MindTheGap
390 posts
Mar 26, 2014
1:17 AM
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I was considering putting in a lower-gain preamp tube in the 5W amp but then tried ditching the mic impedance transformer and just using a XLR to 1/4 cable. I could then get turn up the volume from 3 to 8 (out of 10) to get a similar sound.
Is there likely to be a some other advantage in using a lower gain tube?
PS, it was a trick getting the title short enough, and look, a typo :(
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mtg
Last Edited by MindTheGap on Mar 26, 2014 1:18 AM
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rockmonkeyguitars
46 posts
Mar 26, 2014
5:09 AM
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Missmatching impedance tends to give you background noise and hum. If it's low Z into Hi Z then your 1st gain stage introduces hum you don't want. If it's Hi z into low z then you get line noise amplified that you don't want. Either way you lose. You get a lot less background noise if you properly match impedance and simply use a lower gain preamp valve
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MindTheGap
395 posts
Mar 26, 2014
5:35 AM
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Ah, ok. Thanks. I didn't notice any hum but it was in noisy rehearsal situation. I'll try in the quiet.
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mtg
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isaacullah
2699 posts
Mar 26, 2014
7:28 AM
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If you DO get hum with no X-former, then another option to consider is to add a second "low-z" input. You don't seem to be afraid of the soldering iron, so you may want to do this. It's rather simple, actually: check out the instructions for modifying the the input of a Epi VJ here: http://lonewolfblues.com/projepimod.html. The same mod will work in your amp too.
I did this mod to my EVJ, and it works a charm. I can get the same tone with my Behringer XM8500 mic into the low input as I can using an X-former into the high.
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Greg Heumann
2658 posts
Mar 26, 2014
7:49 AM
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The impedance mismatch ALSO changes the frequency response of your mic - but if you're happy with the results - just use it. You won't hurt the mic or the amp doing this.
The more common problem I see is people doing what you're doing (using a low impedance, balanced output mic with a high impedance/unbalanced cable) and not even knowing it is technically incorrect.
You WILL find that this solution won't work if you add a volume control like my Low impedance XLR volume control.
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DukeBerryman
299 posts
Mar 26, 2014
8:48 AM
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I struggled with this issue - I was never able to turn up my amps past 2 or 3. But then I worked out the impedance issue, added a volume control, and now I run my amps all the way up. Changed my life, haha. Turns out every amp in the world wants to used wide open. Same with a guitar plugged in. I would start with your amp wide open, and change your mic rig to suit your amp.
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MindTheGap
396 posts
Mar 26, 2014
12:20 PM
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Thanks for the suggestions. I tried in a quiet room and it doesn't hum or hiss, and I can't tell any difference in tone. I guess it depends case by case.
Yes, I know it's wrong technically. I don't feel good about that, so maybe the more conventional low-gain tube is the thing.
Isaac - thanks for the alt-input idea, I'll investigate that.
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mtg
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