R&D
Headphone Amplifier |
This Headphone Amplifier is the product of my last research Project started 5 years ago .
Searching for the best sounding diagrams I have prototyped and studied variety of famous circuitry. They appear on the market and manufacturers like to give to give them own names, although they all have been developed long time ago and have been widely used not only in audio applications. |
So.. of course to make my life easy I started with simple. Mosfet follower was the first as I thought that just current amplification will solve "sounding" problems enough. ....This device was not listened more then 10 minutes. It was doing absolutely nothing and I Switched to Op Amp still trying to get out easy . I choose one which has the best by parameters and reviews: |
...it didn't take much time to assemble this Op Amp amplifier on a prototype board and put in a box of old USB device. Sound? Yes it was sounding very well all clear , crisp and even transparent.....seriously, no negative memories I have about it. But....since that time it is somewhere on the shelves and nothing can make me plug it to system and listen again after I have my last tube amplifier done. Why I put it away and start doing something else?- Because nobody could listen to it in my house long enough, as to any other transistor based device. This is how I put the end to my transistor and "transistors combinations" (solid state) vain trials, which started sometimes in 80-s. |
I plunged again into the tube schematics after a long time. Soon I found something interesting: schematics which was developed at dawn of TV era for cable signal transfer was used now for audio signals with lots of public excitements . As it was simple enough schematic I decided to build it again secretly hoping that, this would be the final one. |
I built few of them,one also for my son as well. Curious how it sounds? It sounds good and as it is based on tube schematics and therefore has to have a very good distortions rate.
Also this is why row of annoying harmonics and thereby listener fatigue does not present. We`ve been using them for more than a year. The only thing is that they required High Impedance Headphones . We`ve been losing lower part of musical spectra (from baritone to bass- this part keeps the most information of musical spectra ) when plugging Headphones less than 100 oHms and it was not acceptable at all. And again I had to do something about it... |
As you already know , Output Transformer is the heart of Tube Amplifier and what sound you will get mostly depends on how it is done. To avoid any problem in future with remote suppliers I choose Hammonds Transformers for my output transformers core as their products are unfailing and always available. There are endless combinations of Output transformer winding, sectioning and section separation. Theoretical calculations newer bring you to the precise variant - you have to build them, try, adjust to coupled tube (tubes), take parameters and repeat this until you'll get the sought-for. This is why to get the Top sonic results I had to make all this research for particular transformers types which I choose for this project. My long time experience in transformer building I got the necessary parameters and outstanding sound transparency just after fifth experimental transformer and this one went into the prototype. (secret is in transformer). |
Type of transformer for power supply is not that critical for this stage of amplification and from the beginning of these projects I start looking for well established suppliers, who can be timely reliable and could give me reasonable prices.
Different Power transformers have been ordered at different manufacturers by my Specifications. They have been received and tested in order to complete list of experienced and reliable partners. This Amplifier uses PCB in power supply (only) and the same search was done for these PCB suppliers also. |
Few words about prices for power transformers:
It is possible to find some power transformers locally but when it comes to custom specifications, prices are getting too high. The same story is with Output transformers : you can buy ordinary ones whatever manufacturer thinks is good, but custom order- by my own winding specifications - is that high that the total price for transformers set only exceeds the device Total price- ( two output transformers, Power transformer and Choke). |
I stopped enclosures engineering as I could pick up perfectly fitted to my sizes enclosures from Hammond .
Besides I tested and found their steel good for electromagnetic shielding.
Electronic tests and mode adjustments have been done with different tools and for the final tuning was used Digital Spectral Analyzer which makes researcher able to achieve accuracy impossible by regular measuring equipment like Oscilloscope, multimeter signal generator e.tc..
Signal-to-noise ratio measurements for max. output level at 60/120 Hz with different filters applied. Like an example here I show " A-weighted" and "not weighted" signal-to-noise reading for the same intensity. As you can see there is significant difference in readings for the same signal. Not weighted filter is the most "honest". Pay attention to which filter manufacturer mentions in specifications. Distortions adjustment (electronic tuning) process controlled by Spectra Analyzer. Unique process , often requires to replace all passive parts in circuitry. |
Dynamic (under load) frequency response of this headphone amplifier.
This chart expresses real wideband of the amplifier. Frequency band in no load condition usually easy stretches to hundreds of thousands Hz, but we are not interested in it. 30-20 000 Hz and 20 000- 50 000 Hz ( recession starts at 50 000 with -2 dB) |
When prototype stage was finished and electronic parameters adjusted, I made fixture for fast assembling. It is helpful to put parts together before placing in standard chassis. As you can mention rare spatial 3D point-to-point cross normal connection technics is applied to minimize signal interference in parts as well. No parts are mounted on chassis. Minimum parts used, no wires in amplification path and one central ground point for the whole circuitry. Input signal lines (from RCA input jacks) run through solid steel shielding tube to Volume regulator. (Silver line in the chassis). |