Moskido - Hybrid Aikido/MOSFET amplifier

[kacernator]

Originally posted by JackieTang
bakpaosiomay,

As I know it cannot.

The 2 cap 470nF must connect to the gate as close as possible because of lead inductance.

By the way, may I ask anyone:
Can I connect 2 AC110V transformers in serial to AC 220V?
Does 50/60 Hz cause problem?

Jackie

Hi,

I have cca 15cm long cable from two 470nF output caps to mosfet gate. Is it too long?

I have question about common mode filter. Does is matter in which way the choke is put in? I mean does it have to be oriented by the start of winding or not?

BTW, I borrowed my cap-coupled moskido to my friend. He has very average hifi speakers and he is absolutely blown away by the amplifier!

[JackieTang]

Dear kacernator,

1. Ideally, they should be on the same PCB.

2. As I know, normal Choke does not have polarity. Both wires are same colour.

3. Have you check the DC offset. The ouput stage is in solid state. Unlike, tube amp having transformer. You should better add a speaker protection circuit. Any thing goes wrong may blow the speaker.

Jackie

[kacernator]

OK, as close as possible, but will 15cm of cable lenght cause any problems?

They are common mode chokes, so I dont know if polarity does matter.

DC offset is fine, because it is CAP-coupled moskido, which have capacitor before speakers.

[JackieTang]

Dear kacernator,

I think 15cm should be OK. Cause of heat dissipation, some of the TO-3, unlike TO-220, are mounted apart on the sides of the chassis.

Just a suggestion. If you use Mono Aikido, re-arrange it. So that the output is near to the Mosfet. If you use Stereo one, i think it is quite difficult to arrange.

As I know, only transformer output can protect the speaker. If only DC on the primary, the iron core will be saturated, no voltage on the secondary.

But, for cap output, +ve on one side, there will be -ve on the other side or vice versa because of induction. Any DC on the speaker will blown it within 30 seconds. Some books said when 50W continuously applying on the speaker, the tempurature of the voice coil is near 200 degree Celcius. However, if the cone of the speaker is moving (because of AC), the heat will be ventilated through the center of the cone at the front and through the iron core at the back. But if only DC is applied, of course, the cone of speaker will not move. Thus, no ventilation.

According to your case, if the speaker is not being overload, I think most likely, the amp has output some DC leakage during playing. Check the component. I think most likely the electrolytic cap which is easily blown out (or end of life) if you use the voltage rating is too close to the voltage rail.

Ohs, I forgot to ask have your Moskido still playing fine in your home?
If yes, your friend's speaker was blown because of overload.

Jackie

[kacernator]

Thanks about the cable lenght.

Oh, you have misunderstood the statement, that he "was blown away by the amplifier." I meant he was very surprised how the amp sounds! .
No speakers were blowned out or damaged!

[JackieTang]

Dear kacernator,

Congratulation!

I'm just sourcing the parts to build the Moskido.

What kind of BUZ you use? 900/901 TO3 or TO220?

What heatsink you use?

Do you use VTA55, each US$6? I will try +-0.1% metal resistor from IRC. Each cost around US 1.

Jackie

[kacernator]

Hi,

I used BUZ900/905 TO247. I couldn get enough big heatsinks in my country, so I used fan cooling. You can see it in the pictures I posted earlier in this thread.

I do not use any special resistors, just ordinary 0.5W metal film.

[JackieTang]

Dear kacernator,

I've watched the pics before.
But, you know, I didn't remember the name. Just browsing the forum.

How much the heatsink cost?
Do the fan affect the sound output? (I do not mean the mechanical noise produced.)

Bob (Beau2137) introduced 486K. Each cost US50. Total US200.

If the electrical noise of the fan did not affect the sound output, I would like to try LAM 4K 150 for TO220/247 or LAM 5 150 from FISCHER ELEKTRONIK. The fan only generate the noise at 16-18dBA at 5V.

LAM Series

But I can't it in HK. Instead, I find LA 6 150mm 12v at Farnell HK
LA 6 150 12V

But the sound level of the fan is 41dBA.

However, it only costs US82 (HK$646).

I'm just trying to find another cheap but effective method but only if it does not affect the sound (except the mechanical noise).

Yours
Jackie

[JackieTang]

Dear kacernator,

Sorry, the LAM link does not work properly.

Here is the pic of LAM 4k

Jackie

[kacernator]

Hi,

my heatsink costed 30 euros each. I am using 33dB fan, but I am running it at half of the rated voltage. I can hear the fan, when the music is not playing, but it is not annoying. Absolutely I cant hear no fans even when the music plays on very low sound levels.

From the picture you posted, the LAM seems to me small. That fan must be run quite fast to keep the mosfets down. Try to get biggest heatsinks you can get, then add fans.