My Aleph-p isn't working

[PatPet]

Hello there,

After several weeks of hard work, I have finish an Aleph-X and now I'm working on the Aleph-p, which is still not working.

The 10k volume control is not yet connected to the output.
Input selection is not installed neither.

I just did direct input and output to the pcb(bought from KK)

I firstly connected from my computer with balanced output to Aleph-X, what I heard was beautiful music of a sound level that can be heard with ease.

Then, I added the Aleph-P between the computer and Aleph-X and I could realise the output is somewhat attenuated. It is very very quiet that I have to move my ears near the speakers so that I could hear the music.

I cannot figure out the problem. I have tried to replace the transisters. I have also tried with the mp3 player but the level was at the same level.

Guys, I need help. I really look forward to the day of success.
Thanks!

 

[dzkh63]

I working for the P-1.7 and Aleph5 now.I just finish and can playing music.Every thing is OK,but need burn-in and adjusting.Are you have been check the all voltage are correct ? I thing better connect the volume control to the P-1.7 output.

 

[Klaus]

Hi,

"Then, I added the Aleph-P between the computer and Aleph-X and I could realise the output is somewhat attenuated. It is very very quiet that I have to move my ears near the speakers so that I could hear the music."

Do I understand right: almost no signal comes out of the speakers. So the Aleph is not amplifying +16dB or so, it is almost quiet?

Well, my proposal: check the circuit function. Measure the biasing DC voltages across the coupling caps as easiest way. The output cap must have 27V or so, the input cap half of it. If it is so the bias is ok. Then measure the input/output resistors, switched off. At input measure the right value 10k + 22.1k against ground. At output check 4.75k parallel to 10k = 3.3k. If also ok, apply signal to the input cap, set R_gain to 2.2kOhms, and you should get -4dB gain or so. Bring R-gain down to 200Ohms and get the 20dB of gain.

Good luck! Once the P1.7 will work you will be more than happy!

Regards

Klaus

 

[PatPet]

Thank you Klaus.

I measured the potential difference between the output caps and I got 0.01V on the left channel and about 4.0V on the right channel.

What is the problem?

Wrong resister value? Damaged tansisters?

 

[Klaus]

Thank you Klaus.

I measured the potential difference between the output caps and I got 0.01V on the left channel and about 4.0V on the right channel.

What is the problem?

Wrong resister value? Damaged tansistors?

Hi again,

well, the problem is that there seems to be something absolutely wrong with your set up… To bring the circuit to work means to check step by step the functions. E.g. start to check the current sources – do you get ca. 0.6V across the 22.1 and 33.1Ohm R´s? If not do "correct it" – difficult to give tips via e-mail. If the CCS work the rest should be ok if the signal FET is ok.

Good luck again…

Regards

Klaus

 

[PatPet]

While my eyes were on the circuit diagram, "22,1" floated in my mind. I kept asking myself, "Did I buy this resister from Mouser?"

"No, never!"

So the problem is I installed 221 ohms instead of 22.1 ohms(the resister just next to the power supply cap.

After replacing the resister with 24.9ohms(this is the closest Dale resister I have), the Aleph-P sings.

Thank you Klaus, you've been very help. Thank you very much!

I have another problem, which is not very critical.

Now I measure 54V on the output cap. However my BG N caps are only rated at 50V.

Would it be risky to put the cap to this extreme?

Thanks again

 

[Klaus]

Hi again,

"Now I measure 54V on the output cap. However my BG N caps are only rated at 50V."

Please be a bit more carefully. In spite of your euphoric reaction you have a huge problem: your Aleph P1.7 does not yet work ok!!!!! 54V on the output cap means that something still is totally wrong.

Measure the voltage across the 22.1 and the 33.1Ohm Rs and please report it. With these values it is possible to understand the currents in your wrong set up.

Regards

Klaus

 

[PatPet]

Thank you for your help.

Again I found that I wrongly installed the 33.1 ohms resistors as 331ohms.

I have 24.9 ohms and 41.2ohms in my box. Which one should I get?

Thanks

 

[Klaus]

Thank you for your help.

Again I found that I wrongly installed the 33.1 ohms resistors as 331ohms.

I have 24.9 ohms and 41.2ohms in my box. Which one should I get?

Thanks

You have 24.9ohms in at the upper CCS, giving approximately 24mA at 0.6V, not 30mA like assumed. 41.2ohms in the lower CCS give adequate 15mA. So the difference of 9mA bias current must flow through the work resistor R53 parallel to R56, giving 3.22kOhms. 9mA at 3.22 ohms causes 29V DC bias. Should work fine. Test it, measure all voltages: @24.9ohms, 41.2ohms, C_in, C_out and please report.

The only question: how does it sound? The original P1.7 is biasing the IRF610 at 20mA, it sounds perfect to me. You change it to just 15mA, it could sound different. Since I tested sound versus bias current I know how strong the sound variations are. So if the circuit is running maybe change the values the other day to the right ones…

Regards

Klaus

 

[PatPet]

Hello Klaus

I would like to know if the brand of these resistors will affect much of the sound quality. I would go to buy some replacements, of the correct values, now if they don't.

Thanks

 

[Klaus]

My personal opinion: if your set is 100% tweaked than care about the sound of resistors. If not just forget it forever.

Buy any 1% metal film R you can get. 1/4W dissipation is enough. But first you could check with the wrong value if the amp is ok or if you have other failures in.

Regards again

 

[PatPet]

Hello again

After replacing the right resistors, now I can measure 26V on the output caps and 13V on the input ones.

Should this be the correct value for ideal operation?

Thanks Klaus again.