TGM7 - an amplifier based on Greg Ball SKA

[Bigun]

Boards are on their way to me...

 

[meiborg]

I've bought two second hand assembled GB150 boards including psu, saw them and couldn't resist . I plan to drive my boundary woofers with them, they should merge verry well with the Fetzilla's driving my dipoles.

Problem is, my cornerwoofers both have two Vifa M22WR09-06 drivers each in paralel, the Vifa's being 6ohm drivers, thus resulting in a 3ohm load. Can the GB150's handle this kind of abuse?

Couldn't find the answer with search, hope someone can help me out here.

Greetings Meiborg

 

[Bigun]

Yes, I believe they can handle it. However, you'll probably need to ensure you're using 5A fuses instead of the 3.15A fuses or you'll have nuisance blowing on peaks. It's still pushing them pretty hard mind.

 

[meiborg]

Perhaps I should also lower the current for the psu kust to be safe then?


Greetings and thx for the fast replay.

 

[Bigun]

If you want to make is safer you should reduce the psu voltage, not the current. The current will be determined by the music.

 

[Stuey]

Yes, Mr Ball recommends max. +/- 45V rails for 4 ohm nominal (min 3 ohm) speaker impedance. This is what I did with mine to cover as many possibilities as possible, speaker wise.

 

[meiborg]

Thx for your replies, will do!

Greetings Meiborg

 

[AndrewT]

For paralleled 6ohms drivers, resulting in a nominal 3ohms speaker load, I would recommend that the transformer be, at most, 30+30Vac instead of the more normal 35+35Vac.

It may be safer to drop down to a 28+28Vac, or 25+25Vac, transformer.

 

[Stuey]

Actually, to be totally accurate I used 30VAC myself, rectified to ~41-42VDC.

 

[borys]

Bigun
Maybe You can explain for me somethink please.

Option A:
Front stage two LTP's --> ''supplied'' by two CCS


Option B:
Front stage two LTP's--> ''suplied'' by using stabilised voltage (egz capactance multiplier -- zener+transistor+few caps psu) and single resistor used as CCS

What would be the advantage/disadvantage of option B

Thanks

 

[pinnocchio]

Nice work Bigun! This should be very interesting!

Ciao!
Do

 

[Bigun]

Bigun
Maybe You can explain for me somethink please.
Option A: ''supplied'' by two CCS
Option B: ''suplied'' by using stabilised voltage and single resistor used as CCS
What would be the advantage/disadvantage of option B

I'm not an expert but my thought is that they are both very similar and should 'do the job' in the general sense. However, the active CCS likely has a higher effective impedance, meaning that the current will be 'more constant' when compared with the resistor. The reason - the resistor only has a constant current if the voltage across both ends of the resistor are the same and you are only fixing the voltage at one end of the resistor. I'm sure there are other differences (noise, frequency response etc.)

Important note: In the TGM7 the CCS is an integral part of the thermal control loop so it can't be simply replaced with option B.

Nice work Bigun! This should be very interesting!

Thanks. So far I've learned much and will keep going until I've worked out how to get so much open loop gain under control.

 

[borys]

Thanks Bigun
I am waiting till You finish the amp. Looks very promising

 

[pinnocchio]

Any new development?

Ciao!
Do

 

[Bigun]

Yes - the boards arrived on Friday. Yesterday I started to populate one of the boards - it won't be super-fast due to all the Christmas events but over the next few days / week I hope to get one board fully assembled. This first board will be built with dual LTP input like the SKA GB150.

 

[pinnocchio]

Cool! Keep us updated!

Happy holidays!

Do

 

[Bigun]

Preliminary BOM attached.

 

[pinnocchio]

Looks great!

Looking forward to your listening impressions

Ciao!
Do

 

[Bigun]

I'm now assembling the first board, TGM7-II, re-spun to see if I can quell those MOSFET oscillations. I've installed all the SMT parts for the VFA version. It's not perfect as I took parts off the old board (I'm a cheapskate )

 

[Bigun]

And finally a completely finished (populated) board.