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Messages - dogbox

Schematics and Layouts / Re: LR Baggs Piezo-Pickup preamp
November 02, 2015, 08:27:52 PM
Quote from: J M Fahey on October 28, 2015, 08:59:40 AM
That L R Baggs preamp is *very*  good.
I just calculated the "mystery gyrator" frequency and it's surprising (or not? ) 95 Hz
Clearly it adds body to turn usually famigerated "Piezo shrillness" into nice warm fat sound, without losing top frequency transparency.
AFn excellent design ... although you'll have to design your own PCB .

This one is for dual mics, Piezo and Magnetic, if you use just the Piezo, you can simplify the design quite a bit, since you need neither the Magnetic preamp nor the mixer, in that case V1 volume pot can straight go to output jack.

That's very interesting JM. Can you explain how you calculated the frequency affected by the Gyrator, I'm geussing the Gyrator (i had to google gyrator to find out what it was :-[), acts as an Inductor, so is it some kind RLC filter..maybe a bandpass?? Am I completely on the wrong track?? I've been recently playing around with some homemade piezo disc pickup/contact mics. Still yet to get that magic sound. There sure are a lot of schematics on the web and ideas about how to tame these piezo devils.

Have tried Tl072 chargeamp based circuits, and various well known things like Tillman and offshoots. I got a some largeish discs, some salvaged from buzzer, and these really small ones that are very trebley/high end. Have tried mounting the bassy one and the treble disc feed into a 2 stage jfet preamp that I found on a ham radio site, I added 10m input resistor. I then added a passive mixer - just 2 -  10k pots - 10k resistors. It works but the larger disc really over powers the smaller. I only have 1k, 10k, 20k pots on hand. I tried a 20k pot on the smaller and got more signal in the mix. But it lacks a bit of sparkle, and its now lost a bit of volume.

keen to give this one try on the breadboad before I get out the soldering iron and commit to my lastest version. I have mpf102, and some BC 54x . Would they be ok this LR Baggs circuit?? If you have suggestions..I'm here to learn..cheers
Tubes and Hybrids / Re: Red Knob Fender Champ 12
September 02, 2010, 02:50:15 AM
Quote from: J M Fahey on September 01, 2010, 12:35:18 AM
Start by plugging some audio in the CD inputs, tell what happens.

Hi JM,

Tried that on your suggestion - so far no sound!! Hooked an RCA cable from amp to a ghetto blaster -  switched on the ghetto blaster, then switched on the sound output from the amp.

What next???

thanks for the assist.
Tubes and Hybrids / Red Knob Fender Champ 12
August 31, 2010, 07:59:38 PM
hoping someone can shed some light..
I powered this up the other day, the light comes on but the sound isn't there. There is a really weak signal still coming through - to give an idea how low the volume I can hear the strings being strummed.

I checked the fuse -in tact.
Does this sound like a valve has blown?? I would like to try and fix myself, but have limited knowledge of amps (done pedals and kits) no real experience with mains voltages/valve amps

Any suggestions appreciated on how to tackle this.
Hey Phatt,
That looks great. I take it that IC is an opamp? If so, which do you recomend? I have a bunch LM741's would that work??
Yes true Beenleigh is getting that way too, we were part of Albert Shire (gold coast) then swapped to the Logan Shire after the last election - so you could say we went from Gold Coast North to Woodridge South in one foul swoop ;D

Breadboarding this pre looks like a good project for the weekend-after a trip up to Jaycar on saturday morning.
cheers for that..
Thanks for that Phil. Yep another Queenslander, living at Beenleigh for many years :D I actually grew up in the 70's at Tewantin, and in those days Nambour was considered the big smoke-it used to be the capital of the Maroochydore shire council at one stage!!! Times have changed huh? A number of years ago they moved the hiway didn,t they?. In some ways that could be seen as a good thing-from what I have seen of the rest of the Sunshine Coast has gone mad-they are loving it to death...

OK then, a double-"no" to my questions - I'm thinking the Phabtone may be better suited going into my Epiphone valve Junior which has one volume pot? Not a bad little amp but definitely could benefit from some tone controls PRE the input jack as its a bit of a one-trick pony?  It does sound great with pedals though.

Will try and track down your preamp schemo-haven't found that one yet. Yeah I definitely have got the breadboarding bug and slowly building up a part stash, only working on 9v stuff so far - Ruby amp, tillman jfet preamp, fetzer valve etc etc soldered a couple of jaycar and effects pedal kits - love this stuff.

Will be getting around to doing a LM3886 kit from in the future-have it here, just afraid of getting zapped if/when I start playing around with mains voltages. Will probably annoy the heck out of everyone when I get started on that project ;D

Plenty of reading to be done first though - this forum is a great resource.

cheers Mate
Hi Phatt, thanks for sharing these schematics and all your other info. I plan on breadboarding the Phabtone soon when I get my hands on some TL072's (next trip to jaycar). I was digging around and checking out some your old posts - Your sound clips sounded great!!!

A couple of newb questions...bear with me  as I don't have any history of electronics. Just what I have read on forums, books for past few months.

You mentioned on some older posts that the tone stack section was from a Hiwatt amp.

1. Would it be possible to take the input/tone stack section, say everything from the left of C6 in your Phabtone schematic and add that to ANY low watt SS amp circuit? For example, looking at the runoffgroove schematic for a Ruby amp (apologies if you don't have one handy) - could I take your input section and wire it to pin 2 of the lm386 used in the ruby - kind of in the way there is a Fetzer ruby or Marsha ruby?

2. How would either the tonestack or whole phabtone go as the pre for a LM3886 amp?

I should state that i'm looking for clean(ish) amp tones and tend to use pedals when i want distortion. Is the phabtone what I should be looking at?

Nambour hey ;)!! Not much desert there, in fact the soil is sooo good just look at how big the pineapples grow:)
Also the birthplace of our former Primeminister - Kevin 07 - lets not go there shall we :'(
Quote from: mnturner on April 18, 2010, 09:32:01 AM
hey dogbox,
I just found out about those little valves, I'm pretty interested in getting some to put into a preamp.
How much power do you plan on getting out of the IC amp? LM386's can only really dissipate about 1 watt, which isn't much. And the THD quoted on the datasheet is 0.2% at 125mW, which is fairly high compared to other IC amps. I think you should check out the LM3886, it can produce much more power and has better distortion figures and is pretty much as simple to use as the LM386. That way if you decide you want more power you don't need to build a whole new amp. The only problem you might have is the power supply, the 3886 needs a much higher voltage than the 386; the best way to do it is to run it off AC which is a bit more complicated than using batteries. The 386 isn't a bad option if you only want a tiny practice amp though.
Hi mnturner,
Yeah that jan6418 tube preamp works well-but a bit delicate. Theres a trimpot and 2 sets of dip switches on kit that I built so can equalise and adjust the output to suit whichever amp I use. The only down-side is that the tubes are really microphonic and tend to ring if bumped in any way while being played. can end up with a high pitched squealling feedback real easy - have tried damping with rubber grommets - not made much difference. Its fine for home recording use (if your real carefull) but definitely not good for stage use as any vibrations seem to set off the ringing!! I need to use some kind of padding inside the case and really lock the mini tubes down somehow - thinking about dipping them in liquid silicone rubber?? Unlike normal tubes - these give off no heat or light that I can discern - so maybe thats feasible.

Yes i now have a lm3886 kit from and looking forward to building that one real soon. Have been distracted with playing around with jfet preamps, piezo disk contact mics, ruby and noisy cricket amps, effects and more effects. The penny is dropping and I now can understand schematics and breadboard up small projects. Awsome fun.

Good luck with the mini tubes.
Quote from: phatt on January 22, 2010, 12:09:42 AM
Hello Destroid,

Re this; "I really want to keep my options open in terms of Solid State since I want an amp that'll **sound the same recorded as it does live**."

My setup would qualifiy in that regard, 8)

Of course you would have to build it DIY.
Just wondering exactly what you guys mean by the statement "sounds the same recorded as it does live"?? Maybe I'm reading this wrong and your talking about volume levels and how hard you can drive the amp at low levels in the home environment-if thats the case then ignore the following rant:)??. Any amp can fall into that category - its not up to the amp on its own -  its up to the mics used and the location you record in to an extent. I don't claim to be any expert but have been mucking around recording at home for the past 15 years and have recorded in studios since the early 80s. Sometimes you make a really crap amp sound better after its recorded (pretty rare though).

A trap that many fall into is that when you are playing with your band- jamming and at gigs etc, you kind have a picture in your head of your guitars sound. What you really hearing is your guitar in a "mix" with all the other instruments. You can sometimes get dissapointed when you first plug into your amp - stick mic up and hit record and get this thin sounding guitar track. Even when you know what your hearing is good in the room - sometimes it hard to get that same sound down on tape/hardrive. Theres heaps of info on that subject in other recording based forums (try for a start) - comes down to mic choice and placement and the space your recording in, effects, compression, EQing and good mixing. Don't be fooled into thinking you HAVE to have a really expensive big amp to get an expensive big recorded sound - it don't always work that way.

My preferred way to record my band is to do it live in our rehearsal space with carefully placed mics on cabinets, spinning amps away from each other to get some seperation. Its not perfect as you get bleed from the drums etc - but thats as close as you can get to your live sound - just record live. What you can't do is edit much or tweak a great deal as you have that "bleed" - so you have to get it right at the source. But as a trade-off you get all the energy which is sometimes missed in multitracking!!!
Hey there,
I'm new to the forum and Electronics/DIY, but fast becoming addicted. This forum looks like an excellent resource - so much info. Thus far (since Xmas) I have successfully put together a couple of electronics store beginner kits - .5 watt "champ" amplifier (based on Lm386 chip), FM radio tuner, a couple of general guitar gadgets stomp pedals. My latest "conquest" ;) was this little beauty from Oatley electronics here in Australia - which is based around a pair of Raytheon JAN6418 sub-miniaturepentodes - hmm forgot I even ordered it  - a pleasant "Beerloom" from ebay.

Last night I finished it and attached a couple of phonojacks and tried it out with the little .5 watt amp then into an 8" speaker that lives in an epiphone valve junior that has a phono jack attached (EVJ was not turned on) - sound was just distorted mush. Then I tried it through the EVJ powered up and the thing really roared!! There was massive gain boost, and some nice distortion at low levels. A bit noisy as it isn't cased yet and has aligator clips hanging everywhere and the EVJ isn't super quiet itself. But I really like the sounds I was getting:)

I would like to make myself an amp using this tube preamp and matched to a simple IC based amplifier. The documentation for the preamp states...
"The gain of this preamplifier is adjustable from 0 to 100 times, the output voltage can be up to 5V P-P (1.8V RMS) with a fresh 9V battery, and the widest frequency response extends from 20Hz to 30kHz."

Can anyone suggest an IC amp project that would be suitable-please refer to the specs in the link above for more details-theres a schematic. I'm keen to start making my own circuit boards. Gen Guitar gadgets has some info and a pcb for a Craig Anderton LM383 amp-would this be a good starting point ?? Any suggestions or assistance with this greatly appreciated.

Given that I can't really design or barely read a schematic at this stage (but not for lack of trying), I'm especially keen to find out how to power this amp. At the very least I'm thinking I could figure out how to install the tube pre in a stompbox case but I would love to have it all in the one case. I have an old small behringer bass amp case to house it all.
Any suggestions or assistance with this greatly appreciated.