Hey guys, I recently bought tubes and circuits and have slowly been making my way through the book!  So far it's been a very good read, some of the math is a bit over my head, but I believe I'm getting a better grasp of what's going on.  Anyway, I've been thinking of building the 300b se otl from scratch (possibly 3 of them), but I do have a few questions before I embark on the project.  Has the schematic been updated since the release of the book? Are point to point instructions still available incase I run into trouble?  I was planning on building 3 of these, I have an active crossover and a fully horn loaded system (klipsch la scalas [soon to be a 2 way] and a very large horn loaded sub).  Anyone have suggestions on a better course of action?
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In the book AC is used for the filaments. Should be changed to DC.Also each tube should get its own regulator.

I use active La Scalas (two way,tweeter connected with a passive 2nd order x-over), the mid-horn/tweeter without the "box". This adds a lot of airiness and openness.  I was planning to test the mid-horn/tweeter with my 300B SE OTLs but I have a feeling that this will not be enough for real dynamics. I would recommend the Pinnacles instead which I am using right now.  The mid-horn might need some EQ depending on the room. The Behringer Ultradrive has everything that's needed for best results( EQ, delay, dynamic EQ, selection of x-over filters). Besselfilters sound best IMO in the case of the La Scalas.
I added 2 active OB subs with servo control which replaced my Velodyne 18" active sub. I would never go back to a single sub or listen with anything else for the bass. But a horn loaded sub might also be a good choice with the La Scalas.
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...... but I have a feeling that this will not be enough for real dynamics. I would recommend the Pinnacles instead which I am using right now.... 

With what pre/passive do you drive the Pinnacle? Tks.
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I am useing a EF86 single tube buffer with gain (24dB). This thing can drive anything with extreme dynamics. The Pinnacles really shine when they are getting a strong input signal.

Btw, I have tested in the meantime the 300B SE DC OTL with the La Scalas and have made some  modifications which turned out to be another step up. I use a Maida regulator replacing R8 and C2. The nice part of this mod is that it doesn't need any changes in the psu or additional transformers etc. for the reg. as it can use the 180V DC from the original psu. The reg. also doesn't need a heatsink at only 5mA. So it's a very simple but effective improvement for everybody who has a SE 300B and wants to drive it into stellar regions of SQ.

I also use it with 18k for the NFB resitstor (R15)which gives 7V p-p undistorted voltage swing into 16ohm. The La Scalas midhorn/tweeter  have 11,7ohm impedance (1kHz) which works absolutely fine with these settings. It's still not 100% enough power for extreme dynamics but covers maybe 95% of what can happen with music. I am very satisfied with the results. The Pinnacles still feel to be more dynamic but the SE makes up for it with wonderful sound colors and more subtle details at lower levels.I think that's why people love SE amps.
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Hi Wolfgang:

Interesting qoute "Maida regulator replacing R8 and C2" unqoute.

The last 15 year I only use voltage regulators on pre amps and tube drivers. I use the old fashioned gas filled voltage regulators, have the tube pull around the same mA as the circuit does which is connected to it. The the voltage regulator tube is bypassed with a Russian silver cap of 0.1 uF. Love the sound.

I found it very beneficial if it is used in driver tubes in a power amp where the voltage is rippeling all the time.

I will try you higher NFB resistor value.

Question do you use a small capacitor here to to get the square wave as good as possible?

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Anonymous
No need to go with maida, the stock power supply is good enough.
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Question do you use a small capacitor here to to get the square wave as good as possible?


I don't use one. Don't think it's necessary.

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No need to go with maida, the stock power supply is good enough.


If this is your opinion, well, that's then just how you feel about this topic. But if you want to add some helpful information you should first try and listen yourself. If you simply would have looked at the specs sheet of the Maida regulator you would have realized that no CLCLC psu can match those qualities expressed in those numbers.

Here is the link in case you want to inform yourself: neurochrome.com/collections/power-supplies/products/21st-century-maida-regulator
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PetrL
Wolfgang, the Maida regulator seems worth trying to me, as the board is quite small (would fit in my chassis). However, what puts me off is the high price for 1 regulator, 1 transistor, some diodes plus mini pc board. Do they sell empty boards too? Maybe the price is mostly adequate to sound improvement. But what about reliability, did you have any issues?  The transistor has basically 180V on heatsink, right? Are there any changes in passive parts necessary? (I mean typically the input voltage will be much higher than in an OTL)
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Petr, most of the parts are SMD and  already soldered to the board. That makes it very easy to add the caps, the power transistor, the current and voltage resistors and the trimpot for adjusting the correct output voltage.. That's why this board isn't sold as "empty PCB", I guess, because it needs a smd baking oven for getting all the SMD parts on the board.
I never had any problems and I use  them  for years in phono pre, amps, buffers. The back of the transistor is metal and needs to be insulated. But you don't need a heat sink in this case as it gets hardly warm at 5,3 mA.
It comes with a calculator  written in EXCEL. You just input voltages (in/out) and it calculates the part values for you.
For the 300B, using the existing psu with 180V DC output, you need 200V caps and R3=100R/0,5W and R9=75k/1W. I always use max current setting quite a bit higher because it sounds better. Input of the reg. is hooked up to 180V of the OTL psu , output is set to143V with the trimpot. That's it.

You can also create symmetric voltages (2 rails) which is what I did with the Inverted OTL. Here is a picture of the final version:
https://www.dropbox.com/s/rnxxexpfc07e4cd/InvOTL.jpg?dl=0 

You use 2 regulators/transformers and wire them with an artificial ground. That would also be needed for the Pinnacles in case somebody wants to try the Maida reg. there.


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PetrL
Good to hear  about the reliability. For the time being it is matter for thinking for me, because the cost I find prohibitive (plus import taxes). The SMD soldering is not as messy as it seems. With thin solder wire and soldering tip, it is feasible, even easy for 2 to 3 terminal parts (IC is another story) And magnifying glasses I use anyway.
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Petr, you can find the schematics and more discussions here: https://www.diyaudio.com/forums/vendor-s-bazaar/209067-21st-century-maida-regulator.html

It's doable no doubt and you can also use smd parts only where it's absolutely necessary. I don't think the tight packaging which is only possible with smd is of any issue in case of a regulator. But you will end up probably with a bigger PCB.
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PetrL
Thanks, Wolfgang. I suppose the thread founder is the guy who sells the module. If I figure out all details (setting current you mentioned etc), I probably solder something. What puzzles me, again regarding the price: the Maida regulator is public domain,  the Canadian probably only used up to date parts (low drop regulator) maybe tuned some details, but chooses steep price. That probably means nobody else is making modules for Maida regulator? Strange, if it can be used in most any small signal tube circuit.
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He is the the guy who sells the module. As he also has published the schematics everybody can make those modules but he is the only one (to my knowledge) who offers them together with very a good manual and calculator. As this reg. can  also replace the whole psu(800mA is the limit) it might be  even cheaper than a CLCLC if you can make it yourself. High voltage/high capacitance caps are pretty expensive. And as it outperforms a typical CLCLC in every sense one must wonder why it isn't used more often in tube amps.
This is what you can find now more often: A developer/EE/ hobbyist with some electronic background starts a thread in diyaudio and gets lots of input in the follow up discussion. That helps him to improve the design and to figure out what the people want. People buy "beta version", pay the  full price, and test the modules practically for free, and all the bugs that  show up over time  will be  reported in the thread (happened with the first Soekris DAC modules) and can be fixed by the developer.  Then he offers a PCB or PCB with SMD parts. Like this DIY gets a little harder for DIYers out of obvious reasons. So people tend to buy the partly populated board for which a higher price is more likely to be accepted. Of course it is work to get the layout for the boards and  get them done with the SMD parts but DIY shouldn't use the same mark up as High End audio (300% and more).

It's really a tricky business if you want to make a living with all the competition at your heels and not to fall for the greed.
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Anonymous
I have one extra board, interested please let me know. A little pain to solder the SMD resistor.
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Petrl, a couple of options available to you if you wan't to try Maida Regs.

1. Perhaps contact this guy to see if he has any of his PCBs available.

https://www.diyaudio.com/forums/swap-meet/350806-21st-century-maida-regulator-pcb-thingy.html

The boards are based on the schematic in the DIY Audio discussion thread that Wolfgang linked to above so are entirely 'legitimate'. I've used several of them, including in my scratch built masterpiece HPA, and they work very well. The nice thing about these DIY Audio pcbs is that they include the rectifiers and filter cap. They do involve smd soldering though. If you do get any of these boards I can let you have a BOM with Digikey parts that i know will fit the PCB. BTW, these PCBs include an additional circuit for filament referencing - I can't comment further as I've never tried to use it.

2. I have a spare 'official' Neurochrome Maida Reg board, fully populated and currently configured for, IIRC, 300V @100mA, but easily changed by swapping out couple of through-hole resistors. I also have a separate PCB with a FRED diode bridge and 500V filter caps to go with it. It was installed in a project but then removed when I changed my plans. Happy to provide you with a bargain! Drop me a mail if you're interested.
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