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Old 9th April 2012, 05:22 AM   #1811
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Default Different static on both channels

Hey all,

Looking for some help with my newly cases up DCB1. I got through the initial checks fine and got LEDs up and everything. But I wired up my 20K alps pot today and got some strange behavior through my F5.

Left channel: At no volume, dead quiet. But with increasing volume, I get increasing music with increasing static. Very obvious, not subtle in any way.

Right channel: At no volume, dead quiet. With increasing volume, first thing I get is static. Then music comes on but much more softly than the left channel. Both music and static increase with volume, but like I said, the music is much quieter than in the left channel.

I can't help but think that I messed up the pot wiring, but I double checked and it looks fine. It's not like it's that complicated anyway. I verfied the input grounds are connected. Checked the same for the output grounds.

It's not hum so I don't think it's a ground issue. It's static.

Any ideas?
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Old 9th April 2012, 08:40 AM   #1812
Porfido is offline Porfido  Italy
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Quote:
Originally Posted by syklab View Post
Hi Porfido,
Nice setup on the B1 pre-amp, what do you use for display or volume indicator? How about source selection?
I am also trying to choose for the volume control and source selection for the DCB1.
Hi, Skylab!
In this DCB1 I have no input selection, because only one input...
In the remote control kit I linked before there's anyway a selection board with 5 relais for 5 inputs, anyway, quite easy to use...
The only volume indicator I have is the spot on the volume knob...
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Old 9th April 2012, 08:45 AM   #1813
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Are you sure you mean static or just noise as you turn the pot ?

Don't forget this is the DC B1 so you may have DC across the pot which will cause noise as you turn it.

To iron this one out simply try connecting 1uF caps to the wipers and the inputs of the pot.

This will not give you the DC connection that you are looking for but it will point you in the right direction as to where to look for the source of the noise.

You don't need to be choosy about the caps at this stage - Polydrops will do just fine.

Last edited by KatieandDad; 9th April 2012 at 09:09 AM.
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Old 9th April 2012, 10:19 AM   #1814
Tea-Bag is offline Tea-Bag  United States
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I had something similar to static in a decent project, during turn on for a minute.
Turned out to be a bad solder joint, trying to solder in a small wire into a big hole

I would measure the usual places - where the power supply section stops for voltages there - and across the 2SK's, and then the output as well for DC offset, AND AC.

If you got a scope that would help
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Old 9th April 2012, 10:39 AM   #1815
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Hi poor Fido, 8-)
You do know the Pot needs to be earthed at the screw ?
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Old 9th April 2012, 12:46 PM   #1816
Siberia is offline Siberia  Lithuania
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Quote:
Originally Posted by Siberia View Post
I've tried passive stage. Awful! I've tried my work mac direct to amp. It gives a temporary illusion of firmness but my guess it's coming from midband. Otherwise all the same. I've tried both full output on soundcard and software attenuation, and vice versa.
Hello, all. My DCB1 is back and kicking with gorgeous sound. I've resoldered all my rca-to-pot-to-board-to-rca connections and changed wiring a bit. Now I've got 2 separate L-R grounding wires running to the pot's ground lugs and then 2 wires to PCB. They join only at PCB input. Then, 2 ground wires run from PCB output to L-R RCAs separately.

This was not the case before. Previously, I had L-R rca grounds connected with a short bus wire and ran one wire to all following connections from it.

I still have first steps of my stepped attenuator not working properly. Crackling and huming when touched. Again, on first two, three steps only. But it all can be due to dust as it's not a sealed one. It was on a shelf for some time. I'll report after cleaning.

Revising soldering, I think, helped a lot in this case. Watching these very helpful lessons (all asociated recommended):

Basic soldering lesssons revealed major mistakes I was into.

Wiring rethinking and soldering lessons spotting credit goes to Salas.
Thanks, again!

Now I would like to rethink my transistor mounting.
The sinks are running around 45 degrees celsius. DCB1 is hot-rodded with 5R current resistors, around 400mA.

Here's the link to my sinks. 75mm ones. So 3,6 C/W.

How high I could run my bias with these remains a question for me. But first I would be glad to read or watch proper mounting instructions.

Thank you all for your help.

Last edited by Siberia; 9th April 2012 at 12:50 PM. Reason: Sinks specs updated
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Old 9th April 2012, 12:53 PM   #1817
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Try it and see. I found that the heat started to RAMP-UP considerably above a certain point.

At 600mA I had to throttle back a bit. I opted for 120mA, I could probably have gone for 300mA but I was fed up with changing resistors for no audible gain IMO.

See Post #1795 I seem to recall that my Maplin 2E heatsinks were about 3.6 Deg C/Watt but I only have the two of them.

Last edited by KatieandDad; 9th April 2012 at 01:22 PM.
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Old 9th April 2012, 01:20 PM   #1818
Salas is offline Salas  Greece
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Quote:
Originally Posted by Siberia View Post
I still have first steps of my stepped attenuator not working properly. Crackling and huming when touched. Again, on first two, three steps only. But it all can be due to dust as it's not a sealed one. It was on a shelf for some time. I'll report after cleaning.
Ground the pot's body. There must be some handy metallic point on it to run a wire from.
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Old 9th April 2012, 02:01 PM   #1819
Siberia is offline Siberia  Lithuania
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Quote:
Originally Posted by Salas View Post
Ground the pot's body. There must be some handy metallic point on it to run a wire from.
It's grounded to a case via stand off bracket which holds it near to keep wires short. A screw connects the bracket to the bottom of the case.

I will eventually try increasing bias. Salas, you nicely put the advantages in post #378.
But first would like to know what's the safe bet with these sinks.
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Old 9th April 2012, 02:21 PM   #1820
Salas is offline Salas  Greece
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But the case, is it at PSU ground potential too, or only connected to mains earth?
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