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Noisy E/Bay Remote V/C 128 Steps Pre
Noisy E/Bay Remote V/C 128 Steps Pre
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Old 7th August 2019, 06:30 AM   #1
gigigirl is offline gigigirl
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Default Noisy E/Bay Remote V/C 128 Steps Pre (Now Not Noisy)

Hi, I 1st placed this in the Pass section as I was trying to shoe-hone put a B1 Korg into the case and use the unit as an active Pre. However as it is not a Korg problem & I think several members may have one of these I have started this thread.

I 1st tried it as a passive unit & was very happy with the sound & function, it was overall very, very quiet. However on Vinyl I had to turn it up fully to 128 to get adequate sound levels. However the vol in position 128 was to loud & dropping back 1 notch to 127 reduced the vol by about 3dB, making it to quite, so it is not completely linear.

Volume Remote Control Relay 128 Steps Exponential Constant input impedance 4 CH | eBay

So I decided to insert my Korg board to make it an active Pre. After re-positioning the shielded trans. Using a 24 VDC battery supply to fire up the Korg. Wallah it worked but as I turned up the vol on the 128 step pre, I got a increase of hum at 3 intervals, at vol positions 60, 96, 115 (then when I got to 127/128 the hum reduced to the level of the 96 vol range)
The hum incidentally is the same across all 4 inputs,

Claas kindly suggested this from the B1 Korg thread.
" I don't remember exactly if the relay board had been grounded to the case via the mounting screws, but with no audio cables connected, there should not be an electric connection between these two points and the case. You can check with an Ohm meter. If necessary, you might have to isolate some of the standoffs from the board.

Then, I connected the eyelet "aground" through a CL-60 to the case, but you can use a 10R - 100R resistor for this as well. The case itself is grounded / connected to PE / earth ground.
That gives a defined path between audio ground and earth ground / case without the risk of a ground loop."


I have tried that & isolating the relay board from the case did quieten it a little, but on my board I cannot recognize what Claas refers to as the "eyelet aground"

Hopefully he will see this and kindly assist some more.

Cheers
This cured the hum completely for me.
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File Type: jpg IMG_20190807_173700.jpg (415.7 KB, 129 views)

Last edited by gigigirl; 12th August 2019 at 05:39 AM. Reason: Problem Fixed
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Old 8th August 2019, 01:19 PM   #2
chede is offline chede  Germany
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Noisy E/Bay Remote V/C 128 Steps Pre
Hi Derek,

maybe I haven't been clear enough in my responses #2869 B1 with Korg Triode and #2873 B1 with Korg Triode.

What I meant is:
- connect Audio Ground from the relay board to the case of the preamp via a resistor or a CL-60
- connect the case to PE / house earth.

What I see in your picture in your post above:
Below the leftmost relay on the volume control board, there are two solder pads on the PCB that seem to be connected with a a bridge.

So you might try the following:
- cut the link between these two pads
- the right one of the pads is Audio Ground (the one farther away from the mounting bolt)
- connect the right pad to the case, and the case to PE / house earth

The reason I suggest connecting the pad to the case not directly, but via a resistor is that this breaks up ground loops (current cannot flow easily), but still provides a ground reference in terms of voltage potential.

That is what had worked for me to get the preamp quiet - no hum.

Best regards,
Claas
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Old 9th August 2019, 01:55 AM   #3
gigigirl is offline gigigirl
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Default Still Humming

Hi Claas, Thanks for clarification. Have implemented the recommendation. (See photo) but unfortunately it has not changed the hum. But then perhaps I have done something wrong, always possible with me.
Anyway thanks for taking the time to help, hopefully we can get it sorted.

Cheers Derek
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Old 10th August 2019, 04:54 PM   #4
chede is offline chede  Germany
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Noisy E/Bay Remote V/C 128 Steps Pre
Hmm ... then we need to look deeper into where the hum comes from ...


- do you still have hum with no source connected to the preamp ?

- no source connected and input shorted (either insert shorting plugs, or connect hot and return of the selected input together ?

- does it hum with just one channel (one RCA cable) connected and the other channel open ?


- does it hum with different power amplifiers ?


These could all point to different scenarios for ground loops between source and preamp or power amp.

Hope we get some more hints at would the culprit could be this way,
Claas
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Old 11th August 2019, 05:46 AM   #5
gigigirl is offline gigigirl
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Default Back Again

Hi again, I tried what you recommended.

- do you still have hum with no source connected to the preamp ?
Hum is considerably louder.

- no source connected and input shorted (either insert shorting plugs, or connect hot and return of the selected input together ?
Inputs shorted with shorting plugs, same level of hum with equip connected. short RCA cable loop connection is louder hum, but not as loud as no connections.

- does it hum with just one channel (one RCA cable) connected and the other channel open ?Loud hum when only one RCA connected.


- does it hum with different power amplifiers ?
Sorry do not have a different P/Amp I can use.

- I think it is very curious that the pre has 4 distinct level of hum. With the hum only changing at volume points I previously mentioned.

- Any idea if this pre could work from a DC input, some can, but they do not advise on the add as it comes with the trans build in. Perhaps switching to DC may quieten it down. Have found that with many phono amps in the past.
This one apparently can
Assembeld Motor preamp Remote volume control board+display+PSU+input switch | eBay


Again, thanks for the input.

Cheers Derek
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Old 11th August 2019, 09:20 PM   #6
chede is offline chede  Germany
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Noisy E/Bay Remote V/C 128 Steps Pre
It is interesting that you have more hum with one channel connected than with both channels connected. A ground loop between the preamp and another piece of equipment usually manifests itself in the following scenario:
no hum with no channel connected, no hum or a bit of hum with one channel connected, louder hum with both channels connected.

The disctinct levels of hum are a clue. Depending on the volume level, in this preamp different numbers of relays are active. It tends to be more relays with higher volume, but this is not a strict law, there are certain sequences going on.

I have noticed in my preamps that noise can travel with the power for the relays - when more relays are on, more noise can be transmitted into the audio path.

And I didn't realize that you are still running the original transformer and get AC into the preamp. Throwing out the original transformer was the first thing I did on my preamp, not least because I needed the room (see my posts in the Wayne's BA 2018 thread).

I am using an external PSU and bring only DC into the preamp.

You can connect DC into the control board at the front, right were the transformer secondaries used to be connected. You just have to account for the fact that you lose about 1.5V in the rectifier bridge that is the first element after entry. So voltage of 13-15V DC to connect to the control board is a good range. It is not overly critical, as the control board has regulators, but with more than 15V the relay voltage regulator gets a bit too warm when all relays are powered.

I think using an external PSU and bringing in DC into the preamp is a worthwhile next step to try.

When you use an external PSU, you should bring in PE / earth ground on a separate line so that you can do proper grounding of the case and the audio ground (via resistor) in the preamp.


Hope you get it sorted out,
best regards,
Claas
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Old 12th August 2019, 05:04 AM   #7
gigigirl is offline gigigirl
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Default Well that did the trick

Hi, Well that did the trick, trans is gone & replaced with a DC to DC reducer feeding 15 VDC from my 24 VDC SLA batteries.
Wallah, no hum, or virtually. Inputs 1, 2 & 3 are totally silent & 4 from the Pass Pearl is very, very quite. Not quiet as quiet as the vinyl system was from the DCB1, but I'm sure much quieter that many, many other peoples systems. In my listening chair totally quiet, I only hear a slight noise when up close to the speakers.

I had already bought a Studer 24 VDC power supply

STUDER900 upgrade 25W Talema PSU DC Linear power supply 5V 7V 9V 12V 15V 18V 24V | eBay

to power ultimately power the Korg. I have tested this P/S with my A/K AD797 MC phono amp & know it actually is about 1dB quieter that the SLA battery set up, so when finished it could even get a little quieter, however if that does not happen & will be more that happy with what I've got. The Korg certainly made a significant improvement to my system especially on CD & Wave files.
So thanks for all your help. Now I am not sure why anyone would go another way to implement the Korg. As you know, you get a high end vol control plus remote input and the complete unit is not that much more that a empty case brought from the DIY store.

Just wish I could dim the LED display a little.

Again Thanks Claas, Cheers Derek
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Old 12th August 2019, 08:21 AM   #8
chede is offline chede  Germany
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Noisy E/Bay Remote V/C 128 Steps Pre
Actually, you can dim the LED display ...
On the remote, there is one button that cycles through four different brightness settings ... I think it is the one labeled "DSP", upper middle.

Also, a reason for hearing a bit more noise on your vinyl input than with the DCB1 could be that the Korg B1 has some gain where the DCB1 has none, if I'm not mistaken ... if I remember correctly from the Korg B1 thread, it is 16 dB of gain.

Enjoy your preamp, glad that you got it sorted out,
best regards, Claas
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