hitachi ha-330 modification

[adason]

hi
i have recently obtained two dead amps hitachi
both had blown output transistors, which i replaced
they sound ok, but i would like to improve them to smoother more warmer sound

i was thinking upgrading the capacitors in signal path
maybe bypasing tonal correction completely, even sometimes it comes handy
getting rid of low-filter and so on

there is audible noise on the amps output with highly efficient speakers, which i would like to reduce
any sugestions for transistor swapping?

i do not want to make too much of a rebuilding, they are pretty decent as they are

any suggestions are wellcome
thanks

[adason]

no suggestions?
well, so far i removed low filter, those two mylar 0.15 uF capacitors, R618, R701 and its paralel cap with no name, R704
and conected R616 directly to C703

than i used spare mylars to bypas those two electrolytes in/out Q602
that improved sound a little but there is still an noise to address

i replaced first transistor Q601 with selected low noise one and it helped significantly
i can tell for sure because i must go with volume higher to detect the hiss in headphones and i have two of these amps and i am working on just one of them, so the comparison is easy and almost objective
i think i should go ahead and replace all first five transistors with low noise ones and see how much the hiss goes down
all i need to achieve is no noticable hiss when using headphones
its already fine with speakers

i wonder if any one experienced could tell me what is the critical part to play with which has most effect on noise level
any other suggestion to improve the amp?

[dmunky]

Hi, I recently picked up this amp at a thriftstore. It works and sounds pretty good. One possible mod I want to try is replacing the indicator bulb with an LED. The only problem with this, is that I have no idea what wattage the original light bulb was. I already burned out a blue LED playing around with this. Do you know what kind of resistor is necessary to get an LED in there? Thanks.

[adason]

hi dmunky

well, replacing the lamp with the led is simple, you just have to understand that the lamp is powered with quite high voltage, so you need to put resistor in series with the led

if you look at the schematics, the lamp is powered from one of two secondaries of trafo, those two secondaties aro providing +/- 40 volts after filtration, i would guess those two trafo seconadries are 36volts ac
tha lamp is powered from those 36 vols thru 100 ohm resistor and a diode
i do not know what voltage is actualy on the lamp, I would have to measure it, since there is nothing in manual
since it is not fully filtered, there is no capacitor on the lamp, its hard to say
so to come up with resistor for the led is not easy

you should power the led from well filtered and stabilized voltage, +/- 14 volts available in the amp to power the preamp section

just take +14 and ground and calculate the resistor, that just ohms law

ed

[nioux]

Hi Adason and other readers,

a friend of mine gave me an old HITACHI HA-330 that works bad.
After few minutes of great job, a big "boum" in speakers happens as if the power supply failed. I shut it down some minutes and then I can have it (after power it up ;-) working good for less minutes than first try.

I think (but I'm not a specialist) that the power supply is sick.

I came on this thread because I search Internet to find the schematic of the Hitachi but I found an extract in 'resize.jpg'. Where is it possible to find it entirely ?

More, is anybody has an opinion about my problem ?

Thank you in advance
(and sorry for my poor english)

Nioux

[adason]

Hi nioux,

I have complete schematics and service manual, I can scan it and send it to you. I sent you an email a while back, but you did not reply.

ed

[zeonrider]

First change C705 from 100uF to 220 or higher, after that you will get lower freq. I , don't see all schematic, put on forum & after that we will talk.
Regards zeoN_Rider

[adason]

Hi zeonrider,

I no longer have the amp, I was just offering the help to nioux request.

thanks anyway

as far as I remember, the amp at the end worked perfectly and sounded good for such an old design, I was not too happy with noise, than I bypassed corretion section and all was fine, I left loudness on and off

I gave it to a friend, he is still using it

this is old thread, if nioux or anybody else wants, I can post or email schematics

ed

[zeonrider]

POST !!!
Regards zeoN_Rider

[adason]

i tried, but the images are too big for diyAudio site
if i reduce them to 100k, they are unreadable
i can email them who is interested