NAD C 298 Power Amplifier With Purifi Eigentakt Amplification

[TomekNet]

I hope C298 measures well, as I've already ordered it

 

[TomekNet]

It already came in, but I have a problem to solve.
I get hum / buzz noise in speakers when my Denon 3700 L&R pre-outs are connected to c298.
Either with RCA-XLR Mogami/Neutrik cables (wired properly) and RCA-RCA.
Both Denon and NAD units are plug do the same power strip (I have only a single plug under TV).
Denon is AVC, so no TV antenna. Also no AVR input sources seems to make it (I've tried to disconnect one by one).
The hum is also in NAD standby mode. It disappears only if I switch it off with a toggle switch behind.
What am I missing?

 

[Deleted member 24907]

Is gain on max on the c298? Turn it down somewhat?

 

[darkless]

Whatever noise is coming out of the preamp out will be amplified, so maybe the problem is with the Denon. Do you have any other power amps to try with the Denon or another preamp to try with the C298? Is the hum affected by the preamp volume level or is it constant?

 

[TomekNet]

Is gain on max on the c298? Turn it down somewhat?

I'm using VAR, so gain is not used here.
But I've tried FIX and with gain set to min., hum is only in speakers other then LR. The more gain, the more hum in LR speakers.

Whatever noise is coming out of the preamp out will be amplified, so maybe the problem is with the Denon. Do you have any other power amps to try with the Denon or another preamp to try with the C298? Is the hum affected by the preamp volume level or is it constant?

Yes, I have a small TPA3255 power amp with unbalanced inputs and it doesn't make a hum noise.
But that power amp is not grounded (figure 8 power plug).

It seems like a ground loop, but I have no idea how to brake it. I believe both units have to be grounded.

 

[Kal Rubinson]

Can you clarify this?

I'm using VAR, so gain is not used here.

If you are using VAR, the gain control is in circuit and in operation.

But I've tried FIX and with gain set to min., hum is only in speakers other then LR. The more gain, the more hum in LR speakers.

In FIX, the gain control has no effect.

 

[TomekNet]

I probably got it. I've been disconnecting input sources one by one and hum did not disappeared.
BUT when I disconnected BOTH my HDMI cables connected (input from a DVB-S and output to TV - it;s LG C9 OLED), the hum is gone.
I have no idea how to fix it......

 

[BDWoody]

I probably got it. I've been disconnecting input sources one by one and hum did not disappeared.
BUT when I disconnected BOTH my HDMI cables connected (input from a DVB-S and output to TV - it;s LG C9 OLED), the hum is gone.
I have no idea how to fix it......

I had a hum that I eventually tracked down to the cable service ground on the outside of the house.

It can definitely be frustrating...

 

[Matias]

I probably got it. I've been disconnecting input sources one by one and hum did not disappeared.
BUT when I disconnected BOTH my HDMI cables connected (input from a DVB-S and output to TV - it;s LG C9 OLED), the hum is gone.
I have no idea how to fix it......

Does DVB-S has a coax cable input? If yes, try one of these.
https://www.amazon.com/TII-220-Ground-Isolator-applications/dp/B0070Q6URO

 

[TomekNet]

Yep, that seems to be the case here. When I disconnected all antenna inputs (2 from my DVB-S decoder and 1 from TV) the hum is gone.
I believe I need to consult some CBL/SAT guys...

If yes, try one of these.
https://www.amazon.com/TII-220-Ground-Isolator-applications/dp/B0070Q6URO

Thanks. I'll try some coax isolators

 

[BDWoody]

Yep, that seems to be the case here. When I disconnected all antenna inputs (2 from my DVB-S decoder and 1 from TV) the hum is gone.
I believe I need to consult some CBL/SAT guys...


Thanks. I'll try some coax isolators

Mine was easy to spot once I looked. Bare copper cable with a loose clamp to the side of the service box. See if it's something obvious, but at least you narrowed it down.

 

[beren777]

Yep, that seems to be the case here. When I disconnected all antenna inputs (2 from my DVB-S decoder and 1 from TV) the hum is gone.
I believe I need to consult some CBL/SAT guys...


Thanks. I'll try some coax isolators

You may also want to review the grounding and bonding for your dish mast, and the coax entry points. Done improperly, you may experience a safety issue, not just a quality issue.

 

[TomekNet]

Thank you guys. I will review the installation, but it's complicated. It's an apartment building and DVB-S and DVB-T signals are distributed building-wide (with multiplexer switches). On the switch at my floor I've managed to get two sockets, but one cable goes to flat. So I have installed another magic device thato pushes both signals over a single coax. I've already ordered galvanic separators, will see.

 

[Aventador_SVJ]

I've been looking for a replacement for a recently purchased and highly problematic Arcam SA30.

I've just received the MiniDSP SHD and I've been looking for a Purifi based amplifier made by a recognised brand and the C298 ticks the box.

Mine arrives on Saturday.

I suspect it will measure the same as the M28 (which is just a power amp), rather than the M33 (streaming amp).

Perhaps even better than the M28, as the the variable gain should allow measurements to be in-line with the Purifi reference gain of 27dB.

I believe the C298 fixed gain is set at 28.6dB, so this needs to be backed off a little to achieve similar SINAD to Purifi reference design.

 

[nothingman]

Nice! I’m finding the SHD and C298 to be a very agreeable combination with the LS50 Metas.

Btw, for those following the C298 v1.07 firmware mess: my second unit, also arriving with v1.07, has now started having the same spontaneous shutdown problems. I’m working with Crutchfield on ensuring my next replacement comes with v1.08 or later. I’m not willing to take the time and effort to send in an amp for service that is still in its return period. NAD and their US distributor Lenbrook should have immediately notified retailers to pull the faulty units.

 

[Aventador_SVJ]

Nice! I’m finding the SHD and C298 to be a very agreeable combination with the LS50 Metas.

Btw, for those following the C298 v1.07 firmware mess: my second unit, also arriving with v1.07, has now started having the same spontaneous shutdown problems. I’m working with Crutchfield on ensuring my next replacement comes with v1.08 or later. I’m not willing to take the time and effort to send in an amp for service that is still in its return period. NAD and their US distributor Lenbrook should have immediately notified retailers to pull the faulty units.

Because of this thread, I told Sevenoaks UK to check the firmware (i.e. should be v1.08) before they send it out to me.

Big thanks to this thread as I need the auto sensing to work with the MiniDSP SHD.

 

[Aventador_SVJ]

I received the Nad C298 today.

First impressions:

1. Nice minimalist power amplifier design - tick
2. Checked firmware - 8 flashes, hence v1.08 - tick
3. Auto sense put on low - MiniDSP SHD switches C298 on - tick
4. Placed unit to switch off after 15 minutes (after no signal), this works - tick
5. Tried a few music tracks but need to re-Dirac with new amplifier as the previous curve was set up for Arcam SA30. Sounds very clear, lots of power reserves, very dynamic sounding, barely any audible hiss coming from speakers (this is a first for me, I've never heard any amplifier with such low hiss). Need to set up with new Dirac curve to give full judgement. Will do this tomorrow.

 

[TomekNet]

Can you clarify this?

If you are using VAR, the gain control is in circuit and in operation.

In FIX, the gain control has no effect.

I've mistaken FIX with VAR. You're right, I'm using FIX.

 

[gaburko]

I received the Nad C298 today.

First impressions:

1. Nice minimalist power amplifier design - tick
2. Checked firmware - 8 flashes, hence v1.08 - tick
3. Auto sense put on low - MiniDSP SHD switches C298 on - tick
4. Placed unit to switch off after 15 minutes (after no signal), this works - tick
5. Tried a few music tracks but need to re-Dirac with new amplifier as the previous curve was set up for Arcam SA30. Sounds very clear, lots of power reserves, very dynamic sounding, barely any audible hiss coming from speakers (this is a first for me, I've never heard any amplifier with such low hiss). Need to set up with new Dirac curve to give full judgement. Will do this tomorrow.

Long-time reader and lurker here, finally registered
I've been looking at the C298 as well, just wondering if the auto-sense can be used for both the XLR and the RCA? I need two inputs: one for my phone-stage and one for my RME DAC and was wondering if I can avoid the manual switch every time I want to listen to vinyl?

thanks!

 

[nothingman]

Long-time reader and lurker here, finally registered
I've been looking at the C298 as well, just wondering if the auto-sense can be used for both the XLR and the RCA? I need two inputs: one for my phone-stage and one for my RME DAC and was wondering if I can avoid the manual switch every time I want to listen to vinyl?

thanks!

No, it’s not for auto sensing which input is active. That’s what the bat switches on the rear panel are for.

Also, are you sure about hooking up your phono stage directly to an amp? I don’t know every phono pre out there and I know it’s rather common for DACs to go straight into amps now, but that’s not typical at all for a phono.

Your use case sort of explains why preamps exist.