[Harp-L] Re: Half Watt, Living Room, Harp Amp Design...



Some folks have advised of difficulties accessing the appropriate Myspace photo album, so here's a link to the Photobucket album...
 
http://s1083.photobucket.com/albums/j388/MWJB/
 
Regards, Mark.


________________________________
From: MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>
To: "harp-l@xxxxxxxxxx" <harp-l@xxxxxxxxxx> 
Sent: Thursday, 5 January 2012, 19:51
Subject: Half Watt, Living Room, Harp Amp Design...


After building a low powered but top quality (think Harpgear HG2/Fender 57 Champ/Kendrick Vagabond kind of prices), apartment friendly, practice & recording amp, I wanted to see if I could reduce build costs and still have a high quality, great sounding build.

Ampmaker is a company based in Woodbridge, Suffolk, UK offering great value-for-money kits & one of their chassis suited my needs perfectly, as did the Danbury 5W (190-0-190VAC) power transformer that they offer. (Note: the amp here & in the photo album/ciruit diagrams etc. is NOT an amp design offered by Ampmaker). The design can be easily adapted to fit the more common 5F1/5F2A style chassis, if an appropriate power transformer can be sourced (the 190-0-190VAC Danbury power transformer that I used has the same footprint as a 125P1B style Champ PT, it also has 120VAC primaries for US wall voltages).

The resulting "budget" amp is ironically better sounding & more flexible than the original build and was 2/3 of the cost parts-wise! It also has a low parts count, that & a simple circuit make it a very feasible DIY build.

If you go to... http://www.myspace.com/markburness ...you can hear all the clips & see the photo album "Ampmaker AC04 Chassis Based Harp Amp" for layout, schematic, cab designs & a bill of materials. For an XL file containing these items please feel free to e-mail me at... markwjburness@xxxxxxxxxxxxxxx

"Diatonic/Chro" - "Clean/Bright/Dark" were all recorded with a Zoom H2 placed 4ft from the amp, in line with the speaker (Eminence Alpha 8A).

Also, here are links straight to audio files of the amp moderately overdriven with tone pot fully up/CW for the "bright" clips (vol at 2 o'clock) & tone pot fully off/CCW for the "dark" clips (vol at 4 o'clock). The minimum of limiting was used just to shave a couple of peaks by about a db, in order to get the overall volume to a decent level.

http://www.mediafire.com/?v8l6vhsij97qd4b
Chromatic dark.

http://www.mediafire.com/?3obqwmu7nvdykz8
Chromatic bright.

http://www.mediafire.com/?mg7ir3yj947f6ur
Diatonic bright.

http://www.mediafire.com/?j1y6wwa9hgu7co8
Diatonic dark.

The amp uses a 6SN7/6H8C power valve (dual triode - 2 tubes in one) and a 12DW7 preamp valve was used in the above clips, as this gave the best flexibility accross both clean & driven tones. The amp is "push-pull" (like a typical 15W+ amp), rather than "single-ended" like a champ/<10W amp), the idea being that it should stay smoother throughout more of the volume pot sweep & late to "fuzz up". A switch can be easily added to go between push-pull and single-ended modes.

The amp will take ANY 12A#7 type preamp valve, including 5751 & 12BH7. Lower gain preamp valves, such as 12AU7/12BH7 might be preferred when using the line-out feature, where the sound at the on-board speaker is of secondary importance to that fed to the power amp/mixer. Conversely, where minimum volume is required from the on-board speaker, a 12AX7 might be desirable? In clean mode, the amp can be played at volumes barely higher than the acoustic instrument, but with the benefit of the sound coming back at you, rather than radiating away. 

The cabinet was built by Mark Phillips at AF Custom Cabinets.

Thanks for the bandwidth, Mark.


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