audiomax62
New member
- Joined
- Jan 26, 2014
- Messages
- 2
Hi to all, this is my first post so thank you in advance both for the attention and for the help.
I'm just modding an ADA8000 and I'm experimenting this module (http://groupdiy.com/index.php?topic=21523.0) in the D/A output with very promising results. Due to the floating audio transformer, the +- otuput of the AL1201 can be connected directly to the input bypassing the (cheap) electrolytic capacitors. I'm not in the "metaphysical experience" of new universe of sound discovered bypassing capacitros, but I must see that there is an audible better comprehensibility of what happens in the penultimate octave (5-10KHz), giving sibilants their right place and avoiding the well-known, dull (bad) digital sound in that region.
Again, I can't say if it's due only to the lack of capacitors, I can only say that this arrangement is really a good sonic start.
Unfortunately, I'm a musician and not a techician, so I'm making a lot of experiments basing only upon the sound results. Modding this module, I noted that:
1) a bigger value of input resistor must be used. It seems this module has about 5K input resistance (2K5 for each input, sue to the bridge configuration), but the Behringer scheme use a 7K5 both for + and - output of the AL1201. I noted an evident recovery of punch, dynamics and microdetail while adding resistors in series to the inputs (4K7 each), but output level shifted down, I think more than 6-8 dB);
2) substitution of the 300p ceramic capacitors (see schematics) with silver mica unit give a little bit of elegance in the extreme high frequencies, but nothing more (a well-knowed argument);
3) I tried a lot of OpAmps in the output, surprisingly the original NE5532 sounds very well, even if compared with other newest model (yes, 5532 WAS A REVOLUTION in audio...). For my taste, two AD825 is the best solution. I know that they are quite obsolete and noisy, but they offer a very natural and not fatiguing sound (maybe dued to their speed, I imagine in digital domain an OpAmp must manage a 44,100 to 192 Khz square wave), both relaxed and defined, so I think I'll go by this way. I have to try the new LME49990, but I haven't it in my hand just right now.
At this point, I'd really need an help from people with better knowledge in the technical and engineering fields. The question are:
1) is it possible to recover 6-10 dB of gain in the active circuit changing feedback resistor(s)?
2) if yes, how the input resistance changes?
3) by changing resistor(s) values new capacitor value is needed to mantain the same FT (I refer especially to the 300p capacitor)?
4) If I take the signal form output (Directly form the pin 2 or from the 1 Ohm resistor, I imagine there isn't too much difference in the electric domain), why I can't use this as input to output module? Isn't the output impedance of the OpAmp naturally low enough?
I attahced the diagram I wrote, desoldering and measuring all resistors (a practically desctructive operation, due to the inexplicable lack of quality of the PCB...), since I'm affected by a slight color blindness, this was the only way to obtain the right values
Again, thank to all people for the attention, I'm looking forward for a suggestion.
Keep up the (good) music and happy listening to all,
Massimo
I'm just modding an ADA8000 and I'm experimenting this module (http://groupdiy.com/index.php?topic=21523.0) in the D/A output with very promising results. Due to the floating audio transformer, the +- otuput of the AL1201 can be connected directly to the input bypassing the (cheap) electrolytic capacitors. I'm not in the "metaphysical experience" of new universe of sound discovered bypassing capacitros, but I must see that there is an audible better comprehensibility of what happens in the penultimate octave (5-10KHz), giving sibilants their right place and avoiding the well-known, dull (bad) digital sound in that region.
Again, I can't say if it's due only to the lack of capacitors, I can only say that this arrangement is really a good sonic start.
Unfortunately, I'm a musician and not a techician, so I'm making a lot of experiments basing only upon the sound results. Modding this module, I noted that:
1) a bigger value of input resistor must be used. It seems this module has about 5K input resistance (2K5 for each input, sue to the bridge configuration), but the Behringer scheme use a 7K5 both for + and - output of the AL1201. I noted an evident recovery of punch, dynamics and microdetail while adding resistors in series to the inputs (4K7 each), but output level shifted down, I think more than 6-8 dB);
2) substitution of the 300p ceramic capacitors (see schematics) with silver mica unit give a little bit of elegance in the extreme high frequencies, but nothing more (a well-knowed argument);
3) I tried a lot of OpAmps in the output, surprisingly the original NE5532 sounds very well, even if compared with other newest model (yes, 5532 WAS A REVOLUTION in audio...). For my taste, two AD825 is the best solution. I know that they are quite obsolete and noisy, but they offer a very natural and not fatiguing sound (maybe dued to their speed, I imagine in digital domain an OpAmp must manage a 44,100 to 192 Khz square wave), both relaxed and defined, so I think I'll go by this way. I have to try the new LME49990, but I haven't it in my hand just right now.
At this point, I'd really need an help from people with better knowledge in the technical and engineering fields. The question are:
1) is it possible to recover 6-10 dB of gain in the active circuit changing feedback resistor(s)?
2) if yes, how the input resistance changes?
3) by changing resistor(s) values new capacitor value is needed to mantain the same FT (I refer especially to the 300p capacitor)?
4) If I take the signal form output (Directly form the pin 2 or from the 1 Ohm resistor, I imagine there isn't too much difference in the electric domain), why I can't use this as input to output module? Isn't the output impedance of the OpAmp naturally low enough?
I attahced the diagram I wrote, desoldering and measuring all resistors (a practically desctructive operation, due to the inexplicable lack of quality of the PCB...), since I'm affected by a slight color blindness, this was the only way to obtain the right values
Again, thank to all people for the attention, I'm looking forward for a suggestion.
Keep up the (good) music and happy listening to all,
Massimo
