Moskido - Hybrid Aikido/MOSFET amplifier

[ErikdeBest]

Hi Owen

Just take care Broskie is benefitted by your efforts in some way! I understand you are not aiming at a profit on Broskie's work, but we don't want the man angry, do we?

BTW, the idea of a PCB sounds nice, but I haven't got the money, so I will have to pass this one!

Good luck! Erik

[amp-guy]

actually I was thinking of using Johns great looking pcb
and combining it with a new pcb for the power stage.

[agent.5]

Originally posted by amp-guy
hmmm iam not seeing it there

Are you talking about my link? It is at the bottom of the page.

[opc]

Hey Guys,

Sorry for the late response, we have company visiting and things are pretty busy here.

@amp-guy:

I'm with you 100% on the bipolar design, but unfortunately my friend doesn't seem too keen on making a bipolar supply (not really sure why) so that aspect of the design is pretty much locked into the version of the attached schematics. I cringe every time I see that output capacitor, so I know what you mean. As for the bias and output adjustment, I'll look into it, it's certainly a good suggestion. Also, I'm going to add take-off points to the output section, so if you want to use John's PCB for the tube section, you can just run some jumper wires over to the output stage and power stage and you'll be off to the races.

@agent.5:

I think maybe you misunderstood amp-guy's request (either that or I did). I think he's referring to a bipolar output section, with the coupling cap between the output and the loudspeaker. Your schematic is of a bipolar Aikido section, and I think it adds a little too much complexity to the design, with the input and output transformers. I personally would be interested in a fully balanced design, but the transformer coupled bipolar Aikido section seems a little out of place in this amplifier.

@ErikdeBest

I'm certainly not trying to step on John's feet here, this is a one shot deal, and I'm certainly not planning to make any money on it. I would have just done the power supply and the output stage, but adding in the Aikido stage was a natural choice given that there's enough space on the PCB. If it makes you feel any better, I'm adding in a full set of jumpers so if you happen to prefer John's board, or if you already own one, you can just wire it in and leave the Aikido stage on the PCB unpopulated. If someone cares to measure the hole distances on their Aikido PCB's, I could even put some holes for mounting stand-offs so you could mount one of John's Aikido PCB's directly above the unpopulated tube section on the PCB itself.

Anyways, I hope this answers a few questions, and keep the comments coming!

Cheers,
Owen

[amp-guy]

sorry for the confusion what I meant was that for myself iam
looking towards a design using the international rectifier mosfets
(probably two pairs or more) with bipolar power supplies
direct coupled output . trimpots to adjust bias levels and offset
would be a worthwhile addition as well.


It seems there is a growing interest in hybrid amplifier topologies.
We are seeing a growing number of commercial products that are
including solid and hollow state (?) devices .
Moscode, Counterpoint, Pathos, Vincent all have hybrid products some more succesfull than others.
I think it is time for another DIY adventure.

[opc]

Hey Guys,

Well, the PCB is pretty much finished with the exception of a few minor changes. There will be some small heatsinks added to both the diodes in the 60V supply section, and the Vreg on the side of the board. Also, there will be bypass caps added to all three power supplies, the 60V, the 300V, and the 6.3V

As far as flexibility goes, you could run 6.3V or 12V depending on the regulator you choose, you could run any voltage you want on the tubes depending on the transformer you choose, or any voltage on the fets depending on that transformer. I'll include a full parts list for building it with a 60V SS supply, a 300V tube supply, and tubes that have 6.3V filaments.

Most of the electrolytic caps are Elna audio grade, but you could put pretty much any aluminum electrolytic in that spot. I'm using Solen PP caps for coupling and speaker output bypass, but again, you could use anything that fits.

If there are any questions about the design or parts used, let me know and I'll see what I can do for you. For example, it there are a few other popular electrolytics, I can add more holes for common spacing.

For reference, the tube sockets are octal PCB mount from PCX, the resistors are sized for 1/2W PRP's and the higher power resistors are Mills 5W. L2 is a 15H choke from Hammond, L1 is a 1 mH inductor from Solen, but you could put a power resistor there instead if you wish to cut costs.

The attached picture is pretty poor, but that's all I could do to get it down to 100kb. I have a really nice PDF with the schematic and a much better PCB layout, so if you're interested write me a note and I'll send it to you.

Cheers,
Owen

[plaurine]

Nice looking layout, how long did that take? all the blue, is that a ground plane?

[tinitus]

How about starting a "group buy" to get price down

About caps, I think Mundorf would be fine, ELNA too if I knew where to buy them here

[amp-guy]

looks a little tight around the tube sockets
are you sure there is enough clearance there?

[opc]

Hi Guys,

This is the last post I'll be making on this thread, as I'll be starting a new thread in the Group Buy section to avoid hi-jaking this topic.

@plaurine:

The layout took a few hours to do, but the fellow I'm working with put a lot of work into the schematic and footprints, which take a great deal of time to get done. All together there is a good 30-40 hours of time put into this.

The blue layer (bottom layer) is indeed a ground plane, which helps keep noise to a minimum, and provides a good low impedance path for critical ground connections.

@tinitus:

We're only going to order 20 of the boards described, and 16 of them are already spoken for. If all of these sell, then I'm going to re-design the PCB and only include the power supply section and output section like several people here have requested. This will allow people to buy John's PCB's from him, and buy a ready-to-go add on section to make a Moskido. This way I won't be stepping on anyone's toes, and the price will be lower thanks to the smaller board area. I'll keep people posted on a new thread in the Group Buy section.

As for caps, both the Mundorf and Elna should fit without a problem the standard snap-in cap footprint with 10mm spacing should fit the majority of electrolytic caps in the values of interest.

@amp-guy:

The layout is fairly tight around the tubes, but there is plenty of room for everything there. I always do a test by printing the PCB to scale on paper, and placing the parts where they would go to make sure there are no clearance issues. The tube sockets are actually smaller than the footprint implies, so it's not nearly as tight as it looks in the image. If anyone plans on using really huge coupling caps, let me know and I'll shuffle a few things around to provide more space.

The order for the PCB's is going in tomorrow or Monday, so let me know before then! When we get the boards in a week or so, I'll post a new thread with some pictures in the Group Buy section.

Cheers,
Owen