[Br777]

Just want to say i owned this amp at one time and loved it.  Glad to see its getting a "revival" so more people can experience its greatness
 

 

[civilmonkey]

I read the entire original CTH thread (man what long thread).  I read somewhere that some people were considering SIP sockets for C4 so they could try different capacitors.  Did anyone try this, and did it lead to instabilities?  I have a pair of Aerovox AFPS I would like to try vs the stock bom caps.  Maybe oneday with I decide to order sonic gen II's I would like to try those too.
 
Any thoughts?

 

[wiatrob]

I have built with socketed caps. Wasn't really worth the trouble, as most of the interesting caps will need some creative lead work to get in the amp comfortably, making the sips hard to use with the previous designs spacing. Might be different with the new lead spacing.

Give it a try and let us know?

The Soniccaps are a slam dunk, but even the stock wimas perform admirably i'n this design.

 

[cfcubed]

Now that we have new CTHs & some new CTH builders around, and I've fielded queries about this, maybe good to say something about experiences WRT cans & how CTH drives them.  The bottom line is that, like most gear, there are combos reported to work well together & combos reported to not work as well together.  Know that the vast majority of reports, for most all "common" & many "uncommon" dynamic cans (e.g. Sennheiser IE8s through LCD-2s), are very positive concerning the CTH's synergy.  CTH has been reported to drive cans known as difficult to drive as well.
 
Not unexpected, but based on reports here & my own experiences, the CTH may not be the amp of choice for the "tails" of a Bell curve of sensitivity/impedance of cans (high-sensitivity/low-impedance cans @ one end, low-sensitivity/high-impedance @ the other). 
There is some question whether cans at the high-sensitivity/low-impedance end need amping, but that's another discussion.
 
At one end we have some reports of some IEM users hearing hiss & having little usable volume pot range, and at the other end reports of its e12 circuit tripping for very loud/heavy bass passages.  For example, 96 dB sensitivity 32R & 250R DT880s receive good reports, where (stock 100R R18s) CTH driving 600R DT880s at loud/high levels begins to distort & if driven further can cause its e12 to trip (a good thing - its doing its job if clipping is present or LV supply wavers).
 
The R18 resistors were introduced early on in CTH development as a way to contour/shift its wide performance swath within the Bell curve discussed above.  I believe we suggest R18 values from 0R -> 150R, with the default 100R being best with the majority of cans.  However, if you wish to target the high-sensitivity/low-impedance end consider 150R, the low-sensitivity/high-impedance end consider shorting the positions.
 
If necessary, I suppose runeight could tweak what is said here or provide technical data (e.g. WRT Class-A regime values of CTH's TO92 OB design).  OTOH maybe this is enough said & users can use search to see others' reports.
 
Update:  The way to alter native CTH gain is through tube choice... E.g. 12au7 has lower gain than 6922.  So consider this as well WRT your volume pot range & cans sensitivity.  With the large world of tubes that can be operated in this amp, there are other levels of (tube) gain available as well.  Here again is a tube compatibility post I made (there have since been a few more tubes found that work I think): 
http://www.head-fi.org/forum/thread/398839/a-very-compact-hybrid-amp/2025#post_6785071

 

[Mullet]

cfcubed -- that's quite a nugget of info that I'm sure will prove useful for for the newer builders. What's the deal with the heater currents with regards to 150mA/300mA? Does that mean you can safely run a given tube at both 12v and 6v? Running it at a different voltage would shorten the the tubes life, right?
 
If you guys don't have your hands on the new CTH Rev A BoM and info yet you can get it here... http://cavalliaudio.com/diy/ctha/main.php?page=overview
 
On another note and I think I've come across this in the *old* thread when I read through all 146 pages -- I'm using the RK27 pot for my volume control and every time I touch it I hear a buzz. It goes away when I take my finger off the pot. What was the fix for this? I think its grounding issue. Also, I do hear a slight hum/buzz with some headphones and some tubes. You can't hear it when music is playing. I was under the impression that the 470uF C3H would take care of this. My source is a gamma2 from my laptop. Any ideas?

 

[cfcubed]

>  What's the deal with the heater currents with regards to 150mA/300mA? Does that mean you can safely run a given tube at both 12v and 6v?
 
The 9-pin mini tube spec for the CTH includes 3 heater-related pins; pins 4, 5 & 9.  The usual/series heater voltage & draw (using pins 4 & 5) is what we consider here NOT a tube's parallel heater voltage & draw (its pin 4-> 9 & 5->9 parallel specs are ignored as CTH has no electrical connection for the heater centertap pin #9).  So 12.6v (series) heated tubes (e.g. 12au7) use CTH's 12.6v position,  6.3v (series) heated tubes (e.g. 6922) its 6.3v position. 
The max (series) heater draw we recommend for CTH is 600ma, unless a heatsink is fitted it LM2595 & its coils up-spec'd beyond the BoM spec 800ma rating.
 
>  I'm using the RK27 pot for my volume control and every time I touch it I hear a buzz.
 
Since your pot is mounted to a plastic panel, you need to ground your pot, in CTH to its IG which = its SG.  Easy on RK27 - you loosen one of its back screws & run a jumper from it to the IG pins/connection on the pot.
 
> Also, I do hear a slight hum/buzz with some headphones and some tubes. You can't hear it when music is playing. I was under the impression that the 470uF C3H would take care of this.
 
We believe the old heater "buzz" problem was solved in early 2009 with re-specing C3H to 330u, and we now raised this to 470u as an extra measure.  We know your 1st build has had its problems & repairs, but maybe this is a case ground problem.  You must assure your case is grounded, e.g. running a wire from SG to a contact screw in the case.
 
Bottom line is assure your pot & case are grounded to IG/SG and double-check they are using an ohmmeter (measuring to either RCA-in jack ground).  This should solve it.

 

[cfcubed]

Oh and other usual remedies for DIY amp hum apply as well, like keeping A/C lines short, twisted & away from low-level/input runs, considering shielded low-level/input runs, etc.

 

[rds]

 
The unpopulated PCB.  Very nice look, and great layout!

 

[wiatrob]

Speaking of headphone synergies and SIPs - I have always socketed the R18 resistors in my builds, allows you to swap in different values when you have your build up (but still pretty difficult to do when the amp's cased.) I don't want to be the nervous nellie - but BE CAREFUL when poking around inside a built CTH, as components are very dense, and one slip of the probes can release some Magik Blue Smoke pretty easily...
 
I have stuck with 150R. I rotate through YH-3s, Senn 600s, and JH-13s regularly...
 

 

[civilmonkey]

Quote:

I have built with socketed caps. Wasn't really worth the trouble, as most of the interesting caps will need some creative lead work to get in the amp comfortably, making the sips hard to use with the previous designs spacing. Might be different with the new lead spacing.

Give it a try and let us know?

The Soniccaps are a slam dunk, but even the stock wimas perform admirably i'n this design.

Thanks -- I will skip the SIPs for C4.  I plan on shoe horning some Obligatto Film Cap 0.22uF / 630V from Parts Connexion as I'm also getting my tube socket from them.  Since they are Canadian it should hopefully be easier / cheaper shipping then Sonic Gen II's (despite the slam dunk) for me.
 
Quote:

At one end we have some reports of some IEM users hearing hiss & having little usable volume pot range, and at the other end reports of its e12 circuit tripping for very loud/heavy bass passages.  For example, 96 dB sensitivity 32R & 250R DT880s receive good reports, where (stock 100R R18s) CTH driving 600R DT880s at loud/high levels begins to distort & if driven further can cause its e12 to trip (a good thing - its doing its job if clipping is present or LV supply wavers).
 
The R18 resistors were introduced early on in CTH development as a way to contour/shift its wide performance swath within the Bell curve discussed above.  I believe we suggest R18 values from 0R -> 150R, with the default 100R being best with the majority of cans.  However, if you wish to target the high-sensitivity/low-impedance end consider 150R, the low-sensitivity/high-impedance end consider shorting the positions.

 
My current headphones are 600 ohm DT880's, so this was great information.  My plan will be to use SIP's for R18 resistors, and try shorting, maybe 50 ohms, depending how it goes.
 
Thanks everyone.  I promise to report back, but given that I have a newborn, time is scare!  I will have 1 week end of April when I start/finish this build.
 
 

 

[wiatrob]

Quote:

Quote:

Thanks -- I will skip the SIPs for C4.  I plan on shoe horning some Obligatto Film Cap 0.22uF / 630V from Parts Connexion as I'm also getting my tube socket from them.  Since they are Canadian it should hopefully be easier / cheaper shipping then Sonic Gen II's (despite the slam dunk) for me.
 
The Ob's are BIG, it's not impossible, but I had to fly them on long leads.
 
Argh, I can't insert pictures!
 
 
 
 

 
 
 
 
 

 

[cfcubed]

>  My current headphones are 600 ohm DT880's, so this was great information.
 
Yes, the only cans I've ever found the CTH (w/100R R18s) could not drive well are my 600R DT880s.  I'm not bothering to short my R18s for the DT880s, CTH sounds great with my other cans asis.  I've a couple good SS headamps to use w/the 880s.
 
BTW a crafty builder might try installing 120R or 150R R18s plus a DPDT switch that optionally shorts the positions.  Note though the R18s are "embedded" into the OB circuit, so I'm unsure of the impact (if any) of long leads on their pads.
 
BTW#2 for my "fancy" CTH there was enough room to use a DPDT power switch - one side the A/C  - the other side e12 relay power (e.g. bridged a PCB trace I broke from Q3E/D3E to the relay).  This nullifies the short, sharp harmless "click" one can get at power-off.

 

[Mullet]

Quote:

>  What's the deal with the heater currents with regards to 150mA/300mA? Does that mean you can safely run a given tube at both 12v and 6v?
 
The 9-pin mini tube spec for the CTH includes 3 heater-related pins; pins 4, 5 & 9.  The usual/series heater voltage & draw (using pins 4 & 5) is what we consider here NOT a tube's parallel heater voltage & draw (its pin 4-> 9 & 5->9 parallel specs are ignored as CTH has no electrical connection for the heater centertap pin #9).  So 12.6v (series) heated tubes (e.g. 12au7) use CTH's 12.6v position,  6.3v (series) heated tubes (e.g. 6922) its 6.3v position. 
The max (series) heater draw we recommend for CTH is 600ma, unless a heatsink is fitted it LM2595 & its coils up-spec'd beyond the BoM spec 800ma rating.
 
>  I'm using the RK27 pot for my volume control and every time I touch it I hear a buzz.
 
Since your pot is mounted to a plastic panel, you need to ground your pot, in CTH to its IG which = its SG.  Easy on RK27 - you loosen one of its back screws & run a jumper from it to the IG pins/connection on the pot.
 
> Also, I do hear a slight hum/buzz with some headphones and some tubes. You can't hear it when music is playing. I was under the impression that the 470uF C3H would take care of this.
 
We believe the old heater "buzz" problem was solved in early 2009 with re-specing C3H to 330u, and we now raised this to 470u as an extra measure.  We know your 1st build has had its problems & repairs, but maybe this is a case ground problem.  You must assure your case is grounded, e.g. running a wire from SG to a contact screw in the case.
 
Bottom line is assure your pot & case are grounded to IG/SG and double-check they are using an ohmmeter (measuring to either RCA-in jack ground).  This should solve it.

Good info about why we can't just switch between 12 and 6v on a given tube. So if you have a 6 volt tube run it at 6v. Otherwise, I suppose the life of the tube will be diminished.
 
Once I get back to the office on Monday I'll make the appropriate adjustment to the pot to eliminate the touch sensitive hum/buzz. With regards to the general hum/buzz that is mostly inaudible, I did run shielded belden 1505A cable from my RCAs to the RK27. I used the black lead instead of the normal ground lead. My thoughts were that wire is wire, but I could have been wrong. Also I do have SG going to a one of those washer thingies (that you can attach a lead to) attached to the case. It's supposed to be crimped, but I soldered it because I didn't have the right crimping tool. I guess a poor connection somewhere might be causing the low level hum.
 
Another thing to note for everyone building this new revision. I found that with this PCB it was easy to destroy the solder pads when doing desoldering and subsequently resoldering. I completely lost my pads on my IG and a few other pads on the first replacement. I've read that others have destroyed pads on the previous CTH, but with repeated parts replacements. In the end, I had to resolder IG from the top of the board. Perhaps, this is where the bad joint is and is causing my low level hum issue. With my next build, I'm going to be sure to try not to desolder any wiring and hopefully not fry my OB BJTs. Also, I think I'll lower heat on my adjustable heat iron to see if that prevents the solder pads from being damaged.
 
 
 
 

 

[cfcubed]

Here is some timely & important part info from user rds (thanks!).
 
Though a lot of work went into this new CTH rev & its BoM, when looking for parts subs (since its last rev circa 2009) by and large we didn't investigate uprating/changing parts values WRT newly available parts.  One of the (minor) compromises in original parts spec involved capacitor choice because of space limitations.
User rds came up these parts recommendations from a new series of Panasonic caps available @ Mouser that appear very good options:
 

1. C1H, C2H   150u / 25v  # 667-EEU-FR1E151  (100u likely used in all CTHs to date)
2. C3H   330u / 50v  #  667-EEU-FR1H331L   (reports are that any 50v 330u or above cap works well)

 
Although low-ESR caps are not required for C3H, the option above comes from the same new series and has better attributes than BoM 470u choice (other than its lower 330u which has been found sufficient).  Note it remains to be seen if the recommendations above yield any audible improvement or change, so don't fret if you've already ordered parts or assembled your CTH

 

[runeight]

New BoM posted to website.