5881 monoblocks

[Garyk]

I started with the 5881 mk2 ,loved it but needed a little more power for my neat momentum's
Got the kel 80 monoblocks and they were nice, but is still enjoyed going back to my 5881.
I found a set of 5881 monoblocks on flea bay and brought them home.
They sound lovely and have that snappy bass that I love
I figured that somebody on here put these together.
They came with a huge folder of information including hand drawn schematics and little comments her and there.

I'm really interested in the history of these ....one offs...maybe?
Own up ...who did it?

https://rover.ebay.com/rover/0/0/0?m...m/153522501826

[John Caswell]

Hi Gary,
Well certainly all the three 5881 variations were never ever done as mono blocks so this must be a home-brew by someone. Regret I cannot throw any further light on them.

John

[Richard]

They look a nice job Gary but I can't remember anyone on the forum posting about such a project. Can you email the seller and ask them?

[Garyk]

Hello.
The seller was not the person who built the amps, so there is no contact connection there.
I have a suspicion though..... there was a thread /post on here that raised the idea in 2016 but it went cold after a few replies.
It's just that I'm intrigued really.

I've got some experiments to sort out a ground loop as they are excessively hummy. And when I heard them at the sellers house, they were silent ... even though i brought my own pre amp along.
They sound very punchy and forward so far and even at 40 watts sound much more powerful than the kel 80 monos at 70watts........if , that is you can hear a powerful sound

[Richard]

Was it Colin's post?
http://www.world-designs.co.uk/forum...ight=5881+mono
He mentions 5881PSE (parallel single ended) version though. Perhaps he'll come in with some more info.

Thoughts about yours are that they are badged MkII which suggests they will be very sensitive. The WAD MkII was 75mV for full output. That will make them seem very powerful and loud when using the vol control compared with the 400mV sensitivity of Kel80.

The MkII also had lowered feedback which will increase noise though it shouldn't necessarily make hum worse. If your speakers are quite sensitive (c. 90db 1W/m) you may find the amp too sensitive in a quiet room at your house rather than a demo elsewhere.

What source are you using, vinyl can be more difficult with noise/hum issues than CD for example.

[Richard]

Do you have any circuit info on the amps Gary? The eBay advert shows just one chassis which looks like a stereo chassis. It only has one mains transformer so I assumed there must be 2 of these chassis each wired as a monobloc.


Can you clarify what you have chassis-wise,

[Garyk]

Hello Richard

Yes it was Collins post I had referred to.
So the chassis is a stereo 5881 x 2
So the photo shows 1 of the 2 identical units.
I have taken photos myself but cant make them small enough to fit on the forum as I'm not at all techie.
I have loads of info and hand drawn schematics but I dont understand electronics enough to make sense of it all.
The inputs. One of the two inputs on each mono has a rubber boot on it but internally it is wired and I was surprised to see that.

My speakers are 87.5 db so need a bit of a push....my stereo 5881 struggled a bit if I played it loud.
My sources are a CD player with internal valve dac
And node 2 music streamer.
Preamp is an icon audio la4 mk 2.


I want to do what I can and eliminate the low hanging fruit re the humm before I take it to somebody professionally

So far I've tidied up all my cables , speaker cable and interconnects are well away from the power.
The monos and preamp are run in shielded power cable that I made from 1.5mm sy cable .
Part of my ground loop trials were that i disconnected earth at the ice plug end and connected shield and earth at the mains plug end except for the preamp and then grounded all the gear to the pre ...... hoping that I would reduce the loops but now I've type that sentence, i have realised that all my interconnects have outer connections to ground so I've got loops again.
And this made no difference anyhow.

Weird thing is that my stereo 5881 is quiet when connected to the system.

[John Caswell]

Gary,
You could always take it to someone thoroughly unprofessional, like me
I am in Finchampstead
PM if interested.

John

[Richard]

Yes I see, 2 stereo amps converted to mono blocs then by the look of it. As you have the notes and drawings, and given what you say of your own limitations, I'd definitely let someone more unprofessional like our John look at it for you

[colin.hepburn]

Hi Gary/All
Well I did not build these Amps I wish
That thread was just me bouncing around an idea I had at the time using 5K Hammond single ended Transformers using that 5881 circuit with the 807s not relevant now
But Yes I would get our Dr. John to have a look at the amps he will sort them out for you
Hope that help a bit
Colin