Replacing can electrolytics in Akai M8 monoblocks

[Raul]

A few years ago I succesfully converted two akai M8 amps to hi-fi monoblocks by following directions found in this forum and I am happy with the result. The only caps I didn't replace at the time were the can electrolytics and I want to do it now, but I am not sure about their value and voltage (not easily readable) so I ask for an advice to whose of you that did the same job in these amps, here is the cap

- are these 20+20uf 350V?
- is the negative pole the black lead? Is it correct to connect negatives of the new caps to one of these red circled tabs? Thanks

 

[tubeactive]

Hi...I have seen 20 + 20 uf at 350VDC as well as 300VDC rated electros. For safety and longevity, recap with 350V rated electros. Ground connection is the black terminal/lead. You must discern which red circled connection is directly grounded. If your VOM Ohmmeter reads less than .5 Ohm, you probably have found the most negative ground. The power tranny HV winding CT (center tap) will often also be grounded to the same point...Enjoy these highly underrated amps.

As a FYI, do your amps have a .01 uf across the opt tranny primary to ground ? This acts as a low pass filter (high freq. filter). If you lower that value to .005 or even less, you will get more highs, which you may enjoy...

 

[Raul]

Thank you, I don't know which one is the OPT primary wire, as I am still a bit of a newbie, can you please explain better with a pic, or still better with a pic of the cap that I should check if .01? By the way my amps have stock values as I replaced several caps with the same values of the original

... As a FYI, do your amps have a .01 uf across the opt tranny primary to ground ? This acts as a low pass filter (high freq. filter). If you lower that value to .005 or even less, you will get more highs, which you may enjoy...

 

[Selmerdave]

Thank you, I don't know which one is the OPT primary wire, as I am still a bit of a newbie, can you please explain better with a pic, or still better with a pic of the cap that I should check if .01? By the way my amps have stock values as I replaced several caps with the same values of the original

Here are some pics. In mine one of the electrolytics is rated 300V and the other 350V, no reason not to rate on the high side and make both 350V at least. On the output transformer the impedance is marked on the paper, if you zoom into the photos you should be able to make out "5k" on the primary side (with the cap across - facing the electrolytics) and 8 ohm on the secondary side (resistor across).

 

[tubeactive]

Replacing only one part at a time is a good process for newer techies....

Look at the connections on the opt tranny. There are P (or 5K) and B terminals on the primary plus 0 and 8 on the secondary. The EL84/6BQ5 tube has its' plate connected to the P terminal. The high voltage DC enters the tranny, from the amp's power supply, to the B terminal. Most of the Akai M7s and M8s have a .01 connected from the P terminal to the O terminal of the opt tranny. The 0 terminal is usually grounded. Lowering that cap value should "open" the sound even more. Those opt trannies are seriously underrated.

Simply realize the original intention of the manufacturers. With the included speakers, they intended the sound to be enjoyable, within the limitations of the system. If they extended the treble highs, the bass lows could sound subdued. Likewise, if they extended the bass, those included speakers could distort easily. So, they compromised, within the limitations of the product. Those particular opt trans have impressive low bass potential as well as extended treble response; better than the "stock" circuit can perform.

I know you are enjoying these amps as you have had them a while. The separate power supplies per channel are a great feature. Independent of each other, the perceived stereo "separation" excels with dual mono power supplies. As time goes forward, tweaking the signal circuitry of these amps will yield better performance...

 

[Raul]

Thank you to both for the replies. Here is a pic of mine, is this the .01 cap you are referring to?
Replacding this with a lower value as 0.005 all what is needed to improve the sound (I know this act on highs) or something also on the bass side should be modded? I don't want to go into important mods of the whole circuit as I am not technically good, I prefer a simpler "basic" mod for now

... Look at the connections on the opt tranny. There are P (or 5K) and B terminals on the primary plus 0 and 8 on the secondary. The EL84/6BQ5 tube has its' plate connected to the P terminal. The high voltage DC enters the tranny, from the amp's power supply, to the B terminal. Most of the Akai M7s and M8s have a .01 connected from the P terminal to the O terminal of the opt tranny. The 0 terminal is usually grounded. Lowering that cap value should "open" the sound even more. Those opt trannies are seriously underrated...