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PostPosted: Fri Jan 20, 2017 1:58 am 
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Joined: Fri Jan 20, 2017 1:52 am
Posts: 2
Hello

Both normal and TMB channels on my TMB build have close to 0 overdrive saturation, even with preamp volume maxed out.
The clean sound is really good, I admit, but I cannot get any overdrive. The only overdrive appears with high output humbuckers and master volume at noon or more - then some signs of (slight) crunch appear.
I assume this is a preamp issue. Power amp to me works as it should.
I tried to trace the board for errors, I did not find anything apparent.
The amp is loud and clear, no buzz, noise etc - all seems OK except the lack of darn distortion.
Can you tell, from your experience, the possible culprits/typical causes of such behavior?

I will check again the components values, connections etc but any suggestions are welcome.

Thanks

Gitarzysta


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PostPosted: Fri Jan 20, 2017 1:51 pm 
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Joined: Wed Apr 26, 2006 5:14 pm
Posts: 8659
Location: Truckee, CA
Hi - welcome to the forum!

This is an interesting issue - even with very low output pickups, you should get plenty of overdrive by noon on either volume control.

Here are some suggestions:
- Eliminate all the potentially silly stuff; make sure you are plugging a known working guitar straight into the amp using a known working cable; plug into all of the input jacks; etc
- swap the pre amp tubes around to see if the amp's response changes at all
- the breakup in the normal channel doesn't happen until the phase inverter, so I'd suspect a preamp issue like you mentioned (preamp not passing enough gain); TMB channel should generate plenty of OD on its own before hitting PI, which also suggests preamp issue and not PI or power amp.
- Check your voltages - I wonder if your preamp plate voltages (ECC83 pins 1 and 6) are very low: http://www.byocelectronics.com/board/viewtopic.php?f=49&t=52297
- Post clear, in-focus pics of your build to get more eyes on component placement and wiring

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MasterDelayer/Reverbrador/Ampaholic/TopJacker


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PostPosted: Sun Feb 05, 2017 2:51 pm 
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Joined: Fri Jan 20, 2017 1:52 am
Posts: 2
OK, I'm almost there - the board I bought was already populated and some component values were off completely - now they are exactly as Trinity TMB 18W in the preamp section. Then I noticed the master volume was wired not as it should be - I converted to PPIMV.
And yes, I changed PI tail resistor closer to a typical EL34 application vaule.
Now the sound of the amp puts a smile on my face :)
There's a couple more mod I'd like to try: cascading gain to begin with and see if I like it. I am also tempted to try to convert the whole preamp to a JCM800 type.

Anyway thank you all for suggestions :D


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