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Time Aligned filter upgrade, Really Good!

A

Agent_Cooper79

pfm Member
Hi All!

I really don't consider this to be a mod because I am using Naim specs, but a really good upgrade it is anyway considered (for 102 and probably 72 preamps).

In another thread, TA filter values between different nacs were discussed and I wanted to try using the nac82 T-A specs in my 102.

http://www.pinkfishmedia.net/forum/showthread.php?t=31217&highlight=time

Tonight I did, and I can only say: Success :D:D:D!

What I specifically did (only valid for 102s) was the following; in the scematic here I made the changes below:

http://i113.photobucket.com/albums/n231/peter123aut/pinkfishmedia/Time-Aligned-Filter.jpg

R1 330k to 270k
R2 4k7 to 10k
R3 1k0 to 2k2
R4 62k to 47K
R8 5k6 to 10k
R9 62k to 47K

This is only a few minutes into plugging up, but so far I can only agree with PL135's comments from the original thread; more texture, detail and space (in a natural way), time and boogie also up! Highly recommended!

System: CdSII into nac102 with the above mentioned mods plus MMK feedbacks with improved grounding and Oscon decouplers, pre powered by Superregged Teddy-PSU, 180 into Epos ES11.

Enjoying some Cannonball Adderley now and it is just wonderful, it is as if he were here with me!

/Magnus
 
Thanks for the update....think I've got the necessary resistors in the bits box......
 
I think it would be great if this mod was added to the acoustica page, it should be up there with the decouplers and feedbacks imho.

About a month ago I did some extensive A/B with my MMKed and Osconed 102 against my friends virgin 82. The differences were in the areas where I heard the most prominent improvements tonight. Since then I have fitted some MMKs in his pre, but another trial after todays adventures should prove interesting.

I only have crappy, blurry, rather nonsens mobilecam pics at the moment. My girlfriend is back with her digital camera next week, can post some piccies sometime then.

Cheers guys!
 
The changes to the current sources (R4,R9) might be applicable everywhere such sources are used i.e. gain stage, phono preamps.
 
I'm a bit confused... the resistor values of the NAC82 are similar to those on the NAC72 (with the exception of R2 which is 5.6K on the 72 and 10K on the 82). The 102 which is a newer preamp has different values. I was always under the assumption that the 102 values are an improvement over the older 72/82 design.

BTW, anyone knows what values are used on the NAC202 and NAC282?

I talked recently with someone who upgraded from NAC82 to NAC282 and reported a significant improvement, I was surprised as I thought it was basically the same circuit.
 
This sounds very interesting and if anyone has any info it would be greatly appreciated!

I can just say that the level of detail, timming and sense of musicians playing in the room definitely is up a good level. I prefer this to my old, more shut in sound any day. Also, when comparing the 82 to my 102 in my setup about a month ago, the 82 won it mainly on account of the more alive sound with greater scale, the 102 sounded a bit shut in by comparison. I encourage you to try it for yourself, its only a few resistors, I would love to hear more people try this!

/Magnus
 
teddy_pardo said:
The 102 which is a newer preamp has different values. I was always under the assumption that the 102 values are an improvement over the older 72/82 design.
Click to expand...

Just because the 102 is newer does not make it better.

It was designed to be lower in the range than the 82 so it is unlikely that Naim made it better! They would want to ensure that an 82 running off a power amp sounded better than a 102 running off a Hicap. 'Adjusting' the time aligned filter for poorer performance would be an obvious and easy way of achieving this.

Speculation , of course....
 
OK, let's see what could be the effect of these changes:

1. The two transistors with R4 and the 68R resistor forms a current source of around 10mA (0.7V / 68ohm). Changing R4 to 47K will increase the current through the lower transistor from 0.37mA to 0.49mA (23V / 62K or 23V / 47K), causing a slight increase in the lower transistor Vbe and a slight increase in its hfe. This may cause a slight increase of the current source current (not more than 5% IMO). How much would that effect the sound I don't know... If yes, then I guess that changing the transistors to higher hfe transistors (BC550C, MPSA18) would have similar effect too.

A questions remains though, why do they use in the gain stage (all preamps) 62K and not 47K?

2. Increasing R3 and R8 may have a negative effect on the noise figures. Not sure it's an improvement.

3. Increasing R2 will cut high frequencies. Good/bad thing? Probably depends on the rest of the system.

4. I guess that the change in R1 is required to adjust the input DC as a result of the other changes.

Some time ago someone posted a modification related to changing the current source circuit (using LEDs etc), I can't remember what was the thread title. Anyone remembers? It would be interesting to review it again in light of this thread.
 
Just switched my 102 on after doing these resistor changes.

Agree with Magnus - even cold, there is an improvement.
 
Hi Guys!

I am glad to hear I am not alone (with PL135 from the original thread), to hear an improvement. I do not have the in depth knowledge to study the circuits behaviour theoretically from the changes specified. However, I can tell you this; I certainly did not experience any cuts in the higher part of the frequency spectrum from this mod!

I agree with Teddy and bivalve that it should be interesting to try the 62k -> 47k mod on the gain board, you never know until you try!

Will go on vacation (and away from all computers) the entire next week, look forward to reading your progress when I get back!

/Magnus
 
Finally tried it.

As I was curious to understand which of the resistors is responsible for the change I started by replacing only the 62K resistors. I didn't need more than several minutes to realize that it makes a big change, exactly as described above. It's really a very good mod!!! Cheers Magnus!!!

Les wrote in his DIY tips & tricks that "By simply increasing the power supply voltage from the nominal 24V to around 30V DC, the performance of the NAC range of pre-amp is enhanced. Clarity, leading edge dynamics and solidity are all improved but don't ask me why..!!".

Les, I think that the answer lies here. Increasing the voltage has the same effect as using a lower value resistor (same current). In fact when using 24V I'd recommend using 39-42K rather than 47K for even better results.

Now, I just wonder why they changed these resistors on the NAC102? The only reason that comes to my mind is that they didn't want that a single HiCap-ed NAC82 will sound exactly as a NAC102... The other question is why are the still using 62K on the gain board? Or maybe the changed it to 47K on the NAC52... :)

Given that, I realize that the current source is not less important than the voltage regulator. Now I'm tempted to try more sophisticated current source designs. Maybe even start by using better transistors, maybe jfet, etc. The interesting point is that in my NAC102 I have a dedicated VBE regulator for each current source, and still the effect of replacing the resistor is very noticable.

Teddy
 
So can this mod be extended to the gain and buffer boards in a 32/32.5 (324 and 321)?

Looking at the schematics over on the acoustica web site there is a 62k resistor as part of a current source.
 
So another approach could be to try a 30v traco with no regulation to take the voltage down to 24v but with a vbe to maintain the element of isolation of each circuit? Cheers Andy.
 
Yes - but the output impedance of the supply to each section would be rather high; I'd expect it to sound clean, but compressed / 'small'
 
Carl - yes, this is the thread thanks, however when using a LED the resistor calculation is different as it is biased differently.
 
Having re-read the thread whilst checking schematics, I was hoping to lift my 72 a bit more, it does appear that the 72 is more in line with the 82 and the associated sonic improvement than a 102 and hence all the sage advice over the years on the 102 vs 72 seems null and void.

Am I reading this correctly?
 
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