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Old 24th April 2012, 04:13 PM   #1
maurycy is offline maurycy  United States
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Default My DIY guitar amplifier based on Hitachi HA13118

Inspired by this post, I have decided to build my own small guitar amplifier. The whole build process took me few months but only because I lack time for such projects.

Here are few pictures from yesterday when I finally put the whole thing together:

Box made from pine, stained with polyurethane clear coat on it. Do not laugh at my woodworking skills.
picture 1
picture 2

Front baffle with Jensen MOD speaker. Again, do not laugh at the jagged edges. I do not own a router, only jigsaw.
picture 3
picture 4

Power supply with amplifier board in a plastic box. I have decided to remove the volume pot since I have one on my guitar. Added the switch, LED and fuse. There are few holes drilled on the sides and on the back of the box to help with air flow.
picture 5
picture 6

Assembled box.
picture 7
picture 8
picture 9

The power supply has four 3,300uF capacitors to help smoothing out the DC. Transformer was pulled from a few years old Verizon DSL power supply and measures 13.20V AC. I will have to add another rear cover on the bottom since the build changed a bit once I have decided to build my own power supply.

So far the amp performs nicely. There is a noticeable hum when no guitar is plugged in. The hum goes down when I plug the guitar in. The gain is kinda high since the volume is pretty loud on 2 setting on my guitar (goes from 0 to 10). Overall, I am very satisfied with this build and just wanted to share.
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Old 24th April 2012, 04:44 PM   #2
sreten is offline sreten  United Kingdom
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Hi, You have hum because you've omitted the volume control, rgds, sreten.
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Old 26th April 2012, 05:19 PM   #3
maurycy is offline maurycy  United States
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So now, I have a question. If I do not want to have a volume pot in the amp since I have one in the guitar, should I just bypass it? That's what I have done but now I have this hum.

Here is the schematic:
schematic

Thanks.
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Old 26th April 2012, 06:18 PM   #4
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I think you did a great job with what you had to work with. As for the hum, I agree with Sreten. The hum is because it is running at maximum volume. Have you thought about using a switching 1/4" input jack? Wire it so the input is normally shorted to ground but when the guitar is plugged in, the "tip" goes to the amp input.
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Old 26th April 2012, 06:33 PM   #5
maurycy is offline maurycy  United States
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I can definitely put a switching input jack.

Besides that, is there a way to lower the power of the amp? As I have mentioned, the volume pot on the guitar goes from 0 to 10 and at 2 it is very loud. After the rectification factor, I think I am running very close to the maximum 18W output as my speaker is 4 Ohms and the AC on the transformer is little over 13V. Ultimately, I would prefer to use a wider range of the guitar volume pot than to be stuck with range of 0-2 only. This is a small practice amp and I do not need a lot of power.

Thanks.
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Old 26th April 2012, 06:57 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

The point of a volume pot on the amplifier is so your guitar can go to ten.

rgds, sreten.
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Old 26th April 2012, 07:03 PM   #7
maurycy is offline maurycy  United States
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Quote:
Originally Posted by sreten View Post
The point of a volume pot on the amplifier is so your guitar can go to ten.
OK, I think I know what's going on. The volume potentiometer on the guitar is 500K and the recommended one for the amp is between 10K and 50K. Is that why the slight change of the pot on the guitar bumps the amp volume almost to the maximum?

So should replace the pot on the guitar with a suitable pot for the amp or just add one on the amp side?

Thanks.
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Old 26th April 2012, 10:38 PM   #8
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Don't change the pot in the guitar. There is a reason why they used a 500K pot in the guitar and not a 10K.

If you are absolutely against having a volume control in your amp, use fixed resistors to lower the overall volume level. Put a pot in and adjust it to the volume level you require. Take the pot out and measure it with an ohmmeter and use these resistor values.

If you have the time you may want to experiment by adding an input buffer or tone control circuits to the amp.
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Old 27th April 2012, 02:34 AM   #9
maurycy is offline maurycy  United States
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The space is tight but I can add a volume pot to the amp. That would probably be the correct way of fixing the problem.

Thanks for all the replies.
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Old 12th May 2012, 10:34 PM   #10
n4vgm is offline n4vgm  United States
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Would I need to modify this at all for bass guitar?
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