Variations
I built a board this weekend using the nulling circuit. Need to dial a couple of items to power properly.
Is the gain controlled by the ratio of the 620 ohm resistor to the 330? I do not need gain in my system, a unity gain buffer gives a nice range and rotation on the volume pots.
I was thinking of using matched value resistors here to lower the gain. Something like 480/480.
George
I built a board this weekend using the nulling circuit. Need to dial a couple of items to power properly.
Is the gain controlled by the ratio of the 620 ohm resistor to the 330? I do not need gain in my system, a unity gain buffer gives a nice range and rotation on the volume pots.
I was thinking of using matched value resistors here to lower the gain. Something like 480/480.
George
Thanks YLS for the schematic. I enjoy seeing Carlos's work and others.
It helps me in my thinking process (e.g. what are others seeing.)
Carlos, do you think that adjusting the actual negative rail voltage, with a trimming pot on the negative voltage regulator's leg, may adjust the offset?
Probably a stupid idea.
Bruce
It helps me in my thinking process (e.g. what are others seeing.)
I believe you even more Carlos. I appreciate your working at making a good circuit.carlosfm said:
Carlos, do you think that adjusting the actual negative rail voltage, with a trimming pot on the negative voltage regulator's leg, may adjust the offset?
Probably a stupid idea.
Bruce
BC said:Carlos, do you think that adjusting the actual negative rail voltage, with a trimming pot on the negative voltage regulator's leg, may adjust the offset?
Probably a stupid idea.
Bruce
Pffff... probably. 😀
Sorry, tried to edit, but it was to late. It was a LONG day for me today..... brain is rattling.
😴
😴With a 10K pot infront, now the stand-alone AD815 pre is using to drive my HD600, it could also be an wonderful inexpensive headphone amp.
Dumb *** question
[QUOTE
In that case use 560R for feedback (R5), and remove the 330R resistor to ground (R4 on my schematic).
PS: 620R is not far, you can keep it for feedback. [/B][/QUOTE]
So getting rid of the resistor to ground will lower the gain? I expected the opposite.
I thought matching the value of the two resistors would lower the gain to 2.
Mine is built with both as 480 ohms. When I return home it will get played with.
Love new circuits that are easy to build! I need to play with my camera, the software is not user friendly to shrink down to diyaudio.com friendly.
George
[QUOTE
In that case use 560R for feedback (R5), and remove the 330R resistor to ground (R4 on my schematic).
PS: 620R is not far, you can keep it for feedback. [/B][/QUOTE]
So getting rid of the resistor to ground will lower the gain? I expected the opposite.
I thought matching the value of the two resistors would lower the gain to 2.
Mine is built with both as 480 ohms. When I return home it will get played with.
Love new circuits that are easy to build! I need to play with my camera, the software is not user friendly to shrink down to diyaudio.com friendly.
George
Looking good
That is a really nice looking layout. I hate to show mine done with the SIP leaded version. It looks like rats built it.
Is it completed now? How are the sonics?
George
That is a really nice looking layout. I hate to show mine done with the SIP leaded version. It looks like rats built it.
Is it completed now? How are the sonics?
George
Re: Looking good
thanks George
the preamp is completed and up and running. i quickly took it out to take the pictures.
regarding the sonics. well i couldn't ask for better this is the best I ever heard.
I have one more test to run and that is using a higher value resistor with a film cap on the PI circuit. I will do some listening tonight to see if there were any change from my previous version. the PCB that i made allows for film caps and back to back electrolytic caps
I have a DC offset of 125mv before using the PI circuit and with that i think I can live with
Panelhead said:
thanks George
the preamp is completed and up and running. i quickly took it out to take the pictures.
regarding the sonics. well i couldn't ask for better this is the best I ever heard.
I have one more test to run and that is using a higher value resistor with a film cap on the PI circuit. I will do some listening tonight to see if there were any change from my previous version. the PCB that i made allows for film caps and back to back electrolytic caps
I have a DC offset of 125mv before using the PI circuit and with that i think I can live with
Re: Dumb *** question
George,
Didn't you say you don't need gain?
I was recommending you a gain of 1 (buffer).
You can't remove the feedback resistor and make a shunt, this is a current feedback opamp and you must stick to approximate values of what the manufacturer recommends, if you want to be out of troubles.
480R is not far from the recommended values, though.
Panelhead said:
George,
Didn't you say you don't need gain?
I was recommending you a gain of 1 (buffer).
You can't remove the feedback resistor and make a shunt, this is a current feedback opamp and you must stick to approximate values of what the manufacturer recommends, if you want to be out of troubles.
480R is not far from the recommended values, though.
Another not so smart question
I did not follow what you meant about removing the 330 ohm resistor to ground. Is the completely remove?
Reduced gain is my real aim here. With a normal preamp of 15 -20 db the volume pots are hair trigger. My system makes up for this by having high efficiency speakers.
Gain is fine, I am not sure if this circuit will sound as well as it does if configured as a buffer. Guess it will be easy to check, I can lift the end of the resistor to ground to see, and reconnect if not happy.
I hope to rig mine up this weekend and get it playing.
George
carlosfm said:
I did not follow what you meant about removing the 330 ohm resistor to ground. Is the completely remove?
Reduced gain is my real aim here. With a normal preamp of 15 -20 db the volume pots are hair trigger. My system makes up for this by having high efficiency speakers.
Gain is fine, I am not sure if this circuit will sound as well as it does if configured as a buffer. Guess it will be easy to check, I can lift the end of the resistor to ground to see, and reconnect if not happy.
I hope to rig mine up this weekend and get it playing.
George
Re: Another not so smart question
Yes, that's a buffer.
Should be no problem, if you have very sensitive speakers and don't need gain, use it as a buffer.
I don't see any performance issue here.
Right.
I would help you and then we would make a listening session, some cold beers...
But Houston is not exactly near from where I live...
Panelhead said:
Yes, that's a buffer.
Panelhead said:
Should be no problem, if you have very sensitive speakers and don't need gain, use it as a buffer.
I don't see any performance issue here.
Panelhead said:
Right.
Panelhead said:
I would help you and then we would make a listening session, some cold beers...
But Houston is not exactly near from where I live...
Just something that I don't understand.... 😕
Why you guys use all the cap before the regs ?
Because if you reach the peak, you will lack of capacitance after the regs!
(I see you guys doing this in power amps, also)
How many current can those regs handle ?
Why you guys use all the cap before the regs ?
Because if you reach the peak, you will lack of capacitance after the regs!
(I see you guys doing this in power amps, also)
How many current can those regs handle ?
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