Tír Na HiFi

nige2000 wrote: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

Yeah, I understand all that - my suggestion to try the TVC on the output instead of the input was based on you stating that greater than 2:1 step down on output would probably sound even better Abrax has stated this before). Don't know if the tvc will saturate though - no harm in trying ?

My understanding of it was that the tvc is the same as step down with more secondary windings providing versatility and options
It's actually wired exactly same as the lifepo4 powersupply in increments of 3.3v
Maybe I've misunderstood Richards trafo 101 lessons and gone off on the wrong road
Sounds great though

nige2000 wrote:My understanding of it was that the tvc is the same as step down with more secondary windings providing versatility and options
It's actually wired exactly same as the lifepo4 powersupply in increments of 3.3v
Maybe I've misunderstood Richards trafo 101 lessons and gone off on the wrong road
Sounds great though

I think Richard's concept about step down trafos was that they are used on the output to lighten the load on the output stage of the amplifier (inside the 3875 chip, in this case) - the greater the step down ratio, the lighter the load.

This is not the same as using a step-down on the input

The weak point with a chip amp always seems to be poor immunity to power supply noise - as I wrote over on WBF a few years ago :http://www.whatsbestforum.com/showthrea ... post168384

Stepping down the voltage from its output means less self-generated noise on the rails, its equivalent to adding capacitance on the supply rails. However there is a limit to adding capacitance (at high frequencies) due to parasitic inductance and ESR. There's not really any limit in terms of how far step-down can be taken.

Jeez did you guys sleep at all last night or is the clock wrong on this thread.....I suspect you were up all night though :-))
Sounds really exciting though and I can understand the inability to sleep if this amp has taken another major step forward after hearing it at Tony's this month.

Keep doing what you are doing Nige even if it is just intuition some of the time as the results will speak for themselves, if the well is getting dry in terms of funding due to hits along the way on components and we need to increase projected costs for the optimized TVC then lets do it, no need for a cost benefit analysis here.

Very happy to add more funding as is will be one of the best investments in audio in many years.

Will definitely bring the modified Big7 to the next get together to marry it to the amp and see how it works.
Some travelling coming up in January so I hope I can make it...will be pissed if I cannot hear the amp again!

jkeny wrote:

nige2000 wrote:My understanding of it was that the tvc is the same as step down with more secondary windings providing versatility and options
It's actually wired exactly same as the lifepo4 powersupply in increments of 3.3v
Maybe I've misunderstood Richards trafo 101 lessons and gone off on the wrong road
Sounds great though

I think Richard's concept about step down trafos was that they are used on the output to lighten the load on the output stage of the amplifier (inside the 3875 chip, in this case) - the greater the step down ratio, the lighter the load.

the lesser noise is more apparent than the lighter load though that benefit is obvious too

This is not the same as using a step-down on the input

never said it was on the input?
output transformer

though i did try 15k/15k trafos on the dac with far less improvement, though i feel if loss of volume could be sustained there would be more benefit too

abraxalito wrote:The weak point with a chip amp always seems to be poor immunity to power supply noise - as I wrote over on WBF a few years ago :http://www.whatsbestforum.com/showthrea ... post168384

isnt the issue that it shits on its own doorstep? and does not have the noise rejection capability? and the step down makes it shit less?

Stepping down the voltage from its output means less self-generated noise on the rails, its equivalent to adding capacitance on the supply rails. However there is a limit to adding capacitance (at high frequencies) due to parasitic inductance and ESR. There's not really any limit in terms of how far step-down can be taken.

is there any way of estimating where inductance and esr becomes a problem?

Sligolad wrote:Jeez did you guys sleep at all last night or is the clock wrong on this thread.....I suspect you were up all night though :-))

yea felt the effects of last nights fun this morning

Sounds really exciting though and I can understand the inability to sleep if this amp has taken another major step forward after hearing it at Tony's this month.

Keep doing what you are doing Nige even if it is just intuition some of the time as the results will speak for themselves,

just trying to get the best out of it :)

if the well is getting dry in terms of funding due to hits along the way on components and we need to increase projected costs for the optimized TVC then lets do it, no need for a cost benefit analysis here.

haven't done the sums yet but i've more than likely gone over the initial startup fund, although i dont mind paying for the parts for the experiments, im not santa claus or a registered charity and dont really want to be out of pocket so to speak
i just wanted to turn the project into something people could enjoy rather than just another piece of ply on my floor

Very happy to add more funding as is will be one of the best investments in audio in many years.

thanks appreciate it

Will definitely bring the modified Big7 to the next get together to marry it to the amp and see how it works.
Some travelling coming up in January so I hope I can make it...will be pissed if I cannot hear the amp again!

great idea would be good to hear the combo

nige2000 wrote: never said it was on the input?
output transformer

Oh, OK, I guess we were talking past one another - your tvc is on the output, then?

jkeny wrote:

nige2000 wrote: never said it was on the input?
output transformer

Oh, OK, I guess we were talking past one another - your tvc is on the output, then?

Hehe....

Yes tvc is output


Richard says using the 60v input on trafo for 30v ain't optimal so will have to revise the trafo anyhow