Thanks for the details and pic Mangas, :tu:
You have obviously got it all sorted and should be a darn fine piece of well made equipment when it's finally done.
But it is all rather addictive and your wife probably wants to know if you will ever be finished,, LOL.
Phil.

Quote from: hasss on December 28, 2009, 09:48:04 AM
I think i found what i wanted. I will use the schematic for the tone control which i posted but will cut it right after the baxandall and the op-amp. Then i will use a simple parametric eq for more control of the bass.Here s the schema:

http://tinypic.com/2s7cj

Do you think that the values of the capacitors are ok for the parametric eq or i need to make some adjustments and do you think i should add another section below 100hz because the low E of the bass is below 100hz?

Hi hasss,
            A picture's worth a thousand words so I'll let you ponder this one.
Simulations are not perfect but do give one some idea of the end result.

BTW, the circuit you refer to is just a 3 band EQ not really a parametric EQ.
Cheers, Phil.

Quote from: J M Fahey on December 25, 2009, 09:52:24 PM
OK.
That kind of Fender amp , the one driven by an op amp and 1, 2 or 3 pairs of TIPs , make me nervous, because I see them overbiased but worse than that, unadjustable.
They have to forward bias 4 junctions (two in each TIP , which is a Darlington), so *in theory* the 4 diodes in series they use, *should* be perfect, and *should* not need any trimming or adjustment.
In my experience, that is a difficult balancing act, because 4 "regular" diodes are a little too much. They rely on a specific brand and model there, and the popular 1N4002 which should work well, is too "hot", and, by definition, unadjustable.
I suggest that, to be sure, you turn your amp on, but with all controls on "0", and monitor that heatsink with your high-tech, NASA approved ultra-electronic detector called "finger".
If it overheats quickly with no signal applied ... now you know what's happening.
Just to cover all bases, measure that you have no DC voltage in that speaker out, both with and without speaker. (Up to 100mV is fine)

Thanks JMF,, very well Explained :tu:
I somehow new there was something half cooked with those Fender Amps.
The Performer 1000 I fixed a while back is very similar, From my limited understanding the power stage is just a current boosted opamp.
thank goodness the poweramp was ok cause I would not be able to fix it.
At a guess I think every possible way to impliment feedback is somehow used on that circuit
Phil.

Hello Mangas,
                   First let me say very tidy work, quite stunning in fact.
Your efforts are certainly neater than  mine

Something does not sit right in my head with the first post pic, the bottom pic.
The mains input board has the mains cable *Earth wire* terminated on a PCB. Then I assume a thin copper track back to another terminal and then finally a lead to the chassis bolt.

I'm just wondering if this is safe practice?
From memory this would not pass Austrailian standards but other countries will have differing rules.

I personally would make a *Direct unbroken wire* to Chassis terminal from a mains cord.
In fact when I can I make sure the Earth wire is the longest so that in a worst case situation where the cord is yanked from the chassis the Earth wire is the *Last one to break* thereby minimising the risk of shock to the user.

It's a one in a million chance but that's just me.
Having said all that I probably still do things that more experienced folk would see as risky.
But hey that's what is good about other eyes looking at our work, there is often someone who has thought of something I may miss.

Cheers, Phil.

I'll assume it's a Tube Amp? in that case steer away from headphone ideas :duh
You can do it but a lot has to happen and the complexity and cost will hinder your progress.
Phil.

Hello again madapj,

Go back to ESP schematic and note the *One* ground node is at the input socket. His design, so start there first. If no luck then we will look at other issues.
Phil.

Hi kvandekrol,
                  Refer to above post and note the warning.
I second it,, Hint Hint
Phil

Sorry for my oversight,, yes The *New* input would be on pin7 of V2A as V1 is no longer present.

Be careful comparing other amps of same name.
Has to be EXACTLY the same,, ie same *Model* nu written on the back, don't just assume by a front name plate as it often means little.

Be very aware that manufacturers are always changing things even though it may look identical it may well be a very different amp inside.
Without lifting the hood you can't be absolutly sure.

I believe I've already given you the schematic so this is just getting a little hard to follow. If you wish to continue this maybe PM me and I'll review this thing for you in private. 8|
Yes we do have to consider the other folks who read this.
Cheers, Phil.

Quote from billyjoe;
"It's interesting that you're cutting the same two traces as before,
but I can tell you the hum was still there almost as bad.
There was also very little gain.Low gain in my opinion for lead."

Yes but look at the EFX loop *THAT* is where a lot is lost.
Replace *R15(100k)* with a 100 Ohm to 1k Resistor and Delete R16 (56k)* and you will have all the gain you will ever be able to use.

((This assumes you loose V1 and ALSO disconnect the whole EFX loop setup *permanantly*.))

With V1 left *as is* it will then probably just squeal it's head off.

V1 and the efx loop setup just kills this thing IMO.
A 56k resistor across a tone stack is just about as dumb as you can get.

Oh but the market demands you must have an efx loop otherwise it's unkool.
EFX loops kinda work with SS but on valve amps it's a no brainer.
This amps efx loop is about the worst setup you could possibly design in a valve amp.

I've just done some simulations for you and with the mods suggested the Amp will start to distort at half gain volume. With the master at max this would be a very responsive amp.


The way it was setup;
The original circuit I simulated with a 100mV input and with the gain pot on *1* the signal swings to the supply rails after the tone stack triode. That's around 200 volt swing OUCH! (up the gain and you are probably getting into blocking distortion,, whatever it would sound horrible)

So I'm sorry but with the amp *as is* there's not much chance of any dynamic compression or touch sensitivity.
Not a nice user friendly amp.

If you are still having issues with hum after all these mods then consider the way the heaters are connected.
In an amp like this the tracks tend to run Parallel and often around the valve sockets,, not good.

my only other thought is Tr placement might be a problem,, ie remount. and also the tr's may not be well shielded and if so will induce some 50/60 hZ hum.

An outside possibility; *IF* any of the valves are very close to the speaker magnet that can play merry havoc on the sound.
This subject came up a while back on a valve forum,, a Peavy amp if I remember.
Rule of thumb is about 75mm away, the further the better really.

You mentioned loosing the jumper wires ,,Yes but makes for a lot of work.
You would be far better off gutting the amp and hard wire it all using tag or eyelet boards.
run all your heaters as twisted pairs (read up on How to do it the right way not just flimsy loose hand twisting, needs to be tight twisting).
And learn what is known by the guru's, which is run all the signal wiring at *right angles* to heaters and other power wires.
(just about impossible with single sided PCB valve amps, not all things PCB are good)
You will at least learn a heck of a lot about valve amps in the process and that can't be all that bad
Here is a schematic of what I suggest, only up to the efx loop point.
You should not need to change the rest.
Just to be sure you understand; When AC heaters are used with old designs (Lower valve count)
Then Hum is not normally a problem but start adding extra and the hum will quickly climb.

A friend just purchased a brand new Pro Junior amp which is about as simple as you can get,,
2 by AX7's and a pair of EL84's,  2 knobs vol and tone.
He rang me after a couple of weeks and asked if it was supposed to hum when you turn it up high?,, is there something wrong? Should I take it back?
I laughed and said welcome to the wonderful world of valve amps and good old AC heater hum.
(Understandable as it was his first valve Amp.)

Phil.

One more thing,,I get the impression that you are new to playing with circuits.
If so then;
If you mess with these boards be very carefull when unsoldering/resoldering components.
You will quickly learn that the copper tracks can't handle reheating to many times.
You can solder small standoffs of short wires thereby enabling quick value changes and  not heat stressing the track/solder pad on the PCB.
Phil.

Hi, rednef,,Thanks for the timely input.

I believe I know what ails this amp that being *Deleting* the utterly useless V1 and jumping a few wires to bring back to a more civilised setup.

I'm just going off *billyjoe's* layout so do double check for possible errors.

There maybe even better results by lowering the gain pot to 250k as this amp will likely still have heaps of gain that will never be used.

Cheer's Phil.

Hi John,
           A FET is a *Field Effect Transistor* they work in a similar manner to a transistor but tend to be a little better with high impedence circuits.

I'm with *tonyharker* or similar ideas.
Any old cassette recorder type thingo 's have electret mikes inside them.
If money is tight you at least can source a lot of stuff for nicks by hacking into old worthless electronic bits. Then you can fiddle with a few different ideas without spending a fortune.

One other option would be those *pressure zone mic's* Tandy used to sell.
*I've never used one* but I've been told you can glue them on a table and they pickup spoken voice very well.
To look at they are just a flat plate about 100mm square with a cable hanging from the side.
Tandy in Australia still sell them I think,,, (I'll assume you are an Aussie )
If they are not in the shop, ask as they may still be at the national store room.

But yes JMF raised a good point ,, you may find a standard or electret mic might deliver a better performance over a straight peizo setup.
Phil.

Sorry the old brain fades off at times,, :loco
Yep I now see your point.
YES! a 250k pot was used for the mods.

The use of 250k pot *Full off* does at least impart very little colouration of the original signal. I have no idea whether that be a good or bad thing? sadly you can't *Hear* simulations.

As to where to get parts *electrical hobby stores* Does depend where you live.

If you are prepaired to scrouge junk (Like I do 0:)) then trashing almost any unused home electronic device these days will reap heaps of Caps and Resistors.
Don't bother with computer mother boards and anything that uses surface mounted stuff.
Old video recorders and hifi junk from 20 years ago will have heaps of useful bits that can often be reused.
I collect so much *crap* (as my wife calls it) that I have to have a throw out day every 6 months.
Have fun with it,, it gets addictive after a while :loco  Phil.

There are 3 sim sets.  They are named and colour coded on the left edge,,
sorry not real clear.

Red/dark blue and purple are *tone off*
Light Blue/yellow /green are *full on*

50k=purple/green trace.
250k=dark blue/yellow.
Mods=Red/lightblue.   (note the red line is almost the same as dark blue)
Cheers, Phil.

Quote from: Audiological on December 21, 2009, 12:04:47 AM
Hello,

This is my first post here.  I have a Didgeridoo and I am looking to amplify it so that I can run it through a FX Pedal or grunge pedal and then through my bass amp. 

I have been looking into this and it seems as though a piezo style pickup is the best way to go about amplifying this instrument.  I have also heard mixed reviews regarding a preamp for this pickup. 

I have two questions that maybe the folks here can help with:

Is there any specific piezo pickup configuration or type (as in the type of material the piezo is made of) that would be best suited for a instrument that has such low resonance and low frequency properties such as a didgeridoo? 

and

What would be the best way to go about making a custom, small (possibly able to attach it to the instrument size) preamp for this piezo pickup described above? 

This is merely a hobby project and I want to attempt creating something before I go out and buy one of the numerous piezo pickups already designed that might work for this.  Also, I think it would be REALLY great to run that sound through a distortion pedal of some kind. 

Any suggestions?
Thanks
-John

Hi John,, Have you asked what Double Bass players use,, that might be a start.
Phil.