Dx Blame MKIII-Hx - Builder's thread

[canonnica]

Would the mk3 benefit from more bias ...?

Simulations here: http://www.diyaudio.com/forums/soli...mkiii-hx-builders-thread-146.html#post3270977

Remember? 😉

 

[a.wayne]

Yep ....🙂 Terry , guys , any updates to the the other build Thread ....?

 

[canonnica]

The "silencing the lifted ground" operation makes a heck of a difference. It's now dead silent. I recommend.

 

[still4given]

Cool that we found how to resolve it. This is a really good sounding amp. As good as the Super A to my ears. That is a compliment, by the way.

Blessings, Terry

 

[meanman1964]

The "silencing the lifted ground" operation makes a heck of a difference. It's now dead silent. I recommend.

What did you do then?

 

[Junie]

Martin tell us more.

 

[bonfis]

The "silencing the lifted ground" operation makes a heck of a difference. It's now dead silent. I recommend.

I completed the same mods and also have I hum free amp now. However, mine does not use a ground lift resistor on the board or bridge rectifier between the line cord ground wire and case. I have the line cord ground going directly to the case and ground wires from that point to the input RCA connector grounds. I was able to see the difference that this last connection made on the Arta spectrum analyser display. It produced about a 10 db drop in 60 hz content on the output.

 

[AndrewT]

I have the line cord ground ......... to the input RCA connector grounds. I was able to see the difference that this last connection made on the Arta spectrum analyser display. It produced about a 10 db drop in 60 hz content on the output.

Leach discusses this option in Lo Tim.

 

[a.wayne]

As the Mk3 flies ..🙂
Any improvement on the clipping characteristics ....?

 

[bonfis]

Leach discusses this option in Lo Tim.

Yup it's also recommended in Self's book.

 

[canonnica]

As the Mk3 flies ..🙂
Any improvement on the clipping characteristics ....?

The Baker clamp does eliminate the rail sticking and removing the bootstrap capacitor renders the clipping symetrical. The bootstrap cap is part of this amp's soul, I won't remove it.

 

[canonnica]

Martin tell us more.

Refer to post 2015... too much stuff "lift grounded"

Martin.

 

[still4given]

Read through to 2017

 

[destroyer X]

Here is Carnival time .... a moment to have fun...but i do like to do electronics

Producing transmission line speakers....audio quality result if fine.

Some books says overshot is fine!

regards,

Carlos

 

[a.wayne]

The Baker clamp does eliminate the rail sticking and removing the bootstrap capacitor renders the clipping symetrical. The bootstrap cap is part of this amp's soul, I won't remove it.

You prefer the sonics with bootstrap cap ...?

 

[meanman1964]

Terry,I was looking at your post 2037 and noticed you replaced the 1n4007 diodes with resistors Why?

 

[still4given]

Hi Patrick,

You will have to look back through the thread a ways. Carlos recommended that change. I just followed suit.

Blessings, Terry

 

[wiljj78]

Hi Wayne,

I had to pull the tops of and measure. I have the Super A set at 192mA per rail and +-38.6V. The MKIII is set at 80mA and +-75.5V. They really are just too close to call on my system. Both are crystal clear with great bass.



The mod is not difficult. The most time consuming part is pulling the boards out so you can get to it. I am attaching a pic of how I did R8A. I just drilled a small hole through the board to the trace below and swung the end of R8. Sorry, I didn't take any pics of the bottom of the board. I cut the traces just where I show in the other attachment and the jumpers are easy since the traces have exposed copper.

Blessings, Terry

Hi Terry,

I tried to follow your mod last night but R17 (1K) burns out ...
Please clarify did you really include R17 to the main ground??
I'm confuse between these two mods of you and martin on post 2015 as he keep the R17 on the lifted ground.

Regards,
Willy

 

[AndrewT]

R17 is not a signal current. Connect it to the Power Ground (the other end of R31).

If the Q7 is passing the correct current (~1mA) then R17 will also pass ~1mA.
It should drop ~1V
P = IV = 1*0.001 = 1mW
It can't burn out.

It is there to prevent Q7 burning out.

 

[bonfis]

Hi Terry,

I tried to follow your mod last night but R17 (1K) burns out ...
Please clarify did you really include R17 to the main ground??
I'm confuse between these two mods of you and martin on post 2015 as he keep the R17 on the lifted ground.

Regards,
Willy

Hi Willy-
I made this mod also and had no problem with R17. It doesn't make sense that moving that end of R17 from the lifted signal ground to main ground could cause the problem. You are only reducing the resistance from collector to ground by 10 ohms (1%). I think you must have a wiring error or short somewhere. Are you sure you cut the correct trace?
Steve