Amp Mains.

Just thought I'd post up details of my latest bit of DIY.

Firstly, I upgraded my amp from an Affordable Valve Company EL34 to a PrimaLuna Prologue2 KT88. I initially ran the amp with my old 18AWG mains kettle lead (supplied with the AVC amp). From the off, it is a much better amp...better bass, better treble, better depth to soundstage, better/more focused placement of instruments etc.

I recieved the PrimaLuna lead later that week, and promptly modified it before attaching it to the Prologue2.

Here is the lead:


and here is the MK Toughplug:


1) The lead supplied with the PrimaLuna is a great chunky 3AWG 3-core cable - so cost so far £0
2) I looped the IEC end of the cable 5 times (couldn't fit any more as cable too thick) around an RF ring - cost £1.50 from Maplins, and secured it with a simple tie wrap - cost £0.02 from Robert Dyas.
3) I changed one end to the MK Plug (notice the silver contacts esp on the fuse ) - cost £0 (found in my garage)
4) Just proximal to the plug I wrapped some black insulation tape round and round to make the "stem" thicker - cost £0 (any tape will do here). Doing this a bit further down as well left a 1/2inch gap between them, around which I closed another simple RF ring - cost £2.00 from Maplins

Total cost £3.52
Total time taken - about 10minutes

Effects? definite improvement in sound from amp...not a big step (it's quite subtle) but worth giving it a go considering how cheap and easy it is. Slightly quieter background and improved bass were the most obvious. As a bonus it's also completely safe (you're effectively only getting a better plug, thicker lead and some RFIstoppers).

 

The ferrite ring will strangle your dynamics .....

I don't know the cable you have used ...but in my experience a good shielded three core will work wonders. The MK pluga are ok but take care when you screw down the cable clamps...I've had them snap. One zero cost thin you can do is polish the pins. I use a fine diamond file to level the surface, then a fine diamond buffer in my dremel, and finish with duraglit , you can use cilit bang to chemically clean the brass contact surfaces. You should end up with a mirror finish. The fuse holder and fuse end caps can be polished to ....and get a purple ohp pen [stadler] and colour in the ends. I've no idea why that should do anything but it does[its not a night and day thing,just an extra nth]. If you use a shielded cable only connect it at the wall socket end. Decent IEC plugs will also help.

I you still have a problem still with RF/EMI you need to deal with the source...ie light dimmers or fridges

 

I'n not sure about Ferrite strangling dyamnics..
But an £80 cable from someone like Krystal Cables would get you a solid silver, sheilded power chord that would really make a differnce to the sound. And I suspect the difference would be even more obvious.

That said however, for a virtually free upgrade it is worth a go. I might knock one up this afternoon and compare it tomorrow (got some of the wigwam clan comming round for a bake off.) I'll let you know what we find.

Cheers,
JAmes.

 

The insertion loss at 50Hz of a ferrite ring used in the way shown is going to be small; less than a conventional common mode choke found in a mains filter for instance. For this reason I think ferrites on power cables are the better solution to suppress common mode noise at MHz. I use ferrite clamps internally on my CD player to good effect and externally of my amplifier power cord.

Nice idea. Clean contacts reduce the susceptibility to pick-up of EMI if you happen to live close to a source of potential interference. Not sure about the purple pens?

 

Nowt like good old brasso on your plugs and fuses, finish off with some Isoprop alchohol.

Glad you like the KT88's, as your finding they are quite different from the EL34's.

 

Yes, KT88's make good amps. And you can have one for just £550 delivered, see my ad under Private Ads ! ( Shameless plug )

 

I'm not sure what individually is doing what (it would be a pain to deconstruct the leads and add things bit by bit, now that they're completed).

I do know that swopping from an 18awg kettle lead to:

Thicker 3awg cable and a 'proper' MK silver toughplug and adding the ferrites as shown, all together results in a subtle improvement.

I haven't got any cillit bang but do have some brasso and isoprpyl alky lying around.....i suppose that'll do?

T-bone: yes, the KT88's have better bass and higher sparkly treble.......but I do sometimes miss the old EL34 midrange....I might order some and stick 'em in to see how different they are (with the amp being equal so I am hearing tube rather than amp differences if you see what i mean)


Cloth ears: is it self-biasing with 2 years warranty and newly run-in tubes........or is it manual bias, with no warranty, and used tubes ....I just think the prologue two is definitely worth the cost c.f. the other valve amps out there.

 

Gaffer; think thats a fair comment regarding the EL34's v the KT88's, the 34's are more trad sounding (warmer, cuddly etc) whilst the KT88's are classed as been more modern sounding, I use 34's but would like a set of KT88's and/or some new tung-sol 6550's.

That amp of cloths is a good amp but the prolouge does meet all your criteria, btw I wasnt calling it in anyway over on hfc (it was me who got flamed by that muppet) just giving a balanced view, but Ive got to say this is the closest you'll get to a 'plug and play' valve amp.

Brasso will be fine, give your shiny bits a good scrubbing until you can see your face in them and finish off with the isoprop. Dont forget the fuses, your going to be amazed and the much that comes off.

 

I'm not a hundred percent on the biasing. I think its fixed but you can easily research that. What won't be easy to find is the value , unless you are a suitable technician. Also, just to clarify, the amp is almost two years old , working fine, but will eventually need a revalve, when I don't know. Its a good amp so come on , hurry up and buy it.

 

its is fixed, but easily adjusted. Id have it but Ive no money, which is a stumblin' block really.

 

Nice amp cloth ears, but my prologue 2 is really grooving the more i listen to it.

Thanx to t-bones help (thank you T-bone ) I managed to bias my AVC amp (it was at -40 v dc, rather than 35v) but the primaluna still sounds better.

 

Ah but Gaffer you refer to the EL34 amp don't you? That bias figure will be different will it not, for the KT88. I was concerned someone might write that down and assume it to be correct when they book it in somewhere for revalving. Also, this one is about double the price remember and different valves and transformers so I don't know how it sounds compared to the Prima Luna, not that I'm making any criticism of it. The amp is only £550 delivered.
So come on then, buy my amp folks, :student: , yet another shameless plug.

 

now I am confused!

 

I mentioned it a couple of times in other threads where there was a connection. Shameless.