Group Build: Dynafet

[luvdunhill]

The only logistics question is that his kits are tailored to very specific toroids with certain VA values.. if we want to things like run 2 boards off a big transformer or values not in sync with what he normally kits for.. do we need additional parts? If so what type? I imagine even if we need to buy some parts separately it will make going with glass jar audio worth it since his prices are so insanely low.

no, he can kit for the output voltages we need, and VA isn't really other than whether or not he includes the on board heat sinks, or we would use off board heat sinking or the 2.5" tall versions of that heat sink footprint.

[Icarium]

So Spain is interested in 6 kits then? When will we pin down what output voltages we need or is that more of an individual decision?

[deepak]

Yeah I am in talks with glass jar audio. He said it'd be ~67 dollars a kit without toroids and he might be able to give us an additional 15 percent off for a bulk order and is willing to handle shipping to people provided we give him a list.

If you wanna post the spreadsheet that'd be $$. I was going to do it after work tonight, but yeah that's in another ~8-10 hrs or so

The only logistics question is that his kits are tailored to very specific toroids with certain VA values.. if we want to things like run 2 boards off a big transformer or values not in sync with what he normally kits for.. do we need additional parts? If so what type? I imagine even if we need to buy some parts separately it will make going with glass jar audio worth it since his prices are so insanely low.

I'm in for a S22 kit through GlassJar without tranny if that is possible.

[Icarium]

Sure Deepak. I'll add you in after lunch.

[PICaudio]

I'm not sure, but I think the spanish gang will use the same output voltage as the rest of the group.

Is it possible to use Nuvotem Talema transformers in the S22?, because they are very easy to us get it in Spain and they have a good price.

This is the datasheet of the 2x30v 225VA.

Are Piltron or SumR transformers a better choice than Nuvotem?

Sorry for repeating the question, but for me it is very important to know if we can use these transformers.

-- o --

Rodrigo

[Icarium]

I don't know myself.. unfortunately I don't think anyone really knows unless we get some prototypes made.

[Pars]

I'm not sure, but I think the spanish gang will use the same output voltage as the rest of the group.

Is it possible to use Nuvotem Talema transformers in the S22?, because they are very easy to us get it in Spain and they have a good price.

This is the datasheet of the 2x30v 225VA.

Are Piltron or SumR transformers a better choice than Nuvotem?

Sorry for repeating the question, but for me it is very important to know if we can use these transformers.

-- o --

Rodrigo

The Talema transformers are (IIRC) the same as the Amveco sold here at Digikey (although they don't have one that is big enough here). If you are putting these in a single box build, you would want to get the transformers shielded, and possibly potted in a can. Not sure if electrostatic screening is required or not? So in answer to your question, can Talema provide units like this for you?

As far as I know, the DynaFET would take a +/-30V PSU. If that PSU is a sigma22, then 2x30V is the correct transformer for that. If the PSU were a Gilmore Dynahi PSU, you would want to reduce the transformer secondaries to 2x28V; maybe lower. 2x30V will run too hot on one of these.

[Torpedo]

So Spain is interested in 6 kits then? When will we pin down what output voltages we need or is that more of an individual decision?

I can't speak for Hitori nor Rodrigo, but I think that getting the S22 boards and parts at $67 is a good deal, and if the kits come assembled it will save Rodrigo some additional work. For me it's fine. If they agree they'll say soon.

IMHO it'd be good the kits came with the onboard heat sinks, the ones required to dissipate the power two Dynafet boards ask from one S22. I suppose that'd be the same for everyone. In the same way I guess we all be using 30V output trannies.

Icarium, thanks for updating the spread sheet with the transistors needed.

[deepak]

The GlassJar kits aren't assembled.

[Torpedo]

The GlassJar kits aren't assembled.

Sorry for you Rodrigo

[PICaudio]

Sorry for you Rodrigo

Don't worry Torpedo. :)

The spreadsheet it's ok for me. I want 2 Sigma 22 with his components and 4 Dynafet transistors sets.

-- o --

Rodrigo

[hitoridekimasu]

Hi all,

Sorry for the delay in taking part of this thread. I've been very busy last days.

I'm also interested in 2 S22 kits and 4 DynaFET transistor sets.

BTW, my experience with Nuvetem toroidal transformers is not bad. I don't know if we are running out time deciding if we will go for SumR transformers or not, but, if we are not, I can do my own EM radiation test at my company labs. My company buy to RS every week, so I think I can order one Nuvotemtem unit for these tests.

Cheers

[Pars]

Here's the glassjar spreadsheet for the sigma22.

sigma22 BOM.xls.zip

[PICaudio]

The Talema transformers are (IIRC) the same as the Amveco sold here at Digikey (although they don't have one that is big enough here). If you are putting these in a single box build, you would want to get the transformers shielded, and possibly potted in a can. Not sure if electrostatic screening is required or not? So in answer to your question, can Talema provide units like this for you?

As far as I know, the DynaFET would take a +/-30V PSU. If that PSU is a sigma22, then 2x30V is the correct transformer for that. If the PSU were a Gilmore Dynahi PSU, you would want to reduce the transformer secondaries to 2x28V; maybe lower. 2x30V will run too hot on one of these.

Ok Pars, many thanks for your info.

I don't know if Nuvotem produces transformers with electrostatic screen .

-- o --

Rodrigo

[Pars]

There would have to be a mechanism to specify options... if these are just off the shelf then my guess is they are not shielded, screened, etc.

[luvdunhill]

What about Justin's suggestion of the input filter? Here's one that I used, and I've also swapped the location of R34-R35 to be after the caps. I'm partial to polystyrene caps here (e.g. Newark 96K9640), but micas are another possibility.

While we're on the subject of caps, I've had very good luck using Teflon (PTFE) caps in feedback loops. Would it be possible to add a second pad to support this? This would not be a standard option, but more for me to tweak with The Voltronics stuff at Mouser is good, but very expensive. Another choice would be Vishay/BC sold at Newark. Both places, just search for "PTFE trimmer". All that really needs to be added is one pad... what that be possible?

Finally, what about adding the Wima FKP2 bypasses (edit: across the bulk supply capacitance)? I still think this is a good idea wherever possible.

bump I've found a PTFE trimmer that seems to be a simple 5mm pitch. So, I'd like to add this form factor to the feedback cap, along with the above stuff, if at all possible.

[Pars]

I was asked by Icarium to mention the possibility of incorporating selectable gain into the design. I don't need it, but wanted to bring it up as a possibility. My thought was perhaps two positions? I know there was discussion regarding this in the Dynahi build thread on HF a couple of years ago, and it is certainly doable. Would probably require a different compensation cap, etc. Any interest in this?

[luvdunhill]

I was asked by Icarium to mention the possibility of incorporating selectable gain into the design. I don't need it, but wanted to bring it up as a possibility. My thought was perhaps two positions? I know there was discussion regarding this in the Dynahi build thread on HF a couple of years ago, and it is certainly doable. Would probably require a different compensation cap, etc. Any interest in this?

sure, why not discuss it Any proposition on what needs to change and a mechanism to do so?

[Pars]

The original schematic shows a 1K feedback resistor with a 10pf compensation cap. I'm not sure how to calculate gain in this, so I don't even know what the stock gain is. If it is like the dynalo/dynahi, it is probably around 11?

[Pars]

In the original schematic, it is a 1K feedback resistor with a 100 ohm to ground, so should be a gain of 11 ((Ra / Rb) + 1). Per amb's advice on headwize, in order to change gain it is probably preferable to increase Rb (the 100 ohm) instead of lowering 1K to prevent loading the output. Something like 221 or 330 ohms in series with the 100 ohm and shorted by a DPDT switch (4.1 or 3.3 respectively) might work. Not sure how to adjust the compensation cap in parallel with the 1K. Intuitively I would think its value would need to decrease?

[Torpedo]

IMO it'd be great having lower gain or a selectable one. For most cans, considering a 2-3V output source, 11x is too high, even 8x is very much considering my experience with the Beta22.

Any idea what would be the lowest gain the circuit can take without becoming unstable?

[Icarium]

Okay I think I have enough information to pin down the group buy for sigma22 kits.

So please let me know if you want kits or if you do no want kits! If you want kits then read further!

I've talked to luvdunhill and he says that onboard heat sinking is probably not sufficient for 4 board builds and Jeff from glass jar has agreed he can omit them for a savings of another 6-8 dollars per kit.

He says if we know a particular type of heat sink he can try and order those for us. I don't know if any on board heatsinks can possibly be sufficient, but maybe a DIYer in the know can recommend something.

Other options are upgraded Muse caps for the sigma22.. he says he feels these are not necessary so generally doesn't go with them, but they are availalbe if people want that.

Also he can do pretty nearly any sort of LED colors if people want whatever colors for that.

So within a week I'd like to pin down how many kits each person/group wants and what options they want and the address they'd like it mailed to.

Options are:

1. Onboard heatsinks (Yes/No/Special order?)

2. LED colors

3. Upgraded Muse caps (Yes/No)

Non dynafet people are of course welcome to request kits as well.

Team dreadhead and team Spain will probably want their stuff mailed to one address so just providing me with that address is enough.

After I get all that info I will get precise quotes from him and then we figure out payment.. either you to me and me to him or you to him directly. The latter may be too confusing from his perspective so.. I'll work that out with him in the mean time.

I'd like to get these kits delivered within a month.

1 week to pin down addresses/configs. 2 weeks to get payment sorted out and kits shipped and another week for them to arrive.

Thanks!

P.S. PMing me info is probably the best.

[vvs_75]

Lots of people used S22 with onboard heat sinks in their B22 (balanced configuration) and l do not remember reading problems with overheating.

If we use the tallest 2.5" inch heat sinks and not 1.5" ones with one S22 per stereo channel we could be fine. I built my B22 with off board heat sinks, so I could be wrong.

I think naamanf and n_maher have more experience in this regard.

[Icarium]

Nod. Well personally I may get them anyways... I'm undecided. It's just an option for people who knows they will be using more heavy duty heatsinking and would like to save a few extra bucks a board.

Need to gather the infos!

[Pars]

I would think it would be difficult (or at least not particularly clean) trying to use off-board heatsinks on a sigma22, as the output devices are on both ends of the board.

Maybe I'm thinking inside the box too much?