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Hey all- new to this asylum. I added a new pre amp to my chain a few months back. I was previously using the built in pre amp. I never had any hum with the built in pre amp and I do now. I make my own cables, so tonight I went straight from built in preamp, direct to the amp and bang, no hum.My initial thought is that I had connected the cable shield to the wrong end but cables are as they should be. Both external pre and deck are earthed. I removed the earth from the external pre and the hum got worse.
Any ideas? Typically only hums above 80db.
I'm loathe to buy a new preamp if this happens again.
For reference, the pre is a musical fidelity V90 LPS that get great reviews. I upgraded the power supply to a linear power supply unit as well.
Edits: 01/20/24Follow Ups:
You need to make sure it is actually the Phono Preamp.1. Use shorting plugs on the input and see IF the Phono preamp still hums. Yes or No?
If Yes, it an issue between the Phono Preamp and preamp.
If No, then its either the table or the connection between the table and Phono preamp.
2.Short one end of the interconnects that you are using and the other connected to the phono preamp, does it still hum? Yes or No?
If Yes, then it's the interconnect. If no, then its the table causing it.
Some tables due to how the tonearm interconnects or RCA connectors are grounded can cause this hum with certain Phono preamps.
Some like to have Floating inputs to Phono preamps to work sometimes.
Also, Like how Rod mentioned make sure the cartridges clips are connected securely, I had a hum issue and when I traced it back to the table it was one of of the clips on the Right channel causing it. It seemed to have good connection but I reconnected both and it was all gone after that.
last IF all you checked and it still hums, can be the cartridge causing it.
Hopefully this helps.
Edits: 01/21/24
If I'm getting this correctly, the Musical Fidelity V90 LPS unit is a phono stage. You need to ensure that your cartridge is correct for MM or MC and there should be a ground wire from the turntable. If you have an MM cartridge and have the MC switch selected, it could be an issue because it's got too much gain.
Otherwise, ground loops are typical. Usually I keep cheater plugs that drop the ground leg and try using one on the phone stage. If that doesn't work, put one on the amp, etc.
-Rod
For 1/2 a minute I thought I had indeed plugged the MM into the MC sockets, but not the case.
No hum without pre, hum with pre. Pre sold.
Quick update and sort of review.
Between posting and now, I bought myself a Roskan Attessa TT. What a sound. Just fabulous, to my ears even when using the built in pre. All the reviews about it being a very transparent performer are spot on and I can't fault the sound.
I can however fault the mechanical motor hum that made its way into the tone arm and created a new hum to contend with. I can also fault the near impossible tone arm setup. The anti-skate is a joke and using the arm raise mechanism caused it to skate when lifting it from the record. Near impossible to position it too with the amount of tone arm wobble. As if that weren't enough, the platter ground on the top of the deck while it was starting up too.
Other people also had the same issues and the TT was duly returned.
So, on the subject of hum, I added a new Cambridge Audio Alva Duo that a lot of people had rated very, very well. Sadly, I am not noticing an earth shattering sound improvement with the addition of such a well reviewed pre-amp. Maybe my current TT isn't up to producing anything better than the built in pre-amp puts out.
Disturbingly, I have a hum problem again.
That said, I also have a Reloop Turn 5 arriving at the end of the week and am excited to see if the hum disappears when it arrives.
So- Reloop arrived today and what a tank. Extremely easy to setup and my hum is now gone and a really nice sound to it. The Audio Technica TT must have had a very hi output level or something going on.
The new TT has an Ortofon Red installed that I have read bad things about. I "like" its brightness as I like an overall bright sonic signature on everything.
So, quick question to you all. I am going to replace the Ortofon with a VM540ML that I have read fabulous things about. I might even go for the 740ML but wondering if the Reloop has enough potential to get the most out of the 740. Thoughts?
For 1/2 a minute I thought I had indeed plugged the MM into the MC sockets, but not the case.
No hum without pre, hum with pre. Pre sold.
I'd agree with all of that from Rod except removing ground from the pre amp increased the hum. The TT with built in pre works with no hum at all.
Edits: 01/20/24
It was a Bottlehead Seduction and it had a three prong plug.
When I put a two-prong cheater on it, the hum went away.
The blissful counterstroke-a considerable new message.
It can be exceedingly dangerous to remove the safety ground connection from the chassis, particularly in tube gear. When a ground loop is "cured" this way, it means that one or more pieces in the system have their signal ground connected to the chassis internally. The proper solution is to remove the internal connection between signal ground and the chassis, or replace the unit with one that's not designed that way. A simple ohmmeter test can usually tell you whether the unit in question is wired like this internally.
Edits: 01/21/24
But there was no harm and I never got zapped from any of my gear. The hum went away. That's all I cared about.
The blissful counterstroke-a considerable new message.
The primary risk occurs if the user plugs in the line cords, then makes audio connections. A large voltage can exist between the various chassis until the cable grounds connect everything together. Coincidentally, I have a power amp in this situation right now that I'm getting ready to rewire on the bench.
I believe the OP's preamp uses a 12V wall wart for power. That module might or might not have a three-wire ground pin, and might or might not carry that ground to the preamp chassis. If there's no safety ground connected to the preamp proper, a different piece of equipment in the system might be responsible for the problem.
I had a similar problem many years ago. Too many three prong plugs running from the same power strip. Cured it by using a two-prong cheater on the phono preamp plug.
The blissful counterstroke-a considerable new message.
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