Paradisea DAC hum problem !!

nakolawala · « **on:** 10 Dec 2006, 12:25 am »

Hello

Just received the Paradisea today via EMS. Initial impressions are very positive. Right out of the box it sounds fantastic. But, I am hearing hum when connected to my system. My system hook up was like this

1. SB3 out to Paradisea out to Mcintosh MC275 amp . In this scenario, I am hearing hum thr my spks no matter what I do. If I disconnect the interconnects to the amp the hum goes away. I tried all possible things but the hum is there.

2 SB3 out to Paradisea out to Preamp out to MC275 amp. In this scenario, the system is dead quite.

I have quite a crappy preamp (transformer coupled) and want to get rid of the preamp and directly use the vol control of the SB3 in a CD only system. In scenario 1, the paradisea had plenty of drive and voltage to drive the MC275 and sounds spectacular. Any advice how to get rid of the hum ???
Thanks
:( :(

Gordy · « **Reply #1 on:** 10 Dec 2006, 03:51 am »

Have you read this thread yet? http://www.audiocircle.com/index.php?topic=34151.0

GHM · « **Reply #2 on:** 10 Dec 2006, 04:00 am »

This seems more like an impedance problem. I don't think the Paradisea is designed to run directly into the amplifier. No doubt it has the voltage to drive the the amplifier..just not a good impedance match.

JoshK · « **Reply #3 on:** 10 Dec 2006, 04:05 am »

If it is transformer coupled, it is most likely galvanically isolated (unless it is autoformer, but that wouldn't make a lot of sense). This means that when preamp is inserted, group loop is eliminated. In your case it seems like ground loop. Try a cheater plug, with your SB3 > Paradesea > Mac. Let us know the results.

JoshK · « **Reply #4 on:** 10 Dec 2006, 04:06 am »

Quote from: GHM on 10 Dec 2006, 04:00 am

This seems more like an impedance problem. I don't think the Paradisea is designed to run directly into the amplifier. No doubt it has the voltage to drive the the amplifier..just not a good impedance match.

Maybe so, but that in and of itself wouldn't cause hum.

NewBuyer · « **Reply #5 on:** 10 Dec 2006, 04:11 am »

Sounds like ground loop to me too, since the hum disappears when using the transformer-coupled preamp.

Have you tried all of the following, to see if the hum remains:

- SB3 directly to amp (no Paradisea)?
- A different set of cables between Paradisea and amp?
- An optical connection between SB3 and Paradisea?

Note, the Paradisea is 16-bit only, so you would possibly get better sound fidelity when not using the SB3 digital volume, and instead using your preamp.

By the way nakolawala, what preamp are you using? Transformer-coupling is usually a good thing...

GHM · « **Reply #6 on:** 10 Dec 2006, 04:16 am »

Quote from: JoshK on 10 Dec 2006, 04:06 am

Quote from: GHM on 10 Dec 2006, 04:00 am
This seems more like an impedance problem. I don't think the Paradisea is designed to run directly into the amplifier. No doubt it has the voltage to drive the the amplifier..just not a good impedance match.

Maybe so, but that in and of itself wouldn't cause hum.

I suppose you guys are right about the ground loop now that I think about it. I personally would never run a Dac directly into an amplifier(unless built for it). That's what preamps are made for.

JoshK · « **Reply #7 on:** 10 Dec 2006, 04:20 am »

GHM, your right though....in that, doing the SB3 into Paradesea into amp with the SB3 doing volume control is very suboptimal. That is because SB3 is shaving bits with its volume control and when outputed shaved, the lower bit input is going to be resampled to 16bits if it hasn't been already. Try the SB3 into Mac directly with volume control. If you use the Paradesea you might need to keep the preamp.

nakolawala · « **Reply #8 on:** 10 Dec 2006, 03:35 pm »

Thank you very much for all the input. I have tried the following

1. SB3 directly into Mac is dead quite. No hum at all

2. According to Slimdevices forum I read that SB3 extents the word length to 24 bits and then applies the digital vol control. Hence when using digital vol control, there is absolutely no loss in the resolution up to a certain level. If the vol goes below 40 scale (100 is max) then loss in resolution occurs. That is the reason why I was planning to use the SB3 thr Paradisea without preamp.

3. My preamp is RAKK line stage (from K and K audio). It uses Lundhal input and output trf and is a Parafeed design and fully balanced. I tried Paradisea direct and thr the preamp and I like the sound of the former. Much more impact and smoother. Hence I believe the output stage of the Paradisea is very capable of drive a high sensitivity amp. the Mac has 100K input impedance and 26 db gain.

4. I have tried all possible solutions, cheater plugs, with and without interconnects, optical cable etc but the hum is there.
As Josh mentioned, the RAKK preamp is providing isolation and decoupling.

IS it a good idea to connect the analog ground of Paradisea via a 10 ohms in parallel with a 0.22mfd cap to the ground lug
of the IEC socket ???. Will that help in eliminating the hum.
Thanks

zybar · « **Reply #9 on:** 10 Dec 2006, 04:03 pm »

Quote from: JoshK on 10 Dec 2006, 04:20 am

GHM, your right though....in that, doing the SB3 into Paradesea into amp with the SB3 doing volume control is very suboptimal. That is because SB3 is shaving bits with its volume control and when outputed shaved, the lower bit input is going to be resampled to 16bits if it hasn't been already. Try the SB3 into Mac directly with volume control. If you use the Paradesea you might need to keep the preamp.

I am runing my Bolder modified "analog" SB2 directly into the Moscode with no issues. In fact, this combination is producing the best sound I have had with my HT3's.

As has already been stated, you aren't losing any resolution unless you drop the volume control way down.

George

NewBuyer · « **Reply #10 on:** 10 Dec 2006, 10:24 pm »

Quote from: nakolawala on 10 Dec 2006, 03:35 pm

...SB3 extents the word length to 24 bits and then applies the digital vol control. Hence when using digital vol control, there is absolutely no loss in the resolution up to a certain level. If the vol goes below 40 scale (100 is max) then loss in resolution occurs. That is the reason why I was planning to use the SB3 thr Paradisea without preamp.

...IS it a good idea to connect the analog ground of Paradisea via a 10 ohms in parallel with a 0.22mfd cap to the ground lug
of the IEC socket ???. Will that help in eliminating the hum.
Thanks

The SlimDevices forum advises that a 24-bit external DAC is needed, to keep full resolution when using the SB3 digital volume control. The SB3 outputs the extended 24-bit S/PDIF signal, but the Paradisea is a 16-bit DAC - so the extra 8-bit extension is lost. If you use the SB3 digital volume control with the Paradisea (or any other 16-bit DAC), you do lose resolution bits.

By the way, your idea of R/C to earth ground of IEC socket is interesting, I hope others will advise on this...

nakolawala · « **Reply #11 on:** 10 Dec 2006, 11:05 pm »

The above post is right, we need a 24bit external dac for no loss in resolution. On further experiment, even thr my preamp, at high volume I am hearing a slight hum.

I tried a 10 ohms res with a cap connecting the analog gnd to the ground on the IEC but it did not solve the problem.