tightening up the trainwreck lowend

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RJ Guitars
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Re: tightening up the trainwreck lowend

Post by RJ Guitars »

Thanks Guy,

If I was to speculate what has happened: the 1uF cap simply reduces the signal, especially the low end response. Reading in Merlins book this is exactly what you might expect when reducing the size of the bypass cap.

This might be a mimic of what is happening when you substitute in a 12AY7. If I speculate further, considering the finicky nature of these amps we know that just any 12AY7 isn't the answer. You need a "special" one. Perhaps you (and those that suggested this mod) have found another great avenue around tube rolling to dial in your Express. This is greatly helpful in the event you don't have a major stash of tubes to roll thru.

Reading 67plexi note above I find the 500V B+ to be an interesting tidbit as well. There is a community that believe you don't get the best out of an EL34 until you get the voltage up into this range... but most of those guys don't hang around here. I haven't experimented with it myself but that almost seems like a whole study unto itself.
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Guy77
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Re: tightening up the trainwreck lowend

Post by Guy77 »

After doing an A/B test .... yes you were correct RJ. When going from the 22uf to the 1uf cap there was a definite drop in volume and there was also a drop in low end response.
After trying many different size caps and spending some time playing , I took the switch out and settled on a 4.7 uf cap.

Cheers!

Guy
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RJ Guitars
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Re: tightening up the trainwreck lowend

Post by RJ Guitars »

That is a great test and a great report to put into the archives here. Thanks for posting the results.

There is a guy that hangs around here sometimes called "Zippy" (I think the name has something to do with his BMW biker days) that mentored me through the early days of my amp building efforts. He always advocated taking these kind of mods and putting them on a rotary switch, then giving it a clever label. This something that would be very useful if you were switching between a Tele and Les Paul or some situation like that.
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Roe
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Re: tightening up the trainwreck lowend

Post by Roe »

Guy77 wrote: Sat Jul 30, 2016 10:07 pm After doing an A/B test .... yes you were correct RJ. When going from the 22uf to the 1uf cap there was a definite drop in volume and there was also a drop in low end response.
After trying many different size caps and spending some time playing , I took the switch out and settled on a 4.7 uf cap.

Cheers!

Guy
-update:
I've settled on a 3u3 at the second gainstage. the .68u gave tight bass but it sounded too bright in the mids. I'm also considering a 3u3 at the first gainstage. And the phase inverter input cap is changed from 100nf to 2n2
Last edited by Roe on Tue May 02, 2017 6:41 am, edited 1 time in total.
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BillyBob
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Re: tightening up the trainwreck lowend

Post by BillyBob »

I am also a high gain player most of the time.

What power tubes are you running?
What speakers are you running?

I've built two Express amps. JJ KT77 output tubes gave me more bass, and harder/tighter bass.
NOS EL34s were a bit flubby in bottom end
Roe
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Re: tightening up the trainwreck lowend

Post by Roe »

I'm only using RFT/Simens el34s, biased hot. Speakers are celestion, scumback, weber. I like both g12Ms and G12Hs
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Roe
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Re: tightening up the trainwreck lowend

Post by Roe »

Roe wrote: Mon May 01, 2017 3:44 pm
Guy77 wrote: Sat Jul 30, 2016 10:07 pm After doing an A/B test .... yes you were correct RJ. When going from the 22uf to the 1uf cap there was a definite drop in volume and there was also a drop in low end response.
After trying many different size caps and spending some time playing , I took the switch out and settled on a 4.7 uf cap.

Cheers!

Guy
-update:
I've settled on a 3u3 at the second gainstage. the .68u gave tight bass but it sounded too bright in the mids. I'm also considering a 3u3 at the first gainstage. And the phase inverter input cap is changed from 100nf to 2n2
with a pacific OT, the bass is tighter. Will consider increasing the 3u3 caps on v1a k and v1b k
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