The diyAudio First Watt M2x

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You can also use CL60’s in conjunction with a delayed SSR (solid state relay) as a soft start. That gives you back some voltage headroom without the drop caused by the hot NTC. Also, the NTC is only used for a few seconds to limit the in rush to charge the field of the trafo and bulk caps so doesn’t get or stay hot. Several designs are available on DIYA - check the GB Forum.

My BA3 amp build followed 6L6's build guide to the T, and used the stores board kit (that comes with Speaker protection and slow start boards) to build the slow start. It works great! I haven't used it in my other builds, relying on the tried and true dual CL-60 setup.

Russellc
 
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OK, 15K makes sense :) Overall, I think it's not so difficult to estimate the brightness if you have a datasheet of the LED you are going to use. I can do it, no problem.

But in general, I am a total newbie in electronics, so I would be happy if anyone could comment about my idea of wiring place of these front pannel diodes, as I really do not know if it's totaly fine to stick the diode and the resistor anywhere between the V+ or V- rail and the ground (observing the correct polarity, of course, anode getting "more possitive" side).

So, again, as I will not be using the output snubber, I will have a nice places left on the PCB that looks quite "ingenious" for me to be used for these diodes (R12, C17). OK?

Snubbers on the output side... I thought you were talking about the snubbers before the rectifier. That looks to be a great place to mount a resistor and put wires out to a LED - that would work great.
 
I have not used relays or separate speaker protection boards in any of my builds. I believe they tend in introduce more problems than they are supposed to solve. Especially for newer builders, who may be unfamiliar with the best way to connect these types of extra circuits.
I initially built my M2x according to the online diyAudio build guide. That was a great way to start. I used a single 400VA, 18V transformer, enclosed in a steel case, and a single 'Universal' PSU board stuffed with 22,000 uF bulk capacitors. I used CL-70 thermistors instead of the more common CL-60. These present a higher initial resistance, which drops to a negligible amount once they quickly warm up. There is no need for novice builders to use any of the extra "soft start" or "speaker protection" circuits. The M2x and other FirstWatt clones work best without them.
 
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All good advice, I never use the speaker protection boards but did use the slow start board in the BA3 build. It has functioned flawlessly for several years. At the time, I had no idea what it was, I just followed the 6L6 build guide exactly, and he used it in that build. He didn't use the speaker protection circuit, so that board is floating around the house somewhere.

That said, I cant convince myself that speaker protection circuits don't affect sound, maybe imaginary. Never used them and never had a fried speaker. Yet anyway....

Russellc
 
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Perhaps this idea from the WHAMMY headphone amplifier thread, might be apropos for the current discussion here. I've copied the original attachment and put it at the bottom of this post.

In one of my recent builds I decided I wanted a power indicator LED that stopped glowing the very instant I turned off the power switch. The DC supply rails don't bleed down to zero for many seconds, so I couldn't connect my "pilot light" there; it would remain ON for a long time after the power was switched OFF.

I connected it to the transformer secondary (AC voltage) because that DOES instantly drop to zero when the mains power is switched off. A series diode was installed to prevent the LED from entering reverse breakdown. The diode means I'm applying half wave rectified pulses to the LED, and relying upon persistence of vision to give the perception that this 60 Hertz flickering LED, appears to emit a continuous unchanging beam of light.

The rectifier diode is a 1N3595 because I've got a drawer full of them; they are small and have very low reverse leakage current, so the LED is very well protected. Probably a 1N4148 would have worked well enough. The LED is a wide viewing angle (112 deg) blue diode whose brightness rating is pretty high: 5000 mcd. So I'm running it at about 1 milliamp of RMS current
 

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I recently had a preamp issue which placed 6 volts DC on the input of my Alpeh J . The speaker protector functioned exactly as it was designed. After a simple repair on the preamp I was back in business. I dont build DC coupled amps without a protection circuit. The only degradation to the signal would be the relay contacts, which is a mechanical connection not much different than the speaker connector. That said I use some pretty heavy duty relays. The speaker protector offered by the DIY store is pretty simple and with a external heavy duty relay is a good solution.
 
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M2x is not a DC coupled amp. Capacitor C2 (schematic below) blocks DC from reaching the final transistors and from appearing at the amplifier output.

Some, but not all, of the input stage daughter cards include another DC blocking capacitor. "Mountain View" and "Austin" are examples.

677253d1524762146-diyaudio-watt-m2x-m2x_v1b_mainamp_schematic_image-png


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Two new M2x input stage daughter cards: IPS6 and IPS7

Last month I finished up the designs of two new circuits for M2x daughter cards. Gerber files were sent to Chinese PCB fabs, boards were assembled and tested, and everything worked great. At least to my ears, they sounded great too. However it seemed advisable to send a few sets of boards out to other M2x owners, people who had nothing to do with the creation of either of these circuits (thus no "proud parent" bias), and get their listening impressions too. If disinterested third parties liked the sound, that would be quite encouraging.

I'm pleased to say that all of the listeners gave thumbs up to both boards, so I am now officially releasing the designs into the public domain.

After friendly and productive discussions with the central committee of the diyAudio Store, all agreed that these will NOT be sold as part of an M2x product pack in the Store. Instead, the PCB CAD files (Gerber format) are freely downloadable & attached to this message. Anybody who so desires, can download the Gerbers and send them off to any PCB fab they like, to have as many or as few boards made as they wish. No restrictions. If you have extra boards left over, you can give them away to other DIYA members, or sell them for a modest profit, or put them in your eBay or etsy storefront. Whatever you please.

Because they're not part of the Store family of M2x boards, I didn't give these cards formal names like Ishikawa or Norwood. Instead these are just plain old IPS6 and IPS7. If you send the Gerbers out and have some boards made: you own them! Feel free to name these new boards of yours, anything you want. Reykjavik, Hobart, Podgorica, and Montevideo are open possibilities, among many others.

CIRCUIT DESIGN OF IPS6

All of the existing M2x input stage daughter cards operate as voltage controlled voltage sources. They all have high input impedance and low output impedance; in fact they all have an emitter follower output stage (Ishikawa has a source follower output stage, which is the same thing). The Efollower gives a very low output impedance.

I thought it would be interesting to drive the Edcor transformer from a voltage controlled current source, namely a "transconductance" amplifier, instead. Perhaps the resulting sonics would be different and, I dared to hope, the differences would be pleasing. Readers blessed with excellent memory may recall that another example of a transconductance amplifier here in the Pass Labs forum, is the First Watt F5. John Curl's famous JC-2 linestage is also a transconductance amplifier.

IPS6 uses a differential pair of JFETs, Q2 and Q4, at its input. These are biased by a constant current source, Q3. The left half of the diffamp works into a very high impedance load, namely constant current source Q1. Emitter follower Q5, whose input impedance exceeds 600 Kohms, copies the diff amp signal to the output transistor Q6, without loading the diff amp unnecessarily. Q6, operating as a common emitter amplifier, drives the output. Since it's a common emitter stage, the output terminal of Q6 is its collector, and the output signal is a current rather than a voltage. Q7, a constant current source, biases Q6.

Many M2x builders have urged, and pleaded for, an input stage daughter card whose performance can be improved and optimized by carefully matching transistors. None of the first five M2x IPS cards currently in the Store, offers that possibility. However, the situation has now changed and IPS6 is an answer to your prayers.

The input differential pair Q2 and Q4 can be matched, and circuit performance will improve if you do match them. You can apply any matching algorithm or methodology you wish; it is after all DIY and Y is You. The method which *I* used to match the Q2, Q4 JFETs for the IPS6 boards that I sent off to 3rd party listeners / reviewers, was posted here nine days ago. It is M2x thread post #3377 from 12 August 2020. But feel free to apply your own creative flair, and do the matching in whichever way you like the most.

There's more about IPS6 in another section down below.

CIRCUIT DESIGN OF IPS7

One way to explain the operation of IPS7 is shown in the cartoon attached below. In Part A we see that IPS7 is just an opamp, connected for unity gain (OUT shorted to INminus), with a pair of standard, ordinary "capacitance multiplier" circuits on the power supply rails. R1, C2, and Q3 are a capacitance multiplier for VUPPER ; R2, C3, and Q4 are a capacitance multiplier for VLOWER.

R1 and C2 form a lowpass filter; they remove ripple and noise from the input VCC. The filter presents a much smoother waveform to the base of Q3. This smooth waveform is copied by emitter follower action, to the opamp positive supply rail VUPPER). We have smoothed the opamp's positive supply.

R2, C3, and Q4 do the same thing, but to the opamp's negative supply VLOWER. They smooth the rail voltage.

Now look at Part B of the cartoon. It's the same opamp and the same pair of capacitance multipliers. Only this time we disconnect capacitors C2 and C3 from Ground; now we connect C2 and C3 to the input (music) signal!

The input signal is copied onto the base of Q3, and then emitter-followed onto the positive supply rail VUPPER. Now the positive supply rail is a time varying waveform instead of a DC voltage. It's a DC component plus the input signal.

The same is true of Q4 and the negative supply rail VLOWER. The negative rail is a DC component plus the input signal.

The input signal is superimposed on both supply rails.

This is good for a number of reasons, one of which is: it increases the opamp's effective PSRR to (almost) infinity. Here's why: Undesired noise at the opamp output pin, caused by less than perfect PSRR, equals (rail_waveform / PSRR). However since the rail waveform equals the input waveform, and since (it's a unity gain buffer) the input waveform equals the output waveform, therefore undesired noise at the opamp output pin is near zero. Thus the effective PSRR is near infinity. Very nice.

Copying the signal waveform onto the supply rails is not a new idea; it's been done with opamps for years and years. In textbook circuits the opamp is often configured for a gain greater than one, and generally they copy the output signal, not the input signal, onto the supply rails. This goes by the name "bootstrapping the supply rails". There's a nice article in EDN magazine by Grayson King and Tim Watkins of Analog Devices, entitled "Bootstrapping Your Opamp Yields Wide Voltage Swings", for example.

Another benefit of superimposing the input signal upon the supply rails, is illustrated by resistor R4 on the IPS7 full schematic. This resistor is connected between the opamp output and the negative supply rail. However since the nagative supply rail and the opamp output move in unison, the voltage across R4 is constant. Thus the current flowing in R4 is constant. Bootstrapping has given us, for free, a constant current source that pulls a constant bias current from the opamp output stage. This drastically reduces or eliminates crossover distortion in the output stage, and operates the OPS transistors at higher bias current (thus higher gm), improving linearity.

IPS7 also bows to user requests for more "opamp rolling" opportunities. It has two DIP-8 sockets on the PCB, and you can plug in either a dual opamp chip (like LM4562) or a single opamp chip (like OPA2134). I'm not saying this is a bad idea or a good idea, but at least now it is a possibility with IPS7. If using a dual, plug it into socket U2. If using a single, plug it into socket U1. Don't plug in two chips at the same time!!

A careful analysis of the IPS7 circuit reveals that when the input signal is zero, the opamp supply rails are about 18.6 volts apart. This delta is independent of the external supply voltages VCC and VEE. It's not ((VCC - VEE) - SomeOffset), it's a constant. Changing to a different power transformer or a different rectifier diode scheme, has no effect upon the rail voltages seen by the opamp. Vrail is independent of Vin. Unlike, for example, the Tucson input stage, where every 1 volt of change on Vin produces a 1 volt change on Vrail.

SETTING UP AND FINE-TUNING IPS6

After matching the two JFETs, stuff and solder the PCB. Do install resistors R3 and R4 but leave R5 unstuffed, unpopulated, and unsoldered.

Solder 3 cm long pieces of stiff, solid core hookup wire into the test point holes TP1 and TP2. AWG-22 works well. You will attach your voltmeter probes to these wires using crocodile clips.

Apply power supplies to the IPS6 board and connect your voltmeter to TP1 and TP2. It doesn't matter whether you connect TP1 to Meter+ or Meter-.

Twirl the knob of RV1 whichever direction makes the voltmeter reading smaller. Your goal is to find a setting which makes the meter read zero. When you get close, step away from the amplifier for 10 minutes and let it warm up a little.

Again twirl the knob of RV1 on the IP6 card, to make the voltage between TP1 and TP2 as near to zero as you can get it.

Step away for another 20 minutes.

Now twirl the knob of RV1 until the voltage between TP1 and TP2 is zero. It will still creep around, slooooowly, and that's okay. Just find a setting which makes the meter read zero, all these many minutes after power-on, and then ignore subsequent meter creep. Disconnect the crocodile clips, put a dot of some kind of sealing paint on the RV1 knob (Loctite, nail polish, etc), done. When you power off the M2, cut away and discard the two hookup wires attached to test points TP1 and TP2. You don't need them any more.

OPTIONAL: if you wish you can solder in a piece of wire (a "jumper") for R5. I never did, for all of the boards I built and tested and adjusted and sent out to third party listeners / reviewers. But you can do so if you wish. It's your choice; it's your option.

OKAY BUT HOW DO THEY *SOUND* ??

In my opinion they both sound great. The experiment of using a current source (transconductance) to drive the Edcor (namely IPS6) was, I feel, very successful. The result sounds, to several of us, almost exactly like the Norwood card. This is high praise because we all adore Norwood. One listener even said, if you want the sound of Norwoord but refuse to learn SMD soldering, build IPS6 instead, you'll be thrilled.

Bootstrapping the music signal onto the power supply rails (IPS7) was also a success, I believe. All of us used the Burr Brown OPA134 (which is a "single") for our listening tests, and we felt that IPS7 + OPA134 certainly delivers the goods. The M2x + IPS7 had tremendous agility and a sense of effortlessness no matter what it was asked to do.

Of course, if any of the (so far, anonymous) listeners want to speak up and describe their experiences with IPS6 / IPS7 in greater detail, please by all means do so. With grateful thanks from everyone!

BUILDING IPS6 AND IPS7

Anyone thinking about constructing IPS6 or IPS7 has already built and debugged a complete M2x amplifier; such people are decidedly not beginners. The supporting material for IPS6 and IPS7 therefore assumes an intermediate or expert skill level; there are no "training wheels" tutorials or laborious hand-holding guidelines. Only what you need to get the job done. Schematics are attached below, in pdf and png format. Detailed parts lists are provided as Excel spreadsheets (wrapped inside .zip archives). PCB manufacturing "Gerber" files, the same ones I used to order my boards, are attached in .zip archives

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Hi Gary, I think when you download the Gerbers and put them into your GerberView software, you'll discover they are perfectly compatible with the Store's M2x PCB and hole placement. I think if you compare what you see in GerberView versus what you see in post #56 of this thread, you will conclude: these boards ought to fit into every single third party listeners' M2x amp with no modification, AND they will fit into YOUR M2x amp with no modification. After all, that's how I was able to get reviews from M2x owners without asking them to modify their amplifier.

There are lots of free GerberView software packages; I suggest you just pretend you're about to buy boards from (your favorite PCB fab). It will ask you to upload your Gerbers in order to prepare a price quotation. After you've uploaded, the PCB fab website will tell you the X and Y dimensions of the board. Then simply log off and clear your browser history, without giving your credit card number. Fast and easy.

There's also www.pcbxprt.com which runs inside your web browser and doesn't ask for your email address.


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We knew there would be additional boards, but little did we know when we built M2X that it was going to be a life long project. Thanks Mark for making it so. The parts for my Tuscon and Mountain View boards arrived today and now I have to order for 2 more boards. I promised myself I would get Mark's Softstart H9KPXG up and running before I built anything else but how can I resist IPS6 and IPS7 daughter cards? I think I'll be ordering some more boards soon....
 
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Derek, that's outstanding! Excellent in every way! Did you make creative modifications to the bottom silkscreen layer too?

If you feel like it, you have an opportunity correct my top silkscreen mistake on "IPS6" -- I left the numerical value of R6 visible when I meant to make 200R invisible. (Why? because for most other parts there simply isn't room to display the numerical value. Delete some --> delete them all).
 
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Giving away some IPS6 and IPS7 PCBs

I have a number of extra PCBs for IPS6 and IPS7 left over, sitting on the shelf, unused. Rev.A IPS6 and Rev.B IPS7. I ordered
  • Black epoxy
  • Gold traces ("ENIG")
  • 1 ounce copper (35 microns thick)
I would be happy to give these away for free and I will pay the shipping cost myself, but only to energetic DIYers who convince me they will build and listen to these boards very soon. Members who accumulate/hoard PCBoards, thinking "some day I might get around to this", you have every right to organize and operate your hobby your way, and I applaud your self awareness. But I won't send you these few extra PCBs; my own preference is to send them to DIYers who will build and use them right away.

Here is an outline of my offer:

  1. Good through 31 October 2020. After that: no more

  2. Shipping ONLY to USA. Furthermore, shipping ONLY to USA addresses which do not require a customs form. That means: no Guam, no Puerto Rico, no American Samoa, no USVI, etc. I apologize to members outside the USA but I am unwilling to accept the annoyance, cost, and risk of international shipment including customs forms. When that happy day arrives and we've all been vaccinated, I'll go back to business as usual. Until then please accept my apologies. You can still order PCBs yourself, from the Gerbers I've provided, and have them shipped directly to your address. You can still organize a Group Buy to do this among several members.

  3. Send me your paid invoice from Mouser or DigiKey, showing that you have indeed purchased all of the required parts to build a pair of IPS6's or a pair of IPS7's or both. Use Private Messaging and an image host service such as imgur.com. Also include your ship-to address exactly as you wish it to appear on the shipping label.

  4. I will send you three (3) IPS6 PCBs or three IPS7 PCBs or both, depending on the parts you've bought, and I'll pay the shipping fee. Three boards for two stereo channels means you can make one unrecoverable (fatal) assembly mistake and still end up with a working stereo pair. Don't worry that I might run out of boards; if necessary, I will order more so I can ship to everyone who satisfies all the requirements.

  5. I will send you exactly 3 PCBs. (6 if you bought parts for both IPS6 and IPS7). You'll have to order from a PCB fab, using the Gerber files I provided, if you want more than that.

  6. I'm doing you a special favor. Try not to ask for additional special favors, above and beyond this one. You risk getting put into the "whiner/beggar" category which might receive lower priority.

  7. Pay careful attention to the word all: "... showing that you have indeed purchased all of the required parts".

Happy DIYing, -MJ
 
Class act Mark, I have a lot on the plate right now, but I will build them when I get the M2X Monos done, I got the first one done, but had to do a time out to organize the lab. I was spending more time looking for stuff than I was building.



I hope you will make these available in the future, if you order some, I'd be happy to pay my own way. A realistic time frame for me would be 6 weeks, so Ill let these go to those who have the time to build them right now.



Toss a couple in the drawer for me if you order Mark, you know I build like a madman when I get going. :)


Thanks again for your donations to the community!



JT
 
With preamps like Whammy and BA2018 linestage (with large output transistors) these should be able to drive Edcor directly. Then I was thinking of an input board which only has the green coupling cap to protect Edcor against DC. Would that work?
Maybe a Tucson board could be modified for that purpose......I have several.