It didn't explode....... YET (aka niges amp)

[jkeny]

I had to quickly mop up the drool off my keyboard before it caused damage :)

[nige2000]

actually did a bit of testing with the trafo vol control idea
results are exciting bypassing the trim pot
another increase in dynamics, full live sound :)
listening at low volumes dont suck no more its all there!


this is a pri 2x30 sec 10x3v
implemented as 1x30v 10x 1.5v

theres 11 positions on these switches think a pri 1x30 sec 11x 1.1v would be plenty loud too

amp is 1.5 times as good as it was last meet

think we should pursue optimising the tvc with intent to put it in the group buy
maybe if i got a second prototype built we could ab test a trafo amp vs no trafo amp in january ?

[tony]

only a 50% improvement! I think another meet up is a definite. Happy to go again. Maybe no pizza this time just indian curry.
BTW have the totaldac usb cable working with the xmos card. He put something very heavy in the box. It is all a bit precarious certainly would stand up to any changes of cables

[jkeny]

So apart from the 2:1? step down trafos on the output you're also getting a tvc that varies from 30V to 1.5V (20:1) to 30V to 15V (2:1) step down too?

[nige2000]

only a 50% improvement! I think another meet up is a definite. Happy to go again. Maybe no pizza this time just indian curry.
BTW have the totaldac usb cable working with the xmos card. He put something very heavy in the box. It is all a bit precarious certainly would stand up to any changes of cables

eh yea.... thats me stopping myself from saying it's twice as good ;)
25% for the stepdown trafo idea and 25% for no resistive trimming of input signal

[jkeny]

only a 50% improvement! I think another meet up is a definite. Happy to go again. Maybe no pizza this time just indian curry.
BTW have the totaldac usb cable working with the xmos card. He put something very heavy in the box. It is all a bit precarious certainly would stand up to any changes of cables

eh yea.... thats me stopping myself from saying it's twice as good ;)
25% for the stepdown trafo idea and 25% for no resistive trimming of input signal

Have you tried the tvc on the output to give you more step down & lighter loading on 3875 output stages?

[nige2000]

So apart from the 2:1? step down trafos on the output you're also getting a tvc that varies from 30V to 1.5V (20:1) to 30V to 15V (2:1) step down too?

no as i do nothing by halves i got 3 types of trafos:)
mostly coz having one or two dont really answer too many what if questions
the one in the pic that seems to be the way to go has all the secondaries in series like having 9 centre taps and the switch selects the desired volume level which for me is usually about 9-10v and plenty more in the tank which is selectable between 20:1 and four to one

[nige2000]

only a 50% improvement! I think another meet up is a definite. Happy to go again. Maybe no pizza this time just indian curry.
BTW have the totaldac usb cable working with the xmos card. He put something very heavy in the box. It is all a bit precarious certainly would stand up to any changes of cables

eh yea.... thats me stopping myself from saying it's twice as good ;)
25% for the stepdown trafo idea and 25% for no resistive trimming of input signal

Have you tried the tvc on the output?

yes........probably just the way

[jkeny]

Have you tried the tvc on the output giving you more step down & lighter loading on 3875 output stages?

yes........probably just the way

You mean you have tried it as step down on output? And .......?

[nige2000]

the 2:1 output trafo is what i was talking to you bout yesterday (last page)

the effect the output step down trafo has on the lm3875 outputs firstly lower noise, providing better clarity
the extra leverage over the speakers provides dynamics and deep and wide bass
really keeps the drivers on a short leash

the benefit of the output tvc over the 2:1 is the abilty to remove the resisitive trimmer between the buffer and the lm3875 and none of the signal is wasted or stunted

both combined is a great improvement