• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6V6 line preamp

AAAh! Hum part one solved:)

My mistake is visible on this two pictures.
 

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Thanx bud. I almost went crazy on this. Right now I simplified it to resistor CF, maybe Ill mout the chokes b4 I hit the pillow. Then everything is soldered on and off so many times so I have some fixing up to do. Pot still scrapes and its equal microphonic even hum-free.

Ill make you feel better. When I hooked mine up for first time, I had singing tubes:scratch: I had hooked sensing wires up at wrong point and the damn things actually sang:rofl:

Feel better:D
 
Chokes are way to go after a quick listening. Right now on test rig they pick up a very small portion of hum (i had to stand a long time with the ear in the cone to decide if it was the amp or the radiator behind the bench) from nearby other iron, standing as microphones in the air, but thats fixable.

Hopefully now some tweaking ahead instead of problemshooting.
 
Well. I aint dead yet;)

Infact, I have been amusing myself by starting to fiddle with Arta. I'm ofcourse a total diaster on that to but atleast I managed to get some results.

First pic is testing my soundcards levels.

Then ofcourse I measured the 6V6, standing as it was, with a little bit of hum. Chokes 15 cm from powertrafo. Thats next graph.

Then I moved around a bit so the chokes came around 50 cm from trafo. Everything is still open and unshielded. Unfortunately the connections between SSHVs and load extended a bit, to around 15 cm. Graph 3. Still a 50 Hz problem thats plants some strange harmonics on the way. But quite a bit lower.

I have some groundingproblem still so I tested with removing yellow /green earthground from the audio circuits shielding box (that is connected with chokes. Pic 4. Look how it changes.

Yea. Its still very open and unshielded, standing on my computerdesk with screens and stuff radiating around. Look also as the highs seem to follow the highs on the soundcard.
 

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Last edited:
diyAudio Chief Moderator
Joined 2002
Paid Member
Only watch it not to drive large pk to pk into the card's audio input, it may not have clamping diodes for protection, watch out not to connect DC there too. Don't drive from the Wavetek cranked up and then FFT in the audio card in other words or tweak the pre when energized and hooked up to the card etc.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
P.S. Usually 24bit 48k is good, make sure its the same rate on any driver options for the card, use 65535 FFT (64k). In general if something's wrong with the sampling settings the sign is spikes come up on the chart's right side on self loop test.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
Yes the CF is proof for not adding gain still if a transient happens it can pass very large swing. Say a touch on input or a hot plug/unplug. You remember it passed intact the full 20V pk-pk of the Wavetek and was hungry for more. Its good to have the Zeners in general.