Sunday, January 23, 2011

Altec Lansing ACS33 (2.1 for PC)

Although not really hifi, having a set of decent sounding speakers for the PC does help when you are listening to MP3, watching movies, accessing Youtube, etc - especially when you are used to a decent sound system!

I choose the Altec Lansing ACS33 (2.1) many years ago as I could not convince myself to invest on a pair of nice Klipsch speakers for the PC ($700+ vs about S$135 for the ACS33)!

ACS33 2.1 PC speakers
In stock form, sounds leans toward bass and can sound boomy. Details and highs were acceptable.

Hence I decided to investigate possibilities on improving the ACS33.
With bottom half of the sub uncovered
I removed 6 screws  from the bottom of the sub to reveal the above pix.

Closeup of PCB (after substitution)
Perform the following on the PCB:
  • replace the 1uF EC with a poly (yellow)
  • replace non-essential 1uF with poly (orange)
  • replaced 4x0.22uF (green) poly with 0.15uF Vishay BC (grey) - makes largest audioble difference
  • replaced the 2 caps for filtering power supply with Rubycon 2,200uF
  • add a heatsink to the voltage regulator as it gets hot
  • changed a few caps on the right side of the pix (though not really necessary)
The results?

Bass was firm and quite respectable. High and mids sound pretty decent (to myself)! Don't think I will be shopping for a replacement anytime soon...

Sunday, January 16, 2011

Sansui AU-7900

The AU-7900 is a well known unit in the "black face" line-up of the 70's. Perhaps best known for it's great phono stage.

A feedback at speaks volumes of the AU-7900, especially since it was in a shoot-out by a stereo club!

Internals from top

From bottom

Frankly I was quite surprised by the "kick" from the unit - at the volume setting in the pix, it had enough juice to drive the Mission 753 Freedom to a decent volume - many articles mention the 753 can be power hungry!

No recapping necessary as it still sounds great after all these years! Quality really stood out for something in the 70's.

Wednesday, January 12, 2011

Mission 753 Freedom

I finally laid my hands on the infamous unit. Weighting in at about 25kg each, it is a well constructed speaker.
753 without cover. Meridian A500 (with puppet on top), Quad ESL Pro63 in the rear and the Technics Honeycomb 

Upon initial listening using the copper cable transferred from the Technics Honeycomb, the 753 was disappointing - sounding compressed, glimpse of imaging, restricted headroom, with plentiful of flabby bass???

I was driving it using the Leak Delta 30 with only 15W RMS per channel but enough to drive my other well known speakers ... (not tried the Leak on my stored Celestion SL6s and the Pro63 yet)

Searching the internet, there were many comments regarding using an amp of atleast 50W per channel as well as mods to the crossover, etc to get the best from the 753.

What I did note was that the above setup while had plentiful bass and sounding compress, the 753 did convey the details as per my other speakers.

Hence I decided to try a simple experiment before going for the "works". I replaced the existing copper cables with my old QED Silver Anniversary (newer version has less than half the original core size).

Sounds almost top flight via the low wattage Leak Delta 30 using QED Silver Anniversary speaker cables!!! Like night and day by just changing the speaker cables.


On the following week I managed to add a Sansui AU-7900 to my collection.

Tried pairing it with the 753 via the copper cable (since it has more power than the Leak). Bass was respectable but over-emphasized. The treble had the 'behind the veil'effect. Hence I inserted a bypass using a ROE 0.022uF for the 10uF and 6.8uF capacitor. And insert WIMA 0.33uF bypass for the 470uF capacitors. Furthermore added 2 layers of foam padding to the bottom cavity as the original was empty(?).

The cross-over unit looks a bit different from the pix(s) on DIYAUDIO and other websites as this is the Freedom model - without the 1,000uF capacitors and a simplified crossover board.
After adding bypass to capacitors
Different view of cross-overs

Add 2 layers of foam

Speaker cable from the AU-7900 - more than enough 'juice'to drive the 753F

Been an hour and the sound is beginning to take shape ... vocals are sweeter and bass is firmer. Has the makings of a keeper!


Using the previous setup and copper wires, the 753F seem to slightly warmish. Bass became more firmer, voices were almost "being there" but there seem to be a very light veil still in-place.

Connecting the 753F via QED Silver Anniversary seems to be it. Everything is falling into place, with firm bass!!

Thursday, January 6, 2011

Quad 33 (1st unit of 2)

This particular Quad 33 is part of components from my 1st set of Quad 33, 303 and FM3.

Updates completed were largely according to Dada Electronic suggestions. Electrolytic capacitors used were mainly average quality. Very few Wima and Panasonic FC were deployed. Sounds suprisingly good though.

Bottom and rear
The original plastic feet were replaced by rubberised equivalents, to prevent impacting other components during stacking.

Phono and Tape board

Top view

A bypass was added to the output boards as there was not much improvement in the HF response e.g seem to have been "cut-off". Used a green Wima for the bypass on the output boards. Sounded proper again after the bypass was added.

I was more adventourous with the 2nd Quad 33.

Sunday, January 2, 2011

Luxman T-240

This is the Luxman tuner which is of the same series as per my L-410.
In stock form, the unit sounded nice but (a little) reserve. Due to age, the four power caps of 47uF 50V were replaced with 220uF 50V.

The following section were recapped with better quality capacitors - for the FM outputs.
Mod to FM output section
And the original 1,000uF 6.3V Elna cap was replaced with a Panasonic FC of equivalent specifications.

Sounds more open and realistic after the above recap. One of my visitors was pleasantly surprised when the FM station announcer did his job!!!