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niss_man

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niss_man last won the day on March 2 2017

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About niss_man

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  • Birthday July 2

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    Brisbane
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    Australia
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    Simon

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  1. I have recived interest from a local buyer who will pick it up this week. If the sale falls through I will get in contact with the next bidder.
  2. Item: Behringer DEQ2496 and FBQ2496 Location: Brisbane Price: $150 Plus postage Item Condition: Excellent Reason for selling: Bought a couple of years ago with intent to use but never have. Too many projects on the go. Payment Method: Pickup - Cash, Paypal, COD Only Extra Info: Photos:
  3. Another LDR attenuator. This one uses arduino to create an attenuator that does not need matched LRD's and can be calibrated for perfect channel image and variable input impedance up to 50K ohms to match whatever amp your connecting it to.
  4. As a final post. There is one other mod that can be done to the power amp stage circuit of this amp called a "Baxandal diode mod". I have performed this mod to @lebone 's amplifier so I will be taking this over to his place and making a direct comparison between the 2 before deciding to do this last mod on this amp. The mod is supposed to drastically improve distortion levels. From what audio memory I have, I thought it made the bass slightly tighter and clarity across the audio band seemed to improve. A side by side comparison should be good because audio memory quickly fades especial in between performing hours of modification.
  5. Some final power measurement through the oscilloscope using 7.3ohm resistors as load. Power out both chanels driven just before clipping. 18.8v peak. 18.8 x 0.71 = 13.35V Rms Power = 13.3 x ( 13.35 / 7.3) = 24.2 W both channels driven Clipping on both channels Power output one channel driven = 29.6 W
  6. Some final pics before it gets put back into use as the lounge room amplifier. Wood split gone. After fixing the splits, I gave the wood cover a light sand and sprayed on a few coats of clear laquer satin finish. The scratch is still visible in the right light/angle but is better than before. That cover is sexy A clean up and de-oxit of terminals and connections. The Black base plate had a sand, service stickers removed and re-painted satin black. As good as I can get it. Its funny those marks on the tone control metal cover look like an actual hand print. Maybe from the manufacturing process? who knows.. Power amp board. The pots were originally all quite stiff in their action. Like someone may have put lots of wd40 that had gone tacky with time. So all the pots and switches were removed and cleanned properly to give a nice smooth action. Cheers Simon
  7. Amplifier board parts. Its had a nice clean inside as well. Note the early models have these UFO ceramic transistors. I left them alone as they are excellent Mil spec ones and I like them and they test fine and they look really cool. Pots are changed to multi turn types. After amp was adjusted and bias set now..... Final LC measurement is 1.43 - 1.22 = 0.21 % THD back to correct specs RC 1.45 - 1.22 = 0.23% THD also excellent.
  8. This is the Phono stage board. It has been modded to have a more acurate riaa curve and is the same topology as found in the AU-666, AU-777 and later Sansui phono stages. The modified AU-555A RIAA equalization is accurate ±0.2dB from 20Hz-20kHz.
  9. Tone control board parts. I also replace the transistors on this board with new matched transistors. Well looky here. As suspected one of the transistors thought it would start to identify as a diode, not that I have a problem with that, just not in my amplifiers thank you very much😋. The funny thing is when I bent the pins of this transistor (as a dodgy trans..istor identifier), it now showed ok. This LC pre section only (links removed at back of amp). This is nice 1.26 - 1.22 = 0.04% THD out of the pre section LC. RC has 1.24 - 1.22 = 0.02% THD. Now an excellent result. Again this is pre section only.
  10. This is the power supply harmonics as tested on the LC output before any mods. This is the RC power supply before mods. Pretty much the same. Parts replaced in the power supply include all the capacitors, a out of spec resistor and a couple of old diodes. It is funny how large the old capacitors used to be. The replacements are the same diameters (I wanted them to fit in the same clamps) but are not as long but still the new ones are all of greater capacitance and voltage ratings than the old ones. These caps have 2 - 3 times the capacitance of the originals with a smaller form factor. Upgraded PS. Tick! A big difference now. The harmonics have significantly dropped especially that 2nd harmonic at 100Hz gone into the noise floor. The noise floor has also dropped all across the frequency band. New Nichicon caps in power supply at top.
  11. Now comes the fun stuff Time to put some new parts in this baby and get her back to new spec. This is a measurement of distortion of my chinese signal generator. it shows 1.22% THD on top left corner. So if I measure my amplifier and get 2% distortion. The actual amp distortion is 2 - 1.22 = 0.78% THD. See how crappy my signal generation distortion is I have decided to build another super low distortion signal generator, but that is a project for another day being put under an ever increasing project pile. Left channel before restore. THD = 1.5 - 1.22 = 0.28% THD. all measurements were taken at 1v output into my external Behringer soundcard. Right channel. = 2.11 - 1.22 = 0.89% THD. Now thats a bit different to the left channel. I am begining to suspect dodgy transistor/s somewhere. Maybe in the Tone control/pre stage board. Also with this test you can see this channel has more 3rd order harmonics a 3KHz compared to the left.
  12. I recently was able to aquire an Early Sansui (most likely 1971 model) AU555a from Gumtree. I have previously helped a mate get his late fathers AU555a rebuilt and modded a few months back and really enjoyed the sound these things produced so jumped at the chance to get one for myself with intention of holding onto it for many years to come. Another overhaul was on the cards before it even was in the house. Just recently I did learn to test for distortion measurements by reading this thread (mods please remove if you don't allow links to other forums but it is useful info). https://www.diyaudio.com/forums/solid-state/338511-howto-distortion-measurements-rew.html Also these mods not done out of my own genius so I take no recognition for that. Other more knowledgable folk have done rebuilds on these before and I found a handy thread over here https://audiokarma.org/forums/index.php?threads/leestereos-restoration-upgrade-of-a-sansui-au-555a.816754/ . Anyway this thread will be mainly photos and maybe some useful info so that other prospective diy incensed individuals want to have a go at something like this, it may help them. As you can see the front face is in spectacular condition. No scratches for something nearly 50yrs is pretty good I must say. Looks like it has been services a couple of times. Last time in 04. Cover in excellent nick apart from a scratch. Ends of cover have splits (delamination of ply). I ended up putting some super glue in the split and clamping them together. Original inside before clean. This is for it's age a very clean amp with not much dust build up. It must have lived a good life. The only down side I can see is a bit of tarnishing on the gold metal base plate and tone control cover. Amplifier board before touching.
  13. I quite enjoy the LM4562. A good opamp shootout here https://www.diyaudio.com/forums/everything-else/245455-ultimate-opamp-shootout-decide.html
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