Debug: Almost no amplification

[anilkumar_15]

(Continuing from previous post)
Hi Experts,

I built this smack-amp 2 years ago to give it to a friend, but it never worked.
I never got amplification and it was collecting dust.

Today I checked it again with different source (Oppo Blue Ray palyer & Ibasso X90) .
LEDs are barely glowing in Pre-amp section (B , C4S@15mA-section of the ckt-diagram).
If Q1 and Q2 is blown then it is very unlikely that it will be blown for both channel.
When I tried to read resistance across the Rdb(33K) on assembled board, its value keep increasing ...it may be because Cedaly is getting charged.  Is there anyway you can tell me what voltage is expected at  bB, B or any other net name which I can use for debugging .

I checked all the points and voltages are within the range.

While assembling , I had replaced many resistor with equivalent Vishay resistor as well as filter capacitors were replaced as well with equivalent value.  Volume control pot was replaced with ALPS.

I am not sure how to debug anymore. This product is no longer in production by Bottlehead.

Any suggestion on how to debug or convert into some useful headphone-amp (eg Mainline) will be really appreciated.

Thanks,
Anil Kumar

[anilkumar_15]

One more piece of information...
In one channel, I had assembled output-impedance switch pcb in wrong side for one channel. I still has it in the same way but connections are still correct... checked it 5-6 times.

[Paul Birkeland]

It might help to put all the stock parts back in the Smack, as there may be an installation error with the modified parts.

-PB

[Paul Joppa]

"I checked all the points and voltages are within the range."  That indicates the circuit is functioning correctly, so a lack of sound most likely comes from an error in either the input or the output.

The shunt reg C4S has 3 times as much LED current as the amplifier C4S, so they do normally glow much brighter.

If you can hear anything at all - a bit of hum or hiss perhaps - then the output is likely to be working and the problem likely to be in the input or volume control.

[anilkumar_15]

Thanks for quick support.

 I hear the sound without any hiss or noise. It is as clear as if it is coming from from my Blue-ray player (BP-105).
I am using  Grado 1000, Beyer T-70P and couple of other headphone. I am not noticing any amplification at all.

As LED is not glowing bright enough, actually all four LEDs are not glowing very bright.
But two LED of "B , C4S@15mA" section are barely glowing. As Vreg is at 120V then I am suspecting whether parallel resistance of 33K is bad or there is something wrong with the three resistance (90K, 90K , 2.4K)..

I will update you next weekends.
I am afraid to replace the resistor by stock resistor... I may destroy the PCB.
If you have some more suggestion , please let me.

[Paul Joppa]

I do not understand what you mean by "no amplification".

Before, you said all voltages were good, now you say Vreg is 120v - but it should be 180 volt, so it is NOT good. We need to know the voltages in order to guess what might be wrong.

The terminal voltages are on page 56-57 of the manual, and for the C4S boards they are on the schematic, except for the kreg(A) and kreg(B). I don't remember what those should be.

[anilkumar_15]

Hi,
After many years I took the amp out from the box and trying tot fix it to  fix it . But I lost the CD which came with it . . I  am wondering if any one can send me a copy of important voltage with node name so that I can start debugging  it .
Thanks for your help .
Regards
Anil K .