Koinichiwa!
At last!
Welcome, Kuei.
This thing was getting too confusing...
But I can assure you all that I have between 0.0~0.1 mv DC offset on the two channels of my gainclone.
And that is with a 50k multi-turn pot in place of the 18k resistor, as you recommended me, Kuei.
You can see a picture of the multimeter measuring that on my thread PC Gainclone.
Sayonara!
At last!
Welcome, Kuei.
This thing was getting too confusing...
But I can assure you all that I have between 0.0~0.1 mv DC offset on the two channels of my gainclone.
And that is with a 50k multi-turn pot in place of the 18k resistor, as you recommended me, Kuei.
You can see a picture of the multimeter measuring that on my thread PC Gainclone.
Sayonara!
Nuuk said:
Yep, that's the idea. As I said earlier, the impedances to earth at both inputs should be the same. But the important bit of information was the increase of 220 k to 330 k
More gain, less feedback, better stability and the attenuator can be placed in a lower position (benificial for DACs with a high output impedance, like the TDA1543 passive I/V DACs).
Fedde
Re: Koinichiwa!
Koinichiwa,
Very simple actually. But you do really need to understand how Op-Amp's work, the full story including parasitics, not the abriged one most people learn in EE Classes.
Which is perfectly correct for the schematic you are using. The point is that the value for the correct offset nulling resistor on the non-inverting input varies widely depending upon the schematic used.
Sayonara
Koinichiwa,
carlosfm said:This thing was getting too confusing...
Very simple actually. But you do really need to understand how Op-Amp's work, the full story including parasitics, not the abriged one most people learn in EE Classes.
carlosfm said:
Which is perfectly correct for the schematic you are using. The point is that the value for the correct offset nulling resistor on the non-inverting input varies widely depending upon the schematic used.
Sayonara
Nuuk said:
Now changing the feedback resistor is real dedication. With a hard-wired circuit it is soldered directly to the pins of the chip and virtually everything has to be disassembled to change it!
I'm about to build another GC so I'll leave the higher feedback resistor for the new amp.
It took me little more than half an hour on my GC (unsolder two cables, unscrew four cables). For my amp it was definitely worth the effort !
Anyone tried it yet !?
Fedde
I have just replaced the 18K/22K resistor combination on my IGC with a 216K to ground from the non-inverting input. (My feedback resistor is 216K)
I got 0mV on one channel and 0.3mV on the other but more importantly the 'magic' factor returned. This had been missing since I changed from a straight wire from non-inverting to ground to the 18K/22K.
There is absolutely no doubt that on my GC's this latest arrangement sounds much better. Better tonal balance, smoother, more air around instruments, more presence. It's gone back to the state where I have trouble ending my listening sessions.
It was well worth the time spent last night measuring some old carbon resistors that I inherited from my father. After one hour, I had found a combination of 270K's and 1 megs that provided the exact 216K when wired in parallel (the wide tolerances made this possible).
I got 0mV on one channel and 0.3mV on the other but more importantly the 'magic' factor returned. This had been missing since I changed from a straight wire from non-inverting to ground to the 18K/22K.
There is absolutely no doubt that on my GC's this latest arrangement sounds much better. Better tonal balance, smoother, more air around instruments, more presence. It's gone back to the state where I have trouble ending my listening sessions.
It was well worth the time spent last night measuring some old carbon resistors that I inherited from my father. After one hour, I had found a combination of 270K's and 1 megs that provided the exact 216K when wired in parallel (the wide tolerances made this possible).
Koinichiwa,
I would expect this to be so. Non of the recommended combinations where ever done with a primary view of "sound quality", but in terms of being able to build reliably. With a 50k...100K pot and without input connection the inverting gainclone in the simple schematic is potentially unstable (few people seem to have problems with that though), adding the 18 + 22k fixes that and makes sure that Amp is much more stable.
As many people from Naim via NVA to DNM have found, the more you do to make an amplifier unconditionally stable the worse it sounds.
With a warning label for the unweary "never use without input connections" the stripped down inverting gainclone using perhaps a 330k Feedback resistor (lifts gain enough to be stable with a 100K input pot in all positions) for the "integrated" version and 220k for the "poweramp" version this is likely the best option.
Sayonara
Nuuk said:
I would expect this to be so. Non of the recommended combinations where ever done with a primary view of "sound quality", but in terms of being able to build reliably. With a 50k...100K pot and without input connection the inverting gainclone in the simple schematic is potentially unstable (few people seem to have problems with that though), adding the 18 + 22k fixes that and makes sure that Amp is much more stable.
As many people from Naim via NVA to DNM have found, the more you do to make an amplifier unconditionally stable the worse it sounds.
With a warning label for the unweary "never use without input connections" the stripped down inverting gainclone using perhaps a 330k Feedback resistor (lifts gain enough to be stable with a 100K input pot in all positions) for the "integrated" version and 220k for the "poweramp" version this is likely the best option.
Sayonara
Hard to call Mike because I have now got my system set up a lot better than when I was using the plain wire. However, if pushed, I would say go with the 216K (or whatever your feedback resistor is). I think that may just have the edge and then there is the bonus of the lower DC offset of course!
You must be joking
there are those open baffle speakers to develop, the integrated GC with buffer/low pass filter, the valve preamp and ...... with a bit of luck I may live past 100 and get most of it done!I admit it - I'm an addict. I was with my mother in a garden centre this morning and nearly bought two large ceramic plant pots to try as speaker cabs! If I'm not safe in a garden centre......
Sort of in between but no outer lip so you could have a nice rounded shape of the edge of the front baffle and ......
I propose an Audioholics Anoymous section on this forum You know the drill chaps
My name's Nuuk, I'm an audioholic!
It all seemed quite harmless at first when I was just messing around with interconects and speaker cables.
Then sombody said 'why not build your own speakers?' and I thought what's the harm in that?
But I needed a soldering iron to solder up the crossovers and it seemed a waste to just put it in a drawer and forget about it so I opened up my amp and replaced a few resistors. One thing led to another and now I am in deep, building the damn stuff.
Nothing too heavy you understand, just chip amps but they are the most addictive!
I'm broke or in debt most of the time now but still I get the credit card out and get on to one of my dealers for another fix.
I promised that I would stop but I can't. I keep hanging out on the forums with other addicts and none of us can help ourselves.
A cure? I don't think that there is one......anyone got some lead-free solder....
Nuuk said:
Good idea Fedde!
Superglue just won't hack it - Just put the whole lot in a large box with your favourite leads protruding, don't forget a little hole for the cd's to go in & out, and pour in the concrete.
Better make it fast setting stuff just in case the resolve gives out and your tempted to try a frenzied rescue attempt...
Mmm... that's a thought ...
...concrete... might sound good...
And now there are three
For those of you who like pictures, here is one of my new volume control for my Gainclone monoblocks.
They say that men with small knobs drive large cars so you won't be surprised to hear that I ride a pushbike! Details of making the big knob are HERE (and I promise not to spam you!
So at present my GC system looks like this
I suppose now, the obvious thing is to build two more 'pods' for the PSU's!
For those of you who like pictures, here is one of my new volume control for my Gainclone monoblocks.
An externally hosted image should be here but it was not working when we last tested it.
They say that men with small knobs drive large cars so you won't be surprised to hear that I ride a pushbike! Details of making the big knob are HERE (and I promise not to spam you!
So at present my GC system looks like this
An externally hosted image should be here but it was not working when we last tested it.
I suppose now, the obvious thing is to build two more 'pods' for the PSU's!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.