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Dsavitsk/Beezar Torpedo Build Thread - Page 18

post #256 of 593
Quote:
Originally Posted by tomb View Post

Super-Torpedo.  (I think Dsavitsk hates that name, but I don't have a better one at the moment.) 

Missile?

Put some fins on it...

post #257 of 593
I pushed for Salsiccia, but was overruled.


The slight mod I proposed to Tom is that we can beef up the CCS impedance a little. The CCS forms a voltage divider with the rp of the tube. The higher the CCS impedance and the lower the rp, the less power supply noise gets through. CCS impedance is basically

Hfe1 * Hfe2 * Re (Re is the current setting resistor (R4 and R5))

which is roughly 1M here. Good, not great. Actually, not really even that good. It is only about 50dB noise reduction. However, if we change out the top LED (D12 and D14) for say a 6.8V zener, then for the same current we need a 400R resistor [the current is (Zener voltage - 0.6) / Re], which bumps the impedance up to 6M which is 6x better (about 66dB of PSRR). The downside is that we have to drop an additional 5V across the CCS, which is not a big deal here.

With a 15V zener and a 1K resistor we get 74dB. However, the 15v Zener happens to be quite noisy, and will and up doing more harm than good. 6.8v seems to be a good quiet spot.

This is not a complete fix -- there is some noise that is PS noise getting through CCS that this will mitigate. However, the bulk of the noise seems to be noise from the transformer getting into the case and then getting into the circuit. Not sure how, but that's what is going on.

Also note that the Zener points the opposite direction of the LED, schematically speaking, with the cathode toward the positive marker on the PCB. If you put it in backwards you'll get very little current through the tube.
post #258 of 593

Hey chaps

 

I'm having a problem with my build.

 

Only one channel working.

 

On switch on, D10, D11 and D13 light up immediately.  D14 and D15 light up after about 10 seconds.  D12 never lights up.

 

Any ideas?

post #259 of 593
Thread Starter 
Quote:
Originally Posted by UKToecutter View Post

Hey chaps

 

I'm having a problem with my build.

 

Only one channel working.

 

On switch on, D10, D11 and D13 light up immediately.  D14 and D15 light up after about 10 seconds.  D12 never lights up.

 

Any ideas?

Did you solder the proper jumper(s) at A-B-C-D?  One of mine did something similar when I forgot to solder the power transformer jumpers.

 

Be careful.  What's your house voltage in the UK?  If 120V, then solder a jumper from A-B and then another jumper from C-D.  If 220V, then solder a single jumper from B-C, that's all.

 

Assuming that's the issue, of course ... wink.gif

post #260 of 593

Tom

Thanks for the response but that's not the issue.

Jumper is B-C 220V.

 

As I said, one channel works fine.

 

I just checked without any tubes in and D13 still lights up and it shouldn't without a tube.

I'm guessing Q3 or Q5

post #261 of 593
Thread Starter 
Quote:
Originally Posted by UKToecutter View Post

Tom

Thanks for the response but that's not the issue.

Jumper is B-C 220V.

 

As I said, one channel works fine.

 

I just checked without any tubes in and D13 still lights up and it shouldn't without a tube.

I'm guessing Q3 or Q5

No offense, but your previous post included D11 - that's in the other channel from the other two.

 

There are some versions of MJE's that have different pinouts, but seems that would've affected both channels.  Let's see what Dsavitsk says.

 

Meanwhile, some pics might help.

post #262 of 593

Tom

I hope I didn't come across as 'crabby' :-)

Fault seems to have changed.

Neither D12 or D13 light up now.

 

Happy to wait for Dsavitsk

post #263 of 593
Have you tried swapping the tubes from left to right? It could be a bad tube. Could also be an LED in the wrong way. Otherwise, I'd check the solder joints, look for shorts, etc. If none of that helps, then look to the transistors.
post #264 of 593
Thread Starter 

I like the LED idea.  I've done that a couple of times, myself.  Hopefully, it should be easy to check if the LEDs have flanges.

 

I didn't think you were crabby. Let us know. smily_headphones1.gif

post #265 of 593

SHE LIVES!!!!

 

Swapped the MJE350 and 2N5087.

 

BIG GRIN.

 

Tube rolling any time now.

post #266 of 593
Thread Starter 

Great news!!  It sounds like you were right all along!  What do you think - too much heat during soldering, maybe, or just defective transistors?

post #267 of 593

Who knows?

 

One thing I do know is that I don't have any hum, buzz or noise (I grounded all my heatsinks but no other changes).

 

I'm using Mullard CV4031's and they sound absolutely 'lush'

post #268 of 593
Thread Starter 
Quote:
Originally Posted by UKToecutter View Post

Who knows?

 

One thing I do know is that I don't have any hum, buzz or noise (I grounded all my heatsinks but no other changes).

 

I'm using Mullard CV4031's and they sound absolutely 'lush'

Outstanding! biggrin.gif

post #269 of 593
Quote:

Originally Posted by dsavitsk View Post

This is not a complete fix -- there is some noise that is PS noise getting through CCS that this will mitigate. However, the bulk of the noise seems to be noise from the transformer getting into the case and then getting into the circuit. Not sure how, but that's what is going on.

 

 

 

I'm looking into ordering this kit, since this is exactly what i have been thinking about building myself - but i have a few questions. I have not read the whole thread so this may been answered before, but anyway...
First - if you install a small choke, doesn't this help lowering the noise issue below?
Secondly, with the stock tubes and the amp at either low or high what is the gain of the amp (i assume it is negative?), or rather what is the step-down values of the transformer with low and high gain?
Also, have anybody tried moving the tubes up at the top of the case and thus maybe getting rid of the noise?


Edited by RollE2k - 12/2/12 at 2:37pm
post #270 of 593
Thread Starter 
Quote:
Originally Posted by RollE2k View Post

 

 

I'm looking into ordering this kit, since this is exactly what i have been thinking about building myself - but i have a few questions. I have not read the whole thread so this may been answered before, but anyway...
First - if you install a small choke, doesn't this help lowering the noise issue below?
Secondly, with the stock tubes and the amp at either low or high what is the gain of the amp (i assume it is negative?), or rather what is the step-down values of the transformer with low and high gain?
Also, have anybody tried moving the tubes up at the top of the case and thus maybe getting rid of the noise?

1. Yes, the choke is recommended.  It contributes to lowering hum (it's actually a 180Hz anomaly).

2. Dsavitsk will have to answer this directly.  I can tell you that at Low-Z, Grados are perfect medium-listening levels at 12 o'clock (HF-2, HF-1, SR-225's).  Sennheisers (HD600, HD580) are the same at High-Z - 12 o'clock on the volume knob.

3. Yes - see earlier in the thread.

HiGHFLYiN9 built a very-nice looking steam-punk finished Torpedo with the tubes outside of the case.  The tubes are not causing the noise.  It's the PT reflecting off of the case.

 

Noise: As stated, it's been found to be a 180Hz anomaly from the PT.  With the choke, chances are that you will never hear it with some headphones.  With others, it may be barely detectable.  Besides using the choke and trying Dsavitsk's zener diode fix (I haven't tried it just yet), reducing current overall in the amp also quietens it.  For instance, the 5844 tubes use about 1/2 the heater current.  They are much quieter.  Really, though, the choke does the most IMHO (unless the Zener works even better).

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