My first mod

The little ones are "condensateurs chimiques" (whatever that means) 330uF 15V, dont know the brand...

What, if anything at all, should I replace them with ?

 

I see transistors in the schema, are they on the power supply...

 

After seeing the schema, a friend of mine said I dont need any extra resistors, as the amplifier already has resistors between ground and input gate...

 

Sorry your friend is wrong......there no nice way to say it !

the volume pot contributes greatly to the impedance of the curcuit ..the other resistance to ground is to make the impedance of the curcuit even greater ..ie 100k total ?

There appear to be no dc coupling caps in the input....this can be very dangerous if the source has none either, but it will make the amp sound good !

on the schematic .....

look at the top and middle under the second yellow/red voltage banner ...the component dirrectly beneath is a dc blocking cap to the second half of the amp ..its mate for the other channel can be found as a mirror image ...

the small electrolytic's are possibly to do with the psu ..but the big wimas may be the caps I've mentioned. The wimas are pretty good but pio's in my opinion will be better ...having tried similar swaps in other gear.

 

Antonio,

Why do you feel the need to modify your new amp? What aspects of it's sound do you not like? Unless you are experienced in these matters, I'd be more concerned about making it worse and harder to sell in the future as a result of any mods.

 

Dev,

You are absolutely right, but...

I only need power, it makes me nervous to have all that wire and relays for nothing...

And I need an excuse to buy a soldering iron...

 

He repplies: no problema removing the pot because the tubes are polarized with a 1M resistence, wich is the limit for such input tubes...

 

Hi antonio

A good friend of mine that works on valve amps for a living, when modifying, doesn't change the circuit - simply replaces existing components for alternatives of a higher quality.

He does this because it won't change the fundamental sound of the amp, which may be a negative thing to do, instead it should just provide improvements.

 

Changing the circuit impedance will affect the sound .....if you don't replace the missing portion of impedance created by the vol pot, by subing the required resistance between signal and ground.

wether you do this is entirely up to yourself......but if you don't you will be altering the way the source "see's" the amp .....

I can't say more than that .....personally I'd maintain the the circuits impedances as designed

the resistance you mention may be doing another job...I can't read any of the schematics details to be certain.

 

I dont know why, but lost the will to play engineer...

It is much easier to just buy NOS tubes on ebay...

 

FWIW Antonio, I think you've done the right thing. If you like the amp why tinker with it. If you are confident that you have sufficient knowledge to improve it then that's another story.

Now just sit back and enjoy listening to it.

 

I am playing with tubes, the girlfriend just called saying the Siemens 6SN7WGTA arrived...

And last night I won an auction for a quad of Siemens EL34 at the same price as my SED...

Why SIEMENS, you ask...

I found out they didnt make most tubes, but outsourced from the best in Europe, still most people prefer the "original" brand, so the prices are not as inflated...

 

I was told on a French forum that the "famous" resistor has 1 M, so 100 K more or less shouldnt be significant...

The Siemens 6SN7WGTA are great, ordered another pair as backup...

 

I am very stuburn and decided to try the mod, without resistors...

I bought everything I need but have one question, wich wire of this two should I use...

1 - Coaxial, silver or silver coated multi strand, should I get rid of all the layers, except the central wire and the white plastic cylinder ?

2 - Speaker cable, copper single strand, kind of cloth cover...

 

if you have anything like a solid core ....to hook the signal up ...but you can use the shielded and ground the shield to earth at one end connecting the central core to pass the signal .....

It should not hurt to run without the resistor !

 

The solid core is speaker cable, no shield, I suppose, the coaxial is multi strand, and it seems quite difficult, (for me), to ground the shield. everything is so small...

 

2.5 hours, several times didnt give up only because it was already too dificult to go back...

Even the "motherboard" had to came out to be able to disconnect the leads to amp-in, from volume... In the picture it looked so easy, but I didnt have much more than 1 mm between solder points... Of course the original RCAs where soldered to the input PCB, luckily I suspected it and bought a pair...

But... It worked, without net... open, modified, closed, then power on...

Does it sound better ? Of course it does, minus 3 meters of cable between input and amp, it had signal and ground for each channel to pot and back, 8 runs of wire... minus relay, pot and 8 solder points, or nine, as I shorted the RCAs grounds and made just one connection to amp-in ground...

As I was at it, I also shortened the speaker leads, minus 1.5 meters x 4, nine meters less wire total, in the signal path...

I am tired and excited, so I didnt hear any discs yet, only my usual Mezzo and MCM satellite on hi-def box, it sounds smoother, cleaner, less digital, if you know what I mean...

I am happy, next I have to get proper RCAs, silver/teflon unifilar cable, and replace the shity stuff I had available...

Thanks for your help...

 

Any before/after pics?

 

good work ....it can be very nerve wracking on your first mod.

 

Pics of before (from the net) are allready in the thread, the only differences I noticed where PCBs hidding the output transformers...

I removed the input PCB + wiring from selector, just unplug, bonus, the time counter was powered from the selector, so it is off...

Also, and more important, removed all the wirring of the volume pot, 4 runs of double cable, that was the difficult part...

Didnt take a picture of after, because the soldering doesnt look perfect like elsewhere...

Will after replacing with better RCAs, Zanash, you have message...