[regal]

Quote:

Originally Posted by erikzen /img/forum/go_quote.gif Unfortunately, the buzz I was hearing previously is definitely there. It seems like a ground hum. This surprises me since many of the impressions I've found of the tube state it is one of the quietest. Actually, this is the first time I've heard any type of hum from the CTH and it is almost non-existent with the Denons, but with the Grados it is noticeable although changes when I touch the amp or reposition it. I assume it is the tube that is causing this noise and is there anything I can do to prevent it? .

Usually a hum that is affected by touching things in the amp is ground related. Make sure your inputs, output, and pot are isolated from the chassis. Also may want to look on AMB's site for a ground loop breaker schematic.

 

[erikzen]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Usually a hum that is affected by touching things in the amp is ground related. Make sure your inputs, output, and pot are isolated from the chassis. Also may want to look on AMB's site for a ground loop breaker schematic.

A ground loop hum is what I would think it is too, but it does not happen with any other tube. Plus I am not a DIY guy. My amp was built by cfcubed so I am not going to touch the Master's work.

I was just wondering if an otherwise good sounding tube coudl cause a ground loop and if so if there was anything that could be done to fix it, short of actually modifying the amp. It works perfectly with every other tube I've tried so if it ain't broke...

I may just have a bum tube.

 

[Forte]

I can't see it being a Ground Loop since this amp runs of a Wallwart the amp is not connected to AC earth.

The fact that only one tube does this points to the tube being the culprit, I have a Russian 6h23n which does a similar thing. Put your hand anywhere near the amp and you get a faint hum, move your hand away and all is good.

 

[barleyguy]

Quote:

Originally Posted by Forte /img/forum/go_quote.gif I can't see it being a Ground Loop since this amp runs of a Wallwart the amp is not connected to AC earth. The fact that only one tube does this points to the tube being the culprit, I have a Russian 6h23n which does a similar thing. Put your hand anywhere near the amp and you get a faint hum, move your hand away and all is good.

I have a 6n6p with the same symptoms. I think it's caused by one of the pins not making a good connection, either in the socket or at the base of the tube.

 

[tacitapproval]

If it is the socket making poor contact. You can tighten the contacts with needlenose pliers.

 

[keyid]

probably noisy/bad tube. Got a 12BH7A Tung-Sol Black Plates and ECC82 Tungsram Hungary. I like the 12bh7a (running it 6v is pretty and fuzzy though it doesnt get loud) more then 6n6p but found the tungsram too bright for rs1. After modding my dac abit (upgrade bypass caps, star ground, power supply) the amp responds very well.

 

[erikzen]

Listened to a couple of CDs this evening and the buzz seems to be gone. This is fast becoming my favorite tube.

Now I'm listening to a Sylvania GB 5814A. What a difference! Very warm, with a large soundstage. Very tubey sounding.

 

[stringgz301]

I'ts been several months since I built my CTH from the Spruce Canyon kit. I went with the Sonicap Gen II cap upgrade for C4, and was very happy with the resulting sound. However, lately I've spent a lot of time A/B'ing the CTH against the Audiotailor Jade, and noticed that while I found the sound from the CTH more musical I also hear that the middle of the soundstage of the CTH was more congested. It seemed like instruments toward the center were a little mushed together as compared to the Jade, where every instrument and voice was distinct. I wondered if my choice of C4 was influencing this, hence the start of my cap upgrade search.

The challenge, as anyone knows that has built a CTH in the BOM enclosure, is lack of space. The PCB is very dense and there is little room for high end caps. After a little measuring and reading a number of cap reviews I bought a pair of Relcap RT's (.22mF, 200V) from Michael Percy. When they arrived and I saw their size I gulped, but then took a deep breath and started the process of swapping them for the Sonicaps. As you can see from the attached picture they fit, but only barely. I had to cover the leads with shrinkwrap and slightly angle some of the other caps, but got the Relcaps installed and the CTH reassembled.

After a night of burn-in with pink noise I'm very pleased to report that the soundstage congestion is gone and the sound coming from my CTH is very clear and musical. Overall, the reviews of the Relcaps vs. the Sonicap Gen II seem accurate: the Sonicaps have a slightly juicier midrange and the Relcaps are clearer and more neutral across the spectrum. The most pleasant surprise so far is that the high end, especially for female vocals, is a touch smoother.

Overall, a successful experiment. I'll update my impressions after another week of burn-in.

 

[keyid]

I also tried various c4 caps and settled on Mundorf Supreme Silver/Oil, highly recommended. Im looking at the possibility on using jung or shunt regs for power for one or all 24v, 12.6 & 6.3v. I tube toroid with three secondaries can supply all the power and also replace the switching heater. Any thoughts?

 

[stringgz301]

What enclosure are you using?

 

[keyid]

not encased yet

 

[cfcubed]

@ stringgz301 - Good you were able to tweak CTH sound to you liking w/those Reliable Capacitors. IIRC, your feeling that std CTH sounded a bit congested in mids was expressed by a couple others. And I think they "solved" it in the same manner - upgrading C4 caps to something big (e.g. I think rds got happy w/auricaps).

With compactness being an important goal in CTH design, fitting large C4s is a challenge. And a reason small Sonicap Gen IIs were a recommended upgrade, instead of something bigger like the Sonicap Gen I w/Gen II bypass I used in what ended up becoming erikzen's build.

@keyid WRT PS replacements - My 1st thought is you'd not have a very Compact Tube Hybrid then

But as I recall you were able to detect & appreciate subtleties in changes, so perhaps you would w/such PS upgrades. It is likely CTH's design potential, SQ wise, is held back a bit by its compactness goal. E.g. I did/do find improvement (quieter background) in my larger, more spread out builds (like erikzen's & "Fancy CTH" in sig). Guessing that using high-quality shielded cable everywhere & moving LV reg a bit away may have had something to do with it.

 

[stringgz301]

Thanks for the info Cfcubed.

Question: if you were going to bypass the .22mF C4's what capacitance would you use?

 

[cfcubed]

> if you were going to bypass the .22mF C4's what capacitance would you use?

I think convention is 1/10th or so of the cap you are bypassing, so like .02uF or there abouts. I'm not an authority on it though and, to my imperfect ears, not convinced of SQ gains. Did it in erikzen's build because I'd the space & thought I'd try it.

 

[erikzen]

Is there any technical reason (theoretically) why or why not the CTH amp would work well with the Tesla T1 from Beyerdynamic? I heard this headphone recently and liked it a lot. However, it's expensive and if I bought one it would preclude me from purchasing a new amp anytime in the near future. My first impression was that the bass was a little flabby, as compared to a more powerful amp. Maybe the choice of tube would be a factor here?