Live Lab Hangout #1.1 Posted

[jama]

From today I will try again to connect evolve amp (stopped during some months for build lamp with thf51) because now I know what I can expect of lamp with thf51 (I am love...). Now, with hp8903 I can measure.
I have not heard J2. I got some SS (some R100 and R063). I hope some day, when schematics are free (if this event occurs) I can build it...
Models are not very useful (only for see if circuit works) after I see how are their curves (very different from each other). It is better mount, measure and hear.
Attached all my 2sk180 curves. They are different each other. They can not works equals in this circuit (I think) and if I only get 5Wrms when original circuit says 10W, it is possible that this is the cause. But I do not known a lot of analog electronic (only one year in university). Only mount, measure and decide...
I will put my findings.
Regards

 

[jama]

Well, well. I had an error in circuit and now it is fixed. I have get 10Wrms with 0.4Vrms input. Distortion is 0.08%. This circuit is promising...

 

[generg]

At 1Watt and 8 Ohm load?

 

[jama]

No. At 10w rms and 8ohm

 

[jama]

Look four photo

 

[generg]

That is for 10W really very low.

Can you say OLG and CLG ?

Feedback seems strong.

 

[jama]

Sorry I do not know what is OLG and CLG.

 

[generg]

The difference between open loop gain and closed loop gain allows to estimate the feedback amount....

I am curious to know how much feedback the circuit has, perhaps someone can help us......

 

[jama]

Sorry, I know these concepts. I was thinking in spanish language.....

 

[generg]

Yes I thought you know this.....

 

[jama]

I need measure to reply you. But with this little amp it is possible compare between lamp amp and this amp with feedback. In close loop, gain is 10/0.4. I need break feedback and measure again, I think.

 

[cwtim01]

Can't resist the temptation so ordered a pair

Received them today ..... and they're both BAD

Anyone ordering brand new 2SK180s from Japan, should be cautious and test them either in-circuit, or with a curve tracer asap.

 

[generg]

Tim,

Please tell me which traits of the curves tell you that they are bad.....

 

[cwtim01]

Hi Gerd,

Read post #136 and Michael showed how the bad curves look, basically very similar to what I show above, it was also explained in one of the hangout video.

Compare that with the good one - this is the one you sent me. All the curves are 1V apart.

 

[generg]

Thank you Tim!

Half working......irritating....:-(

What funny effect, sorry you had to pay for it!

 

[stefanobilliani]

Received them today ..... and they're both BAD

Anyone ordering brand new 2SK180s from Japan, should be cautious and test them either in-circuit, or with a curve tracer asap.

Then , it is an difficult very difficult task to find them good .

 

[cwtim01]

Then , it is an difficult very difficult task to find them good .

All the rusty used ones I came across were good (11), but all the new ones (10, from 2 different sellers) were bad.

... What funny effect, sorry you had to pay for it!

I negotiated the refund with the supplier already so not much loss, except the shipments which are quite cheap between China and Hong Kong

 

[jama]

I can confirm this. I have a few 2sk180, oxidized and very uglies.... but they are good. It is possible new ones are rejections of production. Sorry

 

[dady]

At the end the only big problem of the THF51 is the 5nF of in capacity...
Who of us listen over 100KHz?

 

[cwtim01]

... Feedback seems strong.

I'm curious about this also so I simulated the original Evolve circuit (not exactly jama's), OLG simulated to be around 53.4dB by Tian probe method.

CLG is around 26.4dB, hence feedback is around 27dB I believe.