My new NOH doesn't work :(

michaelab · « **on:** 15 Mar 2004, 02:05 pm »

Got my new NOH pre-amp this morning and eagerly hooked it up...but there's something wrong with the left channel

I spoke with John on Friday about some customs issues so I know he's out this week which is why I'm posting here in case anyone has a possible answer.

The right channel is fine. On he left channel though the sound is very quiet (compared to the right) and increasing the volume only makes it slightly louder, until the volume is about half way and then it decreases again as you increase the volume control towards the end!

I've tried switching between balanced and RCA inputs, trying different input and output cables, switching the ground switch from hard to float but it's always exactly the same. I'm using the RCA outputs at the moment because I only have a power amp with RCA inputs at the moment so I couldn't try the XLR outputs.

Anyone have any ideas? Unfortunately I can't open it up to take a look myself because I don't have a Torx screwdriver handy. I really, really hope it doesn't have to go back to John to be fixed

Michael.

Marbles · « **Reply #1 on:** 15 Mar 2004, 02:18 pm »

If it were me, I would buy the torx driver and open it up to see if a wire came loose in shipping, or maybe something else that would be easy to diagnose.

michaelab · « **Reply #2 on:** 15 Mar 2004, 02:29 pm »

I'll be out trying to find a Torx driver this evening. They're not the easiest tools to find unfortunately...

I can only imagine that something has come lose as there isn't really anything else that can break in there!

Michael.

Doc Jr 8156 · « **Reply #3 on:** 15 Mar 2004, 04:39 pm »

Michael,

I agree with Marbles, get the torx. Home depot have thousands. 2 possibilities:

1. Shipping caused the wires from the volume control to be loose. The Left channel of the preamp is the "inner channel" in the volume control. The wires coming from the left transformer are tight fitted and routed in a delicate wavy fashion to reach their soldering points. However, if nothing is loose outside (Volume control, nuts holding the copper brackets for both transformer) I wonder how the wires were loosened.

2. Wrong wire connections. This is a possibility, although remote. The problem is if you follow the instruction in the site on how long the wires will be cut and used that as your guide with soldering you will end up with a situation as you described. Trust me I did this. The instructions on cutting wires for the left side looks like this:

Left side (switch shaft facing towards you)
34 = 4-1/2”
37 = -
40 = -
46 = -
52 = -

Hope John replies. Don't get frustrated, this thing is sweet sounding.

michaelab · « **Reply #4 on:** 15 Mar 2004, 07:25 pm »

OK, got me the correct Torx driver (T9 if anyone's interested) and opened the thing up. Now it all looks absolutely fine. With a multimeter I checked all the connections of the input selectors and they are both fine so it has to be something in the way the left transformer and volume control are wired up.

With the multimeter I could see that something was wrong but I can't tell why. I measured the resistance between the input and output and on the right (functioning) channel it varies between 370ohms at min. vol. and 650ohms at max. vol. On the left (non-functioning) channel it only varies between 370 and 380 ohms. Clearly something isn't right in the left channel.

btw, I didn't build the NOH myself, it was built by John so I'd be very surprised if the connections were wrong allthough I guess it's possible!

My electronics knowledge, especially where transformers are concerned, is a little sketchy so I'm not really clear what I should be measuring with the meter to find out what's wrong. Any pointers? Just printed out the NOH assembly instructions and will follow the "Electrical Checkout/Measuring" instructions there and see if that throws up anything.

I think John's on vacation for a week or so hopefully someone else will be able to help me out!

Thanks,
Michael.

michaelab · « **Reply #5 on:** 15 Mar 2004, 11:24 pm »

Panic over. It's all working fine now

No idea what happened. I opened up the case and followed the instructions on the electrical checkout and everything measured up correctly. I then went back and did the measurements I had done before (see previous post) and now they were the same on both channels so I don't know what changed.

Only thing I can think of is that there was possibly a dirty connection or something somewhere which got cleaned up by my moving the controls around so much.

It's now singing very sweetly indeed

Michael.

Marbles · « **Reply #6 on:** 15 Mar 2004, 11:55 pm »

Congrats!

It should get a bit better over the next 200-300 hours.

I hope you like the Noh as much as I like my Bent pre.

Doc Jr 8156 · « **Reply #7 on:** 16 Mar 2004, 08:07 pm »

Rock on! If you have a FryKleaner, hook it up to one input and the inverted output of the FryKleaner to the output and crank up the volume selector to max (no amps or speakers connected to the other output if you have 2 outs in your NOH). Let them mate for 2 days straight and the break -in time will be significantly shorthened. Enjoy, it will only get better. This is one gear where break in time really contribute in making the sound better. If before break in you can feel the artist in your room, afterwards, aside from feeling them, you can smell their breath! LOL. Happy listening.

michaelab · « **Reply #8 on:** 17 Mar 2004, 12:35 am »

I don't have any type of "burn in" device so I'll just have to let it burn in over time. I find it hard to understand how a passive pre can benefit from burn in though

. In what way's does it improve over time?

I'm already extremely impressed with mine! The way that detail and soundstage are maintained at low volumes is perhaps the most impressive thing about it.

Michael.

Doc Jr 8156 · « **Reply #9 on:** 17 Mar 2004, 04:27 pm »

Michaelab,
Yup, burn-in does improve things. Ask John Chapman (if he's around), this thing respond to burn-in than any other gear from his experience. Remember, there are 2 transformers and lots of wires inside. Also your binding post, selector switches, and volume control needs burn in. If you are impressed on what you are hearing now, after 200 hours, you'll be always smiling. The sound will be more refined, smoother, bigger and punchier bass and well defined highs. Vocals will be more focused, and I guess the position of players relative to each other (imaging) are well deliniated as well. In time, my friend, in time. Happy listening.

Peter B · « **Reply #10 on:** 19 Mar 2004, 07:44 pm »

Hi Michael,

Received my NOH a few hours ago......
At this moment it's already on par with my recent preamp, but I'm really looking forward to the improvements which the burning in process will bring

Best regards,
Peter