Triple Bypsssed Genesis 1 Low Hum Especially on White Screen
Triple Bypsssed Genesis 1 Low Hum Especially on White Screen
I have triple bypassed my early Model 1 Genesis. I'm using a Csync Fortaflex SCART cable from Retro Access and I notice I have a persistent low hum. Its not really noticeable when music is playing, but its pretty noticeable when nothing is playing, and it gets louder with all white screen. I'd say it might be 60hz hum. To power the console I'm using a M1C1 Trio and I have recapped the console with the cap kit from Console5. Any idea how to reduce or eliminate this hum?
Re: Triple Bypsssed Genesis 1 Low Hum Especially on White Sc
Have you tried directly connecting the Genesis to a receiver or headphone amp? That's what I do with my triple bypassed VA6 JP Mega Drive, and it's output is pretty clean. Probably best to keep analog audio away from video whenever possible.
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NewSchoolBoxer
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Re: Triple Bypsssed Genesis 1 Low Hum Especially on White Sc
Can ignore the source of 50-60 Hz hum and just buy a cheap-ish ground loop isolator to plug audio line into that is specifically designed for filtering this out. Since hum could be happening inside SCART cable, plug in isolator right before the speaker or television so the hum doesn't get induced back on the audio.
I'm not in Genesis scene but your description points to possible sources. I assume you did the mod correctly, which from glossing over the details, is difficult and there are several different Model 1 revisions. That's helpful you mention the exact power supply and capacitor kit. Power supply website description states it uses Nichicon capacitors and Console5 uses similarly top brands, so I'll rule out issues stemming from those.
In theory you disabled composite video on pin 1 and replaced it with csync.
So where could the 60 Hz signal interference be coming from? RGB doesn't encode on that frequency but vertical sync does, as does the AC from your power outlet, as does any nearby power cable. That you mention hum is louder with all white screen is important. Luma is at max voltage for white and less for darker colors and shades. More voltage draws more power and more power in a signal means it will cause more electromagnetic interference. The csync doesn't contain luma, so this points to noise source from the voltage regulator in the Genesis that passes on the 60 Hz noise to everything in the console. If mod not done optimally, a nearby composite video pin or trace that isn't disabled could cause the hum.
Do a test if you are using BNC breakout to PVM or whatever. Have console running and hum audible. Remove sync from PVM to prevent it from leaving the console. If no hum then you need VGA or BNC cable or a SCART cable that better insulates audio and sync, or a SCART with audio breakout so you don't run audio alongside anything else. If still humming, do process of eliminating with R, G, B with sync plugged back in but I doubt is cause. If hum only from audio plugged in then interference is coming from console or outside source like power cable to television or monitor.
Possibilities in maybe how likely they are since I don't know Genesis:
1) Your sync line is crosstalking on audio inside of the SCART cable. Described above.
2) Audio is getting interfered with inside console due to mod. Three different Mega Amp 2.0 versions ugh. Could shield the audio traces and components and better insulate it from the video chip (if nearby). Steel is probably best for low frequency shielding but be wary of creating a short circuit.
3) Whatever speaker you're playing the audio on is 8 or 16 ohm versus the optimal 32 ohm speaker that the mod's audio buffer transistor datasheet specifies. Will technically work for lower impedance but has a lot more harmonic distortion + noise as you can see on page 8. I like jd213's advice to use a receiver or headphone amp that is going to be more tolerant. At least try using a pair of headphones to listen if hum is reduced.
4) The mod uses more power than stock Genesis and you're probably using more than one outlet from the wall socket or surge protector. Can cause audio hum from sharing the same ground on everything but fixable with a ground loop isolator described at start.
5) jd213 has other good point, audio wires are paper thin as a rule and any nearby electrical device could induce hum on them.
6) I assume capacitor kid replaces the power supply capacitors on the Genesis. If not then badly filtered power can cause hum. Even though is DC, is created from 50-60 Hz AC that capacitors need to filter out. Replace PSU caps if original and also replace the $1 7805 voltage regulator.
7) If csync SCART cable, I assume compared to Genesis cvbs composite video as sync cable, has a sync stripper chip in it that is powered by the +5V DC on pin 5. The pin 5 voltage could be noisy since it wasn't used for stock composite video and powering the sync chip could induce hum on the nearby sync line. A cvbs cable would not contain this chip so no possible chip noise. I doubt you're using csync cable since Retro Access says they put 470 ohm resistor on it that would drop TTL sync to 75 ohm sync level. Mod description says it outputs 75 ohm sync. If you put large resistor on 300 mV (75 ohm) sync then you get no sync = no video at all.
I'm not in Genesis scene but your description points to possible sources. I assume you did the mod correctly, which from glossing over the details, is difficult and there are several different Model 1 revisions. That's helpful you mention the exact power supply and capacitor kit. Power supply website description states it uses Nichicon capacitors and Console5 uses similarly top brands, so I'll rule out issues stemming from those.
In theory you disabled composite video on pin 1 and replaced it with csync.
So where could the 60 Hz signal interference be coming from? RGB doesn't encode on that frequency but vertical sync does, as does the AC from your power outlet, as does any nearby power cable. That you mention hum is louder with all white screen is important. Luma is at max voltage for white and less for darker colors and shades. More voltage draws more power and more power in a signal means it will cause more electromagnetic interference. The csync doesn't contain luma, so this points to noise source from the voltage regulator in the Genesis that passes on the 60 Hz noise to everything in the console. If mod not done optimally, a nearby composite video pin or trace that isn't disabled could cause the hum.
Do a test if you are using BNC breakout to PVM or whatever. Have console running and hum audible. Remove sync from PVM to prevent it from leaving the console. If no hum then you need VGA or BNC cable or a SCART cable that better insulates audio and sync, or a SCART with audio breakout so you don't run audio alongside anything else. If still humming, do process of eliminating with R, G, B with sync plugged back in but I doubt is cause. If hum only from audio plugged in then interference is coming from console or outside source like power cable to television or monitor.
Possibilities in maybe how likely they are since I don't know Genesis:
1) Your sync line is crosstalking on audio inside of the SCART cable. Described above.
2) Audio is getting interfered with inside console due to mod. Three different Mega Amp 2.0 versions ugh. Could shield the audio traces and components and better insulate it from the video chip (if nearby). Steel is probably best for low frequency shielding but be wary of creating a short circuit.
3) Whatever speaker you're playing the audio on is 8 or 16 ohm versus the optimal 32 ohm speaker that the mod's audio buffer transistor datasheet specifies. Will technically work for lower impedance but has a lot more harmonic distortion + noise as you can see on page 8. I like jd213's advice to use a receiver or headphone amp that is going to be more tolerant. At least try using a pair of headphones to listen if hum is reduced.
4) The mod uses more power than stock Genesis and you're probably using more than one outlet from the wall socket or surge protector. Can cause audio hum from sharing the same ground on everything but fixable with a ground loop isolator described at start.
5) jd213 has other good point, audio wires are paper thin as a rule and any nearby electrical device could induce hum on them.
6) I assume capacitor kid replaces the power supply capacitors on the Genesis. If not then badly filtered power can cause hum. Even though is DC, is created from 50-60 Hz AC that capacitors need to filter out. Replace PSU caps if original and also replace the $1 7805 voltage regulator.
7) If csync SCART cable, I assume compared to Genesis cvbs composite video as sync cable, has a sync stripper chip in it that is powered by the +5V DC on pin 5. The pin 5 voltage could be noisy since it wasn't used for stock composite video and powering the sync chip could induce hum on the nearby sync line. A cvbs cable would not contain this chip so no possible chip noise. I doubt you're using csync cable since Retro Access says they put 470 ohm resistor on it that would drop TTL sync to 75 ohm sync level. Mod description says it outputs 75 ohm sync. If you put large resistor on 300 mV (75 ohm) sync then you get no sync = no video at all.