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KENWOOD L-09 amp MODS

Posted 16th April 2011 at 06:18 PM by tube dog

re: KENWOOD L-09 amp MODS :

Have interest in mods to improve these DC mono block amps. After 32 years of service, a RECAP job of electrolytics ( 2) is in order for my pair (electroylics caps dry-out and BURST/ FAIL - and will take-out 24 output transistors and probably your speakers also ) So while the IRON IS HOT ..... I noticed the following possible mods to improve these amps' performance :
MOD #1- Replace 6 foot # 16/2 ' zip cord ' AC power cord....with 2 foot of # 8/2 ( amp pulls 1200 watts @ full power each ) note; a # 10/4 stranded copper power cable can be wired in 2 pairs ( red+black / white+green ) which eliminates DRILLING chassis opening LARGER to accomadate # 8/2, but will NET #8/2 gauge AND provide added shielding with 4 conductor spiraling ! THIS IS A NO BRAINER AND SHOULD MAKE THIS AMP BREATH a bit easier
(note : factory issue AC cord has NO ground conductor-and I would suggest NOT adding a grounded conductor to new 15 amp plug either- rather use chassis ground binding post located at rear --IF necessary for AC hum condition)

MOD #2 - BY-PASS A/B speaker RELAY - If you dont USE the A/B speaker relay feature.... then by-pass it --as it can only improve performance-if hardwired directly to speaker A binding posts only- bypassing wimpy relay contacts - amp output 4 ohm = 1000watts @ peak per channel AND with DC-100K frequency response- that relay ain't helping

MOD # 3- Replace spkr binding posts - Factory issue sprk posts are plastic grip allowing for a # 12 conductor max-- AND prone to wiggle/ loosen- due to plastic grips !

Anyone having any input on these 47 pound monsters and possible MODS to improve ??

My L-09's amps drive 4 x 15" TAD 1603 woofs @4 ohm load- from 18 hz--200 hz w/ 12 db slope & active tube x-over driven - in 32 cu ft 540 lb enclosures - infinite baffle- for 4 way tri-amped BIG system- and I havent heard or FELT a better bottom-end yet.

enjoy
tube dog
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Comments

  1. Old Comment
    EchoWars's Avatar
    Your mods sound fine, mostly, but you don't need huge wire on the primary side of the transformer. The stock cord is more than adequate. But it's certainly your choice.

    Just a suggestion from working on a lot of these: On the schematic is shown a cap, Cf5, 100pf, from the collector to the base of Qf1 (a Miller cap). It is usually absent from the board itself. Put a small ceramic here, like 3.9pf (rated for 200V). Cleans up the positive peaks of the wave.

    I see a lot of noisy stock fans. The Pabst 9906 (Mouser #5912-9906) fan is a great replacement, but the fan resistors need to be changed. Use a 1.2K 12W ceramic resistor (FVTS10-1.2K-ND) and a 400 Ohm 8W ceramic (FVTS5-400-ND) (Digikey numbers on the resistors). These resistors are hollow, and shed heat very quickly, to help protect the wimpy foil traces that Kenwood put on that PC board.
    permalink
    Posted 18th April 2011 at 07:28 AM by EchoWars EchoWars is offline
  2. Old Comment

    KENWOOD L-09 MOD (follow up)

    now for a follow up to my orig post above :

    despite all other demands else where, and the advice not to waste my time doing this mod- as it was not necessary, I had the urge to see if replacing the orig AC power cable, would make these DC mono block monsters even...' better ' -- well yes- IT DOES
    !
    POWER CABLE MOD : the wimpy factory ac cable ( 6 ft of # 16 ZIP cord ! eeeeck) was replaced with a 2 ft of # 8/2 * stranded copper SO power cable w/ 15 amp Hubbell AC plug -

    .... not that the Kenwoods' EVER lacked a SOLID bottom end & shear power ( 600+ watts per ch @ 4 ohm & DC - 100k +/- .5 db bandwidth & no caps in signal path !.... the are uniquely designed for FLAT RESPONSE TO DC !!! YOWW, thats my kinda amp )

    -but NOW w/ the above mod --- the bottom end is " RIGHT " = from a double bass wailing away- to kick drums to -you name it- the ' impact '-immediacy- transients-and damping' - and UTLRA LOWS are ALL just RIGHT THERE !!! - but again -- i was never complaining before the mod though either - cause they have always 'kicked A$$- even stock --

    -but now every aspect of the "bottom end" was demonstrably improved - and APPRECIATED straight away- example : where i had a hard time ' clearly' hearing the large floor toms while simultaneously having a double bass ' double up ' licks-w/ a floor tom roll -- NOW it is definitely a nice SOLID BIG floor tom --you hear distinctly - where as before-- the double bass masked the BIG floor toms' huge wallop !!! and now you FEEL the drum skin-getting BEATEN --- reaal goooooood ! ...have you ever stood next to the drummer when he lays into the floor toms esp the BIG floor TOM ? truly a dynamic visceral experience .. drummers have there own world of sonics believe me - its ' physical ' -

    ULTRA LOWS = YES-- another improvement here -- the lowest registers on 5 string electric bass passages for example show NO WEAKNESS going all the way down SOLID and maintaining levels and moving HUGE air w/ a 4 x15 system above --- and the kickdrum ? the wallup is to be FELT as though it was JUST THERE-- !!! no bloom, no overshoot, no flab-- no roll- off-( tone sweep response was near flat to 22 hz @ 98 db @ 12 ft & 10 hz @ 35 ft
    ...!! can you say HI neighbors !!! )

    SO WAS THE MOD WORTH IT ? - like YEA
    note ; I have no idea what this mod will do- driving full range spks- with passive x-overs -- as i use a pair of mc-225's amps with a tube tri-amped Luxman 2003 for everthing above 200 hz. -

    TIPS- I choose to use a short ( 2 foot # 12/4 stranded copper SO power cable-and combined 2 # 12's per conductor * netting a total of # 8 x 2 leads - leaving the chassis ground 'open'- as it was originally wired - NO CHASSIS GND on AC-- and that big boy cable size --- WILL require enlarging ( drilling ) the stock hole ( 1/2" ) to 7/8 " to pass it thru the chassis - BUT IT JUST MAKES IT - even allowing for a plastic ' chase' ring to be inserted - making it a PRO looking & functioning improvement --BUT you will need 5 feet to run the new cable all the way into the chassis's power switch and NET the remaining 2 feet with a nice new HD 15 amp Hubbell all copper plug -- and the old stock ' wimpy....cable === bye bye ! ( dont think I will be soldering those back in )

    ---I am frankly amazed the fellow who designed these DC mono blocks couldn't get KENWOOD to spring for a larger sized AC mains cable --- especially delivering 600+ watts each - all the way to DC freq !!!-

    again...-THE 'WEAK LINK' is EXPOSED !!!!!!!!!who knew and I bought these new in 1979 and have never even consider doing something like this... would make such an improvement .... and the cost ? $ 60 maybe and 2 hrs time -- do a good job --its the mains --

    oh and WARNING / CAUTION---be SURE TO PRO DRAIN THE BIG ELECTROLYTIC CAPS with an inline resistor ( 2X) before you start - repeatedly till very very dead-in fact leave them shorted out while doing the mod--- JUST BE SURE TO REMOVE THE SHORTED CAP LEADS before you re-fire the amp up

    ps -- every link counts--- and this was the last link for me re ; ac mains -my system is very efficient, and is powered thru a 40 amp 1 to 1 power conditioner ( ONEAC CCS 1148 @ 115 lbs w/ dual coil secondary ) and I have NEVER seen the KENWOODS CLIPP of even get close to clipping ( led peak clip ) with my TAD speaker load -- in fact the only time i have seen the KENWOOD clip was a 3 ohm load driving the famous AR3a incredible 12 " cloth surround alnico woofers -- it was just a one time ' flicker' -- and those AR3's can suck all the power you got -- having a 12 free air resonance and under 88 db efficiency or s/t
    btw -- the power conditioner is HIGHLY RECOMMENDED and clearly improved EVERYTHING big time when that was installed--across the board -

    THERE ARE A COUPLE MODS YET TO MAKE ( see orig post ) -- BUT AFTER JUST THIS ONE....? I AINT IN NO HURRY NOW FOR SURE .... CAN IT GET BETTER ....? maybe ... but bang for buck ? this is a HOME RUN MOD on these KENWOODS

    and I can ONLY imagine if you are driving less than super efficient speakers than my TAD pro pioneer woofers or JBL equivalents AND / OR are driving FULL RANGE sprks-- what THIS ac mod for the KENWOODS' will do for ya.

    tbc.... i guess
    tube dog
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    Posted 22nd May 2011 at 09:12 AM by tube dog tube dog is offline
  3. Old Comment

    Kenwood L 09 amps ' UNCORKED '

    I had earlier suggested the above mods to improve these mono block S.S. amps- and here is an update :
    Upon recaping these 1972 marvels, I decided to bypass A/B speaker relay feature, BUT then found 2 more relays, in series with this ' protection circuit' and also found a small 10 ohm/ 3 watt resistor IN SERIES, and small air inductor coil ( phase compensation coil ) -- ALL in series - carrying 400 watts ?

    The 3 wimpy relays ( 4PDT) combined with resistor & coil were designed to eliminate DC surge to the speakers, when powered up - BUT at what cost to performance ? = huge (see below)

    The amps are used in a 4 way tri-amp TAD / JBL system- from 20hz- 250 hz. With that, I cannot therefore comment on full range use.

    SO I BYPASSED ALL 3 relays, resistor, and coil. Using a single # 6 copper direct from Spk A binding posts -to- main PC board output trace ) The amps' improved performance was immediately apparent-in ample rock solid bass that extended to the subsonic registers.

    ALL sampled material showed demonstrably improved UTLRA tight, POWERFUL, FULL, SOLID- bass !

    DOWN SIDE - This mod eliminates the factory speaker protection-so caution is needed to prevent damage IE - pre amp ' first ON and last OFF ' is mandatory ! I measured a 11 volt turn on DC surge- THUMP ! so be advised and prepared-

    I ONLY WISH I HAD MADE THESE MODS 39 years ago !

    enjoy KENWOODs' power and performance UNCORKED!

    tube dog
    permalink
    Posted 22nd October 2011 at 02:07 AM by tube dog tube dog is offline
 
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