Quote from: Tassieviking on December 05, 2024, 11:06:33 PM...
I have read somewhere that those small amps have an input impedance of 50k ohms so just a capacitor on the input might be enough.
...

Yep, the manual says so: https://www.farnell.com/datasheets/1712767.pdf

I'd dare say that input impedance that low is actually chopping off a bunch of treble, which translates to more bass when you turn things up.  I'd build a small simple buffer to put in front of it; FET Source follower or non-inverting op-amp circuit powered by 9V, then see what happens.  Or if you have an overdrive pedal around, turn the gain down and the volume up, adjust to taste.

Quote from: Miyagi_83 on May 29, 2024, 09:13:26 AMUpdate

So, I have been tweaking the circuit for the past couple of days and I think I've got it where I like it. Actually, there are a few versions that I'm fond of, so I'm going to make it a switchable two or three-channel preamp. Honestly, this design has enormous potential, afaic. I haven't tried it on 18V yet. That's still on my to-do list.
Now I'm going to need a nice clean channel to pair with it. Any suggestions are welcome.

I've asked before on other forums that if there were such thing as a "clean channel" pedal, what would it consist of, and most folks suggested either completely dry, like plugging into the power section with a tone control, or light-to-medium compression with no clipping.

QuoteIs it OK to post a schematic with my changes? On his site, Joe Davisson put the 'do not copy / all rights reserved' clause, so I wouldn't like to infringe his copyrights, annoy him or anything like that, hence my question.

He hangs mostly at diystompboxes.com, maybe pop in there and send him a personal message.  At the very least, I'd say draw your own schematic and highlight the differences, so you won't be straight-up copying.  Maybe include "modified from Joe Davisson's Vulcan" and a link to his page.
IANAL, so I'd ask him about it first.

Quote from: joecool85 on May 27, 2024, 08:56:13 PMFor those looking for the link to the schematic: https://www.diystompboxes.com/analogalchemy/sch/vulcan.html

I'm curious what the diodes are for between the stages though.  Not sure I've seen that before.

Per the description below the schematic; "The diodes in the bias network prevent hard-saturation of the transistors."

I won't pretend I'm smart enough to know how that works, but it sounds to be in the same vein of putting a diode across base & emitter to prevent zener breakdown events that degrade the junction and cause noise to build up over time.
See here: https://www.diystompboxes.com/smfforum/index.php?topic=132039.0

I wonder if those two arrangements might be considered general good practices for BJT-based preamp circuits?
 

Have you tried a Factory Reset, or tried hooking it up to your computer and seeing if it connects with the Blackstar Insider software?  Do the interface buttons and indicators on top light up?  If you have the footswitch, does the display light up? 

If you don't have the Owner's Manual, you can get it here:
https://www.blackstaramps.com/pdf/handbooks/id-core-high-power-handbook.pdf
And the Insider software here:
http://www.blackstarinsider.co.uk/

If the buttons and indicators light up as if things are normal, check the input jack; it may be that the jack itself or the connection has gone bad or gotten disconnected, especially if anyone has tried to poke around in there.  From what I read of the Owner's Manual, the power section is disabled if there isn't something plugged into the Input jack.  The fact that you can get power output without having anything plugged into the Input jack (or do you? I'm making an assumption...) tells me the jack or the connection may be bad. 

If the Factory Reset doesn't do it, or if it can't connect to your computer with the Insider software, or if the buttons and LEDs don't light up, then your preamp (and all the digital effects and gizmos within it) is most probably toast.  Digital stuff is either working or permanently broken.  Either scrape up the money to get it fixed by an authorized dealer, or use the power section as a means to amplify your coolest pedals.

I think all the mods you're thinking of nails it pretty good.  I'd say crank it until it fries, then get busy re-making it, though it might last until next week or it might last 20 more years, who knows?  I also think what you really got was not a modding platform, but a cab, speaker, and chassis to build your own in.   

Not sure if the SMPS or the DSP or the regulators are the source of the hiss, but I agree that any of them could be the culprit, but it also could be your speaker is an inexpensive variety better suited for hi-fi applications.  The next best thing I can think of at the moment to do for that is suss out a good place to wedge in a 2nd-order low-pass filter around 5-6kHz; most guitar speakers won't go much over that, so you wouldn't be missing much high end. 

If none of those work, gut it and heat up your soldering iron...   

Quote from: troublerat on June 28, 2009, 12:55:55 PM
This is one thing that I may be able to give some suggestions on. If you need 9+9- go to http://www.geofex.com/ the circuit sweeping section and look for 9+9- from an 9 volt supply. Go to http://runoffgroove.com/doubled.html and use the jiggle side for an clean to overdriven fenderish type sound. Then theres my favorite  http://www.muzique.com/schem/projects.htm  the mosboost can be built from radio shack parts and gives an excellent fat clean boost [ you can use bs170, irf511, 2n7000]  Heres one chain to try it involves an boss comp. cs-3 with wampcats mods www.wamplerpedals.com   guitar/cs-3/mosboost/chip amp. I am probably going with the mosboost[one knob booster] [and the rog double d , just the jiggle side.and put the mos on an dpdt to switch it in and out in front of the jiggle. I am seriously pondering on the classic fuzz face circuit, I built one from the schem. at geofex with no variance from the schematic was very pleased with sound. Go to geofex at the top of the page "The tech of series".  Theres just to many good workable circuits  to bang my head and try to reinvent the wheel. All the above work well. I have use them in front of several amps. The hardest thing you have to do is deciding what kind of tone you want. I prefer the one or to knob types and try to keep the face of the amp from getting to cluttered with knobs.

I love MOSFET preamps!  Here's two more for your grab bag:
- Use a CD4011 2-input NAND or CD4001 2-input NOR (unbuffered versions, of course) instead of a CD4049 for the "jiggle"; tie the two inputs of each gate together and wire each like an inverter. The internal structure shifts the bias point for asymmetrical clipping that sounds pretty darn good, and you don't have to worry about "throwing away" all those unused inverters in a 4049.
- Find a complement for the 2N7000 (BS250 probably) and wire the two together like the innards of an inverter.  It actually works, and again you don't have to worry about all those unused inverters, just build as many as you need!
Bonus: Same inverter-from-two-MOSFETs idea, only add another 2N7000 in parallel with the other one so you have a BS250 on top of two 2N7000s in parallel.  That shifts the bias point for asymmetrical clipping like the NAND/NOR gate.

Heh, I noticed that too, and was like "Hey, that name sounds familiar..." 

Sometimes I'm searching the web for a resolution to a problem and stumble across one of my own threads from 10 years ago, still asking the same question. 

Looks like a 2-channel FET preamp with one channel having an extra FET gain stage, mostly normal looking tone stacks, optical tremolo, spring reverb, and transformer-driven power stage with 4 2N3055s.  Doesn't sound like a bad deal, and this article from Premier Guitar 4 years ago says $400-$600, so you're in the ballpark:
https://www.premierguitar.com/trash-or-treasure-sunn-solos-ii

Schematics here:
https://forum.sunnstillshines.online/index.php?topic=4781.0

Never personally played one, but I'll bet it's damn loud, and depending on how the channels are setup, probably fairly grungy.  Probably not the greatest for modern shred metal, but it may surprise you.  Make sure you play it before buying, but you probably already knew that.

JFETs are so inexact in their specs, there's really no way to simply slap on a few pre-determined components and have it come out working exactly as it should.  MOSFETs are a little better, but there's still some voodoo in there.  I'm afraid that as long as you want to design with FETs, you're going to have to live with the reality of trim pots as biasing devices, and manually adjusting each one by ear.  Some think the effort is worth it, others not so much.  I remember someone came up with the brilliant idea of using a diode instead of a resistor at Source.  It worked, but not always optimally.  Sorry I don't have a better answer.

Quote from: Littlewyan on March 18, 2021, 06:37:05 AM
I may have actually just solved this.....possibly. Found an old post from J M Fahey on another forum where he suggested this to someone. It seems to have the desired affect. The only issue I have now is working out what wattage resistor I need to use for the 0.33...

Another reference: https://www.current-drive.info/projects/17

His is based on a TDA2040 with a 0.56Ω gain resistor at 2 watts.  For a 0.33Ω resistor in a slightly higher-powered chipamp powered by more supply volts, I'd go 3 watts at least, 5 watts for peace of mind. 

In LTSpice, you should be able to simply put your pointer over the resistor symbol and click when the cursor turns to the clamp-meter symbol to read Amperage.  If you do a Transient analysis, you'll see Amperage on one side, and click on the wire above it when the cursor looks like a meter lead to get Volts to show on the other side, then do the math.

I'd find a TDA2050 model first to get any kind of accuracy, and understand that Spice modeling assumes ideal conditions; err on the side of more watts.

Quote from: joecool85 on February 17, 2021, 11:17:29 AM

Quote from: phatt on February 17, 2021, 01:00:58 AM

Quote from: joecool85 on February 16, 2021, 08:53:42 AM
For me the short of it is yes, sparkly clean but with tone shaping.  Normally a -10db dip in mids, centered around 600hz.  After that it is up to preference if you drop lows or highs.

Hi Joe, Your observation is correct but sadly it is only one piece of a much larger jigsaw puzzle.
If you insert that tone curve into a generic SS amp it won't sound like it's valve equivalent.

He asked for a clean channel, I figured he meant just preamp.  If that is the case, I stand by my argument.  Of course, taste/preference is relative.

I do agree about what you said though.  I've not tried using a transformer for speaker output, but I've thought about it because I constantly hear about it's magical properties.

Per my (admittedly limited) knowledge, since it's SS, much of the "magic" has to happen in the preamp.  If one wants to mimic power supply 'sag', or speaker reactance, it's gotta go before the power amp because that thing is linear all the way, toots... 

Transformer output is particularly intriguing, because in my mind, it promises to deliver just a little of that non-linear "magic" we hear so much about with tubes.  I am leaning toward a MOSFET power amp due to MOSFET designs being relatively simple to build, but I think it might also be a little easier to design around a transformer output.  However, I don't doubt I may be plenty wrong about that.  Searching around the internet, the general consensus reaction to the idea of transformer output on a Solid State amp is "But why?", and I guess they kinda have a point, I mean why use a transformer if the chips can drive a speaker directly?  MOJO, that's why!   

That said, if anybody has any MOSFET-with-transformer circuits, send them my way, especially if it uses one of those 70-volt PA system transformers; I have one, and they are pretty cheap as far as audio transformers go if I want another.

Quote from: Enzo on February 15, 2021, 05:30:02 PM
Oh, and look at the response curves of popular guitar speakers.

Ya know, I was looking at speaker response charts, and they told me a lot less than what my ears could tell me.  I can look at the steepness of the low- and high-end rolloff and judge how bassy or trebly they might be, but beyond that they don't tell me anything about any give speaker's fundamental character that I can't pick up immediately with a brief listen.  I have a few ideas for what I'd like in a speaker, but that'll require more money than I have at the moment, and even then it'll probably be a Harley Benton twin cab.  Cheapest in their class and they are genuine V30s, you know...

Quote from: phatt on February 15, 2021, 08:15:47 AM
Hi Ed,,Try to keep in mind that there is no one section of a complete system that will reap magic,,
You build the sound/Tone you want out of what is mostly basic circuits most of which have been around for years.
If you want Clean then I take it you are talking about electric guitar?

In that case the clean will benefit from a little edge. (As Enzo just mentioned)
(My Cab sim, compressor, Phabbtone does that for me)

Regards OD and multi channels on amps,,, Been there done that and failed?
Pedals are far easier to get to where you want. It will depend on what styles you want to emulate.
For me it's just older rock and blues which is built from the little rattle of *Mictesters* Comp which is always on.
Then I add a home designed germanium clipper (that is my clean boost with a little more edge and OD) sweet.

For MORE heavy rock stuff (think ZZtop) I add a Boss OS2.
For all out scream I add a Boss SD1 (not totally happy with that but it does the job)

OK by now the bass and drums are playing louder so I press my Level Shift which just lifts the volume enough to lift it over the top.
Except for the Level Shifter all the added dirt pedals are set at much lower gain than most players I've known.
This helps a lot as with 3 Drive pedals it's way to easy to end up sounding like Mud or buzzing fizz with to much gain on any of those pedals.  The Compressor is AFTER those 3 pedals and that keeps it all within a SET SPL of my overall volume,, without that it's a nightmare trying to keep them all within a certain SPL range.

If heavy metal is your taste then you might only need to add the pedal of your desire.

Of course there are many ways to do similar things but this has worked well for me over the last ~10 ish years.

All that is running thru my crappy old Laney which I think I mentioned to you once before is not even a guitar amplifier,   

To do all that in one amp chassis is a tall order. Once you realise that all that would need many relays and a pedal board with many switches.
AND you are still stuck with a friggin pedal on the floor,,,, Naah
As much as I hate pedal boards it's just a lot easier to use pedals.
And if you don't like one you just swap it out,,, you can't swap out things in a complicated amp chassis in a few minutes?? 

Let me clarify: I've tried a lot of dirt pedals and amps (too many to mention) that never left the music shop in my hands, the few that have I don't have any more, and I am not financially flush enough to do any further experimentation with that, and frankly, I'm not all that interested.  If I were to name my dream rig, it would be a Mesa Boogie Mark IIc+ or the Bedrock twin combo I tried out in 1992 or so, but didn't have the cash to swing at the time.  I still don't, so that's that, but the point is I'm a "set it and forget it" sort, which means once I find something that makes me happy, I'll likely be happy with it for a while.  Right now, I'm on a chase of a good clean tone that's not boring, but not over-complicated either.

What I DO have is a few buckets of spare parts, a little time, and a certain tone I'm chasing. I have designed a solid state dirt circuit that I'm about 99.9% happy with, and further tweaking is getting diminishing returns so I know I'm about done.  My ultimate plan is to make everything modular (separate boards with connectors between them), so If I get REALLY unhappy with a preamp or tone control, or if the power amp dies and I can't find a replacement, I can simply swap it out.  It might take a couple of days, but I'm not gigging, so I don't mind.

QuoteI just read your other posting and it seems I promised you some of my circuits 
I'll try and get some up soon,,, life is very busy at the mo but I WILL get something for you.

Phil.

No problem, this endeavor has gone on for more years than I'd like to confess, so I'm OK. 

So, the concensus so far is a bit of compression and judiciously chosen tone control to add some tone shaping and non-linearity to what would otherwise be no different from a monophonic Hi-Fi or PA.
Anything else?

Quote from: Enzo on February 15, 2021, 06:57:13 AM
Crystal clean clarity?  Foo, that would simply be a PA system, and we know that does not make a good guitar amp.   What you think of as clean in a guitar amp is not really very clean.  It just doesn't have the shrill raspy edges of dirt channels.

Agreed.  The problem is, that tube amps have an inherent non-linearity that everybody knows is the bees knees whether clean or dirty, while us SS guys are pretty much stuck with basically a PA powering a Celestion, and I want to do something about that without involving hot glass...    Hopefully without going down the tube emulation rabbit hole that many before me have plumbed to its depths already.

QuoteGo to DUncan amps and download the tone stack calculator and explore the tone stacks, you will see their response curves are not flat.  Putting all the tone controls at center on your old Fender is NOT the flattest setting.

Yep, done that, and looked up and tried at least 10 or 15 various tone controls trying to find the one that hits my ears just right.  Right now, the Brownface Bass/Treble control has my attention for the longest, so I'm sticking with that, but still researching an active Mid EQ to mitigate the -15dB mid scoop.  FWIW, it doesn't sound all that scoopy to me, so maybe I'll leave it.

Back in 2018, I was pondering creating a basic SS amplifier that had all my best ideas in one box.  Now it's 3 years later and I still haven't built it, but I've been breadboarding!  I've re-thought my opinions on 2-channel amps, and eventually came around to a new question... Is the clean channel nothing more than the default when you turn off the dirt?  Like the wire that goes straight from input to output when you switch a pedal off?  That sounds so boring, but can there be more to it? 

I worked up an idea of making the clean channel run through a tone control and then through a single gain stage, which is how tube amps of yore were laid out.  I'm not trying to purposefully emulate tube anything, it just struck me as a novel design decision that will alter the response of the gain stage and maybe introduce some pleasing audio anomalies.  Or at least, that's what I'm hoping...

What do you folks think are essential elements of a good default clean channel?  Squeaky-clean crystal clarity?  Just a little grit on the top for flavor?  Tone shaping ideas?
  Some simple compression/limiting maybe? (Yes, Phatt, I remember your suggestion of the simple compressor.)