I replace 0,1uf capacitor insats 0,22uf , now my preamp have +/-5mW sometimes +/-8mW DC change fast but Voltage more often +/-5mW , can you tell me why voltage is minus please ?
Is that ok my pre 145V insats 130V in cap ?
Sorry for english
With grade capacitor recommend you?
I use also 4x 0,22uf cap for phono stage! Must i change they ?
Many tanks😊🙏🏼
Is that ok my pre 145V insats 130V in cap ?
Sorry for english
With grade capacitor recommend you?
I use also 4x 0,22uf cap for phono stage! Must i change they ?
Many tanks😊🙏🏼
Attachments
Sorry my preamp have DC output
-/+3mW when it is no concet to my Jadis tube amp,when i conect that to my amp and play music i have -/+3 mv, high volym i have -/+ 6mW.
Thanks
A few thoughts:
- In spite of its shortcomings, the Jadis is a much better match for your preamp, the main reason is: tube amps don't pass DC, so any disturbances at the input are ignored. As a bonus, the higher input impedance will not load down your preamp. If it were me, I'd forget about the Hiraga.
- I don't feel too comfy with the Miflex you use: the paper inside can become leaky. In order to be absolutely sure, temporarily replace them with some polypropylene caps (KP or MKP), 400V+, and test again.
- Unlikely, but not impossible, the input transistors of the Hiraga may be faulty. The best fix would be to build EUVL's updated version, with JFet's at the input.
- Unlikely, but not impossible, the power supply of your M77 may be faulty. use 2 DMM, at each end of the output cap, and observe over several minutes if there's any drift.
you are 100% right, kondo doesn't work well with Jean Hiraga!
when my Hiraga 30W is warm have from 0 to -/+ 6mV DC offset with close input and with open input -310mV!
I think allso that -310mV was from Hiraga not from Kondo .
But when it is cold have +70, 80mV DC offset , all parts is matched 1% and all PNP,NPN 2%
i have questions Is my Hiraga work good?
I want to try 0,15uf 400V for my preamp, but my pre amp work good with 0,1uf better that 0,22uf !
Many Thanks
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Ah ha! The culprits!
At the input, the NPN and the PNP have base currents, and their temperature coefficients are not the same. Poor design!
Stay with the Jadis. 🙂
The output stage is a cap followed by a 1Meg resistor to ground, to properly charge that cap so that the output voltage is zero (some time after startup, obviously). Can you please measure the DC offset at the output - without load - after some time, say 5min, to be sure? It should read zero.
The input stage of a following power amp may develop some DC across that 1Meg resistor, depending on the (DC) input current, as Zung stated - not surprising. This may lead to a shift in operating point in the power amp. Best to put a resistor (say 100k) to ground at the input of the power amp, to reduce that voltage.
Zung is also right concerning the lower corner frequency of the combination. Output cap of 0.22uF with input resistance of 100k gives a -3dB corner of 8Hz. 10k will give ~80Hz.
Best to combine with a tube power amp with 100k input impedance.....
Zung is also right concerning the lower corner frequency of the combination. Output cap of 0.22uF with input resistance of 100k gives a -3dB corner of 8Hz. 10k will give ~80Hz.
Best to combine with a tube power amp with 100k input impedance.....
Hi
My Kondo have variable DC offset -5mV and +5mV without load and open input…
I have questions how much DC is normal in output for tube preamp?
Many Thanks
My mono jadis
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Hi Tomas, thanks for this information. I think that with a cap-coupled output (or transformer-coupled output, which is rare in preamps / line stages) the output voltage should be zero.
Now, it is always possible to couple some noise into your measurement, so I would not worry about the +/- 5mV. When I take my DMM and short the inputs, that is what I usually get 😀
Hi 👋🏼
1: I replace 2nF capacitor (this from my Dynaco ) insats 0,1uf , now my preamp have +2/3 mV and this doesnt have negative mV now DC output and when i to connect Jadis and DAC , DC offset is +09mV maximum +1 mV .
2: I change the cathode resistor to 57K ohm .
3: can you help me with gnd please ?! I don't where is (gnd screen ) in my transformer and how can i fix that i attach photo of that !
Thanks
1: I replace 2nF capacitor (this from my Dynaco ) insats 0,1uf , now my preamp have +2/3 mV and this doesnt have negative mV now DC output and when i to connect Jadis and DAC , DC offset is +09mV maximum +1 mV .
2: I change the cathode resistor to 57K ohm .
3: can you help me with gnd please ?! I don't where is (gnd screen ) in my transformer and how can i fix that i attach photo of that !
Thanks
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Hi
you mean i replaced 2K resistor with 100K in my amplifier? I change resistor befor that was 2K see schematic please.
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I am not profesional sorry 😅
It is my misunderstanding
1 you say:
Best to put a resistor (say 100k) to ground at the input of the power amp, to reduce that voltage.
Mean you put 100k resistor same this photo ?
Or how i put resistor, can draw schematics please!?
I am not professional sorry for that
Many Thanks
It is my misunderstanding
1 you say:
Best to put a resistor (say 100k) to ground at the input of the power amp, to reduce that voltage.
Mean you put 100k resistor same this photo ?
Or how i put resistor, can draw schematics please!?
I am not professional sorry for that
Many Thanks
Attachments
@tomashans
Think it helps, if you read properly what´s written.
In the amp, that is connected to the KSL-M77, NOT in the KSL-M77.
Or easier....... 100Kohm across the rca-plug, that connects to your poweramp 😉
