Decware // Reference ZMF OTL

[Kagora]

Looks like it was not the Sophia Aqua II 274b that caused my problem. The harsh static crackling in the left channel when turning the volume knob is back with the TAD 5U4G.

The TAD 5U4G has barely lasted a week after switching back to it, while putting less hours on it than I usually average a week.
I do not see any abnormal glowing, flashing, or anything out of the ordinary like the Aqua II did.

The static crackling was fairly quiet when I powered on the amp earlier, so I tried swapping back to the full stock tube setup, but swapping made it much worse, and now it's just as awful as it was with the Aqua II.

Maybe it has something to do with the tung-sol 5687s? I did not see any visual changes in them, and they were fine for two weeks with near daily usage for multiple hours a day with the Aqua II.

I don't think it could be from any form of power related issue. I have all my equipment on an UPS that is overkill for the load.

I have not swapped or messed with the fuse at all.

I did get in touch with Zach and he was able to resolve the shipping issue with the Aegis for me very quickly, so I could try the stock 5AR4 that came with it and see if the issue persist, but I am hesitant to try, as I don't want to damage any more rectifiers/tubes.

Other than that, does anyone have any suggestions or should I just go ahead and try emailing ZMF about this amp again?

The timing of this issue reappearing couldn't be worse. I was just about to try using it as a pre-amp into the Aegis.

 

[theveterans]

Try swapping (input and output tubes) left to right channel and see if the noise swaps to the right channel as well

 

[Kagora]

Try swapping (input and output tubes) left to right channel and see if the noise swaps to the right channel as well

Thank you for the suggestion.

Swapping the between my 6922 input tube and the stock 6N1P tube has no effect on it.
I had tried swapping the adapted 5687 driver tubes the first time this happened and I never swapped them back, and it reappeared in the left channel so I don't think it is a driver tube issue, and even with the stock 6N6P tubes it is still there in the left channel.

Swapping rectifiers temporarily fixed it the first time but I'm starting to run low on rectifiers.

 

[Relaxasaurus]

It seems the amp has an uncertain future:

Post in thread 'ZMF November 2024 // Schedule - Announcements and MEGATHREAD!'
https://www.head-fi.org/threads/zmf...uncements-and-megathread.974608/post-18405218

I consider myself lucky to have one.

As soon as I'm finally ready to buy one I see this post. Just my luck, haha.

Primarily need a tube pre for the 2 channel system but it would be nice if it had a headphone out. May just go CSP3 unless I see a ref otl on the used market, but that sounds unlikely.

 

[goldwerger]

Thank you for the suggestion.

Swapping the between my 6922 input tube and the stock 6N1P tube has no effect on it.
I had tried swapping the adapted 5687 driver tubes the first time this happened and I never swapped them back, and it reappeared in the left channel so I don't think it is a driver tube issue, and even with the stock 6N6P tubes it is still there in the left channel.

Swapping rectifiers temporarily fixed it the first time but I'm starting to run low on rectifiers.

It doesn’t seem like it’s a tube issue, but to rule it out you can just get also a cheap trio of 6dj8 / 6922 / 6n1p and full of out

When not tube, noise is commonly a result of tarbeformer

It may be just a good idea to send it to Decware for repair

My OTL (now in use close to 2 yrs) is dead quiet as either headphone amp or preamp

 

[Kagora]

My OTL (now in use close to 2 yrs) is dead quiet as either headphone amp or preamp

That was why I had to send back my first unit. It had horrible buzzing that was too loud to ignore, and it was unaffected by any of the volume pots, but flipping the cathode bypass switch up towards the input tube would raise the volume even more to the point where the mode was unusable.

ZMF support were very helpful in trying to help fix it and ended up sending this replacement unit after I RMAed the first one. They tested this unit before shipping it to me and this one sounded completely silent at first but a few days later I started hearing the buzzing again, except it was much much quieter this time. At the time I assumed it was there from the first day and I just happened to miss it, but looking back I remember trying my hardest to listen for it and hearing nothing so perhaps it did manifest back.
Ether way it was quiet enough to ignore so I just accepted it as I was finally able to enjoy the amp.

A month later I ended up getting a Philips JAN 6922 tube to try out and with that tube the background was finally as dead quiet as everyone kept describing it, but instead of buzzing I would get microphonic ringing any time a switch was flipped, a headphone was plugged in, or if something bumped the wood housing of the amp.
I just assumed it was the tube's fault and had nothing to do with the amp but it maybe it could be the same issue with this amp and it's just dependent on the type of input tube?

Has anyone else had any form of noise from input tubes with this amp?

Thank you for your suggestions and help once again goldwerger, I really appreciate it.

I think I will email ZMF support again before I do anymore testing.

 

[erics75]

That was why I had to send back my first unit. It had horrible buzzing that was too loud to ignore, and it was unaffected by any of the volume pots, but flipping the cathode bypass switch up towards the input tube would raise the volume even more to the point where the mode was unusable.

ZMF support were very helpful in trying to help fix it and ended up sending this replacement unit after I RMAed the first one. They tested this unit before shipping it to me and this one sounded completely silent at first but a few days later I started hearing the buzzing again, except it was much much quieter this time. At the time I assumed it was there from the first day and I just happened to miss it, but looking back I remember trying my hardest to listen for it and hearing nothing so perhaps it did manifest back.
Ether way it was quiet enough to ignore so I just accepted it as I was finally able to enjoy the amp.

A month later I ended up getting a Philips JAN 6922 tube to try out and with that tube the background was finally as dead quiet as everyone kept describing it, but instead of buzzing I would get microphonic ringing any time a switch was flipped, a headphone was plugged in, or if something bumped the wood housing of the amp.
I just assumed it was the tube's fault and had nothing to do with the amp but it maybe it could be the same issue with this amp and it's just dependent on the type of input tube?

Has anyone else had any form of noise from input tubes with this amp?

Thank you for your suggestions and help once again goldwerger, I really appreciate it.

I think I will email ZMF support again before I do anymore testing.

what you're describing definitely sounds like the tubes vs the amp itself. I recently got some untested nos input tubes for my Aegis which is normally dead silent. when i listened for the first time i thought i broke the amp. any vibration manifested in the headphones as horrible ringing and chiming. i put the old pair back in, and dead silence again. buzzing also tends to be tubes from my experience. it's picking up rfi from something. in my case it was my cell phone, which was 6 feet away. moving it another few feet silenced the buzzing. also if you stack anything under the amp, that transformer can put out some serious rfi. I used to slide my dac under my amp for space savings, and got all kinds of annoying buzzing and popping. thankfully by chance i lifted the amp up while listening, and the buzzing ceased. I put it back down, and there was the buzzing. tube amps can be a headache at times when they're misbehaving. thankfully most of the time placement and good tubes solves noise issues. hope you get it resolved without having to send back another amp.

 

[goldwerger]

I would get microphonic ringing any time a switch was flipped, a headphone was plugged in, or if something bumped the wood housing of the amp.

I can't advise on that specifically as my amp is set aside with nothing bumping next to it. However, what you are describing does not sound like a problem - if you knock or bump into any tube amp, the vibration may translate into your headphones. That isn't so much as a bug, as a feature of tube amps (not uniformly or conclusively, but very commonly). If the amp is completely quiet when playing music (or when music is paused) and you are not touching it, then it works fine.

Quick note on plugging headphones in with this amp - never do this with your headphones on your ears. The pop you hear is expected. Just plug the headphones in, then put your headphones on. (also, as an important side comment: never keep your headphones plugged in when you turn the amp on/off; the voltage surge/drop can be damaging. So: turn the amp on, plug the headphones in, put them on your head; and repeat the process in reverse when you are done)

It's best not to bump anything against a tube amp. Tubes don't like vibration.

+ agree with @erics75 sound advice. For any tube amp, keep it isolated from any near proximity interference (cell phones, wifi routers, other electronics or devices with transformers that can cause EMI/RF interference).

 

[G8torbyte]

I can't advise on that specifically as the amp is set aside with nothing bumping next to it. However, what you are describing does not sound like a problem - if you knock or bump into any tube amp, the vibration may translate into your headphones. That isn't so much as a bug, as a feature of tube amps (not uniformly or conclusively, but very commonly). If the amp is completely quiet when playing music (or when music is paused) and you are not touching it, then it works fine.

Quick note on plugging headphones in with this amp - never do this wtih your headphones on your ears. The pop you hear is expected. Just plug the headphones in, then put your headphones on. (also, as an important side comment: never keep your headphones plugged in when you turn the amp on/off; the voltage surge/drop can be damaging. So: turn the amp on, plug the headphones in, put them on your head; and repeat the process in reverse when you are done)

It's best not to bump anything against a tube amp. Tubes don't like vibration.

+ agree with @erics75 sound advice. For any tube amp, keep it isolated from any near proximity interference (cell phones, wifi routers, other electronics or devices with transformers that can cause EMI/RF interference).

Thank you for the tips and advice. I've had the Decware CSP3 a few days now and putting in the recommended hours to "season" the components according to the CSP3's guide. After getting the hours in I'll try out a few rectifiers (5U4G/GB and a 5Y3GT) to "voice" the amp which is how the guide describes altering the sound. So far I am really enjoying the performance with ZMF dynamics. I also found out how sensitive tube amps are to mobile phones and WIFI. The Icon Audio HP8 would pick up signals with a static-like noise if those electronics were in close proximity. Putting some distance between them resolved it.

 

[goldwerger]

Thank you for the tips and advice. I've had the Decware CSP3 a few days now and putting in the recommended hours to "season" the components according to the CSP3's guide. After getting the hours in I'll try out a few rectifiers (5U4G/GB and a 5Y3GT) to "voice" the amp which is how the guide describes altering the sound. So far I am really enjoying the performance with ZMF dynamics. I also found out how sensitive tube amps are to mobile phones and WIFI. The Icon Audio HP8 would pick up signals with a static-like noise if those electronics were in close proximity. Putting some distance between them resolved it.

Nice!!

Since the ZMF version is a close relative, you may. find that "voiving" (ha!) this amp can be achieved tube rolling all tubes. Lots of fun, as Decware amps use tube types that are relatively common and inexpensive (even for some NOS). Enjoy!

 

[LXMc]

Curious if anyone here has used the ZMF/Decware OTL as a pre-amp with solid-state amps? Particularly Violectric (or particularly particularly the V550 )

Basically, the scenario I'm considering: Before getting the V550, my OTC amp (Cayin HA-3A) was my preferred amp over my solid-state across the board. However with the V550, I've been strongly considering changing out the HA-3A for the ZMF/Decware OTL as I've been preferring the V550 with my Caldera & Dahlia (and it's still quite good with my 300-ohm ZMFs) so the versatility aspect of the HA-3A isn't really being utilized much. My thought was the ZMF OTL would be an even better match for those 300-ohm ZMFs and also add an additional element/option to the V550 through pre-amping.

I know @goldwerger has been a strong proponent of the OTL & Taboo combo (and maybe this would end up there at some point, space allowing) but I haven't found a great deal of impressions when the Decware is used as a preamp into other amps, particularly solid-states. My hope is it would bring enough of that tube 'flavour' over that I wouldn't miss the straight OTC.

Appreciate any experience or impressions that can be shared.

 

[Frankie D]

Curious if anyone here has used the ZMF/Decware OTL as a pre-amp with solid-state amps? Particularly Violectric (or particularly particularly the V550 )

Basically, the scenario I'm considering: Before getting the V550, my OTC amp (Cayin HA-3A) was my preferred amp over my solid-state across the board. However with the V550, I've been strongly considering changing out the HA-3A for the ZMF/Decware OTL as I've been preferring the V550 with my Caldera & Dahlia (and it's still quite good with my 300-ohm ZMFs) so the versatility aspect of the HA-3A isn't really being utilized much. My thought was the ZMF OTL would be an even better match for those 300-ohm ZMFs and also add an additional element/option to the V550 through pre-amping.

I know @goldwerger has been a strong proponent of the OTL & Taboo combo (and maybe this would end up there at some point, space allowing) but I haven't found a great deal of impressions when the Decware is used as a preamp into other amps, particularly solid-states. My hope is it would bring enough of that tube 'flavour' over that I wouldn't miss the straight OTC.

Appreciate any experience or impressions that can be shared.

I love my ZMF OTL. Just phenomenal with dynamic HPs. I have connected it as a pre to my Zahl-HM1, but have not noticed any substantial change in sound from the Zahl. I have not fully tested this config, but briefly using an HD600 as well as a Sol P, I was able to volume match quickly and move from input A on the Zahl to input B and did not hear an immediate difference. As I have a few amps I really did this more for connectivity at this point, but will eventually get further into it in the future. I also have not changed the tubes from stock which might also make more of a difference.

 

[LXMc]

I love my ZMF OTL. Just phenomenal with dynamic HPs. I have connected it as a pre to my Zahl-HM1, but have not noticed any substantial change in sound from the Zahl. I have not fully tested this config, but briefly using an HD600 as well as a Sol P, I was able to volume match quickly and move from input A on the Zahl to input B and did not hear an immediate difference. As I have a few amps I really did this more for connectivity at this point, but will eventually get further into it in the future. I also have not changed the tubes from stock which might also make more of a difference.

Thanks for sharing, that helps a lot, even if just to temper expectations. I use my dynamic headphones enough it's not a dealbreaker if that did end up being the case in my setup as well, but would certainly be nice if it were on the more noticeable side. I expect I will find out for myself sooner than later..

 

[LXMc]

Bit of a cross-post from the Watercooler thread, a couple days into ownership on the ZMF OTL and very impressed with it so far. Really (really) excellent with the Auteur Classics and Atrium Closed. Dahlia not so much with a monster mid-bass hump, which was the likely scenario, it actually works well on bass-light acoustic music.

I'm also impressed at how quiet the amp is. With the Cayin I always had some level of background noise. With the Caldera it was nearly silent but with the 300ohm ZMFs it was pretty noticeable, particularly on the higher-gain XLR output. On the OTL the only noise is a barely audible hum in one channel and I'm betting that's a tube. Expecting some new Norne interconnects soon and then want to look at improving my power situation a bit more.

Currently I'm mulling through this thread [again] noting tube recommendations. The flexibility on the driver and rectifier tubes is a little overwhelming coming from the HA-3A which was basically 6v6 and 12AU7 (and e80cc if you wanted to push it). I did see at one point @busseysound tested out some e80cc's, I'm assuming those would require an adapter similar to the 12au7? Would be nice to be able to use a few of my existing tubes, and I'm hoping some different rolls will produce more audible results using this as a pre-amp for the V550 as currently I'm not getting much difference there. Pretty much my only disappointment with my current setup.

 

[carboncopy]

Bit of a cross-post from the Watercooler thread, a couple days into ownership on the ZMF OTL and very impressed with it so far. Really (really) excellent with the Auteur Classics and Atrium Closed. Dahlia not so much with a monster mid-bass hump, which was the likely scenario, it actually works well on bass-light acoustic music.

I'm also impressed at how quiet the amp is. With the Cayin I always had some level of background noise. With the Caldera it was nearly silent but with the 300ohm ZMFs it was pretty noticeable, particularly on the higher-gain XLR output. On the OTL the only noise is a barely audible hum in one channel and I'm betting that's a tube. Expecting some new Norne interconnects soon and then want to look at improving my power situation a bit more.

Currently I'm mulling through this thread [again] noting tube recommendations. The flexibility on the driver and rectifier tubes is a little overwhelming coming from the HA-3A which was basically 6v6 and 12AU7 (and e80cc if you wanted to push it). I did see at one point @busseysound tested out some e80cc's, I'm assuming those would require an adapter similar to the 12au7? Would be nice to be able to use a few of my existing tubes, and I'm hoping some different rolls will produce more audible results using this as a pre-amp for the V550 as currently I'm not getting much difference there. Pretty much my only disappointment with my current setup.

Just for reference, I am extremly sensitive to noise and this amp has none. Absolutely nothing. I even connected my Grado Hemp (which is like IEM sensitive) to see lf it picks up any noise. Nothing.