View Full Version : Neurochrome Modulus 686 Monoblocks
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I picked up my 686 Monoblocks yesterday from Joe Henry in Coventry.
I could have built them myself, but when I got a look at Ali's Amps, that Joe built, build quality was first rate and Joe's pricing is fair, for the amount of work involved.
Without a decent place to work, I thought it was easier all round, just to buy them ready made.
Here are some pictures Joe took of mine during the build.
https://www.jkwynn.co.uk/686_Mono/Pics/686_01.JPG
Each unit has 188,000 uF of capacitors in the PSU.
https://www.jkwynn.co.uk/686_Mono/Pics/686_02.JPG
The toroidal transformers are 500VA
https://www.jkwynn.co.uk/686_Mono/Pics/686_03.JPG
Speaker protection is built in.
https://www.jkwynn.co.uk/686_Mono/Pics/686_04.JPG
Final soak test.
https://www.jkwynn.co.uk/686_Mono/Pics/686_05.jpg
The Amps are fully differential balanced circuits so just an XLR input.
https://www.jkwynn.co.uk/686_Mono/Pics/686_06.jpg
The fronts carry just an illuminated on/off switch.
https://www.jkwynn.co.uk/686_Mono/Pics/686_07.jpg
Waiting to be set up in my system, I need to build some stands, so each Amp can sit under its speaker.
Each produces 360w into 4ohm, which is what my Canton CT-1000 speakers present as a load.
They sound great out of the box, but presume they will smooth out a little as everything settles in.
https://www.jkwynn.co.uk/686_Mono/Pics/686_08.jpg
This is what I have in mind for the stands.
That should be a very sweet set up Ken. Love the aesthetics.:thumbsup:
Thanks James
Yes there is great synergy between the 686 Mono's and CT-1000 speakers.
Its what I heard at NEBO last time out and was determined to go this route.
Being fully balanced, these amps make better use of my Pass Labs XP-12 balanced Pre Amp as well.
It all works beautifully together.
Well done!
I use monobock amplifiers located directly behind each speaker, fed by balanced line cables back to the preamp. The advantage of such an arrangement is that the speaker leads need only be less than 1m long (or in my case 30cm).
Great amplifiers and speakers - going to be a killer system I think.
The Black Adder
17-04-2024, 04:46
Looks great. Keep us updated on the progress
Sent from my BBC Microcomputer 32K
Well done!
I use monobock amplifiers located directly behind each speaker, fed by balanced line cables back to the preamp. The advantage of such an arrangement is that the speaker leads need only be less than 1m long (or in my case 30cm).
Thanks Barry
I made up some 60cm speaker leads, which should work for my set up, once the stands are built.
The beauty of such short distances is you can use more exotic speaker leads and the cost is still very reasonable.
I used Atlas Bi-Wire but configured it for single connection.
It has one pair of single strand, meant for HF/Mids and one pair of multi strand meant for Bass.
I twisted one of each type together and put it into a single "Z" plug.
A couple of users have said this arrangement sounds better than just using the heavier grade Atlas Hyper 3.5mm or 5.0mm multi strand.
A used unterminated piece came up on the Bay, so I thought I would try it, though I doubt such a short length is going to make much difference.
https://www.jkwynn.co.uk/Cables/Pics/Cab_03.jpg
Ali Tait
17-04-2024, 11:25
Looking good Ken, identical to mine in fact. :-)
Hope you enjoy them as much as I do mine.
Yes - it does mean speaker cable costs are minimised, but also it gives you the opportunity to try other 'exotic' designs for minimal costs.
Looking good Ken, identical to mine in fact. :-)
Hope you enjoy them as much as I do mine.
Ali, did you find there was any kind of break in period?
Mine are sounding pretty good straight out of the box.
Ali Tait
17-04-2024, 18:29
I didn’t really notice any to be honest. Guess Tom soak tests the boards before he sends them out.
Ali Tait
18-04-2024, 10:30
How are you getting on with them?
Ali Tait
18-04-2024, 10:34
I didn’t really notice any to be honest. Guess Tom soak tests the boards before he sends them out.
On further thought, I would caveat this by saying that I didn't get to use them on a regular basis as I now live with my partner, so only am only at my place infrequently (work gets in the way!) so it may well be I just didn't notice any changes in sound.
I love how they sound though, have no inclination to look for anything else as I have always done in the past. :-)
The Pass Labs Pre/686 Monos/ CT-1000 speakers is a cracking combination.
Loving the sound, even at low'ish late night volume, when the missus has gone to bed!
With this set up, vocals are very natural and clean, good timber, I would say synth. bass is not quite as hard hitting as my Yamaha set up, but is better textured and detailed, I'm talking very small differences though, plenty of slam there when needed, the Amps stop/start the drivers on a dime, so no overhang.
Overall its a very musical presentation, easy to listen to, I forget about the gear and get engrossed in the track, which is the way it should be.
I think my amps smoothed out in the first few days, there was a hint of grain at the top end during my first session, which seems to have gone now.
I can't position the Amps under the speakers until I have made some suitable stands, so they are presently located at the side, connected by some 2m speaker leads I had to hand. I've got to prep the motorhome for this season, including fitting a new solar panel, but I'll get those stands built fairly soon, working on a cutting list right now.
I'll drop some pictures in when done.
Ali Tait
18-04-2024, 12:08
Having tried various Tripath and Hypex modules in the past, it's interesting how much better the Neurochromes sound to me. Despite their excellent measured specs, I never really got on with them- something about their sound just didn't sit quite right with me. No such issues with the 686 though (or the 86 I had previously). I know it's a bit of a cliche, but they really are as close to a straight wire with gain as I've come across, and they let you know exactly what the rest of the system is doing- changes elsewhere are immediately apparent.
The only other amps I've heard that were equally as good on kit I'm familiar with (compared them to the 86 I had at an Owston) is Nick's P6100M monoblocks. Couldn't tell any difference between them.
I have to agree Ali, the only sound signature these Amps have, is carried over from other associated gear.
The comparison you make with Nick's Amps is interesting, I have his MCj3 (entry level) Phono Stage and its the best I've owned.
I love its robust full bodied sound and simple no frills approach.
By the way, I got round to adding a tone arm rest for the Mission arm on my TT.
I adapted the original Lenco GL75, with its adjustable height to fit.
https://www.jkwynn.co.uk/Lenco/Pics/Lenco_4_16.jpg
The Black base is a knob off a set of drawers, I drilled and tapped it M8 to suit the locking/mounting collar on the Lenco rest and just glued this assembly to the plinth with epoxy. It means I don't accidently catch the arm and send it flying and it gives a good anchorage, to tie the arm down when transporting the deck.
Ali Tait
18-04-2024, 20:44
Nice job Ken, looks good.
I am glad you are both enjoying them.
I stopped looking for a power amp when I built my “dual mono” 686.
It is all the amplifier I will ever need.
Had a 686 here a few years back, absolutely perfect sound.
No different to my usual amp - Krell KSA50S - but when you think that the Krell would retail today for around ten grand, inflation adjusted... the Neurochrome has more power too. And isn't as big or as heavy.
If I had to get a new power amp I wouldn't think twice.
Kevin/Martin I think every person I've talked to, who's heard these Amps, either in dual mono (single Case) or monoblock form, has said something similar.
Seems to be universal praise for their sound, or lack of it!
Update
https://www.jkwynn.co.uk/686_Mono/Pics/686_08.jpg
This is R19 a surface mount resistor of 1kohm value, I removed it from each of the Amps.
Removing it reduces the gain and by doing so, gives a better gain structure overall, while lowering the Amps already low noise floor even further. It's a recommended modification by the Amps designer Tom Christiansen, as an improvement, if your not concerned about THX gain compatibility, which I'm not.
Its a fiddly little sod to remove, but it's a fairly quick and free modification.
I found it gave an even clearer window into the music.
In my set up, the lower mids and upper bass became fuller and richer.
I think this was because my Pass Pre Amp was now contributing more into the overall gain structure and its character was coming through more.
This really is a cracking amplifier set up and my end game.
Big thanks to Ali for a heads up on this mod. :thumbsup:
I thought you were going to say you lost a filling Ken!:lol:
:lol:
I wish they were that small.
That's alien implant small.
Ali Tait
16-08-2025, 19:28
Aye a bit fiddly to get to and out, but well worth it as Ken says, a free upgrade!
My end game amps too Ken, not heard anything I'd swap them for other than Nick's amps, but having heard them side by side, I couldn't hear any difference.
IMO the gain balance between preamp and power amp should be that for your normal listening level, the volume control on the preamp should be about halfway around its travel. That is, if it can rotate between 7 or 8 o'clock (where it is 'off', or at its minimum) and 4 or 5 o'clock (where there is full output), the volume control should be around 12 o'clock.
Ali Tait
16-08-2025, 20:52
Another reason for me doing this is because of the stepper on my Graaf pre, not enough control on volume- one step being a little too quiet, the next a little too loud. Doing this has solved it. Saves me buying a stepper with 47 ways to swap for the 30 step Noble it comes with.
IMO the gain balance between preamp and power amp should be that for your normal listening level, the volume control on the preamp should be about halfway around its travel. That is, if it can rotate between 7 or 8 o'clock (where it is 'off', or at its minimum) and 4 or 5 o'clock (where there is full output), the volume control should be around 12 o'clock.
My thoughts as well, no point in attenuating the hell out of your source signal.
The Pass volume isn't a single rotation.
If I remember correctly 89 on the display is unity gain (0dB)
Reasonably loud listening is now at 50 on the display, where it was 40/42 previously.
killie99
17-08-2025, 08:08
I’ve had mine set like this since day one as I couldn’t see the sense in that resistor being there - if memory serves me right this sets the gain to 20db?
Ali Tait
17-08-2025, 16:39
Yep correct.
I’ve had mine set like this since day one as I couldn’t see the sense in that resistor being there - if memory serves me right this sets the gain to 20db?
Yes that's right.
--------------------------------------------------------------------------------------------
Assuming 200W (8ohm):
Stock Amplifier to meet THX Standard: Resistor(R19) of 1kohm = Gain 26dB x20(Lin) 2.0V Input Sensitivity.
Mod. for best Gain structure/Lower noise floor: R19 unpopulated = Gain 20dB x10(Lin) 4.0V Input Sensitivity.
So that's 3/3 of us agree the modification is worthwhile and with the amps working within different systems.
My configuration is: Pass XP-12 Balanced Pre Amp/Schiit Lokius Balanced EQ/686 Balanced Monoblocks/4ohm(Nom) Canton CT1000(2) sealed 12" speakers.
Note, I only use one of the filters on the Lokius, to give a mild deep bass boost, centred on 20Hz. It adds nothing (Audible) to the noise floor when switching it in/out.
Just love this set up, it's not the most detailed sound overall, or the deepest bass I've had in my room, my modified NS1000m set up held that position, but it's not far behind.
Where it scores is musicality, it breathes new life into old 60's and 70's vinyl, well recorded pressings in good condition are incredible.
Simple acoustic music, female vocal, is handled just as well as Rock Guitar, Yellow, or a full Orchestra.
This amplification set up will not be changing, its taken me a long time to find the sound I'm happy with, where I can stop listening to the system and focus on the music. I never feel nervous about what's playing or coming up and can relax into the sound.
My vinyl front end is also not going to change: DIY Direct Drive TT/Modified Transfi Linear Arm/Van Den Hull One Special/Pass XP-17 Phono.
The only thing that might change in the future is my Streaming DAC.
I'm quite happy with my modified Eversolo DMP-A6 ME, but this is the area where change is quite rapid and Everchanging if you pardon the pun.
Its interface is lovely, so convenient in use and it sounds detailed and sweet, if maybe not state of the art.
With the next big leap in digital technology, I would consider upgrading this, but only to another combined Streamer/DAC. I think this combination is like fish and chips, meant to go together and with the size of the components, a one box/shelf solution is logical.
The one negative I have, is that my system takes a long time to warm up and hit its sweet spot.
This is not down to the power amps, the Pass Pre Amp takes ages to find its groove. It starts out just a bit sibilant and a bit thick sounding. As it warms up it smooth's out at the top and generally just opens up. It sounds better after 30/40mins, but better still after a couple of hours and improves in smaller increments beyond that.
I'm sure I read somewhere on the Pass website, a remark from Wayne Colburn, designer/partner, that it takes up to 10 hours for it to fully warm up, hence their recommendation to leave it switched on permanently. I've never liked the idea of this, from an energy conservation or safety point of view.
That's my only gripe, once its had an hour or two the magic starts to happen and its well worth the wait.
When I take my set up to the Maverick Show, I fire it all up the day before and leave a digital track on repeat overnight at low volume. Then I crank up the volume when I get up and go for breakfast, which gives it a couple of hours to fully warm up, before folks start arriving.
Had some great comments on the day, with some folks coming back for a second listen, so it must sound good to folks other than myself. :)
hornucopia
22-08-2025, 16:05
You-all can wince now. I plan-initially - to run mine via a Hafler DH 110 pre-amp, (re-capped) .
Sometimes oldies CAN sound good.
I’ve intermittently used a DH 101 over the years, having bought mine in 1982!
Will give me time to mull over things-the acquisition of the 686 rather sudden- I swerved away from initial chase of an Avantgarde Zero set up.
The 686 is a Bigbottle special, with overkill power supplies. Thanks Oli.
Dac is a Reimyo dap 999.ex. Speakers Diptyque DP77s.
Chris in Shirehampton.
Floyddroid
29-08-2025, 12:22
After listening to Ali's last year i would love a pair. Are you bringing these to NEBO Ken?
After listening to Ali's last year i would love a pair. Are you bringing these to NEBO Ken?
Hi Steve, sorry for delay in reply, been on me Hols.
Not sure what to bring this year, as I will only be in a small hatchback car and have little space.
Had to drop out of the Maverick Show for same reason.
The Speakers will have to stay at home, as they wont fit.
Could bring the Neurochrome's and my Pass Pre?
Or a Turntable and Pass Phono?
Will leave it to the last minute and make a decision, based on what other folk will be bringing, but the Amp combo, might be good?
I could also bring the Schiit Lokius EQ unit that sits between Pre and Amps.
P.S. It was mine you heard last time, Ali's the time before :lol:
Ali Tait
09-09-2025, 17:40
Let me know if you're not bringing the amps Ken and I'll bring mine.
Aye a bit fiddly to get to and out, but well worth it as Ken says, a free upgrade!
My end game amps too Ken, not heard anything I'd swap them for other than Nick's amps, but having heard them side by side, I couldn't hear any difference.
Just how fiddly is this?
No need to answer. It is done.
A half hour job. :thumbsup:
Ali Tait
24-03-2026, 14:33
Good stuff. Do you feel it's an improvement?
Hard to tell. I have changed the preamplifier at roughly the same time.
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