the CTH (Compact Tube Hybrid) Rev A thread...
Mar 30, 2011 at 10:13 PM Post #61 of 607

BK_856er

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Quote:
 
BK,
 
What caps did you get? Wiatrob sent me some of those green Russian PIOs. They look like they might be a pain to solder in. I'm wondering how they compare to the Wimas I'm currently using in my CTH. Not sure if they're the BOM ones because I acquired them from cfcubed.
 


I got the tiny BOM Wima caps with the initial parts, then later some larger Wima and Kemet (?) along with another order just because they were cheap enough.  Spearately I ordered 400V Sonicap GenII and Auricap units.  Not sure yet what I'm going to install - probably the Auricap.
 
BK

 
 
 
Mar 30, 2011 at 10:23 PM Post #62 of 607

Lil' Knight

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I haven't got the boards or seen the case but you guys might want to try the Russian FT-3 teflon caps. Stunning performance, build like a tank for dirt cheap price. Look for the 200v ones which are smaller than the 600v. Used them in my tube DAC and they have almost the same performance with the Vcap and Jensen. Didn't really like the Auricap though. Russian PIO caps are also great for the value but somehow they make the sound a lil' slower, which is not my taste.

I'll use a custom made case anyway so space is not really a trouble for me. Also thinking of putting a GrubDAC to make a small, high performance USB DAC. Any idea on about an easy to switch between RCA and USB inputs?
 
Mar 30, 2011 at 11:17 PM Post #63 of 607

Mullet

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You're probably having charge build up on your case.  It should be grounded for safety, and this will solve the issue you mention.
 
Here's how I did it:

 
fyi the other white wire goes to the pot (to stop hum when you touch the volume knob) like so:


The weird thing is that I've grounded my case from star ground. I guess ill have to check the connecton one more time. It might be slightly loose. The only difference is that I have my pot grounded to input ground and it seems to be working with regards to fixing that annoying hum. Maybe i should switch it to SG instead.
 
Mar 30, 2011 at 11:24 PM Post #65 of 607

Mullet

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I haven't got the boards or seen the case but you guys might want to try the Russian FT-3 teflon caps. Stunning performance, build like a tank for dirt cheap price. Look for the 200v ones which are smaller than the 600v. Used them in my tube DAC and they have almost the same performance with the Vcap and Jensen. Didn't really like the Auricap though. Russian PIO caps are also great for the value but somehow they make the sound a lil' slower, which is not my taste.

I'll use a custom made case anyway so space is not really a trouble for me. Also thinking of putting a GrubDAC to make a small, high performance USB DAC. Any idea on about an easy to switch between RCA and USB inputs?


Hrmmmmm, now I'm thinking that I might want to try and find the wima caps I used in my first CTH. I'm not so sold on the Russian PIO caps being that they are "slower". What would be the benefits of going with them over the BOM Wima caps? What exactly does slower mean?
 
Mar 30, 2011 at 11:42 PM Post #66 of 607

Lil' Knight

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It's just my feeling about the sound. Some might prefer the PIO caps for tube amp, which makes the mids lusher and sweeter but speed is not fast. The green K75 caps are cheap enough so it's still worth trying to see they fit your taste or not. Hard to describe exactly the sound because I'm not really good at writing flowery stuffs. From my own experience, PIO caps like K75, Vitamin Q, Gudeman... make the sound more colored in the relaxing way, while the teflon ones bring up more details and clearer highs.
 
Mar 31, 2011 at 1:10 AM Post #69 of 607

rds

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Quote:
The weird thing is that I've grounded my case from star ground. I guess ill have to check the connecton one more time. It might be slightly loose. The only difference is that I have my pot grounded to input ground and it seems to be working with regards to fixing that annoying hum. Maybe i should switch it to SG instead.



 
     I'm not sure what you mean by star ground since this board has a ground plane.  SG is a point on the ground plane which is connected to the power supply ground.  Also, your case and pot should be grounded to the same point unless your pot is well isolated from the case.  
 
 

Quote:
Wow, rds, you really puch those transistors low! i always thought they should be up a bit for heat disipation...
 


Yeah... I have my reasons but they're mostly idiosyncratic 
redface.gif
   Having longer leads might reduce thermal conductivity to the board, but a 1mm space vs a 5mm space under the transistor won't do anything to increase heat dissipation in my opinion.  In fact if we assume that shorter leads increase thermal conductivity and that the board dissipates heat then short leads would increase dissipation.  
 

 
 
Mar 31, 2011 at 10:19 AM Post #72 of 607

cfcubed

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Opinion here...
rds - Yep, good points WRT transistor height... I too always left room under for airflow but whether that is truly a heat-diss. advantage is unclear.
   As far as getting them that low, the PCB is designed for the "triangle" base pin TO92 layout not the in-line one (tech terms escape me:)  I don't pre-bend, although that may be good to do, I find the leads have enough flex to get them pretty close to the board if you want.
 
grounds - like rds says but I'd always ground the pot if its not going into grounded metal.
 
Lil Knight - Yep, as before the board is tight for sure & this PCB rev is better than the last in that regard.  One of the prime CTH goals was a full-featured, through-hole DIY desktop headamp in its 3" x 4.8" space (see 1st "A Very.." thread post).  When you review its features, operating points, SQ as reported by owners, etc. it seems to have met & exceeded its design goals.
 
WRT C4 coupling caps I've heard most of the usual suspects in CTHs.  This is really IMO but I'd not obsess about this.  Reports say the amp sounds great w/any C4s used to date, but there are subtle diffs amongst them and you can find others' opinions in the "A Very.." & Tube and Tweak threads.  My own experiences & opinion echos those like Lil Knight's above.  Note: There is no reported lack of "crispness" for CTH, so IMO "slower" caps that trim upper-treble a wee bit are something to consider.  But again IMO we're splitting hairs a bit here esp when you consider the many tube-rolling possibilities to get similar effect.
 
BTW fitting fancy caps is easier using the new PCB rev but keep in mind well-soldered & secured C4s are a must.  Here's my latest, next-to-last CTH buildup (prior board rev):
 

 
Mar 31, 2011 at 1:42 PM Post #73 of 607

Mullet

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> I'm not sure what you mean by star ground since this board has a ground plane.  SG is a point on the ground plane which is connected to the power supply ground.  Also, your case and pot should be grounded to the same point unless your pot is well isolated from the case.  
 
I have SG connected to my case. I assumed SG on the board meant Star Ground. I could be wrong. My pot is mounted to the plastic panels that come with the Hammond case. So it is isolated. However, I was having the hum issue when I was touching the pot. Cfcubed suggested that I loosen one of the screws on my RK27 and connect a lead or wire from that to IG. I just took a piece of wire and connected it from the pot to the wire that goes my G+/IG terminals on the pot to IG on the board. The hum then went away.
 
Apr 1, 2011 at 12:03 AM Post #75 of 607

Mullet

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Quote:
The board is really cramped. Just wondering if the PCB layout will fit the CMC teflon tube socket?



Some how looking at pics of this socket online it doesn't like it would fit well. Is it made for pcb mounting? This is what I'm using on my CTHs... http://bit.ly/elHoQV They seem to work well. I still might get a socket saver to prolong the life of the socket.
 

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