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Messages - phatt

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My money is on a blown chip.

Preamps and Effects / Re: pre-amp suggestions
« on: April 27, 2021, 02:00:16 AM »
Ta mate ,,Yep I found some of your circuits on MEF and when time permits,,, one day :(
I notice your circuit also uses a CD4069UB which I can find locally but I'm a little lost as to how the pins are all wired up. ???
Anyway no hurry as my Bread board is full up with another project at the mo and once I've resolved a couple of small issues on that circuit I'll try it out. :tu:
I'm not looking for the metal Shred grind ,,more like a sweet smooth OD if that is possible.

My experience is limited but I do recall using a small Laney HC15R (I think) which has something similar to get the OD effect. It sounded ok but like a lot of Amps as well as a lot of those all in one pedal boards there is just way too much bandwidth giving that brittle edge which is just horrible. (to my ears at least).
I'm really happy with what I've designed and achieved over many years and it does a darn fine job,, but always interested in other ideas.

If you have Hum,,,Measure the DC voltage at the speaker output and post your findings.
It Should be VERY close to Zero Volts if not then remove the speaker connection or you could burn out the Voice Coil in the speaker.

Preamps and Effects / Re: pre-amp suggestions
« on: April 24, 2021, 04:14:47 AM »
Thanks , interesting. Q Will a 4007UBE work in this application?

Schematics and Layouts / LM386 H/phone amp options
« on: April 18, 2021, 09:55:38 AM »
The recent Honey amp got me searching my backups and I found The Nobels Mycro Amp circuit.
I don't know if this is of any use but this is a Headphone circuit using the LM386 chip.
Gives clues as to how to implement a preamp with clean OD and Dist.
Of course it does require more parts than the honey amp but the second stage has filtering which may help with small speakers. :-\

Sorry but you are doing it the hard way.  xP
It's a common mistake to assume that the ACTIVE components make or break the mojo.
OK you had a win by replacing some opamps but mainly that improved noise issues.
But note;
wide bandwidth requires hi spec chips OK fine BUT if the bandwidth is limited then by design you remove most of the hizz fizz and buzz which means that lower spec chips work just fine. (That's a general comment and not always so but still worth noting)

Tone is all about the circuit design and that comes from the passives, not the quality of the passives but the Values of those define the final result.
Sure speakers and power stage can have effect on this as well as PU's in the guitar but a whole world of tone mojo comes from knowing how to tweak the circuit and most of that is PASSIVES. in guitar circuits it's often just understanding some R/C maths

Doing this by willynilly swapping out parts and hope for the best can end up destroying the PCB tracks so I'd suggest learning how to use simulations and a Bread board and recreate some of the Showman preamp to test out the many options before you open up the lid on the amp.

I would recreate the 2 preamps on a testboard then link into the power amp of the Showman to hear how tweaks alter the sonic result.
No need to do all the switching as that has little to do with tone shape.

The Dirt circuit is a little tricky but still doable.
It has the CD4007 which I'm assuming is just a bunch of mosfets setup to create a lot of Dirt but as there is little tone shaping after it then likely a lot of fizzle and hash is the result.

Note that a lot of amps are built to what the market wants and many amps are built to create a whole lot of hashy distortion which the kids with tin ears seem to like,, so if you want sweet OD then it's unlikely to work well for a sweet OD tone without a lot of tweaking.

You can always Bboard some cab sim circuits and temporally insert them in the FX loop or Preout /PwrAmp input to wipe of the excess bandwidth. That would be less work than testing out the whole preamp section.
I'd guess that the preamps will still be an issue.

If I had a clear schematic to work from I could simulate some of the preamp sections to get some idea where the tone is going wrong,, no chance as that Schematic is unclear.

Good work and you learned from it all.  :dbtu:
Don't worry you will find a new project soon enough. ;)

Yep not surprised at all as there is likely a fair bit of loss and noise in all that switching circuitry.
I doubt it is faulty it's likely working as designed but these things are called design over sights. :-X

I have no idea why the gain pot does not work?
Regards finding where the noise might be;
You could try and bypass IC4 (TL604) & IC5 (TL607).
To do that take the Graphic output at R19 (P1-1) then connect that wire to terminal 6 (P3) which is on the bottom page. (the preamp output/ poweramp input sockets)

You may have to disconnect pin7 of IC4 as well as pin4 of IC5 as signal and hiss might bleed through.
This is all guessing as that schematic is missing quite a few connections. so do check 8|

That leaves the Channel switch & Reverb still stock but graphic EQ is permanently engaged wit FX loop bypassed.

If hiss is still an issue try lifting one end of R2 (at pin4 of IC2) that is the return mix resistor for the reverb.
Some reverb circuits can introduce a lot of buzz/hiss.

Amplifier Discussion / Re: 1983 Fender Showman Channel Switching Issue
« on: March 16, 2021, 12:32:33 AM »
Re distortion on clean,
                               As mentioned a lot of circuits will have some clipping once the signal level gets high enough.
Maybe try and turn off the reverb and GEQ and just use the 3 pots of the clean ch.
If the clipping is still evident then maybe the gain is a bit high at some place in the preamp circuit or there is an issue inside all that switching crap.

As the schematic is very hard to read I'm guessing that after the signal leaves the preamp it runs through IC1, IC2, IC3, IC4 & IC5.
If it's possible you could break into the preamp output at R18 then plug direct into power amp input.
 That would bypass all the switching circuit.
If you still have the distortion then you know it's in the clean preamp and not the switching circuit.

Amplifier Discussion / Re: 1983 Fender Showman Channel Switching Issue
« on: March 14, 2021, 07:58:18 AM »
Hi DJ,
Ok thanks, now I see where you are coming from an that's cool.
Just be aware this stuff can become very addictive, my wife thinks I'm quite disturbed,  :lmao:.

Most young guitar players will tend to fall for the hype that if you have the latest model Amp/Gear/Guitar you will be in mojo heaven and will play better and you will be BROKE $$$.
Reality is with some basic gear and some understanding of electronics and Sound you can escape the hype bubble easy.

Read Bobs comment for just how cheap you can run a big rig setup.;topicseen#new
Note the Amp used is one of the cheapest model amps you can buy.
Very Clever for a chap who has little electronics knowledge  8|

Re modding amps;
Yes you can alter some PCB's but depends on how much work is involved. Some circuits leave no room for much alteration and it's just not worth the trouble. (your amp is likely one I would not bother to try and alter).

For me, Having tried all sorts of ideas I've found from experience that a lot of Dedicated guitar circuits are way to extreme and many owners of multi channel amps tell me they like one channel and end up back at relying on there pedals for all the other sounds.

So as you wish to learn my advise is buy a Bread board and start building circuits to see what suits your playing style. You are welcome to my circuits if you so wish ,, most of them are on this site anyway but there have been a few alterations in the last couple of years.
To understand whatzhappining; :duh
By shear design the power stage of old Valve amps limited the bandwidth of the signal.
Most valve amp circuits have a lot of Decoupling between each stage including the power amp. They also have a Transformer coupled output to speaker.
Most guitar OTx's are often low speced and can't transfer really hi frequencies so straight up limited bandwidth by design. Add things like miller effect and you have an amp that sounds sweet even when distorting.

NOW Enter SS where most power stage circuits are DC (Direct Coupled) so no caps to wipe off a little bass,,, and no OTx to wipe off excess hi freq content. The result is often HARSH TONE. :'(

But don't panic,, there are many ways to recreate the sweet stuff most of it can be done in the preamp stages.
It's not about the Mil Spec transistors or the Gold plated print on Valves it's about understanding what is happening inside a circuit.

It's the RC coupling and boring maths stuff that makes the mojo not the cost of fancy mil spec Chips/Valves actives.

90% of the freq of guitar is under 1khZ,, add for some harmonics gets up to around 3khZ. Past 5khZ is just adding crap that will destroy the CLARITY and Definition of the notes you play.
Of course we all tend to fall for the MORE is always better than LESS,, humm.
Not so once you understand what is really going on. To cut through you only need to focus gain at say 1khZ to maybe 3khz.
This is where the whole system has to come together to create that TONE FOCUS. So when you turn up the treble knob you don't want to turn up frequencies way past what is needed,, otherwise your tone will be way too harsh/brittle. Add a lot of distortion and now you just annoy people.
My cab sim which is permanently on for that very reason to help tame that top end fizz.

Regards to OD/Distortion.
I have 3 OD pedals,  ALL 3 the gain is never above 2. I've found trying to get the OD out of one stage or circuit never works.
The idea is you build that OD each pedal adding a little more Grit/Edge.
With all 3 on, I'm into ZZ Top kinda distortion.
No reason you could not build some of the these into a rack case but you will still need a control board.
My pedal board can go direct into FX return of the Laney but I do like my Spring reverb and that extra Volume control on the Amp Cab is handy. :tu:
I've added a pic of my home made pedal board. 4 are obviously brandname the others are my own designs.
The ugly black box has a Compressor and Cabsim.
The white GeOdrive is my design and my favorite the PhAbbtone.
Enough for now I have work to do. bummer.
regards,, Phil

Amplifier Discussion / Re: 1983 Fender Showman Channel Switching Issue
« on: March 12, 2021, 10:40:41 PM »
well that was an interesting experiment. the speaker is A-OK.
That tells you the preamp circuit is Noise Prone,, not uncommon even with big name brands.

preamp out to another amp: white noise and some distortion- but of a different character.
Most likely because something has changed (different circuits and diff speakers)
Your Fender has Excess hi frequency again a common issue with clean channels,, not enough thought in design stage.
They build these things and unlikely they do any R&D

preamp out to mixing board: same result, white noise and occasional static, but not the light distortion tail.
The signal in this case might not be passing through the rather complex switching and that might be where the signal is clipping,, way over my head to guess why.
I steer clear of amps like this that try to do all this fancy switching,,, xP
IME I often find the Audio is fine it's the switching crap that fails. ::)

stomp box/amp sim into power amp in: near-perfect. If i just wanted a speaker only, all would be well. Going in this way it sounds great, aside from barely noticeable noise.
The sim is likely limiting the bandwidth and hence a much sweeter result because you have bypassed the crappy preamp
The Fender preamp has likely way too much bandwidth and that is evidenced by the harsh brittle sound in your recording.
without a scope it's a guess as to what part of the preamp is causing the problem.

So the speaker definitely is not the problem.
Agreed. :tu:

Does this experiment rule out the filter caps?
You have already proved the rectifier and main filter caps are working as they should,,, don't try and fix what ain't broke. 8|

Understand that amps like this are very complex are often a nightmare to resolve.
I've built several dedicated preamp systems for players and bypassed the whole front end of there crappy combo rigs.
The chance of finding let alone fixing the problem is low. All I can say is either sell it or bypass the preamp. :-X

Only other option might be to try the stomp box and Sim into the front end and see if that improves the outcome.
My hunch is the switching chips maybe at the root of this,, along with bandwidth issues.
Others here might have better options for you to try as some here have way more experience that myself.

Amplifier Discussion / Re: 1983 Fender Showman Channel Switching Issue
« on: March 12, 2021, 08:06:12 AM »

Q Does it get worse when up very loud?
My ears tell me its a fairly large signal and although a lot of clean amps might sound clean there is often a bit of distortion if you listen hard but at a gig you would not notice it. To me that is normal.
If you have another Amp try sending a signal to it from the Preamp output of the showman, see if that makes a difference.

One possible reason for a tiny fizz is speaker Voice coil starting to rub the magnet, often worse at certain frequencies.
To check for that,
You can often tell a speaker is starting to rub by gently pressing the cone. You should hear nothing but if it rubs you will hear a scratching sound through the cone. Apply gentle pressure to several points around the cone. You may need to remove the speaker if you can't get access to the cone easy.

Amplifier Discussion / Re: Fender M-80 Chorus Bias/Avalanche
« on: March 02, 2021, 10:33:15 PM »
These amps with darlington type power transistors are especially picky about proper heatsinking and go into thermal runaway if it's not right.
Is the heatsink compound old and dried out?  Are the power transistors mating well to the heatsink?  Also check that the diodes in the heatsink are placed the same as on the good amp, and whether there is heatsink compound there.
Also possible the transistors are fakes depending where they were sourced from.

Hi *g1* regard proper heat sink,, If it's the Amp model I think it is it only has a bar of alloy for a heat sink. I once fixed a Fender bass amp of similar design, it had melted the back panel plastic face plate. I simply added a big chunk of 4mm alloy with fins and it never over heated again.
I don't know enough to make a judgement on my above suggestion but I've bread boarded many Power amp designs and that boot strap divider section is always a bit touchy on many designs.

Amplifier Discussion / Re: 1983 Fender Showman Channel Switching Issue
« on: March 02, 2021, 10:10:19 PM »
Q, Is it more like a Hiss?  Hiss is often normal, especially with high gain circuits.
A lot of amplifiers do have a certain amount of circuit noise (google resistor noise for info)
When in a quite bedroom circuit noise can be quite annoying but at gig level you never hear it.

Amplifier Discussion / Re: Fender M-80 Chorus Bias/Avalanche
« on: March 02, 2021, 06:35:11 AM »
Thanks, now I see what you mean. :-[
Sorry I can't be of more help but my guess is that if the voltage divider of R127 & R128 are heating that is a sign that **Something else is causing the issue.** In my limited experience my guess is Q8 is being allowed to pull too much current and although it can be resolved a little by that Mod it may not be enough.

Now As I'm not the expert proceed with caution.

Having sent many transistors to silicon heaven trying to build and understand SS power Amps I believe that issue is not uncommon.
A while back I rebuilt my SS Laney Amp so as to achieve more Clean head room and it took me quite a while to resolve that very problem in the power stage.

Now I don't know if it would help on The M80 amp as my amp design was very basic but I finally resolved thermal run away issues by simply inserting 47R series resistors at the base of the output devices. (mine has 4)
That amp has now been running for ~6 years with no sign of any over heating. It's super clean up to (Ed removed the !) 80Watts @ 8-Ohm. I gig twice a month and sometimes more. After 2 hours at gigs the heat sink is only room temp. Yes I play LOUD <3)

While researching options I tested the final design flatout into a load box for hours over several weeks and was never able to get any part hot enough to burn a finger. Without those series 47R resistors it would run a lot hotter and like you say that is concerning. :grr
My circuit runs 45Volt rails and those resistors are 3k9 and 2k2 on my amp. (the boot strap section)
On your Schematic that would make R27=3k9 and R28=2k2.

**Now of course Your amp is a little more complex so it may not work. Others here would likely know far more than myself,, if it were my Amp I'd be setting up a lightbulb limiter and trying it out.

I have no doubt my simple design could be improved but cricky it's a guitar amp and simple is all you need.  8| There are a lot of designs that might perform far better than my simple circuit but I've noticed a lot of these over engineered designs seem to have issues while the basic designs don't. :-X
Evidenced by the sheer lack of breakdowns of simple designs. It seems to be always the complex units. ::)

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