Pre amp mods

Having recently bought blind of ebay.......a valve pre amp whose provenance is probabley china and sold through Hong Kong.

The unit out the box worked and had a fair sound, a bit warm and muddled but not unacceptable. So a quick look inside revealed a NAFF [and I now know what it means, thank you bbc2 !] vol pot of such limited quality it make my previous worst [the one out sonic impact] look positively good. So out with the soldering iron, out with the pot, and in with a 50k alps blue I just had around, wired up with silver in ptfe to loss the rather nasty looking ic wire. Now for a listen, less warm more detail and definately more dynamic but still veiled. It was at this point it went to Rsands place for the cable comparisons. If you look in articles section you can see a pic of the pre, is that garish brown thing on the floor.

So after getting crimble out the way and a couple of cable builds, I decided to have a longer look at the signal input side of the pre. The fist thing is the sockets these don't look too bad, on a par with the best maplin do, so they can stay for now. These car connected to the selector switch via short length of Oehlbach the pure sound IC cable then from the selector switch to the pcb by more of this blue cable.
At this point I though it a good idea to have a quick search of the web to see if it was a pucker cable, supprise supprise it is

http://www.bestes-kabel.de/CMS/product-detail.php?sprache=en&artikelnummer=1014

As I expected this is billed as mid price cable, I wonder how many people have been fooled ! More of that later!

The cable is a typical foamed insulation with lap screen and a silver plated stranded core. To cut a long story short I ripped it all out and rewired with solid twisted pair of 0.5mm 4n silver in ptfe sleeve. Rebuilt, put back into system switch on leave to warm up, play cd .......

I don't often get those bloody hell moments but I had on ...so were did the music come from! fast clean dynamic full bass sharpe imaging. That cable was strangling the pre, it must be utter shi*e.
So hears a warning if anyones got any Oehlbach the pure sound , throw it away now do yourself a massive favour!

I was going to have a swap of some of the resistors in the signal path but its now sounding so good I'm going to wait a bit !

Oh didn't I mention what the pre was, silly me! see here.

ebay item number: 5786540808

With the obvious caveats listed above this is a fine pre for the price...[mine was just over half that price !!] so making it excellent value. As to the vendor can't fault him, he even answers emails!

My next mods for this pre will be to loose the front panel and replace with 5mm mirror black perspex and some black knobs of my own design.

 

Hi,

The Circuit is basically a Matisse Reference line. A Preamp BTW that shares the honours as "sonically most manipulative" together with the Jadis DPL in my list.... So it may be better termed an effect unit. That said, if you like the effect, n'joy the results.

When you get tired of it drop me a line and I'll show you how to convert it to the Kondo M7 Line design, something that sounds much more balanced but still "nice".

Ciao T

 

Your on .....I'm always looking to super charge things....

Do you think there's more milage in your mods over component swapping ?

 

Hi,

Component swapping can make more or less small differences, changes in topology make for a much bigger change.

I'm short on time right now so keep the preamp for a few weeks as is or play with passive components, we'll talk again about this one then....

Ciao T

 

Cheers.....I'll be in touch

 

Nice post Pete and thanks for sharing, I'd certainly take T up on his offer, the guy knows his valves :MILD:

 

So .....what arrived in the post today

a set of relays to switch four source and a hundred step relay driven attenuator.

The Qestion now is does it matter that I'm moving the volume pot from beyond the valve stage to before it?

 

So more work done today.....

the two switching/stepped attenuator boards, there associate psu and IR controler have now been fitted.

Definately a much cleaner sound, must have been the nasty selector switch and the alps pot having there wicked way with the music signal. Though the dynamics have not improved to match ?

I've fitted a filter switch iec assembly to the rear cutting the 50mm by 20mm whole in the sheet metal was a beach. Not certain about the filter may be squashing the dynamics...so I may have to butcher the assembly.

The controler board has a numerical display in bright and I mean bright blue... this will be behind a perspex fascia I was hjoping the black that I have was going to be translucent , but it isn't so it looks like I've to chop out a window. At least perspex is relatively soft!

 

Where from?

Was it one of these? Electronic Relay Control 256 step Volume, 4 Channel I/P

And have you had a look at these? http://electronics.dantimax.dk/Kits/index.html

How are you progressing?

 

It looks very similar though mine has a board for each channel with input switching on board, the romote is the same.

I'd look at the motorised alps but I've always felt the alps was loosing something, I had a standard 50k blue fitted to start with.

I'm working on the preamps valve section at present running it in passive mode ie the input through the selectors and the vol pot output straight to the out puts of the pre. Sound is clean fast and a little laid back but better than almost everyother passive that a I've used [which is not many].

 

Just got sent a dead NOS III .....this one appears to have standard components anyone else had a look ?

I've some obvious mods ...silver rewire etc but anyone done anything else ?

posted in the wrong place ....duh!

 

Hi,

Obvious ones:

1) Adjust Reference Resistor, I/V Resistors and Supply Voltage for best dynamic range (needs FFT).

2) Change Series regulator for DAC to CCS powered TL431 Shunt regulator.

3) Fit (switchable?) "anti-sinc(x)" filter.

4) Slow the Receiver PLL down as much as possible without taking more than 10 seconds to achieve "lock" or fit 2-Speed PLL.

Any single one of the above will have a much bigger imapct than silverwire....

Ciao T

 

Pete,
Look forward to hearing the pre later in the year.
Ref the DAC, errr, guess that one's my fault. Ooops.

 

There is a NOS 3 now?

 

Just replaced the valves from the cheap chinese ones to cheap russian sovtecs ....cleaner faster sound bass in oodles. Now sounds better in active mode than passive.