HF Noise and cracking noise from Gainclone - Help

[syklab]

Hi Peter,

Starting building my gainclone from the kit, transformer is 300VA 25VAC,
DC offset is around 6-7 mv, I started with one channel first. Checked all the connection and looks fine.





When first power up without connecting to the source, noise was acceptable and appear only when I turn the volume all the way up, the noise sounds like Di..Di..Di...

When I connect it to my CD player and start turning the volume up by just a bit, the Di..Di.. HF noise start getting louder. I try playing around with the SG from the RCA port and the groud pin (4th pin) of the volume, the RCA ground and Volume ground are connected to the SG but still no help. I also try connecting the CG to the metal plate too, no help.

I also hear a loud cracking sound when someone turn on/off the light ( they are no connected to the same power socket)

Can you give some suggestion?

Thanks

[nightanole]

did you install your input rf high pass filter, dc blocking cap, output output Zobel filter? Also an emi filter at the powe plug can help with the light switch problem

[syklab]

Hi nights ole,
What kind of rf high pass filter should I be installing and where should it fit in the circuit?
I did not install the Zobel output filter since Peter doesn't think it is necessary, so if I Need the Zobel then what value should I use for the C and R? Do I need to increase the ps smoothing cap as well? i am using 1500uF 50V for each rail. I will try to install the emi power plug filter next.

Sorry for all these question, thanks

[nightanole]

for a low pass filter you can use this:
Guitar Pedals: R-C Filter Calculator

I dont know how you have your volume control setup so i cant tell you where to put it, normally it goes right next to the rca's input.

Bert - RC filter

you want something around 100khz-200khz.

1500uf seems low, but you have a huge va transformer and high quality caps. i used 10,000uf caps, but only a 150va transformer for 2 channels.

zobel should be something low like 2-3ohm(2watt) and .1uf. In a perfect world you would not need one, but in the real world it prevents your gain clone from turning into an unstable am amplifier.

[syklab]

Hi nightanole,
I just installed an ps emi filter but cracking sound from turning off light still there.
My volume is right after the RCA input, RCA + goes to the input pin of the volume, center pin of the volume goes to the Signal in, both RCA - and the volume ground pin go to the signal ground.
Once I got things working then I will start to try with larger caps and CRC ps filter. But one thing at a time, first thing is to clear all the HF noise.

[nightanole]

Is Gainclone Direct Coupled? Appropriate Preamp?

[nigelb001]

Of course, this is an Audiosector board so will obviously not have high pass, low pass, Zobel, Schmobel or any other bits of circuitry that some deem essential. These boards work perfectly well in the vast majority of situations and yes, mine works absolutely beautifully in standard minimal form.

Keep lead lengths short and direct (<4") and get it cased in an aluminium enclosure. Then ground the case securely to AC mains earth which you haven't got going anywhere. Then connect CG (chassis ground) to the mains ground point. Your board is open to the elements so get that sorted out before adding all the networks etc., there are audible benefits in keeping it minimal if at all possible. If you are unsure about the DC offsets in whatever you are connecting to the input, then you will need a DC blocker capacitor (4u7 polystyrene works well) - mine is DC coupled.

Nigel

[syklab]

Hi,
I got it sorted out now by replacing the 10uf 50V(C1/C2) with 47uf 50V and all that HF noise are now gone. I added a 4700uf 63V Cap to the 1500uf 35V cap on both rail for 1 channel just to see how it will turn out. I also use 4.7uf NP Cap in place of the R1 in one channel see if that makes any different.

I am keeping the signal cable to 12" before I transplant it to the aluminum enclosure and that doesn't seems to pickup any noise there.

Anyway the sound is good and the heatsink doesn't get hot, just warm so far.

[corlickmark]

to stop this frequency interference you need to add a high pass or band pass filter. otherwise, the problem will continue. from my point of view you should attach a EMI filter with your power supply. if you tell me the details i can help you to calculate the required rating of the filter.

[syklab]

Hi Corlickmark,
Now I Have attached a EMI/RF filter with a 250VAC 5A rating to the power supply before feeding the 300VA 25VAC x2 transformer, the initial problem is gone but now I have another hum problem when attaching both channel to the same transformer.

Originally Posted by syklab

Hi Dean and Peter,
Sorry for riding on your thread on this issue, I have similar hum issue with my 2 channels setup. I have 1 transformer with 2 secondary (2x 25VAC) feeding 2 x 3875 Chipamp modules with both having it's own PSU module.

Trans(1) -P1 feeding PSU1 of AMP1 and PSU2 of AMP2 on positive rail
Trans(1) -P2 feeding PSU1 of AMP1 and PSU2 of AMP2 on Negative rail

When I isolate one PSU-AMP module by disconnecting the power rails on one module, no hum, very quiet on the other module. This applies to both PSU-AMP module when I swap it so this shown the PSU-AMP module is working fine. Only when I connect both PSU-AMP to the same transformer then it hum. Please note that I have not connect the SC ground and no ground breaker yet, the whole thing is on a cutting board for modup.

I followed Peter's grouding method for each module, do I need to handle the start ground differently when connecting a single transformer to 2 PSU-AMP module? Any suggestion?

Thanks