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HeadLine
Page 3, Construction. December 10, 2006
Some important things to remember are:
And let's not forget how to connect the headphone connector to the amp. On
wikipedia I found the following picture.
I found a nice die cast aluminum enclosure in the webshop of Conrad. These enclosures are relatively cheap, yet sturdy boxes that are easy to work with. Only the enclosures are not finished.
After drilling the holes for the feet, the enclosure looks as follows:
After a while, it is possible to mount the feet. Not shown on this picture are the input connector for 20Vac on the back and the two cinch connectors (line in).
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The following pictur is taken halfway. As you can see I decided to use a step-up
transformer
for the B+. It is the blue transformer on the top-left which I glued to the
enclosure using silicone kit. Normally the kit will hold just fin, but I may
decide to screw the transformer to the top of the amp just in case.
the two caps on the right are the output caps of the amp. They are both 250V/100uF. The two blue caps in the middle are BC 1uF MKP.
I use a separate external transformer of dual 12V to supply the amp with power.On the top left corner the inlet is shown and just below the voltage regulator for the heaters. The power of the regulator (78S12) is 3A and this may be just the right regulator. The small voltage regultor board is a kit sold by Conrad Electronics .
The choke has nog yet been connected. I'm waiting for the kit to dry so I can start testing the powersupply.
The moment of truth: The amp is more or less finished. Of course I need to get rid of all kind of temporary stuff such as a volume pot that will be replaced by better stuff in the next week. Nevertheless, I decided to give the amp a burn in; the amp need to lay on its side as I needed the tubes to be in place and at the same time be able to work on the guts of the amp.
I tested the amp with my Apple iPod (old model) and a pair of Senheisser HD 424 headphones.
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This
little amp is my reference as far as headphone amplification is concerned. It's
a Little Dot II++ The ++ tell you that this is a modified version of the modified
version. The Little Dot 2 a headphone amp with standard tubes which are microphonic.
The 2+ version contains Wima MKP capacitors and a pair of NOS EF92 pethode tubes.
The 2++ version does contain two military output tubes 6C19P (Russian 6S19P)
which are a lot better than the standard output tubes supplied with the cheapest
version.
Of course I will compare my HeadLine amp with the LD at some point in time, but since my amp has not yet been finished and the little dot is only a few days with us, serious reviews have to wait for a while.
Nevertheless, first impression of Annemarie listening to the the headline amp is: "Hmm, am I wrong or does this one sound as least as good as the small amp upstairs ?" (on my desk).
Still, I like the Little Dot 2++ a lot, so today I ordered a few spare tubes
for the amp. After all, the 6C19P is a rare animal that may not be available
in a few years.
On the picture one can see that I still have to populate the stepped attenuator
or buy a decent ALPs pot (in the meanwhile I use a cheap pot).
I'm also thinking whther I need another cap with a small value in parallel with the 2 blue 100uF caps on the left. I have a few Blackgate N 2.2uF caps available.
As said on the next page, the sound of the amp was good. However there was always a slight noise (humm) coming from the amp even at the lowest volume settings. When looking for the source of this humm I found out that there was a ripple on the B+ lines coming from the step-up transformer. Initially I thought that it was due to the cheap transformer being put to the max but I found out that the same transformer did not give any problems outside the enclosure.
Hmm, I've had that before with a phono amp, the transformer is not right for mounting either on that position or it is not suitable at all for mouting in a metal box. The latter applies I'm afraid.
Luckily I received a small toroidal transformer (for another project) that I could misuse for the HeadLine as this transformer proved to be very quiet in this setup. Problem was that I had to redesign the layout of the internals of the amp since the toroidal was too big to be used in the same place as the original blue flat tranny.
While taking apart the amp I decided to enhance the amp in a few other areas as well, before putting it together again:
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New PSU with 10nF caps and toroidal Step-Up
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After putting everything together again I can say that the amp now is finished... (as long as it lasts)
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| Cooler for Voltage Regulator |
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Hardwired CLC filtering
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