New Amp Demos

Here is the first demo of my new battery powered amp  described in the last few posts – more demos to follow this week.

The tracks will all be recorded on a Tascam handheld recorder with the built in  MICs @ 1 foot from the speaker.

Demo 1 : No reverb – jazz tone on floating pickup arch top – simple chord melody

https://circuitsaladdotcom.files.wordpress.com/2013/04/walking-my-baby-home.mp3

Demo 2: Old beater electric guitar, small room reverb, lot of treble, bridge pickup and noodling around on B minor. As a side note: I am also using  some compression with the newest opto-compressor described in a previous  post.

https://circuitsaladdotcom.files.wordpress.com/2013/04/bathroom-tile-blues.mp3

More Amp Updates – Revised schematic – Very minor mod to PCB – this should be it!

I have one guitar that belts out a huge signal from the neck pickup. I was able to  make the first stage just start to distort. To correct this,  I have changed R5 to 1K and R3 to 4.7k  also I have un- bootstrapped R4 and directly connected to ground. I thought the bootstrapping was a good idea – I must have eaten too many Twinkies that day.  C30 and R29 are still optional but could be used to give treble boost or hi/lo gain boost etc.

If you have already obtained the earlier board rev, you need to cut the trace from the emitter of Q1  going to R4 and ground that side of R4 to the ground plane.

I am posted a link to the new board rev here and obsoleting the schematic and layout in the old post. All I did was eliminate this trace and add a couple of wire connection pads to allow making R29 a POT for variable gain. If you have the old board it will work just fine – with the mod described above.

Updated Schematic:

https://circuitsaladdotcom.files.wordpress.com/2013/03/portaamprev1-1-1.gif

Updated Layout:

http://www.fileswap.com/dl/EDZsklrqcT/

Couple other minor notes: C16 may need to be increased to 22pF or so if you have a sluggish crystal –  had one out of five that needed the bigger cap. Also with the mods above you may find that C21 should be increased to .22uF or more depending on the range and level of treble boost desired.

Portable Battery Amp – thru-hole version Schematic and layout link

Took me awhile, but here is the new design. It’s very similar to my original design https://circuitsalad.com/2012/08/31/20-watt-battery-powered-guitar-amplifier-circuit/. I am still  using the FV-1 DSP chip for reverb which sounds great – but you can leave it out. I moved the position of the volume control after the first preamp and this helps the loading of the guitar and improves the noise figure a bit. I added a presence control in the negative feedback loop between the final amp the driver stage – this really adds some nice high end sizzle – if that’s your thing. The topology including: the fender type tone stack and the output feedback from the speaker back to the driver is much like a classic tube amp and to my ear has a nice sound. One big change was the replacement of the JFET preamp stages with Darlington transistors. You can make your own out of two generic npn’s or use another than the one I specified. Alternatively, you can use a Mosfet like a 2N7000. This may require some adjustment of the biasing. The reason I changed this was that the JFET biasing from device to device was fussy and so my schematic biasing values did not always work out correctly. The Darlington biases very consistently and I love the sound. Another reason was just for the fun of it ( don’t usually use the Darlington much).

Lots of options to adjust the tone stack, treble boost  in the first stage, the feedback loop on the final and the reverb tone shaping. I am sure if someone puts some effort into it, they can dial in some further improvements. The FV-1 has multiple selectable effect programs. The last reverb program is hard wired( all three pins pulled high) but these traces are on the bottom and can easily be cut. There are ground connections right next to these pins so that  one can cut a given trace and connect the pin to ground,  changing the program.  The FV-1 has a good data sheet and explains this in more detail.

The final amp is the TDA7396 which is capable of cranking out up to 65 watts(2 ohm speaker) – it is easy to work with and current in production. It works well with 10 – 16 volts and in this design is intended to be used with a generic SLA 12 volt battery or  a 12-14 volt @ 3 amp supply.

There are only a few surface mount parts, the PMOS FET I use for polarity protection, the FV-1 and the 3.3volt regulator. The polarity protection can be left out or a rectifier can be used instead. Other 3.3v regulators can  be used also. If you leave off the FV-1 – you don’t need the regulator at all or the two reverb controls, and it will just work as is.

the controls on the AMP are: Volume, Treble, Bass, Reverb room size, Reverb level and Presence.

For the speaker I used a $22 Jensen 8″ MOD 4 ohm. I highly recommend this speaker – its cheap and sounds just right for this amp.

Go here for the correct schematic and layout:

http://www.circuitsalad.com/2013/03/27/more-amp-updates/

Schematic: 

https://circuitsaladdotcom.files.wordpress.com/2013/03/portaamp31.gif   (updated in later post – do not use)

Link to the expresspcb layout:

http://www.fileswap.com/dl/mp258DXnm/ (updated in later post – do not use)

Prototype Images (the posted board artwork is slightly different than what is in this image because of corrected errors):

IMG_5307

IMG_5305

IMG_5313

New Amp Completed

IMG_5318

New Amp Showing Back

IMG_5319

14.4V Drill Battery Power Pack

Sound Clips: (coming this week)

20 Watt Battery Powered Guitar Amplifier Circuit

 

This is an amplifier I designed for busking and just so I could play crazy sounding stuff in the fields around my house here in Sandy Mush.  The design is tailored around some key criteria, namely; be able to provide 15 – 20 watts from a nominal 12 volt supply (10-16 volts), have a tube amp sound, reasonable simplicity and great sounding reverb. I am very pleased the final design. This is my primary practice amp now – mainly because I love the way it sounds and also I like seeing the bile drool out of the mouths of my mortified neighbors as I “rock out”.

I am posting links to the original schematic and a version without the reverb – which simplifies the design a bit. I am also posting some pictures of the circuit board, a completed unit and some sound samples.

NOTE* Have updated design and thru-hole layout here: https://circuitsalad.com/2013/03/16/portable-battery-amp-thru-hole-version-schematic-and-layout-link/                                                                                                                                this new version uses a new final amp TDA7396 (TDA7360 discontinued)

Click Here To See and Hear:

Schematics:

https://circuitsaladdotcom.files.wordpress.com/2012/08/portaamp.gif

https://circuitsaladdotcom.files.wordpress.com/2012/08/portaamp-no-reverb.gif

Pics:

https://circuitsaladdotcom.files.wordpress.com/2012/08/20-watt-battery-amp.jpg

https://circuitsaladdotcom.files.wordpress.com/2012/08/battery-amp-circuit-brd.jpg

Samples: recorded with DR1 pocket recorder about 2 feet away

 Neck pickup,  bass/treble middle setting – no reverb

https://circuitsaladdotcom.files.wordpress.com/2012/08/dry-blues.mp3

 Bridge pickup , bass/treble middle setting – small room reverb 1/3 depth

https://circuitsaladdotcom.files.wordpress.com/2012/08/not-fade-away_small-room.mp3

 Neck pickup,  bass/treble middle setting – large room reverb 1/3 depth

https://circuitsaladdotcom.files.wordpress.com/2012/08/large-room-reverb-noodle.mp3

Features:

Power – I used as the final amplifier a TDA7360 car stereo amplifier in bridged mode. This amp sounds great and can provide 20 + watts through 4 ohms with a 14v supply. Some may shuddered in horror at the thought of this used for a guitar amp, but it really works well and is reasonably efficient, requiring only the circuit board ground plane as heat sinking. I use a small lead/acid gel cel to power this amp but also have used drill batteries and a computer wall wart, etc.

Tube Sound – To achieve a tube like sound I used a classic fender type tone stack, discrete signal chain using jfets (up to the power amp) and negative feedback from the speaker to the final preamp stage. If you look at the circuit, you can see that basically all of the active devices could be replaced with tubes and the TDA7360 with a couple of output tubes and a transformer. The negative feedback from the speaker is a classic technique in tube amps and applied here, has a noticeable effect on the sound.

Simplicity – I set a limit on physical size and number of knobs which forced me to keep it simple.

Reverb – I thought seriously about integrating a spring reverb, but went with a DSP circuit, the FV- 1  chip, instead. This IC provides a number of reverbs and other effects which are selectable via switches(jumpers). It is easy to use and I was able to color the reverb with filtering to my taste. It is essentially an effects  unit on a chip. I very pleased with its performance. The reverb has both room size and depth control, and provides all kinds of variation.

Design Notes: There is flexibility in this design – you don’t have to use a switch mode 3.3v power supply for the FV-1 like I did – you could just use a linear regulator. I use a PMOS FET as a  NO VOLTAGE DROP protection diode. This could also be omitted. I hate to lose .7 volts with a regular diode though – so I recommend the PMOS approach. The choice of JFET was based on what I had kick’n around – nothing else. I also tried it using LND150’s with similar results. My tone stack is nothing special and many other variations could be used. The volume control at the very front may seem odd. In fact, at very low volume settings, there is treble roll off because of stray capacitance of the POT. The reason I did it was to maximize headroom of the preamp stages and simplicity.  This is a design choice that merits a second look. The amount negative feedback from the final to the driver stage is adjustable or can be omitted. A high-end treble control (presence) is realised by bypassing this feedback for very high frequency. This too can be omitted.

For the speaker I used a $22 Jensen 8″ MOD. I highly recommend this speaker – its cheap and sounds perfect.