the CTH (Compact Tube Hybrid) Rev A thread... - Page 2

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

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?

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

>  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.

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.

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

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...

Quote:

Originally Posted by 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.

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:

Originally Posted by cfcubed 

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.
 

>  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.

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:

• C1H, C2H   150u / 25v  # 667-EEU-FR1E151  (100u likely used in all CTHs to date)
• 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:)