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Messages - edvard

Schematic says it's a 2K linear.

EDIT: Ooops... 5 days too late... Have you fixed it yet?
According to the datasheet, full power on a LM1875 requires a power supply of +/- 30 volts.   That's 60 volts across peaks.  Are you using a 60 volt power supply? Your schematic calls for a 30V supply, which is not going to give you full power.
Also Single-supply requires a virtual ground made by the junction of two equal resistors that only the amplifier component uses (this is an OLD stompbox trick when using op-amps with a 9V power supply).  On the circuit you provided, this is found at the junction of R24 and R25.  Here they are designated as 10k resistors, which I think possibly puts a bit of load on the power supply (but I could be totally wrong about that). I would try changing those to 47k or 100k to see if you can get a stiffer output.
Amplifier Discussion / Re: EBay TDA2050 boards
May 04, 2019, 01:01:31 AM
Congrats, 2 years is a long time to take on a project, but I'm not one to talk (took me 2+ years to finish building my guitar...  :loco)

The reason your TDA2050s sounded so bad could be because they are cheap knock-offs; the TDA2050 has been discontinued for a few years now, and new ones are just as likely to be filled with wet sawdust as silicon.

Counterfeit VS. Authentic TDA2050 audio amplifier ic test
Counterfeit parts have been a problem for many years. Let's do a comparison test of the TDA2050 audio IC to see the difference in performance.

Glad to hear that your Class D amplifier sounds good.  I may be going that way eventually, but haven't taken the plunge yet.
Amplifier Discussion / Re: Etching your own boards
January 04, 2019, 12:23:58 AM
I've used some thinned-down model paint and a dip pen with very good results.  Speedball "B" series or Cartographer nibs.  Sharpies always drove me nuts, though my first Big Muff box was done with a sharpie.  I drew the circuit, waited for it to dry, and drew over it to get better coverage.  Sometimes, drawing over it would erase the original, so I'd have to re-draw the trace and do a second coat with a lighter hand. 
With the dip pen and paint, I never had to re-draw any, and the traces were solid.  Depending on the nib size, I could do thick, thin, or medium lines as needed.  I used two different sizes of pencil eraser as a "stamp" to make off-board wiring pads; big pads for pots, small pads for other wires.
Quote from: dazz on November 25, 2018, 01:44:14 PM

So someone suggested a charge pump chip to produce the symmetric supply (an LT1054 or ICL7660(S)), but I decided against it because for all I know, the result is not really symmetric, being the negative rail weaker (my LTSpice simulations show that with a 10mA load it's more like +17V/-16V) and I fear that might induce asymmetrical clipping. Are my concerns here justified or am I simply talking nonsense?

Many, many, many distortion circuits utilize asymmetrical clipping as a desired feature, so I think you're OK there.  As far as clean headroom, I think you're still OK as long your preamp isn't overloading the front end of the power stage.  Even the venerable TDA2050 had a maximum input voltage of ±15v, and for most real-world situations, it was probably much less than that.
Tubes and Hybrids / Re: Vox hybrid project
November 25, 2018, 04:38:25 AM
Be sure to read the datasheet docs very carefully.  Class D amplifiers can be somewhat different beasts from 'normal' ones, and I don't have any personal experience with them; I just noted what is on the datasheet.  I also noticed that the input pins are supposed to be differential.  Does that mean the INN pins can be grounded and the INP pins carry signal?  I don't know, and it would probably be worth it to find out.  Read the docs and do a little searching around.  It may turn out that you'll need a phase split circuit between the preamp and power amp.
Tubes and Hybrids / Re: Vox hybrid project
November 24, 2018, 11:33:10 PM
You should be able to simply hook it right in.  Make sure you have a large-ish decoupling capacitor at the power amp input.  I see from the datasheet they recommend 1uf caps at both INPR/L and INNR/L pins.  That should be a good start. 
Interesting... if you look at the "Footswitch Circuit" part of the manual (page 5), it says that the voltage drop across the LEDs is what actuates the switching functions.  Maybe check the LEDs and their respective resistors (R140 and R141) for  flaky operation.  Sure they light up, but is the voltage drop still on-spec?
Preamps and Effects / Re: Strange pedal issue
November 10, 2018, 11:56:49 PM
Quote from: flester on November 10, 2018, 03:27:41 PM
Yes the plug that won't work is TRS and it's the same with my other pedals. Explain?

Sent from my SM-G935F using Tapatalk

In a lot of pedals, the input is a stereo jack that has the (-) lead from the battery or adapter on the R lug, so that when you plug in a TS, it shorts to ground and you have power.  Your cable's TRS end obviously doesn't have any wire connected to the R lug, so the power never makes contact in the pedal.  Sounds like the cable is a home-build?  If so, simply open up the TRS plug and solder a wire from R to S.
I fried a Crate Mini-stack yeeeeeeeeaaaaaaars ago by accidentally plugging the speaker outs into each other.  Smoke smell and buzz were the result.  I'll hazard a guess that it's the same thing here.  If you open it up, you'll most likely find a chip-amp handling the speaker output, and the smoke will have escaped.  First thing I'd do is replace the chipamp and the output capacitor, then work backwards from there if that doesn't cure it.  I couldn't find any schematics or specs to suss out what variety of chipamp is loaded in there, but talk around the 'net says contact Crate and they can advise you on that detail.

Are you handy with tools and a soldering iron?
Amplifier Discussion / Re: parts
July 18, 2018, 05:18:19 AM
Quote from: dlbraly on July 17, 2018, 10:50:51 PM
Let me rephrase that
Please teach me how to figure out a replacement part.
Do I look at data sheets?

quick google someone said 2n5457 - so I guess I need to compare data sheets on those.

The 2SK30 is an N-channel MOSFET, not a JFET like the 2N5457.

I would go to, do a search for N-Channel MOSFET and plug in all the details you can from the 2SK30 datasheet in their search filter.

As far as suppliers, I tend to order a lot of parts from Tayda Electronics, but I've used Futurlec and Mouser a few times as well.
Tayda keeps up on what's in stock and available, and their shipping is reasonable.  Futurlec can have stuff you won't find anywhere else, but there are complaints all over the net about their shipping time, mostly because they will hold up your entire order for one item that's out of stock.

Tayda says 2SK30 are out of stock, Futurlec says they have them in stock, but don't believe them until you get a positive response.  Their "Contact us" page has phone numbers and email addresses.
Quote from: phatt on June 17, 2018, 08:20:21 AM
As to tone controls, be aware that "Tone mender" has a noise penalty but then most passive tone circuits do come with the old *Insertion loss* and as they are Hi Z they tend to pickup noise if your design and layout is a bit sloppy.

I spent many years bread boarding and building tone control circuits and the one that impressed me most was the HiWatt circuit. <3)

The most frustrating part was learning how to circumvent the noise problems. I doubt one will ever win the S/N battle but my PhAbbtone circuit is very quite when compared to Tonemender.

This will certainly work and (unlike fender and similar) has a midrange control that actually WORKS. ;)
This gives a big round bass as well as bright treble,, May even be too bright for your liking but you mentioned adding a top cut which is a good idea,, I just use a cab sim which has similar effect.
I've recently run across your PhAbbtone circuit, and will be the next thing I test.  A usable midrange would be nice, though I've found a flat midrange is enough.  I haven't noticed much issue with noise in the ToneMender circuit, but then again, maybe I'm just used to it :P
What impressed me about the ToneMender (with my subtle tweaks) is that when I cranked a knob, I FELT it.  Most generic FMV and the Baxandall circuits I tested were way too subtle, and the ToneMender even had usable tones at extremes of the knob positions, which I found amusing.  Hopefully, I can give a good report on the PhAbbtone...

QuoteThe other circuit that impresses me is a simple compressor that a FSB
member *mictester* designed and posted.
Original post here BUT you will have to be a member to read it.
I've seen that one as well.  I like the simplicity.  I've thought about having a compressor/limiter on the end of the chain just before the power amp just to keep things tame going into the watt generator, but that might not work as well as I think.  I prefer a comp at the beginning of the chain, and even then mostly for clean stuff.  Come to think of it, maybe a good compressor circuit might work well as a second channel if I decide to make this a channel-switching amp.  Not that I do much clean playing...  8|

QuoteIf any interest I can post my Cab sim circuit as well?
By all means.  That might make a good dedicated-out for headphone practice or in situations where I don't have access to a computer to play cab simulator (Yes, I know...).  Most cab sim circuits I've tried range from "is this thing on?" to "Good lord, what speaker is THAT supposed to be?".  Hopefully yours is different.

QuoteRegarding Power Amp design.
In My limited experience (hey it's only a hobby for me)
I've researched and tested Current FB setups on SS power amps and although it does alter the outcome it's a not mind blowing difference.
I've played a few SS peavey amps with Sat control (I think that is what it's called) and it does alter the outcome a bit but I suspect that a SS power stage running an output transformer might reap far better results.  but that bumps up the cost :-\
At high volume CFB seems to help but for home use it may not be audible.
I have a massive Factory type PA amp which has 70/100 volt output transformer as well as an 8 Ohm tap which does a good job of replicating a cranked Valve power stage but same limitation, you don't notice it at low volume.
Thank you for your insight on that.  When I first ran across the CFB idea, it simply made sense to me, even though I suspected it wasn't a huge difference in the sound (or else we'd ALL have CFB amplifiers in our home and car stereos).  That and Rod Elliott mentioned that CFB might add a little margin of safety for the speakers (emphasis on 'might' and 'little' :P).  I also have one of those 70 volt PA distribution transformers, which I bought a loooooooong time ago in anticipation of building a low-wattage tube amp.  Maybe I'll save that one for the eventual MOSFET experiments...

QuoteOh yes,,good looking job on that guitar. :dbtu: :dbtu:
Thanks, I haven't been able to put it down since I built it, which makes things a bit inconvenient when I think about doing a few details like shielding the cavities, taming a few wily fret levels, or tweaking the tone control.  I've also noticed it really does need a belly cut.  Age and a wife who's an amazing kitchenista has not bode well for my midsection.  ;)

Quote from: J M Fahey on June 17, 2018, 11:10:38 AM
here´s some of the new stuff, which I introduced at the 2018 Convention of the Audio Engineering Society Buenos Aires branch:
Holy smokes JM, those are some fancy lookin' amplificators.   :dbtu: :dbtu:

Quote from: R.G. on June 17, 2018, 01:31:56 PM
As usual, I have a mildly heretical viewpoint.   :)
I remember you from the stompbox forums.  Your viewpoints have always been helpful, heresy or no  8|

QuoteChip amps do have fundamental limitations on their ability to dissipate power. As a practical matter, the TO-220 packages like the LM1875 can only really do a 20W amp out at the edge of reliability. The LM3886 and similar packages can get to about twice that and be reliable without gigantic heat sinks.

My solution to this is to use the LM3886, which is an incredible deal at about US$5 each, and use more of them. There are circuits to parallel them up for higher currents and better power dissipation, and to run them bridged for higher voltage. However, I would not use them that way.

The LM3886 is quite reliable (given a decent heatsink) at 30-40W output. Most guitar amps run one 12" speaker on about 30-50W of amplifier power. When it gets over that most amps run two 12s or four 12s. Why fight the 30W per speaker practice? Why not make one highish quality amplifier per speaker. They're easier and more reliable that way, as well as more adaptable to situations and portability.

I just went through this in designing a replacement/repair power amp for the Thomas Vox amps. I opted for using an LM3886 per 30W speaker load. This covers the Buckingham and Viscount with 8 ohm loads with one amp each. The Royal Guardsman needs two modules to run two 12s at 60W, and the Beatle needs four for 120W.

It is far easier to get a 30W amp to run right than to get a 120W or higher to run right. And replicating several small things can be simpler than making one big one.

I did a PCB that is about 2" by 3" and runs one LM3886. I found a suitable heat sink for under $8 at Antek offers the AS-0522 toroidal transformer for $17.50, and this is a nearly ideal transformer to power the LM3886. You can fit the whole amplifier on one heatsink serving as a sub-chassis, power supply included.

And if one fails, you've thoughfully made one more power amp module than you really needed, so you swap in the spare while you fix the broken one.

Just sayin' ...
Thank you for the insight.  My current intention is to refill the unfortunate carcass of a late-80s Crate 'mini-stack' with my own design stuffed in the head and replacing the two 4x6" speaker arrangements with one 12" per cab.  Using one chipamp per speaker would fulfill my wattage desires, and have a little more beef than what was originally there (two TDA2030s, one for each speaker, running at 10 watts each).  Making these higher-powered chips run a little cooler would save me on power supply and heat sink costs.  Glad I wasn't the only one thinking on those lines. 
I'm really only intending to use the chipamps to get the thing making noise, and go discrete or MOSFET later.  I might even dip my toe in the Class D water someday, but today is not that day.
Thanks for the insight JM.  I knew the 2050s had gone out of production, but I didn't know it was that recent.  If I'd been paying attention, I would have snapped up some myself.  Either way, such is the fate of specialized devices, which is why I'm debating making this thing modular at the least.  I'll most likely build a proper discrete power section at some point, I'm leaning toward MOSFETs, but not sure if that's the best choice.
Until then I got these chipamps to make noise with, and that's what counts.

Back to the bench!...
Quote from: flester on June 16, 2018, 06:03:28 AM
I like the guitar project. I also took inspiration from Ovation electrics using the Viper body shape.

Those Vipers are pretty sweet, minus the pickguard; never liked those bubbly pickguards on the Viper or the Preacher, though I admit if I could own one of each, I probably would...

On to tone controls.
I've tested a few different takes on the Baxandall and the classic FMV tone stacks in my breadboarded preamp, and the one that ended up staying the longest is a slightly tweaked version of RunOffGroove's "Tonemender".  I wanted to like the Bax, I really did, but it's just too subtle for the duties I have in mind.  However, I've noticed a bit of high-end unpleasantness on higher gain settings of my preamp-currently-under-test, and now I'm wondering if there's something different that might work a bit better...
I'm thinking two gyrators for Bass and Mid, and a cut-only Treble.  The Bass control will be a 'shelving' control that cuts and boosts.  The Mid control will be centered at ~650 hz that only goes flat or notch. I may make it adjustable from ~350 to ~1200 hz because it's just only one more potentiometer, though I'm kinda questioning the usefulness.  Lastly, a cut-only Treble because the last thing most folks need is shriller highs from most amp topologies (mine included) that tend to end up on the sharp side of the spectrum just before tone controls anyway.
Thoughts?  Opinions?
If the capacitors have paper sleeves, a good trick to upgrading but keeping the "vintage" look is to put new caps in the old paper sleeves.  Done correctly, nobody will tell the difference.