As always, I am in a problem. 🙁
Just too much current at power up. I checked again the hfe of transistors and they show the same values as before.
I suspect these ;
My Jfet is 13mA grade. Is this fine?
The small red LEDs I use give 1.3V across them without light. What is the target voltage of LEDs?
I used 10 ohm pot between sources of K170 and J74, with wiper to the 220ohm R should I increase this value?
Two channels show similar voltage with mirrored values at voltage rails, so I think I did not miserably fail. 😀😀
One thing funny I did was using the terminals for all parts..
Just too much current at power up. I checked again the hfe of transistors and they show the same values as before.
I suspect these ;
My Jfet is 13mA grade. Is this fine?
The small red LEDs I use give 1.3V across them without light. What is the target voltage of LEDs?
I used 10 ohm pot between sources of K170 and J74, with wiper to the 220ohm R should I increase this value?
Two channels show similar voltage with mirrored values at voltage rails, so I think I did not miserably fail. 😀😀
One thing funny I did was using the terminals for all parts..
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What is you current or voltages across r2/3/4/5? Your psu is 12v?
Are you saying the preamp is drawing too much current? Do you have a short or just drawing to much current across r2/3/4/5?
Are you saying the preamp is drawing too much current? Do you have a short or just drawing to much current across r2/3/4/5?
The voltages across r2/3/4/5 were more than 6V, with offset around 4.5V with no change from the center pot adjustment. Today I will check the wiring again and hopefully play with higher values of r2/3/4/5 by trimpot.
l may have to replace the small red LEDs.
l may have to replace the small red LEDs.
Yes, something is definitely not right. Check your wiring...that is much more current than expected.
😀😀😀
I found that 47R for R2 R4 were 47K...... my aging eyes made mistakes again.
I checked the sign waves, voltages across the R2~R4 all fine at 0.4~0.6VDC, and LEDs are on.
Now I am putting this into my BA-3 pre chassis ... 🙂
I got the feeling that I may not need the cap at the output.
I found that 47R for R2 R4 were 47K...... my aging eyes made mistakes again.
I checked the sign waves, voltages across the R2~R4 all fine at 0.4~0.6VDC, and LEDs are on.
Now I am putting this into my BA-3 pre chassis ... 🙂
I got the feeling that I may not need the cap at the output.
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Thank you all, now it is working.
I disconnected the signal board from my BA-3 pre and used batteries for now because the supply board cannot go to 12VDC. The output is via the 3.3uF Jupiter Bewax cap. LDR volume and DEFiSIT using 2SK182ES to Altec Valencia.
The feeling of 'SPACE' is different with this pre. Some well-recorded music makes you appreciate the stage width and depth. 🙂🙂🙂🙂
I somehow feel the sound is more solid, maybe due to this soundstage?
I'd like to thank Nelson Pass, Juma, and Hikari1 for this build.
I think I have one good pre to compare the DHT pre that I am planning.
Now I have to work out how to house this pre... 🙂
I disconnected the signal board from my BA-3 pre and used batteries for now because the supply board cannot go to 12VDC. The output is via the 3.3uF Jupiter Bewax cap. LDR volume and DEFiSIT using 2SK182ES to Altec Valencia.
The feeling of 'SPACE' is different with this pre. Some well-recorded music makes you appreciate the stage width and depth. 🙂🙂🙂🙂
I somehow feel the sound is more solid, maybe due to this soundstage?
I'd like to thank Nelson Pass, Juma, and Hikari1 for this build.
I think I have one good pre to compare the DHT pre that I am planning.
Now I have to work out how to house this pre... 🙂
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Chul, I agree. I think what makes Juma’s current mirror version special is the sense of space and the way it presents the music naturally in space. It just feels right to me.
Glad you like it too.
Glad you like it too.
No, I had actually built another of Juma's preamps amp and the follower stage to try it but I couldn't get the follower working...I am sure it can be done. But I got distracted and had to use the Jfets for another project. So I never completed the project. Plus, I have my doubts it would sound better unless you need the current drive, which I do not. But it would be nice to have for headphones. But I don't really like headphones that much...
If Juma gave us this current mirror preamp with laterals on the output I would build it.
This preamp is also the gain stage of his "cubie" amps which I am guessing sound very good as well. Maybe your next project?
Oh I see that there is Juma's follower stage too.
I have Whammy PCB and I can try the output stage only per your drawing.
Power supply is 15VDC that I can source and current is enough.
This may be easier for me than trying Cubi amp of Juma, and I can go back to the current pre any time...
I have Whammy PCB and I can try the output stage only per your drawing.
Power supply is 15VDC that I can source and current is enough.
This may be easier for me than trying Cubi amp of Juma, and I can go back to the current pre any time...
This curremt mirror pre by Juma is some thing better than a "taste" I think.
Then I feel more energy at the higher frequency compared to BA-3 pre. So I got intrigued by your drawing that seems to have the merits of both. But like you said we never knows...
Then I feel more energy at the higher frequency compared to BA-3 pre. So I got intrigued by your drawing that seems to have the merits of both. But like you said we never knows...
I put 10uF Russian oil cap, replacing 3.3uF Beewax, and the balance feels in the middle.
Or does this oil cap(?) roll off some high or does this cap break in, I do not know.
Then I checked the DC offset at the output, a few millivolts, and removed the coupling cap. Now I have this solid feeling without the cap. 🙂
DC offset seems to drift within tens of millivolts. I need to watch this for more time or in the actual case.
Or does this oil cap(?) roll off some high or does this cap break in, I do not know.
Then I checked the DC offset at the output, a few millivolts, and removed the coupling cap. Now I have this solid feeling without the cap. 🙂
DC offset seems to drift within tens of millivolts. I need to watch this for more time or in the actual case.
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Hello Zen thx for help. It is so strange a newbie like me to understand a resistor right behind out is input resistance of preamplifier.
with JFet and mosfet after it , it is , tnx to practically no gate current
with bjts it isn't the case , mostly
with bjts it isn't the case , mostly
I am eager to use LSK BAF 2013 but my dac oouput impadance is few hundered ohms. So is there any way to increase LSK BAF 2013 input impedance?