F6 Amplifier

[2 picoDumbs]

Added my own asymmetric mod.
I'll do my own listening test later. One channel is stock and the other is modified.

While I was at it, checked the noise at output, getting less than 100uV (averaging around 30uV to 50uV), based on the fact I have 4 times more capacitance than stock this seems correct.

 

[fabrice63]

Hi Pico , how do you measure accurately such very low voltage ?

.

 

[2 picoDumbs]

Guess. Haha.

I'm not sure if this is accurate or not but this is how I put blind faith in Fluke.

First I measured the noise floor of my Fluke meter which measured 320uV.
I then measured the amp which was below the noise floor of 320uV.
I then used a function on the meter called RELATIVE, this basically zeroes out the noise floor (Blind faith here) and then remeasured the amp and got around 50uV, let's call it less than 100uV, I always prefer understating results.
I might give Fluke a call to check whether this a reliable way to measure noise.

The good news is I should have a brand new Keysight Audio Analyzer to play with in about a month, when it arrives I'll see what that can do.

If you're instrumentation is not great you can measure noise by feeding the output into a low noise amplifier with say a gain of 100, then divide answer by 100, eg 10mV/100 = 100uV

 

[fabrice63]

Thanks for your reply , i have an Fluke 287 , i will see if it has the relative function like your .


.

 

[2 picoDumbs]

Decided to measure capacitance across primary and secondary windings of a brand new set of transformers, got a figure around 11nF datasheet says 18nF.
Has anyone else measured this?

Edit: Nothing wrong with my meter as I measured a 4nF cap and it measure correctly.

 

[Zen Mod]

which transformers ?

signal ones ?

 

[2 picoDumbs]

which transformers ?

signal ones ?

Jensen JT-123-FLPCH

 

[Zen Mod]

yeah

l'art pour l'art ........

 

[2 picoDumbs]

Do you have a spare one you can measure?
Do you get the same?

 

[grimberg]

Did you just attach the capacitance meter to the disconnected transformer terminals?

 

[2 picoDumbs]

Did you just attach the capacitance meter to the disconnected transformer terminals?

Yeah, brand new straight out of the box.
Just want to confirm if someone else gets this figure.

 

[grimberg]

I measured 2 different JT-123-FLCF units, the version with wire leads. Winding to winding capacitance at 1KHz is about 10.5 nF in both of them. The datasheet claims 24.5 nF.
Looking at the current datasheet for JT-123-FLPCH, claimed capacitance measurements are:
winding to winding, 1 KHz: 24nF
winding to frame, 1 KHz: 35 pF

 

[2 picoDumbs]

I'm getting around 11nF for flpch

 

[Zen Mod]

if Mithrandir chose them for task , I'm just going to blindly accept them

just as one thing less to check , knowing in which circuit they're good

there are few other things about every xformer more important to know , than winding capacitance

 

[2 picoDumbs]

I'm not being critical, just wanting to be certain about the value.
I'm simulating versions of this circuit with some added tricks and different devices, so being able to model it correctly is important to me that's all.

 

[Zen Mod]

in that case , do not let me spoiling your fun

while you at it , measure bandwidth and saturation level with intended load

 

[2 picoDumbs]

Still loving this circuit.

 

[Zen Mod]

Pioneer SX1000T
receiver from Yore , nuvistors in FM FE , all germanium , silicium just T03 outputs

it's great that The Funny One is un-dusting some things for us , usually memory-challenged audiophools

 

[2 picoDumbs]

Cool circuit.

 

[Nelson Pass]

it's great that The Funny One is un-dusting some things for us , usually memory-challenged audiophools

Usually I am creating from whole cloth, later finding that someone else
has already signed the guest book.