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Tube
Phono Equaliser
“Loekie”
part 2: Construction and Assembly
Last modified: 20-Apr-2003
I will be using the same little Conrad housing for Loekie as I used for Tweety. And, I've ordered an additional one because knowing myself a little I expect that after the amp I might want to improve Granny as well.
Fortunately, a lot of the required components I do already have at home, and
still the 
assembly
can only start if I have that stupid little housing (Conrad takes more than
two weeks to deliver even the simplest orders). A few times already I mounted
the tubes in a horizontal way, so this is not new to me anymore.
But fitting the tube sockets and the soldering strips is not my favorite work. First I have to get 10cm of the aluminum L-profile I bought in the local shop. It is available in 2-meter lengths and the L-shape has a short side of 2cm and a long side of 5cm. The 5-cm leg is standing upright and we have to drill the holes for the tube sockets and nuts'n'bolts. Depending on the tube sockets used you may have to "share" the little mounting holes between two adjacent tubes. I position the aluminum bracket such that the tubes are facing forward to the front plate. Since we are short on floorspace mount the tubes as close as possible to the front plate but remember that you have to be able to remove tubes without having to take your amp apart. In other words: Not too close.
Behind the aluminum bracket I placed two strips with soldering lugs parallel and two cm. apart. It will allow me to free-wire all components in the amp without the risk of short-circuit.
In the back plate I drilled holes for the RCA chassis connectors, and the Hirschmann power connector (3+a) I use to get both heater supply and B+ to the amp. I used the same layout for the Hirschmann connector as I did for Tweety/Granny which will enable me to switch between Tweety and Loekie and the power supplies without having to require stuff.
When all components were in, I started with designing the layout of the housing, connectors and the components including soldering strips (plumbing).
In
the output section I used this blue Jensen audio cap. I'm still thinking of
replacing this cap with a later yellow model or even another type (Auricap?).
But most likely this will be a future mod.
All resistors are 1W/1% metalfilm types or better. In a phono amp I do not think that carbon resistors are a good choice. And I have good experience with these metal film resistors.
The tubes I used are ECC83 type from JJ (former Tesla). These are newly manufactured but very good types sold by AE-Europe in NL. I'm very happy with my expensive NOS tubes in Scratch, but I must say that the new JJ's are very close.
I have tried Sovtek tubes but I'm not very happy with their sound. Many people use the LPS types and are very happy with these, I've the WA types and these are not so good imho.
I want to highlight the differences between Tweety and Loekie as far as the difference in components is concerned. Inside the amplifier itself, in tweety the B+ is last corrected by two Philips/BC capacitors. In Loekie however these caps are replaces by Black Gate caps of 350V/22uF.
For the coupling caps in the cathode I used Black Gates of 100uF as well. There are the more expensive FK types. I have the standard types as well, but do not have a one to one comparison with the FK types. For the Cathode decoupling I did the same: Here I substituted the standard type Elco's by Black Gate (100uF) types.
The audio cap used in Tweety is a Audyn tin-foil type. I like this cap very much, although I did not hear much difference with the standard MKP types. In Loekie I have used an Auricap of 0.47uF between first and second stage. The 100nF capacitor in the mu-Follower is an Auricap as well. The 22nF capacitor in the RIAA filter is a Styroflex type (1%) and the 2.2nF cap is a Polypropylene 1% type. For the design of the RIAA filter please read the background section.
The audiocapacitor used at the output is a Blue Jensen capacitor of 0.36uF. I received warnings that these may not be the best capacitors for that place, so I may be upgrading these caps at a later stage for a better alternative.
The box I will use for Loekie is a well-known old friend I also used for Tweety.
It's compact dimensions do have a disadvantage as well: It will be difficult
to layout all components in Loekie. Especially as the mu-follower and filter
circuitry requires even more space than before. Anyway, I do hope I have enough
soldering lugs 
available
to connect all components.
Something that really pisses me off is when I do not succeed in getting the holes for all connectors perfectly in line. This of-course can be avoided easily when buying better drilling tools, but I do not have the money to buy all the tools just when I think I could use them. I therefore hope to find a nice package under the X-mas tree, who knows. Well, fortunately I did succeed in getting a nice hole for the Hirschmann power connector and that made me feel better. Well, it's good but not perfect but it works.
Anyway, apart from the cosmetic scars the housing was put together quickly and therefore the work on the inside could begin.
Just like the previous time I will position the three tubes horizontally on a L-shaped aluminum profile and the tube positioned to the front bezel. This way I will make room for all the components that need to find a place at the other side of the aluminum strip where I need to connect many components to the sockets.
I
begin with my(?) standard layout by connecting the wires for the heater supply
to pins 4 and 5 of the tube sockets. The middle tube is used for the input stage,
with the two output tubes for left and right channels on the outside. On the
two outer tubes I connected a capacitor of 22 uF over the heater pins.
In order to give all components their place in this small box and still be
able to use free wiring I make use of two parallel strips of soldering lugs
about 2 cm apart so that I can layout components between these two strips. Even
more than for Tweety I was concerned about the space being available to me during
this phase of the project, and also because the Black gate caps used for the
Cathode were of the Radial type and had to stand upright in 
the
box between the two soldering strips. And as a mu-Follower uses more components
anyway than a SRPP I had to find room for more components in the same claustrophobic
box with internal dimensions of 16*10*10 cm. On the picture on the right above
one can see that there is less structure in the box than before. That's a pity,
because modifications to Loekie will be a pain in the future (so a better motivation
for doing it right the first time is hard to find), as I know from a past experience
of modifying Tweety that there is no soldering iron in this world that is thin
enough.
For a first listening impression of Loekie continue reading on page 4. After having listened to Loekie for a day I finished the cosmetic by adding a nice red LED to the front-panel of the amplifier (Tweety has a yellow one). I fastened the tope plate and gave it a place in my audiorack (see top picture).
As explained above, with the new setup I got rid of the remaining Humm in the circuit. Like always some experiments with ground connection between step-up, phono pre and the amp were necessary for the best noise and humm results. Also I changed some interconnects and repositioned the power cables to avoid parallel position of phono interconnects and power cables.
Hmm well, sure, just to name a few:
I
would like to know whether I will get even better sound when I decouple the
Alu L bracket from the rest of the chassis. At this moment shocks etc. coming
from the environment can reach the tubes (microphony).However, for the moment I'm finished with Loekie and it's time to have it break in during a period of at least 4 weeks. During this period I will keep it on 24 hours a day in order to have the Black Gates and other components get used to their new environment. According to the manufacturer, Black Gate capacitors need at least 2 months to break in before they perform at their best, and I will wait in patience (not)...
Fortunately, the X-mas holidays are there again and therefore the break-in
period can take place in the family environment while listening to music with
a good glass of wine and a Dutch "Appelflap" or "Olieboll"
(Silvester cakes).
| << Part 1: Introduction and Schematics | Part 3: A Power Supply for Loekie>> |
© Maarten&Annemarie, November 2002, 2003, 2006