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Old 7th October 2010, 12:57 AM   #1
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Default miniblok 2 distorted sound

i built this amp but the sound is distorted is it because i used the wrong PP OT?

the one i used is rated at 10watts 10k and 60H.

both amps are distorted so i assume it's something in common to them. the design calls for a OT with 28 and 42 - 1 windings i'm not sure how this applies to this OT.

any help would be appreciated

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Old 7th October 2010, 01:51 AM   #2
kevinkr is offline kevinkr  United States
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Do some voltage measurements (B+, cathode voltages, grid voltages) and let us know the results. I once swapped center tap and the outer leg of the primary in an amp I was building, dc voltages measured fine, the amplifier behaved very strangely to put it mildly..

Is the -15V correct? The output section of each triode is operated with combination bias. (Both fixed and cathode bias) You did not swap the sections did you because these are dissimilar triodes. (Probably obvious, but best to know)

I don't think the transformer is the issue here, if anything the higher primary Z would result in somewhat lower power, higher damping factor and probably a little less distortion..

Do you have scope and a generator?

Some pictures of your build may help as well..
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine

Last edited by kevinkr; 7th October 2010 at 01:57 AM.
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Old 7th October 2010, 02:52 AM   #3
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thanks kevin

the B+ voltge is too low and the tank caps drain but without the tubes in they hold a good charge so i guess i made a wiring error and repeated it in both builds. i would like to post a pic but no cam.

im only getting 10.5 volts where it should be 15. probably where the problem is

it's good to know the OT is alright. the amp sounds really good in essence very accurate just need to get rid of the distortion. ill go over the wiring again tomorrow. maybe i have the zener in backwards or something
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Old 7th October 2010, 04:57 PM   #4
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fixed it. some shielding was shorting out the circuit. nice sounding project, highly recomended
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