[zhoufang]

will be adding a build in charger later

I did not expect the Q3 rail isolation J-FETs to eat so much voltage (5-6V per rail), so I will increase the battery from 16 cells to 24 cells in the future (MAHA AA 1800mAH NiMH)

The mind casing is my previous project, a Pimeta clone

 

[morsel]

Quote:

I did not expect the Q3 rail isolation J-FETs to eat so much voltage (5-6V per rail)

Try using FETs with more Idss. Good luck!

 

[@sia@home]

Is that a pimeta clone in the altoids tin.

Because from looking at the components it sure does look like one.

How does its performance compare to a bigger one?

 

[Dreamslacker]

As stated in Tangent's guide, the closer the current consumption is to the IDss of the rail isolating Jfet's, the higher the voltage drop across them will be. The benefits would be better isolation. =)

Try using Jfets with higher IDss as Morsel has suggested. If you want, you can get some BF245C's off me. They (those that I have) have an IDss of 15mA to 19mA so you can even run power hungry AD843's off them.

 

[Syzygies]

Quote:

Originally Posted by zhoufang The mint casing is my previous project, a Pimeta clone.

Quote:

Originally Posted by @sia@home Is that a pimeta clone in the altoids tin?

Yes, see his earlier thread PIMETA clone in a mint tin, my 1st amp!.

 

[Dreamslacker]

Where did you get the Suzurando knob? I'm pretty sure I bought the last 2 pieces available in Singapore from Well Audio Labs and Larry Hifi. Is there another shop selling them?

 

[zhoufang]

I have measured all the IDss of the J-FETs and paired the J-FETs in such a way that the total IDss per rail is between 22.5-23.5mA.
Any currently the total current draw per op-amp section is only 7.5mA MAX according to datasheet (class A bias not connected yet).
with the current draw only 1/3 of the IDss, that's why I'm surprised by the amount of voltage drop.

Anyway, since the HA-5002 is rated for higher voltage than all the op-amps of my choice (OPA627/637 AD8066 AD8610 etc), this just help the chips at both stages get the voltage they need. I will supply more voltage to it, and this will also help the C1 electrolytic caps to perform better.

 

[zhoufang]

Quote:

Originally Posted by Dreamslacker Where did you get the Suzurando knob? I'm pretty sure I bought the last 2 pieces available in Singapore from Well Audio Labs and Larry Hifi. Is there another shop selling them?

I got it from Well Audio over 2 months ago...

 

[morsel]

Quote:

with the current draw only 1/3 of the IDss, that's why I'm surprised by the amount of voltage drop.

Something else must be wrong, then. Try measuring the current draw in circuit. I'm guessing you measured the FETs before building the amp, but perhaps an unexpected short is draining more current now that the amp is assembled.

 

[zhoufang]

Quote:

Originally Posted by morsel Something else must be wrong, then. Try measuring the current draw in circuit. I'm guessing you measured the FETs before building the amp, but perhaps an unexpected short is draining more current now that the amp is assembled.

I'm too lazy to unsolder the circuit to measure the current directly, so I measured the voltage across R8 (from PPA v1.1, the resistor in the RC noise reduction network).
The voltage of all three channels reads 60mV. Since my value of R8 is 10ohm, so the current works out to be 6mA, within expected range.

I know that there may be leakage somewhere higher up at the TLE or C4, but the chances of such accident happening to all 3 channels is really low.

 

[doobooloo]

That amp looks slick. Very well done! Looks like a pretty souped-up PPA. How do the SILMICs (I or II?) sound? I've been wanting to get my hands on some for a while, can't find a good distributor though.

Sort of reminds me of Dr. Gilmore's saying of there's no such thing as overly excessive or something like that...

Gotta love all those caps there. Nice battery pack too!

 

[ppl]

Quote:

Originally Posted by zhoufang I'm too lazy to unsolder the circuit to measure the current directly, so I measured the voltage across R8 (from PPA v1.1, the resistor in the RC noise reduction network). The voltage of all three channels reads 6.0V. Since my value of R8 is 10ohm, so the current works out to be 6mA, within expected range. I know that there may be leakage somewhere higher up at the TLE or C4, but the chances of such accident happening to all 3 channels is really low.

Morsel is correct somthing is amiss in your amp and based upon your assesment of the proper voltage drop across the Rail noise reduction resistors i would suspect that the fets used on each rail have dramaticaly different idsss. this can cause unuasaly high current consumption

 

[zhoufang]

Quote:

Originally Posted by ppl i would suspect that the fets used on each rail have dramaticaly different idsss. this can cause unuasaly high current consumption

Do you mean the FETs used on different rails have different idsss or the pair of fets used in the same rail have different idsss?

And I don't quite understand why this cause a current consumption?

Thanks!

 

[Dreamslacker]

Quote:

Originally Posted by zhoufang I'm too lazy to unsolder the circuit to measure the current directly, so I measured the voltage across R8 (from PPA v1.1, the resistor in the RC noise reduction network). The voltage of all three channels reads 6.0V. Since my value of R8 is 10ohm, so the current works out to be 6mA, within expected range. I know that there may be leakage somewhere higher up at the TLE or C4, but the chances of such accident happening to all 3 channels is really low.

6.0v across 10 ohms works out to 600mA actually.

I just realised something: Are you using BF245 Jfets? If so, you may have orientated them wrongly.

 

[ppl]

Quote:

Originally Posted by Dreamslacker 6.0v across 10 ohms works out to 600mA actually. I just realised something: Are you using BF245 Jfets? If so, you may have orientated them wrongly.

I am uncleer as to the 6 volts of drop is that across the resistors or the fets. 6ma across 10 ohms is 60 mV not 6 volts. if you are indeed getting 6 volts arcoss the 10 ohm resistors are nor your opamps smokin after power up and is this amp actualy working and reproducing cleen undistorted sound? what about the TLE rail splitters are thay also not burnning hot.