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Messages - SurreyNick

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Amplifier Discussion / Re: What Op Amp for 20W+ Busking Amp?
« on: August 08, 2019, 07:25:27 AM »
Thanks.  The OEP30w appears to be an excellent choice.   :tu:

Amplifier Discussion / Re: What Op Amp for 20W+ Busking Amp?
« on: August 07, 2019, 07:11:34 AM »
Thanks for the suggestions Phil

The Compact 2 x 20WRMS Stereo Amplifier isn't really what I'm looking for.  I prefer to buy an IC loose and build into my own circuit board, or at a push buy an op amp on a small pre-built board.  The Kemo MO32 could be a runner, but if I've done my calcs right with a 12VDC supply and 2x8ohm speakers in parallel it'll only give me 12W of power.  The speakers can handle considerably more than this.  I will consider the MO34 though, which is the 40W variant you mentioned, but at UK£25 just for the IC it's quite pricey!

I came across the TPA3110 and the TPA3118 and wonder if anyone has any views on their suitability?


Amplifier Discussion / What Op Amp for 20W+ Busking Amp?
« on: August 06, 2019, 11:02:24 AM »
For a bit of fun and to see what can be achieved, I want to build a compact busking amp using two Jenson MOD5-30 8Ω speakers which I have kicking around.  The speakers have a rated power of 35W and I was thinking of using them in parallel to give me a 4Ω load.  Power will come from one (or two) Ritar RT1250 which is a 5.0aH, 12V SLA battery.

I was thinking of using a TDA1524 in a pre-op stage, which should work well at 12VDC and give me controls for volume, balance, treble and bass.  What I can’t decide upon is what Op Amp to use.  Should I go for a dual channel op amp and try to bridge it (such as the TDA1554 2x22W power amp), or is there a decent single channel op amp I could use?

I want to get maximum power fully exploiting the potential of the two drivers, even if it means only getting an hour or two of play time.

Any thoughts on what op amps would work well?

Just gathering the components together for the build and I find contradictory recommendations for the pots and jack sockets.

In a couple of blogs/threads authors recommend a stereo socket for the input and I can't see why.  Most others recommend mono for input and output.  Is there any reason for a stereo input?

When it comes to Pots, for the Gain pot the original DIY MXR spec calls for a reverse log pot, but in a lot of threads/blogs there are various recommendations for log pots and also for linear audio taper pots.  There are three pots needed: One for Gain (1M ohm), one for Volume (500K), and one for Tone (1M).  I can find a 1M reverse log pot but the max power rating is just 0.1W and I don't know if this is sufficient.  For the best result what should I use?


Mmm. That's seems to be pretty much ideal. Thanks  :)

I think I'll still build the modified MXR, just because I've come this far thanks to all the help I've had here.  I'll post a picture up once it's built. Then I'll have a go at tackling this 20 watt beastie  :tu:

Some advice that will help;
1/ The circuit you post is not the best design as it's a pedal not really intended as a dedicated preamp, unless you just want distortion all the time with no real tone control.

If you want a small battery powered amp then just build a simple preamp and add dirt circuits afterwards.
Just track down some easy small amp circuits,, try Vox pathfinder 10 comes with clean and dirt. :tu: The preamp will work from single supply with some modifications.

Thanks for the advice, which I would love to adopt, but I fear modifying the Vox Pathfinder 10 (or similar) to run from a 12v SLA is a bit beyond my expertise.  I'm disappointed to hear my proposed approach is likely to have disappointing results.  I did try and find instructions for a 12v battery-operated amp with decent wattage but had no luck, 6W was about as good as it got and the design of that looked pretty poor.  :(

Also, I don't know how 1W resistors could give "better results".
Better how? Please define "better".

You only need higher watt resistors (1 watt and above) if the circuit demands require it.
Brush up on ohms law and calculate the current flowing in the circuit to determine if the higher wattage resistor is needed.

I certainly don't need higher watt resistors, by my calculations 1/2W is more than enough.  I don't know what the author meant by 'better' when he suggested a 1W resistor.  It was someone who posted online a variation of the MXR Distortion Plus and all the instructable said was "1/2W is sufficient, but 1W will be better".  No explanation what 'better' means.  I'll stick to 1/2W  ;)



I was thinking of using electrolytics for the caps rated 1uF and 47uF, any suggestion for the others (tantalum, ceramic, polyester, polystyrene etc.)?  I think the original spec called for ceramics, but just wonder if anyone has had good results with something else.  I'll be assembling on a veroboard or perfboard.

I believe 1/2W resistors will suffice, but I think I read somewhere that 1W will give better results.  Is this true?

Thanks galaxiex.  I think that sorts out the circuit now  :)

Out of interest what would the effect be of pushing 12v through this circuit instead of the 9v specified?  I know the LM741 is optimised for 15v and can take 22v, but would any of the component values need to be changed?

Thanks galaxiex

I'm building from scratch as I want to use this modified MXR Dist + as the pre-amp stage for a battery-powered amp.  My idea is to use a TDA2005 in bridged mode for the amp and drive a single Jensen Chicago 8/20 MOD Speaker (8 inch, 20 watt, 4 ohm) with the whole thing powered by a Ritar RT1250 12v 5.0Ah SLA battery.

Could you suggest what values I should use for the components which I have a ? against (see below)?

On Brian Wampler's modified schematic, off pin 3 is reference to 4.5 something. I can't work out if this should read 4.5v or 4.5uF.  On the Effects Layouts version it is shown as a cap rated at 1uF.

Off pin 7 on the Effects Layouts version is a diode marked D9. Any suggestion what one I should use?

Also off pin 7 on the Effects Layouts version is a cap the value of which looks to be 47uF.  That seems very high.  I've proposed 0.47uF in my drawing but is 47uF reasonable?

The only other question I have, which perhaps you could help with, is for the caps which should be ceramic, poly, electrolytic etc.?


OK I have had a go at drawing the schematic for the Effects Layouts version and this is what I think it looks like.  I have highlighted in pink the additions of the Effects Layouts version.  Is this what Brian Wampler intended?  It looks quite different.

A couple of the component values weren't clear so I have put a ? next to those too.

I’m confused.  I want to build Brian Wampler’s modified MXR Distortion Plus but the board layout I have found produced by storyboardist on the Effects Layouts blog ( differs from the schematic I found which is apparently the one produced by Brian Wampler and which appeared in the article in Premier Guitar.  They both claim to be from the same source though.  Are there two different Wampler mods to the MXR?

Both versions (see attached) have distortion, tone and volume pots, plus switches for smooth, bass and compression but the version on the Effects Layouts blog has 9 diodes instead of 8, has 7 resistors instead of 4, and has 9 capacitors instead of 7.  Some of the values are different too.

Am I going mad, and which of these two versions should I build?

Amplifier Discussion / 20 Watt Battery-Powered Amp Concept
« on: March 05, 2018, 05:55:14 AM »
I thought it might be fun to try and build a c.20 Watt battery-powered guitar amp from bits and pieces I have lying around and would invite thoughts and ideas on the proposal.

My initial idea is to use a TDA2005 in bridged mode for the amp, which the spec claims will typically produce 20 watts at 14.4 volts on a 4 ohm load, and precede this with a pre-amp stage based on the MXR Distortion Plus using a RC4558, the circuit driving a single Jensen Chicago 8/20 MOD Speaker (8 inch, 20 watt, 4 ohm) with the whole thing powered by a Ritar RT1250 12v 5.0Ah SLA battery.

The amp would only have volume and gain controls and the battery would probably be exhausted within two to three hours at full volume, but these are components I have lying around so I won’t have to go shopping for anything.  However I’m open to ideas, especially those where the build is quite straightforward.

What do you reckon?

Amplifier Discussion / Re: Power supply question
« on: March 04, 2018, 01:58:58 PM »
Definitely an option.  I have the 5Ah already so I'll start off with that, but taking your suggestion I'll build the cabinet so that if the amp works well I can upgrade to the 9Ah in the future.
Thanks :)

Amplifier Discussion / Re: Power supply question
« on: March 04, 2018, 12:38:53 PM »
Ah, that makes sense.

Yes, it's a guitar amp I'd like to construct using up bits and pieces I have kicking around.  My initial idea is a mono guitar amp employing a TDA2005 20W bridged amplifier with a pre-amp stage based on the MXR Distortion Plus using a RC4558, driving a single Jensen Chicago 8/20 MOD Speaker (8 inch, 4 ohm, 20 watts) and the whole thing powered by a Ritar RT1250 12v 5.0Ah SLA battery.

By and large 2 hours playing time will be enough anyway, so I like your proposal :)

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