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NAP250 - The Mojo Mod

I must admit the MOJO mod made sound my NAP250 much better, then I realized it was too hot and oscillating. I can't wait to fix it when new caps arrive.
Years back I did the same mod to my NAP110 follwing advice from the two respected gentlemen running the Acoustica website but I can´t remember being pleased so much then, Thanks and I'll report back
 
Vishay axial caps fitted and now all mods done. BAR between the big Kendeils and run thick wire to the middle of the 0-0. Mind you. I had to take it to a friend tecnician who has a 150w solder iron to do the job properly. He also soldered the return of the 4 - 220uf caps of the MOJO mod. Done bias adjustment and job done.
Sound: more precise and present. I like it. NOw it's a contender against my Voyager (sort of) and Hackernap.
I´ll let you know when a few miles have been run.
Cheers
 
That sounds like a successful result Harthold. Good to get it done properly, you do need a powerful iron to solder onto the earth bar properly.

I've added a separate earth return too and it's sounding great.

mat
 
I've yet to do the MOJO mod, but I have added the thick wire from centre of the previously fitted bar between the kendeils to the middle of the 0-0. This seems to have tamed the top end, but the sound is more 'dull' and two-dimensional. Is this in line with others' findings? I'm not too sure it's actually an improvement
bry
 
Harthold said:
Vishay axial caps fitted and now all mods done. BAR between the big Kendeils and run thick wire to the middle of the 0-0. Mind you. I had to take it to a friend tecnician who has a 150w solder iron to do the job properly. He also soldered the return of the 4 - 220uf caps of the MOJO mod. Done bias adjustment and job done.
Sound: more precise and present. I like it. NOw it's a contender against my Voyager (sort of) and Hackernap.
I´ll let you know when a few miles have been run.
Cheers
Click to expand...

That's better news. A 250 in need of a service can be a fairly miserable sounding thing IME, probably with borderline stability a lot of the time - excess temperature being another warning sign. Let us know how it sounds when you get a chance.

Mr Tibbs
 
Grateful for the support received here. The 250 is sounding very good indeed. (Won´t go on describing speed, punch slam etc which I do not make up properly what these terms purport). It seems a more powerful and pricise amp now It´s powering my SARAS (cones refurbished professionally and crossover by yours truly) No way to restort back to NAP110 -also MOJO modded). It's pity does not pair so well with one of my B4´s which I find slightly better to my supercharged 72 -more revealing. Anyhow, I will give a try to the B4 with a non Naim standard interconnect again and listen. Every owner of a 250 should try this mod by themselves
 
Harthold said:
Anyhow, I will give a try to the B4 with a non Naim standard interconnect again and listen. Every owner of a 250 should try this mod by themselves
Click to expand...

I definitely prefer the amp plugged into the preamp rather than via the Hi-Cap. Glad you got it all sorted :)

Mr Tibbs
 
The thing is there seems to be an orthodox reaction to go back to Naim´s ^proprietary' interconnection and abandon all the step-by-step sound quality gains after so many years and people experimenting (including you Mr Tibbs) at the expensense of new High Tech cards from across the pond.
Cheers
 
I've used 100uf caps, with -ve's starred back to the centre of the link bar between the main caps courtesy of Les's advice and recap kit.
Result?
Oscillation- OK, All seems reasonably cool and calm within the 250.
SQ- An improvement in clarity. Sound is perhaps a little more forward of the speakers, and as Mr Tibbs better explained previously, low level sounds which were previously 'lost' in the mix seem to be more audible.
A good result and a big thanks to Mr Tibbs and Les.

However, to ensure this isn't just a psychological effect, I'm planning to temporarily reverse this mod in a couple of weeks to see if I perceive further improvement!!!
Now onto implementing Les's output inductor to hopefully eliminate several metres of ridiculously stiff and unsightly cable...
 
Very good - we seem to be getting a similar set of results.

Having had more time to listen to a wide range of stuff I'm surprised at how much the bass has improved, with better definition and 'grip', for want of a better word.

Mr Tibbs
 
I've just re-read this thread, and realised I have a response outstanding...
I experimentally removed the MOJO mod some time ago, allowed everything to warm up and listened again.....
Well it was different, but the difference seemed very very subtle, so I never got around to replacing the capacitors.
Very strange, I seem to recall the difference being much greater when I added the mod.
Ideas, anybody? Psychological or some sort of strange memory effect (?) in the capacitors?
 
Thanks for getting it up again, I missed it in the first place.. :)

I'm not sure if I got something wrong, but if I understood Mr.Tibbs right,

he sorted the 250 out in the first place bc due it's regulation,

it sounded not as good as 110 & 160, which sound better bc they have no regulation.

The MOJO mood is a smoothing of the regulation...if I got it right?

What do you smooth in the 110 when it has (obviously) not this regulation stage that can be smoothened..?

But the similar seems to work in the Nait2, which certainly isn't more advanced than a 110 or 160.

I'm driving an Isobarik, but active with 1x NAP180 and 2x NAP140.

Would you suggest I use 220 mü Farad, too ?

Or would you suggest the load divides by 3 and I use like 75 mü Farad or similar?
 
Sorry, I'm not that tech savvy to answer your questions, however I expect Mr Tibbs may be along soon to help!
 
torstoi said:
Thanks for getting it up again, I missed it in the first place.. :)

I'm not sure if I got something wrong, but if I understood Mr.Tibbs right,

he sorted the 250 out in the first place bc due it's regulation,

it sounded not as good as 110 & 160, which sound better bc they have no regulation.

The MOJO mood is a smoothing of the regulation...if I got it right?
Click to expand...

Correct.

The power regulators in a 250 (and 135 for that matter) give superior smoothing at LF but have inferior smoothing at HF than a simple unregulated supply with large capacitors for smoothing. This IMO is why a 110 (or 160) has the edge over a standard 250 everywhere but the low bass. The Mojo mod has the effect of improving the poorer HF smoothing of the regulators and so allowing the 250 to perform much like a 110 / 160 does but retains the better bass control of the 250.

Adding a small amount of extra capacitance to an unregulated amp like the 110 / 140 / 180 does not have the same effect as the small amount of extra capacitance would be swamped by the existing large smoothers in parallel.

Mr Tibbs
 
Thank you Mr.Tibbs.
I wasn't aware my 140 & 180 were unregulated like 110 & 160, but from the hierarcy it surely makes sense.

So in plain theory, I could expect a + in the lower registers if I managed to add power regulators a la 250 into the 140 & 180 & do a Mojo Mod then.

Do you think that's possible ?
In the 180, possibly but in the 140 space will become an issue I suppose..?

Thanks again for sharing your knowledge & findings ! :)
 
torstoi said:
Thank you Mr.Tibbs.
I wasn't aware my 140 & 180 were unregulated like 110 & 160, but from the hierarcy it surely makes sense.

So in plain theory, I could expect a + in the lower registers if I managed to add power regulators a la 250 into the 140 & 180 & do a Mojo Mod then.

Do you think that's possible ?
In the 180, possibly but in the 140 space will become an issue I suppose..?

Thanks again for sharing your knowledge & findings ! :)
Click to expand...

Regulation starts with the 250.

I wouldn't try adding power regulation to an unregulated amp, but it would be worthwhile to regulate the 'front end' of the amp and leave the output stage unregulated. Do a search here for plenty of info on how to go about this if you are interested. The Mojo Mod is really just a fix for a specific weakness in the 250 (and 135) and is really not transferable to any other application. It's a minimalist mod that does the job without the need for major surgery and is very reversible - that's the kind of mod I like these days :)

Mr Tibbs
 
That's good advice, thank you for the answer, Mr Tibbs ! :)

I have intended to build up 3 Hackernap-Voyager double monos & from what I read as far, TimH's variant of it sounded promissing to me.

But it will, no doubt take a while till I have them all 3 up & running,
& the now existing devices will move on to a good second system then.
(Kans, maybe active, possibly later followed by an attempt on Ergo IX)

So I thought I might as well stick my toe into the water with the now existing amps and get a bit of xp what the matter is all about, before going all in.
I'm not overly experienced yet, as you may sense.. :)

I've started on collecting parts for the 3 amps, I don't nessesarily miss sheer power in first place now, but a more refined performance of my now existing 140s & 180 would make a nice difference & ,more cultivated presentation, I think.

Do you think regulating of front end will fit into the 140, too ?
And would you suggest a re-cap in the process of is this not necessary in amps the way it is with HiCaps?

I will look around for front end regulation a bit, thanks for your advice, again ! :)
 
Mr Tibbs said:
OK, first thing you need to do is make sure the amp is working properly before attempting any mod's. Replace those blue Philips 10uF caps but use a decent 105C rated cap instead since the originals can dry out in as little as 5 years use. These cap's are absolutely critical to getting stability and good sound, as is the correct bias setting.


Mr Tibbs
Click to expand...

Hi,
my NAP250 that arrived yesterday (bought via the forum) had those 10uF completely broken. One was only 2uF, the best one only 7uF. According to the previous owner, the unit was serviced in 2008! So checking those is always a good idea.
On top of it, the idle current was set too low with 2.3mV across the 0.22 Ohm resistor.

Fortunately, I got those 125° VISHAY caps in 10uF, 47uF and 100uF - so I replaced the ones on the regulator board, changed the feedback capacitor to 47uF MKT (AVX) in parallel with a 47uF Cerafine, changed the Tantalum to fresh originals and added the 100uF Mojo capacitors.

Did a quick listen (as I did when it arrived, but it sounded awful) and decided to let it run over night before doing more.
To be honest, I thought my NAP160 was sounding more open with more lower midband The NAP250 had the better dynamic for sure, but sounded a bit too hot in the upper midband that made it a bit lean.

I did not change the main capacitors yet - just waiting for a fresh set of Felsic.
As alternative, I have a set of KEMET here as well - maybe I'll try them out first and add the bar across the terminals same time.

ATB KH
 
finkaudio said:
Hi,

Did a quick listen (as I did when it arrived, but it sounded awful) and decided to let it run over night before doing more.
To be honest, I thought my NAP160 was sounding more open with more lower midband The NAP250 had the better dynamic for sure, but sounded a bit too hot in the upper midband that made it a bit lean.

I did not change the main capacitors yet - just waiting for a fresh set of Felsic.
As alternative, I have a set of KEMET here as well - maybe I'll try them out first and add the bar across the terminals same time.

ATB KH
Click to expand...

You have changed several caps in the signal path. I suggest you leave the amp running for a few days and then listen again- letting the caps burn in, especially in the feedback loop which has tiny voltage and current to deal with, can make a surprising difference.

If after a week you are still unhappy, then make changes.
 
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