Resistor value in the feedback loop

FredG · 3rd February 2004, 11:59 AM

Hi,

I'm currently listen a NIGC with a combination of 25K (MK132) + 750R (RC55) for the feedback loop.
Previously, I was listening with 14.7K (RC55) + 442R. (RC55). The sound is much more natural now, with a :lot of details but less involving than before.
Did someone listen to different combination of resistors values in the feedback loop, leading to the same gain ? Is it better to use 15k or 25K in the feedback loop ?

FredG.

Nuuk · 3rd February 2004, 08:36 PM

You can change the sound of the Gainclone (IGC or NIGC) by experimenting with resistor values and the arrangements for reducing DC offset.

In my own experience, reducing DC offset can result in more detail but the music is somehow less involving.

The answer to your question lies in your own experiments!

GregGC · 3rd February 2004, 09:41 PM

Quote:

Originally posted by FredG
Hi,

I'm currently listen a NIGC with a combination of 25K (MK132) + 750R (RC55) for the feedback loop.
Previously, I was listening with 14.7K (RC55) + 442R. (RC55). The sound is much more natural now, with a :lot of details but less involving than before.
Did someone listen to different combination of resistors values in the feedback loop, leading to the same gain ? Is it better to use 15k or 25K in the feedback loop ?

FredG.

Do you have a cap in the Feedback network (in ser to 442R)? If you do, the smaller the value of this res. the less the low frecuencyes will be amplified. In that case I'd opt for larger values of the res. so that the cap has relatively lower value.

Can you show us the sch. you use?

/Greg

FredG · 4th February 2004, 09:31 AM

Nuuk,

For the moment, I think the not so involving (but fully transparent) sound comes from the MK132 and not from the value itself. I’m perhaps wrong. I just put this resistor in the amp and I’m waiting a few days to carefully listen to it. But the first listening session is often relevant.

GregCG,

No, I’m not using any cap in conjunction with the 750R. The offsets are about 20 mV and 29 mV.
Here’s the schema I’m currently using :

FredG.

loong · 4th February 2004, 12:03 PM

I experienced with a NIGC: 22K + 680, with 20K pot and C 2.2UF (SCR), 35+35V, with (1000+1000+10) UF per rail. All register are normal metal oxide film. It's really good!

FredG · 4th February 2004, 01:06 PM

I don't say that with caddocks the sound is not good, but the music lacks. With this shema, I tried different resistors and all of them have their own sound... MK132 is really famous among audiophiles and I'm a bit puzzled by the result I have.

PauSim · 4th February 2004, 06:00 PM

Hi FredG

I saw an on-line commercial version featuring 180k/10k/22uF63V in the feedback loop plus a 1k in series/1M/1uF63Vin series/22k to +in.
Most people (myself included) is using 22k/680 because it´s close to what is stated in the NS specsheet and the original GC (LM3875) circuitry.

Given this disparity of values for the feedback resistors, seems like the combinations are endless.
Me, I think I´ll try the Final Labs approach, to apply a variable resistor (not a panel pot though, but a trimmer soldered right next to to the IC´s pins) to fine-tune the loop.

Being an insane tweaker .:3 with KEIN degree in Electronics

(mind), here´s what I´ll do: connect 47k trimmer pin 3 to LM1875 pin 4, trimmer pin 2 to IC pin 2, trimmer pin 1 to ground; maybe small value resistor offsetting trimmer, from IC pin 4 in series with trimmer pin 3. Haven´t a clue if it will work at all.

I´m not advising you to try it, just my 2c. Opinions are welcome as usual, both pos or negs.

Bonne chance!

macboy · 6th February 2004, 12:37 PM

FredG,
Your schematic seems very strange. The 25K in series with the input followed by a 1K to ground makes a voltage divider which attenuates the input signal by -28 dB. Why are you doing that?

GregGC · 6th February 2004, 01:53 PM

Quote:

Originally posted by macboy
FredG,
Your schematic seems very strange. The 25K in series with the input followed by a 1K to ground makes a voltage divider which attenuates the input signal by -28 dB. Why are you doing that?

Good observation. Change the 1K res to gnd with 25k and you'll luse only 6dB instead of 27dB.

FredG · 6th February 2004, 02:13 PM

25k + 1k is my fixed pot ! It fixes the level I listen. I don't have any pre, just the output of the CD player and the NIGC. I don't want to introduce a pot when i'm trying to listen to resistors...
FredG

3rd February 2004, 11:59 AM	#1
FredG diyAudio Member Join Date: Feb 2004 Location: ROUEN	Resistor value in the feedback loop Hi, I'm currently listen a NIGC with a combination of 25K (MK132) + 750R (RC55) for the feedback loop. Previously, I was listening with 14.7K (RC55) + 442R. (RC55). The sound is much more natural now, with a :lot of details but less involving than before. Did someone listen to different combination of resistors values in the feedback loop, leading to the same gain ? Is it better to use 15k or 25K in the feedback loop ? FredG.

3rd February 2004, 08:36 PM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	You can change the sound of the Gainclone (IGC or NIGC) by experimenting with resistor values and the arrangements for reducing DC offset. In my own experience, reducing DC offset can result in more detail but the music is somehow less involving. The answer to your question lies in your own experiments! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

4th February 2004, 06:00 PM	#7
PauSim diyAudio Member Join Date: Jan 2004 Location: Portugal	resistor value in feedback loop Hi FredG I saw an on-line commercial version featuring 180k/10k/22uF63V in the feedback loop plus a 1k in series/1M/1uF63Vin series/22k to +in. Most people (myself included) is using 22k/680 because it´s close to what is stated in the NS specsheet and the original GC (LM3875) circuitry. Given this disparity of values for the feedback resistors, seems like the combinations are endless. Me, I think I´ll try the Final Labs approach, to apply a variable resistor (not a panel pot though, but a trimmer soldered right next to to the IC´s pins) to fine-tune the loop. Being an insane tweaker .:3 with KEIN degree in Electronics (mind), here´s what I´ll do: connect 47k trimmer pin 3 to LM1875 pin 4, trimmer pin 2 to IC pin 2, trimmer pin 1 to ground; maybe small value resistor offsetting trimmer, from IC pin 4 in series with trimmer pin 3. Haven´t a clue if it will work at all. I´m not advising you to try it, just my 2c. Opinions are welcome as usual, both pos or negs. Bonne chance! __________________ Paulo

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4th February 2004, 09:31 AM	#4
FredG diyAudio Member Join Date: Feb 2004 Location: ROUEN	Nuuk, For the moment, I think the not so involving (but fully transparent) sound comes from the MK132 and not from the value itself. I’m perhaps wrong. I just put this resistor in the amp and I’m waiting a few days to carefully listen to it. But the first listening session is often relevant. GregCG, No, I’m not using any cap in conjunction with the 750R. The offsets are about 20 mV and 29 mV. Here’s the schema I’m currently using : FredG.

4th February 2004, 12:03 PM	#5
loong diyAudio Member Join Date: Feb 2004 Location: Earth	I experienced with a NIGC: 22K + 680, with 20K pot and C 2.2UF (SCR), 35+35V, with (1000+1000+10) UF per rail. All register are normal metal oxide film. It's really good!

4th February 2004, 01:06 PM	#6
FredG diyAudio Member Join Date: Feb 2004 Location: ROUEN	I don't say that with caddocks the sound is not good, but the music lacks. With this shema, I tried different resistors and all of them have their own sound... MK132 is really famous among audiophiles and I'm a bit puzzled by the result I have.

6th February 2004, 12:37 PM	#8
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	FredG, Your schematic seems very strange. The 25K in series with the input followed by a 1K to ground makes a voltage divider which attenuates the input signal by -28 dB. Why are you doing that?

6th February 2004, 02:13 PM	#10
FredG diyAudio Member Join Date: Feb 2004 Location: ROUEN	25k + 1k is my fixed pot ! It fixes the level I listen. I don't have any pre, just the output of the CD player and the NIGC. I don't want to introduce a pot when i'm trying to listen to resistors... FredG

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