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Old 13th June 2018, 05:02 PM   #101
Gnobuddy is offline Gnobuddy  Canada
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Join Date: Mar 2016
Quote:
Originally Posted by THRobinson View Post
Down to the debate of 30w or 50w...
In case it helps - that's only a 2.2 decibel difference. If you were testing the amp with a sine wave at 30 watts, and switched instantly to 50 watts, you could hear the change - but it would be slight. One decibel is considered the smallest detectable change in level.

With the sine wave test tone removed and actual guitar music being played, I doubt one could even tell for sure if peaks were at 50 watts or 30 watts. If anything, it would be like the merest tiny smidge more volume.

There is a story I read on some audio forum, about a guitar amp tech who had a customer bring in his powerful 50 watt guitar amp (or something close), complaining that it was not quite as loud as it used to be. He was still gigging with it, but felt that it wasn't as powerful.

On the test bench, it turned out something was indeed very wrong: the amp was only putting out about 2 watts!

The thing that struck me, was the fact that the guitarist had been doing his normal gigs with a 2 watt amp for some time, before he even noticed he didn't have 50 watts at his disposal any more!

Other straws in the wind: Printer2 made a 2-watt guitar amp using a pair of 6AK6 output valves in push-pull, and measured around 104 dB SPL in the room with the amp at full blast. That is LOUD!

Inspired by Printer2's design, I also built a 2-watt, push-pull, 6AK6 amp. I put it through an 8" speaker rated at 92 dB / W / metre ( GRS 8FR-8 Full-Range 8" Speaker Pioneer Type B20FU20-51FW ), and it was too loud to use at full power at my weekly jams - I couldn't overdrive the output stage until I added a home-made speaker attenuator using an L-pad.

The same amp was not loud enough if I hooked it up to a thrift-store Sony boom-box speaker, which was much less sensitive. I don't have an official spec, but it was probably in the range of 82 - 85 dB@1W@1m.

Many gigging guitarists say you need 40 watts to compete with an acoustic drumset, so I believe that's true. But there's a reason most drummers wear earplugs - drums are insanely loud! Take those obnoxiously loud drums out of the equation, and you may very well find 2 watts is all you need or want for your guitar.
Quote:
Originally Posted by THRobinson View Post
...mahogany...small cheap bits are hard to find, being exotic/endangered woods and such.
This is one of those things that makes me sad whenever I stop to think about it. Mahogany furniture was everywhere when I was a kid, often with single planks two or three feet wide of solid mahogany. My mom had a clothes bureau made out of solid Indian Rosewood - big wide planks of it. Now, just a few decades later, those woods are endangered, and furniture like that only a distant memory.

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Originally Posted by THRobinson View Post
Sadly, no 1 place has everything I need...
I miss the days when my projects were straightforward, and the local electronics shops stocked all the parts I needed. These days I sometimes spend months accumulating parts, and then more months actually building, snatching an hour here and an hour there where I can find it.

-Gnobuddy
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Old 13th June 2018, 05:58 PM   #102
Printer2 is offline Printer2  Canada
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Join Date: Apr 2010
Quote:
Originally Posted by Gnobuddy View Post
Other straws in the wind: Printer2 made a 2-watt guitar amp using a pair of 6AK6 output valves in push-pull, and measured around 104 dB SPL in the room with the amp at full blast. That is LOUD!

I need to make another one of those, but then again I have so many ideas I want to get out. I am going with a 24V supply and one of those TPA3118 boards. I think it should be plenty especially at home. If you can't get the drummer to behave get a new drummer. Hearing is precious.
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Old 14th June 2018, 04:37 AM   #103
Gnobuddy is offline Gnobuddy  Canada
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Join Date: Mar 2016
Quote:
Originally Posted by Printer2 View Post
I am going with a 24V supply and one of those TPA3118 boards. I think it should be plenty especially at home.
I took my project from the "Portable Princeton" thread to my weekly jam last night, to test it at higher volume levels than I can use in my apartment.

It's a pair of thrift-store Sony speakers glued together, a Yeeco class-D board ( Yeeco 2X100W Dual Channel Digital Stereo Power Amp Module DC 24V Class D Audio Amplifier Board for 4Ω 6Ω 8Ω Subwoofer Sound System Speaker Car Vehicle Home Theater: Amazon.ca: Tools & Home Improvement ), a nominally 20 volt cordless tool battery pack, and a Joyo American Sound pedal for somewhat Fendery sounds. Last night I also used a Mooer delay pedal and a Biyang reverb pedal to take the edge off the Joyo's overdrive (and compensate a little for the lack of tubes in the clean rhythm tone). First in the chain was a Danelectro Fish-n-Chips 7-band graphic EQ to dial in a good clean tone.

All things considered, my kludged-together little battery-powered amp gave a pretty good account of itself - it was more than loud enough (and I don't think I got anywhere near clipping it.) Somewhat to my surprise, the pair of little 4.5" woofers coped just fine with my guitar signal, both clean for rhythm, and slightly overdriven through the Joyo for solos. Also somewhat to my surprise, the little speakers actually sound bass-heavy for guitar, though the Fish-n-Chips EQ pedal soon fixed that.

For reference, one of the other guitarists was using a Fender Acoustasonic 90, which she also uses professionally on stage with her country-music band. She plays rhythm guitar, at reasonable volume - not ear-blasting, but not whisper-quiet, either. My thrift-store-special amp let me play guitar solos at a volume comfortably balanced with the rhythm guitar from the Acoustasonic.

With the battery pack at 19 volts, I estimated a maximum output of 25 watts RMS per channel into each of the two 6 ohm speakers, assuming 2 volts lost to output device saturation and battery voltage droop. So, if those two weeny little woofers don't fry first, 50 watts total combined power from both speakers should be possible.

I also experimented with using my Digitech Trio+ pedal with the battery-powered amp last night. This pedal auto-generates drum rhythms and a bass line to go with your chord progression, and you can also loop a recording of your guitar with that. Everything worked, and the Trio's bass line was clearly audible, but the drums sounded boomy and lacklustre, because of the limitations of the little Sony speakers. (The drums sound much better through my usual P.A. system.)

I still want to design and build one or two microphone preamps and a simple mixer before the actual outdoor jam happens. But the basic guitar amp half of this thing already works.

So far, so good. I'm quite pleased with the way this has turned out so far.



-Gnobuddy
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