#hk980

After a long long hesitation i decided to replace the voltage regulators for opamps / volume control.

The original 7815 and 7915 were replaced with TPS7A4700 and TPS7A3301 which i found here. I specifically searched for pin compatible PCBs since i didn’t want to do any PCB mods that could end up in a non working amplifier.

Sound now is incredible. A lot of details everywhere... vocals stand out... highs are very detailed.. bass a lot more detailed and louder.

I still need to try something like this in a DAC or similiar equipment to see if it also improves the sound like it did on the amplifier. So stay tuned for the information from first hand :)

Another modification that has been done very recently to my main amplifier is the replacement of filter capacitors on amp boards.

I settled on Mundorf MCap Supreme based on my previous experiences and with the help of the website located here.

The main thing that has changed is the high end.. more controlled and very very detailed.

Overall the sound is very different from original setup. Since i managed to get another same amplifier which had a small problem with 12V regulator for relays and overheat protection i can now compare both amps easily.

The sound on the original amplifier is a bit muddy and less detailed compared to main amp. Sometimes maybe too harsh in the high end too... very aggressive and shouty instead of detailed and laid back.

Additional things were removed in the Frankenstein 2

- BL1 replaced this time as it started to develop the failure

- R171 / R172 removed

- Q21 / Q22 removed

- DW6 / DW7 removed

- C24 / C63 removed

- C162 / C23 replaced for Nichicon Muse KZ 100uF / 25V

- Added additional TPS7A4700 / TPS7A3301 instead of all the above removed components to generate the needed 7V for the volume control chip ( HK990 has a similiar thing but with LM317 style regulators and the same volume chip )

After a long while of "why am i not satisfied how my HK990 sounds" i decided to dig a little deeper into this.... Turns out HK990 is NOT suitable for high efficiency speakers as it's not linear in sub 1W output. ( i can prove this easily with calibrated mic measurements of each amplifier ) After i've seen the response of stock HK980 that my parents use compared to my lightly modded HK990 i decided to get another HK980 and finally do all of the treatments that i ever wanted to do. Below you will find a log of what was changed ( for now ) if you want to do something like this yourself. The change is very drastic coming from stock HK980... even my first Frankenstein HK980 or lightly modded HK990 can't come close to this in terms of sound.

The sound output now is truly something else... highly detailed... dynamics are typical HK sound but much more pronounced.. very nice soundstage ( you can clearly hear what is happening far away from the mic if you are listening to classical music or some of the beatles / acdc tracks ). All in all about what i would expect from stock HK990 but sadly my dream amplifier dissapointed me... I wouldn't reccomend this to someone that's new to this as there are some challenges space wise and i don't want you to damage something just because you have seen some random guy on the internet :)

Incase someone decides to do this the 4x Nichicon KS holder is here.

There is also updated version of phase plug for Fostex Fe206En ( courtesy of hundreds of measurements with the amps ) and you can find it here. This design might change as i'm still experimenting.

The changes are as follows:

Main board - IC20 (KA7815) / IC21 (KA7915) replaced for  TPS7A4700 and TPS7A3301. the "drop in" replacements i found here years ago: https://www.ldovr.com/category-s/117.htm* - IC11 / IC12 (OP275) replaced for 2x OPA1612 - C57 / C58 / C64 / C65 replaced for Nichicon Muse ES bipolar capacitors 100uF 16V  ( on my board C53 / C54 are bridged... if they exist on your board replace with the same Muse ES capacitors ) - C55 / C61 replaced for Nichicon Muse KZ 100uF 25V ( couldn't get the 16V like the original on the board ) - C120 / C121 replaced for Nichicon Fine Gold FG 2200uF 25V later replaced for Nichicon Muse KZ 2200uF 25V since it's smaller ( originally it's 1000uF 25V but i wanted to see if there is any difference ) - C116 / C117 replaced for Nichicon KA 1000uF 25V ( originally it's 220uF 25V again... testing for differences.  Also KA was chosen because there was no space on top of the board and this one is quite compact ) - BL2 replaced for HFA08TB60 ( mainly because of soft recovery characteristics ) - BL1 can be replaced with any rectifier bridge just in case you get random overheat errors ( wouldn't be the first HK980 i've seen where 2W06M rectifier fails randomly )

Amplifier board(s) - BR1 replaced for HFA25TB60 ( previous amplifier was done with HFA08TB60 which is 8A rectifier diode but it's bigger brother is now in to test the differences ) - C2 replaced for Nichicon Muse ES bipolar 470uF 25V - C3 / C4 replaced for Nichicon Muse KZ 47uF 100V - C5 replaced for Nichicon Muse KZ 470uF / 25V - C7 replaced for Nichicon Muese KZ 10uF / 25V - C13 / C14 replaced for Mundorf Supreme 0,22uF - C17 / C18 replaced for 4x Nichicon KS 12000uF 63V ( compacter version of KG type I ) - C20 replaced for Nichicon Muse KZ 100uF / 25V - PETG 3d printed capacitor holder with bottom cover for isolation purposes

As a last bit of news...

The absolute last mod on the HK980 was replacement of the original opamps to LM4562 which opened up the amplifier massively.  I almost dare to say it sounds better than my newly acquired HK990 but it lacks control that HK990 can put out.

That’s right... I got a second HK990 so now i have 2 of the same amplifiers again. One working and one broken still. You know the drill. Fun times ahead :)

Small update regarding my frankenstein Harman Kardon HK980

Capacitors on the signal side replaced with Nichicon FG / Muse BP. Some things also shifted on the bottom to make room for any potential upgrades on the OPAMP side which are in the signal path.

First experimental recap. Not that the amplifier needed one but i’m experimenting to see if i can still squeeze more out of it.

So far the amplifier still responds great to mods and that’s why this time the target were the two amplifier boards.

Signal cap was upgraded to Nichicon Muse ES bipolar cap and the others were upgraded to Nichicon Fine Gold.  If anyone is wondering why not Muse instead of Fine Gold the answer is: dimensions... most Muse caps are way too big for this layout. Even the Fine Gold ones don’t fit entirelly.

Seems like Harman went the Samxon route because all the caps are quite small ( at the expense of quality ) and in turn also smaller PCBs.

Sound opened up a bit more. As usual for the caps i go to... Better bass, less shouty midrange and very nice highs.  ( i also needed to change the dsp crossover from 100Hz to 50Hz to get the optimal experience )

The regulators are now done.

I also 3d printed a spacer to avoid bending/breaking off the contacts.