridge is a MC AT/F3-III with 0.35 mV out.
The phono previo is a ECC83 classic RCA, but de out-Z is too high.This is the problem.
I use also uncommon balanced connection between SUT and cartridge.It works fine , very noisless at this delicate place.The load is 47kohm at secundary.No add an other resistence for low the input load and EQ.I need "Grid -stoppers" because I can heard very clair Radio Mongolia without them.
Cheers
Last edited:
Hi Salas / All,
Im back from a two week holiday, now to pick up the Itch
Salas told me "As Massimo wrote you could check any resistor in series to a valve in each stage totem. Using Ohm's law you can divide the voltage drop across a resistor by its value. That is the current. "
fitted diodes to V1 cathodes, still Rev1.1.
I'm not sure I have measured or calculated properly, but V3 is way out.
here are the results;
B+293, no SSHV2 yet.
V1
pin 1=102
p6 =112
V3
p1=275
p2=274
p3=173
p8=182
50K 190v check = left 172v right 181v.
Voltage drop across R1 47 Ohm
Left 173.3 - 173.1 = 0.2 drop = 4.26ma
Right 181.8 - 181.7 =0.1 drop = 2.13ma
V2
p2=91
p5=93
p3=1.96
p6=1.93
Voltage drop across 560 Ohm cathode to ground
Left 1.96 - 0.2v = 1.76 drop = 3.14ma
Right 1.93 - 0.2v = 1.73 drop -3.09ma
Can you steer me in the right direction?
Many thanks
Ian
Im back from a two week holiday, now to pick up the Itch
Salas told me "As Massimo wrote you could check any resistor in series to a valve in each stage totem. Using Ohm's law you can divide the voltage drop across a resistor by its value. That is the current. "
fitted diodes to V1 cathodes, still Rev1.1.
I'm not sure I have measured or calculated properly, but V3 is way out.
here are the results;
B+293, no SSHV2 yet.
V1
pin 1=102
p6 =112
V3
p1=275
p2=274
p3=173
p8=182
50K 190v check = left 172v right 181v.
Voltage drop across R1 47 Ohm
Left 173.3 - 173.1 = 0.2 drop = 4.26ma
Right 181.8 - 181.7 =0.1 drop = 2.13ma
V2
p2=91
p5=93
p3=1.96
p6=1.93
Voltage drop across 560 Ohm cathode to ground
Left 1.96 - 0.2v = 1.76 drop = 3.14ma
Right 1.93 - 0.2v = 1.73 drop -3.09ma
Can you steer me in the right direction?
Many thanks
Ian
Hi salas/ all,
Updated to rev 1.2, fitted ft3 0.1uf caps and the caps Fran Kindly sent me, one had
15.743uf written on it
Latest measurement's.
B+ 268 vdc
165v checkpoint, left=146v, right 157v
190v checkpoint, both =172v
V2 left=4.88mA, right=4.79mA
V3=0.55ma both
V4 left=5.32mA, right=5.25mA.
HiFi news 300hz tone, measured left=2.6mvac, right=2.8mvac, from my grado gold cartridge, 4mv output I think.
How does it look?
Cheers, Ian.
Updated to rev 1.2, fitted ft3 0.1uf caps and the caps Fran Kindly sent me, one had
15.743uf written on it
Latest measurement's.
B+ 268 vdc
165v checkpoint, left=146v, right 157v
190v checkpoint, both =172v
V2 left=4.88mA, right=4.79mA
V3=0.55ma both
V4 left=5.32mA, right=5.25mA.
HiFi news 300hz tone, measured left=2.6mvac, right=2.8mvac, from my grado gold cartridge, 4mv output I think.
How does it look?
Cheers, Ian.
You may reduce distortion and noise by replacing the second SRPP with this circuit.
Attachments
I'm also puzzled by the reference to reduced distortion - in my experience a real world mu-follower implementation is generally more linear than an SRPP provided that the external load impedance is reasonable for the operating point chosen. (i.e appreciable power is not required - if otherwise the SRPP can do quite well into the appropriate load impedance.)