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post #106 of 577

 

Quote:
Originally Posted by cfcubed View Post

Not sure about long leads on R18s.  You may check the actual buffer offset that's causing the relay trips by measure OG vs the channel input pins on the relay.  I'd tack little wires there for the test.

Maybe IG -> PCB will help.  Also consider searching orig "A Very Compact.." thread for cycle,   cycling,   latch  for other idea.s


 

IG -> PCB definitly helped.  The amp lives and plays music quite nicely! The latching is a little finicky right now.  Right now, the long wires exist, but are not connected to anything, so the amp is works (gentle hum) with my ER6's.  I haven't try anything else yet, but with R18=120 ohm, if I brush the amp or anything like that it'll cycle off, but if I don't touch it, it plays fine.  I had the pot grounded to IG, and it made it worse so that anytime I touched the pot it latched off.

 

I will play with R18 values to see if I can get the amp stable.  If so, then I'll test the bypass setting after.

 

How much does actual temperature affect the latching?  If the tube can't get warm enough will that negatively affect it?  I ask because I'm working in my garage and it's maybe 0 to 5 degrees Celcius.

 

Thanks very much for your help cfcubed!

 


Edited by civilmonkey - 4/6/11 at 5:09pm
post #107 of 577

>  anytime I touched the pot it latched off.

 

The only time I've experienced this is when I'd a static charge & by touching something released the charge into a circuit.  Guess it could also come from the live circuit building up a charge & you grounding it by touching.  Either way I'd expect the problem to go away when boxed up & properly grounded (pot, case to SG/IG).

 

>  How much does actual temperature affect the latching?  If the tube can't get warm enough will that negatively affect it?

 

I'd not think you have to worry about this.  Would think hot environs would be worst than cold ones.

BTW WRT ER6s I'd not expect CTH to be at its best w/sensitive IEMs or inefficient 600R+ impedance cans (as I posted earlier).

post #108 of 577



Quote:

Originally Posted by cfcubed View Post

> Either way I'd expect the problem to go away when boxed up & properly grounded (pot, case to SG/IG).

 

Just to confirm, Pot and Case are grounded to both SG and IG, i.e., tied together?  On the wiring diagram I see Pot to IG and Case to SG, but in this thread from a picture earlier I see IG and SG tied together.

 

EDIT:  As indicated by cfcubed, the problem went away when boxed up and properly grounded!  I tied Pot (IG), PCB (IG), and SG together, and bolted then all to the bom case.  No latch problems anymore.  So for my CTH, latch cycled until it was cased up. 

 

Also, as indicated, the CTH unlatches with DT 880/600 ohms with heavy bass.  With RE0's there is a slight hum but it's not too bad.  Both were tested with R18=120 ohm.  As the DT880's are my main headphones, I have bypass wires on leads at R18 to test out.  I'll let people know how it works once I've had a chance to test.


Edited by civilmonkey - 4/7/11 at 6:42pm
post #109 of 577
Thread Starter 

The way I have it is this...

 

I have two RCA jacks. Their respective ground wires come into G+ and IG. Then I have a wire that goes across both terminals and goes to IG on the board. At first, I had problems with the amp buzzing when I'd touch the pot. Cfcubed suggested that I unscrew one of the screws of my RK27 and tie a wire from that to IG. I did just this and the buzz went away. I've also read via a post from rds that you can run a wire to your chassis from your pot and it should get rid of the hum as well. Never tried it so I don't know how it works. I'm in the camp of people who has been doing a bit of DIY for a while now, yet still doesn't really *get* the ground thing yet. I get the basic idea, but that's about it.

post #110 of 577

Thanks Mullet.  The amp works and I have tied POT,IG,SG all together.

 

I sanded the top panel with 150 grit sanding disks (needed 2 altogether) using a random orbit sander and it turned out quite nice.  I'm not completely happy with the hole layout but that's what I get for rushing / not measuring anything.   All in all it looks pretty good I think.  Inside pictures will get posted once I fix the birds nest of wires inside!

 

Photobucket

Photobucket

post #111 of 577

I wasn't sure if I should just edit my post above, but I am considering my CTH 95% done. They last item is to replace the cheap linear 50k pot with a log 50k. I tested bypass wires on R18 and...... It works! I could detect no differences in SQ or distortion.

  1. Base case: BOM C4's, 120 ohms at R18 positions. Moderately heavy bass music (Orange Sky - Alexi Murdoch) at normal listening volumes causes CTH to unlatch
  2. BOM C4, bypass wires were 6" long each. Soldered bypass wires together, turned on amp and it latched. Played bass heavy music with DT880's. At more than satisfactory volumes, my CTH is fine with no distortion. Played Orange Sky again, LCD Soundsystem - Daft Punk Is Playing at My House, and others. Volume wise, I had the CTH at volumes which would cause hearing loss and made my ears tingle. If you really crank it up, distortion and unlatching kicks in.  EDIT:  The CTH does occasionally unlatch with the DT880's when I crank it up for a really good song.  In general, I find this a great amp with the DT880 and I love the sound, one just needs to use reasonable volumes.
  3. Replaced C4 with 0.22 uf MultiCaps from Partconnexion. Same result as #2, amp sounds great with DT880's. As an aside, I noticed an immediate improvement with the multicaps. To me, more details and a definite wider sound stage. I have not heard the amp with any other C4's except BOM C4s.
  4. Shortened bypass wires to around 3" and wired them to a switch on the front panel. Same result as #3, amp sounds great with DT880's.

 

Final set up is R18 = 150 ohms, with a DPDT to bypass each position. I have tried both my RE0's and DT880's, and find both very great. However, I feel the synergy between the 880's and CTH better than the RE0's but a) I haven't tried many tubes, b) The linear 50k pot severely limits usable range on the POT and c) I find the RE0’s improve with amping, but you don’t need much amping. I replaced the polished top (previous post) with a clear lexan top. Material was from Homedepot. I cut it down to size and used a router with thin the length wise edges so it would fit.

 

CTH - lexan top top view CTH - lexan top back CTH - lexan top front

 

All in all, I'm very happy with this amp, and my DT880s sound great.  The only other Tube amp I can compare this to is a my Little Dot MKIII amp.  In very general terms, and with the tubes I own for each amp, the MK III is more relaxed and sounds more 'tubey' where as the CTH is more detailed, more punch, and less 'tubey'.  I guess this makes sense given that the CTH is a Hydrid amp. 

 

I have built multiple SS amps (typical progressing from CMOY, to perf board 'maxed' CMOY, PIMETA, MINI 3, etc) and a few Alien USB DACs.  This was by far the hardest build yet.  If this is an intermediate level build, I *might* now barely be considered intermediate!

 

Thanks again to all who made the group buy possible and the support in this thread


Edited by civilmonkey - 4/24/11 at 6:28am
post #112 of 577

Thanks civilmonkey for the detailed feedback & great its working well & you're liking it.  So you were able to accommodate two very different headphones w/the R18s/R18 bypass.

Nice too that you can view inside & less of a one-way street than making it one solid block of plastic:) 

I wonder if you find there is enough ventilation esp. for the 24V reg... Are there any holes in the bottom?

post #113 of 577


Originally Posted by cfcubed View Post


I wonder if you find there is enough ventilation esp. for the 24V reg... Are there any holes in the bottom?

 

I wonder about that too.  There are no holes in the bottom, but I thought about adding some last night and it wouldn't hurt.  My multi meter has a temperature probe on it and I thought it would be a neat test to run the amp for a while and measure inside temp near the 24V reg.  Perhaps if I manage to, I'll test before holes on bottom and after.  
 

 

post #114 of 577
Just got the PCB today. What a cramped board it is! Now I have to find time to source for parts. smily_headphones1.gif
post #115 of 577

 

Quote:
Originally Posted by Lil' Knight View Post

Just got the PCB today. What a cramped board it is! Now I have to find time to source for parts. smily_headphones1.gif



We prefer the term "compact"  biggrin.gif

 

It's an enjoyable build - have fun!

 

BK

 

 

post #116 of 577
Sure it is cool.gif

Anyone knows the part number for the blue Dale resistor? Thinking of using it, the brown one is too 'boring' redface.gif
post #117 of 577

I remember those are Dale RN50C. I have them in the gamma-2 and the alpha20 buffers. Oh, and yeah, this IS a cramped board! 

post #118 of 577
Yeah, that are also the ones in the Grub DAC. I've just taken a look at the specs, the wattage is only 1/20w but the voltage rating is 200v. Would it be fine to use?
post #119 of 577
Originally Posted by cfcubed View Post

I wonder if you find there is enough ventilation esp. for the 24V reg... Are there any holes in the bottom?


I ran a small temperature test to assess interior temperatures. I checked a few specific locations for a short period of time, only one trial, a low to moderate volume, etc.  The entire aluminum side panels got quite warm, around 35 deg C as well.  Given the variability of each setup, the following may not apply to your CTH.

 

For my setup, here are the results.  I think based on datasheets, 75 C is okay (someone please correct me if I'm wrong).  Still, lower temperatures mean more stable components and longer life, so I will add a few holes in the bottom and maybe some on the top panel to see if that affects anything.

  

CTH Temperature Test (minimal venting)

 

Notes:

- Tested on April 11, 2011 with DT880/600 ohm, R18=0 ohm, tube was RCA Cleartop 12au7

- Listening volume was moderate.  Qualitatively, louder than normal conversation (I would not have heard someone talking to me while listening), but less than a telephone dial tone.

- Venting consists of space around tube (29 mm dia ID, minus 22 mm ID of tube saver) and 4, 7mm diameter holes above 24Vreg.

- Beside HS = 2-3 mm away from HS fins, approx 10 mm down from top panel

- Top of HS = temperature probe pushed against top of heat sink

- Inside case temp = In front of tube, approx halfway between PCB and top of panel

- I think the slight dip in temperature on the second last measurement is due to less bassy music (Alan Parsons Project came on for a song).

post #120 of 577

Holes in the bottom will help a lot, Hot air will escape much easier if there is a way for fresh air to enter the case.

A dozen 3/8" holes spread across the base of my CTH made a noticeable difference.

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