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Topics - joecool85

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Amplifier Discussion / Highest efficiency 8" guitar speaker?
« on: May 11, 2011, 04:04:47 PM »
The best I can find right now is 93.2db/w spl and that is the 8" Jensen Mod 20.  Anyone know of an 8" guitar speaker with better output?  I can't mash a 10" into my K20-X, just won't happen.

There is also the 94.4db/w spl 8" Jensen Mod 20 C8R although some sites list that as 92.7db/w spl.

Amplifier Discussion / 5w boutique solid state amp?
« on: May 10, 2011, 12:43:59 PM »
It seems there are quite a few boutique 2-5w tube amps out there, some even smaller.  Fender, Epiphone and Vox all have ~5w tube amps as well.  Think there is any market for a 5w all solid state amp with the same minimal controls the tube guys have?  Normally the controls on these little amps are just volume and tone, some just volume! 

I was thinking that maybe a small amp with volume, tone and gain on it could be interesting.  Probably use a TL071/2 for preamp into a TDA2002 poweramp section feeding either an 8" Jensen Mod or a 10" Eminence Legend depending on what size cabinet you wanted to make.


Amplifier Discussion / Speaker level high pass crossover
« on: April 21, 2011, 12:06:04 PM »
My brother plays bass and just added a 2x10 cab to his setup.  He normally just uses his 1x15.  He likes to boost his EQ around the 30hz mark but the 2x10's hate that and distort badly.  So he has asked me to make a high pass crossover for him.  I'm thinking a ~10db of cut at 50hz should keep them from distorting.  We're going to try some different values to see what he likes best.  I just want to make sure I'm on the right track.

I used this site for the calculator:

And this one for some information:

His 2x10 cab is 8ohms (not sure if it's 2x16ohm or 2x4ohm inside, but that doesn't matter).

From what I figure, if we use a 100uF cap in series with his cab it would give us:

3db cut at 200hz
6db cut at 100hz
12db cut @ 50hz
18db cut @ 25hz
24db cut @ 12.5hz

Is this right?  If so, I think something I might make a switchable box with a 47uF and 100uF caps with a parallel position giving 147uF for 3 distinct crossover points.

Amplifier Discussion / "Fatboy Effects" by Ricky Don Vance (RDV)
« on: April 15, 2011, 01:22:52 PM »
Ricky Don Vance, RDV, passed away on February 5, 2010.  He was an avid guitarist that was into diy electronics.  He was one of the people from that suggested someone start a site all about solid state guitar amps - without Ricky, very well may have never come to be.  He was also one of our Moderators here as well as someone I was honored to call my friend.

Ricky shared many schematics and sound clips online and I have collected as many as possible.  

Enjoy.  We'll miss you Ricky.

I found a neat place for handles, speaker covers, cab corners and all kinds of other neat bits and pieces that are useful for our hobby via Google Ads - who'd of thought it would actually find something useful?  lol.

Anyway, here is the link:

Tubes and Hybrids / Hughes & Kettner Blues SS Clone
« on: March 24, 2011, 11:47:09 AM »
Hello all!

I am having a heck of time trying to get a little circuit to work. I am trying to do a tube to JFET conversion based on the preamp section of a Hughes & Kettner Blues Master. I already know how to do these type of conversions but the Blues Master uses a NE5532 chip in a bipolar configuration. I have a variac with plenty of amps and built a couple of rectifiers which produced +-15v but the thing just makes a low hum. Any pointers or tips would surely be appreciated

I tried many times to get my attached schematic pics up but they would not post in the original message. Now I cannot even open the message up to edit it with nonstop "Error 500" so I am adding this link to my schematics in hope that this will assist anyone out there that may be able to help me out:

Please help if you can - Thanks in advance  :o

Note sure what was going on, that one thread was damaged.

Amplifier Discussion / What causes a rectifying diode to fail?
« on: March 10, 2011, 07:56:30 PM »
I'm working on a Genz Benz Tranzamp g30 and it has at least two shorted out rectifying diodes.

When I got the amp on my bench it wouldn't power up.  It had a blown fuse.  Not seeing anything obviously burnt, I grabbed a new fuse and plugged it in.  When switched on the speaker hums really loud and when I disconnected the poweramp totally out of the equation I still get quite a bit of hum...but from the transformer.  If it stays on for more than 4-5 seconds, one of the rectifying diodes will start glowing and then start to smoke the PCB.  They are 1n4002 diodes.  I have 1n4004 on hand I am planning on replacing them with.

So my question is, should I be able to just put in the new diodes and be on my merry way?  Or is it more likely something else is wrong and that's what caused the original diodes to short?

Amplifier Discussion / SSGuitar Contest: Most Interesting Enclosure
« on: February 17, 2011, 09:04:31 AM »
It's that time of year again folks, time to give away some stuff.  This time the contest is for the most interesting enclosure.  It can be a custom built amplifier or a rehousing of an old one.  Whether it's in a shoe box or a VCR chassis, we want to see it!  To be eligible you must post at least one picture in this thread by March 6th at midnight EST.

The winner will get a free already stuffed LM3886 "amp on a board" from, valued at $50 USD.  Shipping will be paid for by  The winner will also receive 25 chip points.

Let's see your creations!

Amplifier Discussion / Mechanical connections - pots, jacks etc
« on: February 16, 2011, 03:01:07 PM »
Do you guys do anything special when attaching a pot to an enclosure?  I normally clip the "tab" so I don't have to drill two holes per pot, then hold it still from the back and put the nut on pretty tight from the front.  I've been thinking about selling some effects pedals and want to make sure that the pots don't come undone (board mounted to the pots, so it could cause damage).  I'm thinking about putting a knurled (toothed) washer between the pot and the enclosure the using a dab of blue loctite (the stuff made for being able to remove nuts later, and it recommends 2-3 drops for a 1/4" - 3/4" shaft).  Sound like a plan?

Do you guys do anything special?  Do you leave the tabs on your pots?  What about jacks?

The Newcomer's Forum / Where to begin?
« on: January 31, 2011, 02:15:10 PM »
So you're new to electronics and want to start building your own effects, amplifiers, guitars or repairing your old gear...where do you start?

Here of course!

If you don't have much prior electronics experience, I recommend reading this before you get too into things:

If you do know basic electronics (how capacitors, resistors and diodes work at least), I recommend getting your feet wet with a basic project like's Little Gem.  It is a 1/2w amp that runs on a 9v battery.  It's simple to put together and also makes an excellent "pocket amp."  I built one into a small clip-on radio that I got for $1 USD - now I can rock all around the house!

After you feel comfortable with that if you want to pursue a "real" amp I would highly recommend building a chip amp kit.  These are offered from several places, are easy to build, are normally very well designed and aren't too expensive either. offers a TDA7240A kit called the Tiny Giant (20watts RMS) that includes a built-in preamp so you can run your guitar straight into it.  For $18 this is the best deal I've ever seen for a quality kit like this. offers LM1875 (20watts RMS) and LM3886 (50wRMS) stereo and dual mono kits.  Stereo kits have two amplifier boards that share a single power supply board.  Dual mono kits have two amplifier boards and two power supply boards, this allows you to build two separate amps if you so choose.

Amplifier Discussion / Cool looking small copper heatsinks
« on: January 26, 2011, 03:31:34 PM »
I found some Swiftech MC14 heat sinks that someone used on a small amplifier over at

They are rated for 5watts, but I'd imagine that for our purposes they'd be good for ~10watts.  The guy at had two of them on his 20watt amp (one on a LM338 5amp voltage regulator) and one on the TDA7240A (20w audio chip).  I'm thinking it won't be enough heatsink for the TDA7240A if he drives it hard...but I could be wrong - I always over heatsink things.  I've never had a heatsink get hot enough I couldn't hold it in my hand indefinitely.

This was the circuit:

Tubes and Hybrids / Valvestate - tube magic or in my head?
« on: January 20, 2011, 07:22:20 PM »
This is in reference to my new to me Vox AD50VT.

I haven't ever owned a tube amp before (except for the 12v Sopht amp I built while in college) and wow, my Vox sounds awesome.  It just has a great sound to it.  Very clean, but warm.  And with the overdrive on it seems to be more mellow than my solid state gear.  That said, I've yet to get a good metal sound out of it even with an overdrive in front of it and in the highest gain setting.  I miss my Black Coffee Metal Pedal...

Back on topic though, is it just me, or is the 12AX7 really helping make the amp sound great?  Or maybe it's just that Vox makes a good sounding amp?  Whatever it is, it makes me want to play it ALL the time.  This is probably the most I've played guitar (in one sitting) since I started playing 8 years ago.

Amplifier Discussion / Fender Mustang I and Mustang II DSP amps
« on: January 13, 2011, 01:15:01 PM »
Anyone checked out the new Fender Mustang I & II amps?  They have 24 presets, 24 effects and all of them can be modified via USB connection to your computer with the included Fender FUSE software.  NEAT!

Musician's Friend has the 20w/8" speaker Mustang I for $99 right now and the 40w/12" speaker Mustang II for $199.  Both of them come with a coupon to get a free channel switch pedal in the mail if you buy it before 1/31/11 - oh yeah, and free shipping.  I'm really really close to getting the Mustang I and letting my brother in law have my coveted K20-X.

Forgot to note that you can also record via the USB for a direct to digital situation.

**edit 2**
Oh yeah, and it has a built in chromatic tuner.  This thing is packed with action-packed excitement!  Only down side is it is made in China and I try to purchase items made in the USA...or at least North America.  Although my current amp was also made in China...

Amplifier Discussion / Watts vs Volume (db)
« on: December 22, 2010, 08:56:56 AM »
Everyone seems to think that they need more watts to get more volume.  While it is true that more watts will be louder than less given the same speaker, it is also true that the speaker is more important than the watts in most cases.

For every 10db gain (double perceived volume) you need a 10x multiplication of wattage.  So a 100watt amp is only twice as loud as a 10watt amp.  The reason this doesn't normally seem so is that 10watt amps normally have poor spl rated speakers, making the 100watt amp sound more than double the volume.  Playing through a better speaker will help increase your db rating, and hence your overall volume.

I've attached a chart to give you an idea of how an efficient speaker is louder than more watts on a less efficient speaker.

With this chart you can see that a 90db speaker on 100watts is less volume than a 102db speaker cab with only 10watts.  Most inexpensive amps come with speakers of about 90-93db.

To keep up with an average drummer you will want about 110db.  To reach this level you could use a 100watt amp with a single 90db speaker or you could run a small 10watt amplifier through a cab with rated 100db or better.

The calculation for total db is this:
{log (watts of amplifier) x 10} + speaker spl rating in db at 1w = total db output

Or if you want to figure out what db speaker (or cab) you need to hook into to get a certain desired db output:
Desired db output - {log (watts of amplifier) x 10} = Necessary speaker/cab db rating at 1w

Here is an excellent calculator for adding up speaker db and finding what the total output is:

And thanks to Roly, another good table:

Speaker sens. (1dB/W@1m) Required power (watts)
Listener range 8 feet, desired listener SPL 80dB, amp headroom 15dB

Does this look like it would work?  I would like to take just the OD circuit from the Dean Markley K-20X (as seen here: ).  Will this work?

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