[hp4fun]

I did have noise issues and I discussed them in this thread a week or two ago but my noise was coming from my DAC to the 339i vía a ground loop. It bothered the heck outta me and was more pronounced in my low impedance headphones.
Do you get the noise when you just plug into the 339i? If not it may be introduced from the 339i to the Marantz,
If you don’t mind what looks like a cheap add-on but worked for me you could try this and put it on the RCA cable from the 339i to the Marantz. It will stop the ground loop hum and doesn’t affect the sound for me.

https://www.amazon.com/gp/product/B077Y5DLBB/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

It cleared my noise problem right up and my system has been relatively quiet with all tubes since.
I say relative because if you turn the 339i way up you will still hear the tube hum but that is natural.

You also have the option of not using the 339i as a preamp but it is up to you.

Just tried this and does not help. Sad!

I can hear from the headphone driver when I tap the LF 339i surface. Must be some ground loop issue. But it is so weird.

I guess the LF 339i preamp out was not super mature?

 

[Galapac]

Just tried this and does not help. Sad!

Not sure by your reply what was tried, the ground loop isolator?
My ground loop was introduced coming into the 339i and not out from it.
I applied the isolator to the input RCA.

I can hear from the headphone driver when I tap the LF 339i surface. Must be some ground loop issue. But it is so weird.

I guess the LF 339i preamp out was not super mature?

Are you talking about micro phonics from the tubes(a ringing sound) when tapping your 339i?

 

[hp4fun]

Not sure by your reply what was tried, the ground loop isolator?
My ground loop was introduced coming into the 339i and not out from it.
I applied the isolator to the input RCA.


Are you talking about micro phonics from the tubes(a ringing sound) when tapping your 339i?

Possibly yes? and the sound is louder when I tap harder.

To be more specific, it is like hearing a blacksmith hammering something in a distance, when I tap the surface.

I also tried the usb-powered dac, so there is no ground loop from the dac to the external power strip.

Also tried to use the isolator both ways. The hum is the same, the tapping interference is there. Not sure what went wrong ......

The last thing I tried was to use the 6080 (low gain) instead of the 5998 (high gain). It reduced the noise level but it is back when I increase the volume. Not a surprise because it only changes the gain. The hammering tapping sound still the same

 

[tintinsnowydog]

Possibly yes? and the sound is louder when I tap harder.

To be more specific, it is like hearing a blacksmith hammering something in a distance, when I tap the surface.

I also tried the usb-powered dac, so there is no ground loop from the dac to the external power strip.

Also tried to use the isolator both ways. The hum is the same, the tapping interference is there. Not sure what went wrong ......

The last thing I tried was to use the 6080 (low gain) instead of the 5998 (high gain). It reduced the noise level but it is back when I increase the volume. Not a surprise because it only changes the gain. The hammering tapping sound still the same

Is there still extraneous sound if you don't tap the amp and just let it play normally? Most tubes will exhibit some kind of noise or microphony if subject to mechanical vibration.

 

[hp4fun]

Is there still extraneous sound if you don't tap the amp and just let it play normally? Most tubes will exhibit some kind of noise or microphony if subject to mechanical vibration.

Just the noise. It sounds more like 60hz than 120, so I guess it is the internal wiring issue?

I will try to use my small sp200 and see if it is Marantz problem.

 

[Galapac]

Just the noise. It sounds more like 60hz than 120, so I guess it is the internal wiring issue?

I will try to use my small sp200 and see if it is Marantz problem.

.
If the hum increases with the volume it is usually not a ground loop issue. Ground loop hum stays pretty consistent at any volume level.
If the hum increases in volume when you turn the volume up, it may be the tubes or the amp.

What are you using for drivers? The stock Russian tubes that come with the amp were pretty microphonic for me and I quickly changed them out to RCA 5693 and it negated the microphonics for me.

 

[hp4fun]

.
If the hum increases with the volume it is usually not a ground loop issue. Ground loop hum stays pretty consistent at any volume level.
If the hum increases in volume when you turn the volume up, it may be the tubes or the amp.

What are you using for drivers? The stock Russian tubes that come with the amp were pretty microphonic for me and I quickly changed them out to RCA 5693 and it negated the microphonics for me.

Let me clarify myself: the hum is at the constant level for the same tube sets, even when the volume is 0.

The reason I increased the volume is because 6080 is low gain so it is at a lower level.

I did switch the Marantz to SMSL SP200. I cannot hear the hum. Do you think it is the mismatch between a headphone preamp and a stereo amp?

Sound comparison is a byproduct of the gear changing. The LF339i does bring the SMSL SP200 to the next level, by bringing the soundstage and the tube warmth. It is so sad that the SP200 is not powerful enough to drive the HE6. But now I do seriously consider using LF339 as the preamp, for low impedance hps.

Still a great day for the learning part!

 

[tintinsnowydog]

Just the noise. It sounds more like 60hz than 120, so I guess it is the internal wiring issue?

I will try to use my small sp200 and see if it is Marantz problem.

Just how loud is the hum? 60hz is mains hum, hearing 120hz is often just the resonant frequency of it. All tube amps that operate on AC heating will have some degree of hum, this is minimised by braiding heater wiring, better power filter caps, chokes, better diode bridge rectification etc. If the hum does not increase with the volume pot, there is likely no wiring issue and you're just hearing the inherent working of the tubes

I'm not well versed on stereo amp impedance matching etc. but it is possible that the Marantz is more sensitive to signal input than the SP200 which enhances the hum. If through the SP200 there is no hum then it would be safe to confirm there is no problem with the preamp out wiring in the 339i. Is there hum through headphones when no inputs or outputs are connected to the 339i?

 

[hp4fun]

Just how loud is the hum? 60hz is mains hum, hearing 120hz is often just the resonant frequency of it. All tube amps that operate on AC heating will have some degree of hum, this is minimised by braiding heater wiring, better power filter caps, chokes, better diode bridge rectification etc. If the hum does not increase with the volume pot, there is likely no wiring issue and you're just hearing the inherent working of the tubes

I'm not well versed on stereo amp impedance matching etc. but it is possible that the Marantz is more sensitive to signal input than the SP200 which enhances the hum. If through the SP200 there is no hum then it would be safe to confirm there is no problem with the preamp out wiring in the 339i. Is there hum through headphones when no inputs or outputs are connected to the 339i?

Excellent point! No input physically connected to 339i and I still hear the hum. The marantz output itself is fine if I connect the DAC directly to it.

So, it is likely that I am just hearing the tube working noise because the Marantz does not match the preamp out for whatever reasons

 

[Galapac]

https://www.psaudio.com/ps_how/how-to-find-and-fix-hum/

So you unplugged the inputs and outputs from the 339i and the hum was still audible through the headphones?
According to the above link that would not be ground loop as you have no feed in or out of the 339i.

I would still try different driver tubes as that could be where all of the hum/buzz/microphonics is coming from.

 

[xmdkq]

Please input the signal to the ground to listen to whether there is a short circuit, if there is no indication that it is coming from the outside, or try to change the tube.

 

[hp4fun]

Please input the signal to the ground to listen to whether there is a short circuit, if there is no indication that it is coming from the outside, or try to change the tube.

All my 5998/7236/6080 produce the constant hum at different levels. I also tried the stock russian driver tube, same thing. I am waiting for my EF86 adapters and this will be my last attempt.

Today I used the SMSL T1 as the preamp (with the same set of cheap cables, if anyone wonders). No hum, so the hum I have in the LF339i + MM7025 combo is probably because the mismatch in gain / voltage / whatever between them.

Certainly, LF339i is a much superior amp. While SMSL T1 still sounds great, I feel I am in the 30th row of the concert hall instead of the 5th row. I might change the stock 6992 and give it a try again, but it is a different thread and different topic.

Thanks everyone for the help!

 

[hp4fun]

Please input the signal to the ground to listen to whether there is a short circuit, if there is no indication that it is coming from the outside, or try to change the tube.

I misunderstood your first sentence, sorry about it. Can you elaborate how I should "input the signal to the ground to listen to whether there is a short circuit"? Thank you so much!

 

[tintinsnowydog]

I misunderstood your first sentence, sorry about it. Can you elaborate how I should "input the signal to the ground to listen to whether there is a short circuit"? Thank you so much!

A way to check that the hum does not come from the signal path is to short from the centre of the RCA jack to the outer jacket. You can do this with a wire or alligator clips.

 

[Galapac]

Is this a rebranded Bendix?
https://www.ebay.com/itm/6080-WB-Ch...=true&nordt=true&rt=nc&_trksid=p2047675.l2557