[mrhk13]

Here are some pics of my stock CTH. Front shows on/off switch, voltage switch. And yes, I did do a fuse and on/off switch: I'm not yet that confident in my soldering skills! I'm annoyed I mis-measured the hole for the power plug. I still need to drill holes in the top plate, mostly trying to figure out how to drill a hole big enough for the tube! So that will come later. Tomorrow night the wife is out and I have a hot date with an iron (not of the soldering kind, sadly!) but plenty of time standing in one spot means I'll be able to listen to the amp for a goodly while.
 
MisterRogers, I'll consider the upgrade. In the short time I've listened it's sounding much better than my other option (my first DIY amp: a cmoy), so I cannot imagine upgrading it just yet. Plus, I have a feeling the bottleneck is elsewhere: my cans. But as the Lowes website says: "never stop improving".
 

 

[BK_856er]

Looking good, mrhk13!  

 
Cmoy to CTH is a huge step up in terms of build complexity and SQ.
 
Options for the center tube hole are a greenlee type hole punch, a uni-bit. or a dremel and lots of patience.  The hole punch makes the cleanest hole, which can be important if you don't plan to "finish" with a trim ring.  Strategic vent holes or mesh top is always a good idea to keep the temps down.
 
BK
 

 

[Misterrogers]

nice work mrhk13! When you do decide to try the Super Regulator, you'll probably need to switch cases. While pin compatible, the high current (2A) super reg needs a bit more room than is available in the stock case. I'll upload some photos of my install in a day or so and you can see my approach. Essentially, I used 3 pin connectors to mount the reg horizontally off to the side. This gave plenty of vertical space for my heat sink. I second the hole punch. It was easy (though I finished with a tube ring) to punch a 1in whole.
 
Btw all - sachu suggested this awhile back somewhere in some thread; track down an RCA Clear Top 6CG7. Clear Top + Super Reg + good caps = 

 

[Mullet]

No joke. You got the Lyr for sale.
 
I'm so tempted to crack open one of my CTHs to do some cosmetic surgery and add a Super Regulator. I always use a perforated metal top for ventilation so it wouldn't be hard to cut a small hole in that area and let the Super Regulator pop out. It may look ugly, but it won't sound ugly. Dimensionally, is it taller or taller and wider?
 
On another note I'm about to build "The Wire" and after that I have an EHHA Rev A on deck (clearing some desk space will make this happen sooner) so perhaps I'll be less likely to want to go mucking around with my CTHs.

 

[Misterrogers]

Since a handful of you are considering adding the Belleson, here's a top down of my build. The larger case obviously helps here with the reg and caps. Mullet - mounting the reg vertically is a bit tight with the smaller caps right next to it on the board. Rather than figure out how to get it in there without shorting, I used some 3 pin male/female connectors and went horizontal.

 

[Mullet]

Back again... After building so many CTH's I'm finally having an issue with my latest build. Everything checks out fine with regard to OL, OR, OG. My TB+ is fine. Pin 6 is fine at 77.8v. Pin 1 is where I'm having an issue. I was originally getting 100v, but after some probing around I shorted something out and now I'm getting close to 35v on Pin 1. If I pull my 12v tube I get a reading of 105v on both pins 1 and 6. If I take the opamp out I get pretty good reading somewhere in the 70s. I've checked to make sure I have the right parts in the right places and they all appear to be fine. I could swap the TL081 but I'm worried I might damage it. I'm about to start ordering parts for the whole left input stage. Besides the opamp any ideas on what would cause this?

 

[Mullet]

Here are some measurements that I took with both the tube in and out...
 
ICL without tube = pin 2 3.141v; pin 3 .115v; pin 6 .026v; pin 7 23.99v
ICL with tube = pin 2 1.025v; pin 3 .150v; pin 6 .148v; pin 7 23.99v
ICR with tube = pin 2 2.343v; pin 3 2.373v; pin 6 3.091vl; pin 7 24.02v
 
Don't necessarily want to jump the gun and order...
Q4P, R3L, R4L, R5L, R6L, R7L, R8L, ICL just yet...

 

 

[Mikael109]

Anyone know where I can pick up one of these PCB's?
 
I'm looking to build this for my first DIY amp. (Cmoy seems like just board population and I've done that before.. I'm not feeling too confident in attempting a SOHA II though)
 
I can't read the schematic on CA's Rev A power supply, but I'll only be using the 2-position heater.. So I imagine I can just use the "wiring diagram" on CA's CTH section, and the BoM to correctly populate which cap/resistor/ect goes where on the PCB?

 

[Mullet]

@Mikael109 -- Looks like another group buy is in order. I've done one before for this amp and I can tell you -- there needs to be enough interest of at least 30-40 boards to make it worth it. And yes you should be able to populate the board with double checking the BoM. Knowing how to read the schematic is good for troubleshooting. The hardest part is making it fit into that small hammond case.
 
By the way I fixed my issues. Just did the shot gun approach and replaced most of the left side input stage.
 
On a side note -- I've been looking into the whole question of output impedance of the CTH in conjunction with using LCD-2s and Thunderpants (orthodynamic headphones). The CTH has a default output impedance of 104 ohms. 100 ohms comes from R18 and 4 ohms come from the CTH's output impedance without R18 installed. This impedance of 104 ohms is way too high if going by the 1/8 damping ratio ie your output impedance of your amp shouldn't be any higher than 1/8 of your headphone impedance. From my understanding, R18 is used to offset the high gain of your 12au7 or 6dj8 tube(s) -- respectively 17 or 33 mu -- especially for highly efficient cans like Grados, Denon, etc. This way your volume doesn't get too high too fast. However, if we're using this amp with orthos in mind is it better practice to jumper R18? Do we also need to raise a higher ohm pot like 100k instead of 50k? At this point, I have R18 set to its default at 100R. I'm using a 50k pot and my orthos are driven well at 12 o'clock on the pot. But are they driven, correctly? CTH Orthoheads how are you dealing with R18?

 

[Avro_Arrow]

I think you can get boards here now.

 

[Mikael109]

Quote:

@Mikael109 -- Looks like another group buy is in order. I've done one before for this amp and I can tell you -- there needs to be enough interest of at least 30-40 boards to make it worth it. And yes you should be able to populate the board with double checking the BoM. Knowing how to read the schematic is good for troubleshooting. The hardest part is making it fit into that small hammond case.

 
Perfect!
 
Thanks! The only issue I see is that I wouldn't be able to ground the case from the Star Ground pad because the case will be made of wood. I'm thinking this should be fine though because a wood case shouldn't build up charge like a metal one would.
 
I still have one last arcade stick to finish and sell off, so hopefully there will be a GB sometime in the near future If not I'll snag a board from the link above.

 

[Mullet]

@Avro_Arrow -- That's great to know that boards are easily accessible. Props to MisterRogers for hooking it up.
 
...still wondering about my output impedance query...
 
If you're using a wooden case I don't think you have to worry much about SG. I could be wrong, but logic tells me you'll be ok.

 

[mmayer167]

Thanks again Misterrogers for making more boards appear! 

 

[Misterrogers]

More than happy to help Gents! It's a fantastic little amp that many should be able to build.

 

[kchapdaily]

quick question. im not sure if this is the best place to ask, but i figured it would be better than starting a new thread.
 
i have a set of hifiman he-4's in the mail. ive heard the cth is a good amp for them.
 
until i build a new amp, i will be driving them with my starving student. it should be fine for now, but an upgrade might be in order.
i would like to roll tubes, so im stuck between a cth rev a and a soha II. would the cth match better? and would i have to make any modifications to the bom to drive the he-4 specifically?