Reduction (+ Integration) Build Feedback Hum Problem [resolved]

[Pflugshaupt]

I just finished building my reduction and now the integration update. My package was a little bit off to the parts list, I was missing 2 washers (easy to replace), two resistors had a much higher wattage which made the placement tricky as they were way too big. I got a different type of 8 pin terminals (dark brown and smelly when hot).. these change the spacing because they have more distance to the screws and therefore all cable lengths crossing terminals were too short in the manual. One of the vinyl standoffs included with the integration update had the wrong length.

The manual could be fixed in a few spots: The reduction manual never tells you to solder the b output rca center and the integration manual has a copy/paste error, it twice tells you that you've now built a partial update that can already be used.

But, those are all minor problems because I do like the sound I'm getting very much! There is however one problem I'd like to get some advice with. When I tried the reduction alone, I thought I'm getting quite a bit of 50 Hz hum (230V/50Hz power here) and was hoping the integration update would help, but it just didn't happen. It's not a crazy amount, but from what I read I think the amp should have less 50 Hz hum. The amount I am getting is a bit audible in soft sections of music. (I'm using an AT440mlb cartridge btw.)  I tried to isolate all other possible sources, but now I'm pretty sure the problem is internal. I am getting the hum even without the turntable attached.

During the build I might have damaged the shielding of the shielded wire used for the heaters. Is this a possible source of hum? What else are the most likely hum problems? Is there a way to measure the hum and an amount that would be considered normal? I do have a test lp with a silent track. Is it possible the hum is coming from my outside power? I read reduction+integration provides great isolation from mains power, but I do know my house has a very old and a bit weird power system. Thanks in advance for any help!

[fullheadofnothing]

FWIW, I stopped using a 440MLA because it picked up noticeable levels of hum.

What is the rest of the system (table, preamp, poweramp, cables)? Are you being careful to keep your audio cables away from power cables and transformers?

[Pflugshaupt]

Thanks for the reply. Yes, power cables are very well separated. I use a pro-ject xpression III with motor upgrade and a pro-ject speed-box S. Cartridge is as said an AT440MLB. The TT goes into the reduction with integration and that is connected to a crack with speed which drives my HD800. Everything is set up in close proximity to avoid long cables. My noise is a 50Hz hum with some overtones, on both channels. I also get a slight bit of the same noise in the crack alone, but it's like 10x less. If I hook up my old preamp (cambridge audio azur 540p if I remember correctly), I get no noise at all. I also have a german kit preamp called "superb phono preamp" with a pair of telefunken valves and it also does not pick up any hum.

I have a terrible wall-wart (from pro-ject!) that really messes up things when plugged in and it makes an enormous difference. With that the noise is terrible, without it's annoying in soft passages and between songs only. However it's loud enough that I think it produces a bit of a mess around 50 hz being close the bass notes etc.

I am using the stock tubes (russian 6n23p), but I also tried a pair of vintage Voskhod rocket 6n23p and with both sets I get the same issues. I prefer the stock ones because the rockets are a bit too tube-y.

I will now try to move the internal audio signal cables around while it is running to see if that makes an audible difference. I saw some posts from people who had similar issues and switched to shielded cable for inputs which I'll do in case the movement makes a difference.

Any other ideas would be very welcome.

[Pflugshaupt]

While I'm waiting for some varnish to dry on the reduction case I did some experimenting on my crack + speedball. I did a better braid on the input wires and added insulation to them. This has reduced the hum a bit, but I found out something very odd. If I touch the big metal plate on the underside with a finger, the hum is almost completely gone. What does that mean? Is something wrong with grounding in my unit or maybe in my house? The power lines are 100 years old and have caused big problems in the past.

[Doc B.]

There was a long thread recently about similar problems. After a great deal of analysis at a distance it ended up being fixed with proper orientation of the shield connection on the interconnect cables. I would suggest starting there.

[Pflugshaupt]

Does that mean soldering the bare wire on the correct side of the shielded connections (as indicated in the manual) or something else? Can you add a link to the long thread this was discussed? Is it in the reduction forum? Sorry, I couldn't find it and did search quite a bit.

[Doc B.]

The best interconnect cables have an internal shield around the conductors. The internal shield is best if it is grounded to the RCA plug shell at only one end of the cable. That lets you connect it to the chassis with the lowest ground potential. If you have that type of interconnect simply try swapping it end for end between the Reduction and the Crack.

[Paul Birkeland]

Can you also tell us a bit about the wiring in your home.  Do you have 3 prong outlets, and are the ground lugs connected to earth?

Though the last time this came up it proved to be a cable issue, if you have unearthed outlets, you can end up with the same circumstances.

Though we don't have perfectly targeted answers for your situation, working through these kinds of issues is a very valuable learning experience. 

[Pflugshaupt]

The wiring in my home is terrible. Very old, paper-wrapped wires in the walls that short if you touch them.
I tried various outlets in different rooms and got different types of hum. I did reflow most of the ground connections in the reduction, but unfortunately it's not gone. Listen to it again I now hear there's a bit more hum on the right channel, but the left also has some. I realized that my old preamps have external transformers that don't even connect to ground. I measures the electricity in my room. I get 234V@50Hz as I should, but I also measure 1-2V@50Hz when I measure between the ground connector and the wall heater. If that's what I'm hearing, what can I do? I can't switch the house .

[Paul Birkeland]

Tell us about the rest of your system.  It may help to run some extra grounding wires between components.

[Pflugshaupt]

Ok. It's a very simple setup:

Pro-Ject Xpression III with AT440Mlb Cart
Reduction with Integration
Crack with Speedball
Sennheiser HD800

Everything is set up in very close proximity and power comes from the outside while the phono cable and the interconnect are 50cm good quality and go nowhere near power.

[Paul Birkeland]

Try connecting each chassis plate with a piece of wire.  Also try your interconnects in both orientations.

[Pflugshaupt]

I connected the chassis plates but that makes no difference. Flipping the interconnect also doesn't help and I even tried running reduction + crack with a modified power cord that doesn't connect the ground. That last dangerous idea made things worse. The only thing that helped so far was touching the chassis close to the inputs from the inside while reduction was running, but that's of course not possible to do when using it normally. While being flipped I also hear big difference in the hum if I move my hand over the two RIAA filter circuits (without touching).

Maybe it's just normal hum.. how little can I expect? It's easy to hear even the faintest noises with the HD800 and I am turning the crack up to the max volume to hear it clearly. At medium volumes I can't hear any noise.

[Pflugshaupt]

Doing some more experiments I tried adding some shielding to my Crack case. I used a wide aluminum tape and ran it once around the inside of the wooden crack case. This definitely makes a difference, but it makes things a crazy lot worse, the hum gets very loud like that. Does this mean I pick up hum that coming from inside the case?

I also figured that turning the crack or reduction in space changes the intensity my hum. What does that mean?

[kgoss]

Do you have a friend close by who would let you try your reduction at his/her house?  ideally you would also bring your turntable.  It won't solve your hum problem but if there is no hum at your friend's house then you can stop focusing on the turntable and reduction, instead concentrate on your house wiring or other environmental influence causing the hum.