[FallenAngel]

I should have enough 2SC1815/2SA1015 in the parts bins to populate a board, you can have for free, and they're already grouped by hFE (well, most are O and some are GR), PM me your address and I'll drop them in the mail.

 

[the_equalizer]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif I should have enough 2SC1815/2SA1015 in the parts bins to populate a board, you can have for free, and they're already grouped by hFE (well, most are O and some are GR), PM me your address and I'll drop them in the mail.

Oh my... thank you so very much!

 

[breizheau]

I replied Oscar and i have to check the 2SA & 2Sc

 

[Bizzel]

Apologies for resurrecting this thread but I felt this was the most appropriate place to ask, rather than starting a whole new thread for one question.
 
I'll be using a Sigma22 power supply for a balanced dynalo build and I wondered how this affects the choice of toroidal transformer to use. The AMB site has a nice table that shows VA ratings but only when used with beta boards and I imagine they draw a fair bit more power.
 

Number of B22 Channels	Recommended Transformer Rating
2	50VA
3	80VA
4	100VA

 
Could I get away with 80VA or even 50VA with 4 dynalo channels (2 boards)?
 
Edit: With some further searching I found an earlier post from amb recommending a 50VA 2x 18v toroid. Hope that helps anyone else in my position.

 

[bidoux]

"Current consumption for the Dynalo if I remember right is around 100mA per channel" from Pars here

 So four channels is 400mA. If you power the sigma22 with 2*18VAC input it should be P=36*2^0.5*0.400=21W or 21VA. 25VA should be too low (transformers heats up). Now, I'm not sure about the consumption of the Sigma22.

 

[bada bing]

I've built a couple 2 channel dynalos powered by S22s with 35va xformers.
The transformers have no problem at all and I set my amp bias on the high side.
Most likely, you'll want to be on the low side with your bias because of the additional
heat. The dynalo outputs get pretty hot for little TO92 devices.
 
I believe that when set with specified bias, with all but the lowest impedance phones,
the +-16.4v runs out of voltage (clips) before it falls out of class A.  If you're happy with
the heat and power when unloaded, it shouldn't draw any additional current or get any
hotter under normal loads.
 
Yours should make a very nice amp. I like the dynalo and S22 combo a lot.
 
I was surfing around the headwise library a few months ago and got interested in the
balanced bridged output option KG wrote up in the original project. 
The dynalo topology has the inverted differential signal created at the input fets but not used. By adding 
2 output channels, it can run either balanced or SE output off a SE input. A servo centered, balanced
output from a SE source and a 2 deck pot. Very cool. Very little cost for the addition. just output
transistors-n-glue and a PSU big enough to drive them. I wonder why there hasn't
been more interest in the addition ? Has anyone played around with this ?  I haven't found much
discussion of it.
 
I've been slowly cleaning up some board files for an add-on board
with the two additional output channels.  Maybe this winter I can get it done.

 

[Bizzel]

I didn't know that, thanks for the info!
 
Quote:

The dynalo topology has the inverted differential signal created at the input fets but not used. By adding 
2 output channels, it can run either balanced or SE output off a SE input. A servo centered, balanced
output from a SE source and a 2 deck pot. Very cool.

 

[Pars]

Quote:

"Current consumption for the Dynalo if I remember right is around 100mA per channel" from Pars here

 So four channels is 400mA. If you power the sigma22 with 2*18VAC input it should be P=36*2^0.5*0.400=21W or 21VA. 25VA should be too low (transformers heats up). Now, I'm not sure about the consumption of the Sigma22.

Actually, I was corrected by Dan Gardner in that thread that it is more like 150mA per channel. I would probably use 80VA myself, but that is overkill. 50VA would be fine. As a point of reference, the transformer used in the headamp gilmore v2 was an amveco TE62074, which is 35VA.
 

 

[FallenAngel]

I don't get it, 150mA/channel, 600mA for full amp, 2x 18V secondaries, so 36V * 0.6A = 21.6VA.  35VA transformer should be fine with enough overhead.

 

[bidoux]

Sorry for that. 150mA it is.

 

[Bizzel]

What's the disadvantage in over-provisioning - if I have a 50VA toroid and I'm using, say, 25VA will that generate more heat than if I had a 35VA transformer?

 

[Pars]

^ I don't believe so. The transformer will not regulate as well being more lightly loaded. The raw AC output will be a bit higher because of this.The power draw from the transformer is dependent upon the amp/PSU draw, so it won't go up simply because it is available. Larger transformers will tend to be noisier, but probably not enough (within reason) to worry about. 500VA, then you could probably worry.
 
I'm not sure that the previous power calculations are correct. 150mA x 2 channels will be 300mA, not 600 (unless the calculation was for balanced, i.e. 4 channels). The draw is rail to rail, not each V+/V- rail to ground.

 

[Bizzel]

Thanks for the info. This is a balanced build so 600mA sounds like it's in the right ballpark. I'll probably end up getting the 50VA toroid since the price difference is pretty small.

 

[Bizzel]

Well the build is going very nicely so far. Apparently I haven't lost all my soldering skills which is a relief! 

 
I have a query about the gain resistors if anyone's in the know about that: I want a gain of 6 so I bought 10K and 2K resistors which I fitted to locations R16, R46 and R7, R37 respectively. Is this correct?
 

 

[Ferrari]

Quote:

 
I have a query about the gain resistors if anyone's in the know about that: I want a gain of 6 so I bought 10K and 2K resistors which I fitted to locations R16, R46 and R7, R37 respectively. Is this correct?
 

Yes, R16 = R46 = 10K and R7 = R37 = 2K.