I fixed it!
Yes. Turns out that R3 does require its original position. I simply relocated one end of R3 to a pad on the fet drain trace on both sides of the amp, and the dc offset settled right down.😀 Today, I will get to listen to it for the first time. I can't wait to see if the buffers make an inprovement.
Happy, happy, happy.
John🙂
babowana, I just borrowed Nelson's feedback configuration for ZV4.
Yes. Turns out that R3 does require its original position. I simply relocated one end of R3 to a pad on the fet drain trace on both sides of the amp, and the dc offset settled right down.😀 Today, I will get to listen to it for the first time. I can't wait to see if the buffers make an inprovement.
Happy, happy, happy.
John🙂
babowana, I just borrowed Nelson's feedback configuration for ZV4.
I fired it up.
And what I don't understand is why the buffer has less gain than when I bypass it at the coupling cap. When played at the coupling cap, the volume is nearly double!
The amp is just georgous sounding; I can't believe Nelson has given us such a gift!
John🙂
And what I don't understand is why the buffer has less gain than when I bypass it at the coupling cap. When played at the coupling cap, the volume is nearly double!
The amp is just georgous sounding; I can't believe Nelson has given us such a gift!
John🙂
I thinking of trying a few little mods to my buffer. It seems to me that the buffer should allow the amp to play louder than just hooking the preamp up to the primary gain stage as in the original ZV7-T. For some reason, my buffer dampens the amp's output. I'm borrowing ideas from Nelson's Zen Blues.
When bypassing my buffer stage, the amp sounds so sweet. I'm using a TDM active crossover to drive the ZV7-T.
John🙂
When bypassing my buffer stage, the amp sounds so sweet. I'm using a TDM active crossover to drive the ZV7-T.
John🙂
Attachments
Thank-you Choky!
My little folder, called "Choky's stuff", is getting larger all the time🙂
John
My little folder, called "Choky's stuff", is getting larger all the time🙂
John
I just wanted to thank you, babowana, for pointing this observation out to me. In Nelson's "Zen for Blues" I see that you can send dc to the gate, but only if you reference to ground. Your suggestion made me wake up and explore the entire feedback loop.
You're a gem🙂
John
Well now... I just soldered in a 221K resistor from the gate to ground of both ZVP3310s.
Now I have the most realistic sound of the ocean coming from my horn!
Back to the drawing board.
btw, the gate voltages are not the same. One is 3v the other is around 15v. The resistance value at one buffer gate is 110K, the other is 37K. Perhaps the 37K fet is blown?
John🙂
Now I have the most realistic sound of the ocean coming from my horn!
Back to the drawing board.
btw, the gate voltages are not the same. One is 3v the other is around 15v. The resistance value at one buffer gate is 110K, the other is 37K. Perhaps the 37K fet is blown?
John🙂
One of the buffer fets (the one with the 37K resistance) died; the funeral will be held this Monday.😀
Ok, now the volume through the buffers is better, but the amp plays with less authority than when I drive the gates of the IRF044N transistors. The upshot is that the highs (symbols, high-hat, etc.) are more noticeable!
How do I lower the input impedance of the buffers?
Obviously, there's more to learn...
John🙂
Ok, now the volume through the buffers is better, but the amp plays with less authority than when I drive the gates of the IRF044N transistors. The upshot is that the highs (symbols, high-hat, etc.) are more noticeable!
How do I lower the input impedance of the buffers?
Obviously, there's more to learn...
John🙂
One of the buffer fets (the one with the 37K resistance) died; the funeral will be held this Monday.😀
Ok, now the volume through the buffers is better, but the amp plays with less authority than when I drive the gates of the IRF044N transistors. The upshot is that the highs (symbols, high-hat, etc.) are more noticeable!
How do I lower the input impedance of the buffers?
Obviously, there's more to learn...
John🙂
Ok, now the volume through the buffers is better, but the amp plays with less authority than when I drive the gates of the IRF044N transistors. The upshot is that the highs (symbols, high-hat, etc.) are more noticeable!
How do I lower the input impedance of the buffers?
Obviously, there's more to learn...
John🙂
John, I was just wondering, why did you go to the buffer input anyway? I went back and started re reading this thread but, I just thought it would be quicker to ask😀
And as long as I'm asking, what are you currently using as the load L😕
Also have you had any destruction you might attribute to the big chokes doing a flyback thing? Have you always had those 36 ohm Rs in there?
BTW, have you seen the Pathos Amps and http://www.diyaudio.com/forums/showthread.php?s=&threadid=10258&perpage=10&pagenumber=1
Or http://www.diyaudio.com/forums/showthread.php?s=&threadid=24737&perpage=10&highlight=&pagenumber=1
Thought you might find some of that interesting
And as long as I'm asking, what are you currently using as the load L😕
Also have you had any destruction you might attribute to the big chokes doing a flyback thing? Have you always had those 36 ohm Rs in there?
BTW, have you seen the Pathos Amps and http://www.diyaudio.com/forums/showthread.php?s=&threadid=10258&perpage=10&pagenumber=1
Or http://www.diyaudio.com/forums/showthread.php?s=&threadid=24737&perpage=10&highlight=&pagenumber=1
Thought you might find some of that interesting
Hi flg,
I have lost a dozen large transistors in the past. What helped was connecting a cheap speaker to the amp as I dialed it in -- I use a variac.
The current amp has the 36ohm resistors you mentioned, and came up to speed without a hitch. Perfect results.
I tried the buffer out of curiosity. It does deliver more delicate high notes, but I have to run my crossover at full gain for the ZV7-T. When I run straight to the big transistors (bypassing the buffer) I can turn the x-over back down.
Since I use this amplifier from 450hz to 20K I only need two air-core, 10mH chokes wound on the same bobbin. I've compared the ZV7-T channel to the other (Hafler P-3000) and they sound like they cover the same frequency. The Hafler does a fine job, but isn't buttery-smooth like the ZV7. So I'm quite comfortable with the current choke arrangement.
Thanks for the lead on the Pathos amp. As you can gather, I need all the educating I can get.🙂
Good to chat with you,
John
I have lost a dozen large transistors in the past. What helped was connecting a cheap speaker to the amp as I dialed it in -- I use a variac.
The current amp has the 36ohm resistors you mentioned, and came up to speed without a hitch. Perfect results.
I tried the buffer out of curiosity. It does deliver more delicate high notes, but I have to run my crossover at full gain for the ZV7-T. When I run straight to the big transistors (bypassing the buffer) I can turn the x-over back down.
Since I use this amplifier from 450hz to 20K I only need two air-core, 10mH chokes wound on the same bobbin. I've compared the ZV7-T channel to the other (Hafler P-3000) and they sound like they cover the same frequency. The Hafler does a fine job, but isn't buttery-smooth like the ZV7. So I'm quite comfortable with the current choke arrangement.
Thanks for the lead on the Pathos amp. As you can gather, I need all the educating I can get.🙂
Good to chat with you,
John
carpenter said:
I think that the input signal sees
47.5K
ZVP3310's Gate (Very high R so ignorable as an open)
221K (to the ground)
221K (to the output)
Therefore the answer might be
Reduction factor x (each of 47.5K, 221K, 221K)
Papa's values are not absolute
We could cook them for our taste, maybe better taste 😀
By the way
Now your Vdc across ZVP3310's DS is about 23/2+4=16V
Mmm . . .
30-16=14V
14/1.6=9mA (ZVP bias current)
You could increase this ZVP bias current a bit higher if you want
by reducing R13 of 1.5K
And
I recommend to have input coupling cap in front of 47.5K (R2)
Regards,
Hi babowana,
I added a parallel resistor to R2 so that value is now 23.75K. I'm also thinking about lifting the R4 resistor (as an experiment). Now, if I do that, then I probably need to run a resistor from the buffer gate to ground. But, I remember the static I created when I added 221K resistor gate to ground earlier today. Maybe that's not such a good idea...
I might just add a series resistor to R4. Wouldn't this eliminate some of the feedback? Feedback reduces gain; yes I remember that this is a unity gain device.
Making R13 a smaller value will create more amperage, will that make a stronger signal to the IRF044ns?
I am rambling a bit here...
You know what? Maybe I should add drain resistance, draw from the drain and just make the buffer a gain device.🙂 Can the N channel IRF044 use a drain signal from a P channel mosfet?
John
I added a parallel resistor to R2 so that value is now 23.75K. I'm also thinking about lifting the R4 resistor (as an experiment). Now, if I do that, then I probably need to run a resistor from the buffer gate to ground. But, I remember the static I created when I added 221K resistor gate to ground earlier today. Maybe that's not such a good idea...
I might just add a series resistor to R4. Wouldn't this eliminate some of the feedback? Feedback reduces gain; yes I remember that this is a unity gain device.
Making R13 a smaller value will create more amperage, will that make a stronger signal to the IRF044ns?
I am rambling a bit here...
You know what? Maybe I should add drain resistance, draw from the drain and just make the buffer a gain device.🙂 Can the N channel IRF044 use a drain signal from a P channel mosfet?
John
carpenter said:
I think that you need to run a resitor to the ground in any case
Otherwise, the buffer gate will always see all DC of +23V
Then, we will lose good chance to control the DC level across R9 and R13
carpenter said:
I think it would provide enough (or more than enough) current to the input capacitace of the power mosfet, and might improve high frequency response
And again I highly recommend input coupling caps
I always protect source seeing DC directly through the input node
Regards,
I always protect source seeing DC directly through the input node
Regards,
Thanks for taking the time to read and offer suggestions, babowana. I will study and ponder your thoughts.
I listened to my system for an hour tonight. With the buffer stage, the highs are much more apparent. I can hear detail that is missing when running the preamp to the gates of the power fets. The buffer does lose a smidgen of mid-range vigor--how unfortunate. Still, I'm quite pleased to have such detail on the top-end. The buffers will remain part of my amp's repertoire. I just have to learn how to use them to their best advantage.
My poor, little Hafler P-3000 just doesn't stand a chance against the ZV7. It's driving the right channel horn. Although it has plenty of guts, there's just no flavor.
I tried connecting 221K resistors from gate to ground earlier today. The horn made the most beautiful hiss I've ever heard. Pink noise would be the closest guess. I must admit that one of the buffer fets was dead at the time. I may give it another shot later, but I must admit that I love the dead quietness of this amplifier. A speck of dust lofting onto the floor makes more noise.
Have a wonderful day,
John🙂
I listened to my system for an hour tonight. With the buffer stage, the highs are much more apparent. I can hear detail that is missing when running the preamp to the gates of the power fets. The buffer does lose a smidgen of mid-range vigor--how unfortunate. Still, I'm quite pleased to have such detail on the top-end. The buffers will remain part of my amp's repertoire. I just have to learn how to use them to their best advantage.
My poor, little Hafler P-3000 just doesn't stand a chance against the ZV7. It's driving the right channel horn. Although it has plenty of guts, there's just no flavor.
I tried connecting 221K resistors from gate to ground earlier today. The horn made the most beautiful hiss I've ever heard. Pink noise would be the closest guess. I must admit that one of the buffer fets was dead at the time. I may give it another shot later, but I must admit that I love the dead quietness of this amplifier. A speck of dust lofting onto the floor makes more noise.
Have a wonderful day,
John🙂
Yesterday, I took a volt-ohm meter to my cross-over's output. There was no dc voltage what-so-ever. If I build an amp for a friend, I'll be certain to include the input caps.
Many thanks for your concern,
John🙂
Many thanks for your concern,
John🙂
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