Followers and Quickie

[Doc B.]

Are there any 120V versions left and what is the V swing on a Mailine.

Jamier

Yes, there is at least one 120V version of the Mainline left.

[Jamier]

Doc,

     Thanks for that update, but PB is saying that the Mainline won’t quite drive the big MoFo version. Is there a mod, like the one he was suggesting for the Crack, that will increase the V swing without severely altering the character of the amp. I would not want to change an amp like a Mainline, irreversibly, anyway.

Jamie

[Jamier]

PB,

     How short of full power would the Mainline come up when driving the 22W version. If it’s close I’m interested. And in the end if it doesn’t work out, at least I have a Mainline, right? It would drive my F4 well, right?

Jamier

[Paul Birkeland]

The F4 is usually the companion product paired with the Mainline as a power amp buffer.

I think you'd make about 14W.  Have you evaluated the realistic power handling of the speakers you're using?

[Jamier]

PB, I use speakers that are mostly built by myself. Most of these operate well, outside of that figure. I listen semi nearfield so large output is not needed but the 20W rating associated with the big MoFo would be great for some of them. Several of these speakers are designed around 7 inch Seas midwoofers which do have good thermal compression and power handling capabilities. One of my dilemmas about the MoFo is how to  increase the Current in order to drive the 4 ohm MTMs that I made designed around Seas ER 18s. I’m wondering if using the 193V inductor will accomplish this goal.

Jamie

[Paul Birkeland]

Increasing the power supply voltage isn't going to help with 4 ohm speakers.  Increasing the idle current as much as possible would be a good idea, which would mean the beefier chokes and the same power supply.  The 2.5A limit implied in the article will be your limiting factor, not the swing from the Mainline.

You could also investigate paralleling pairs of boards to increase current availability. 

[Jamier]

PB, the increased idle current is what equates to the increased heat, right(?), so I still need the fan (or a bigger heatsink), even with the smaller SMPS, right?

Jamie

[Paul Birkeland]

Basically the whole DC rail appears across the fet, so you multiply that by your idle current and you get dissipation.

If you go from 12V DC to 24V DC at the same bias current, then you double the dissipation through the fet.

If you go from 12V DC 1.25A to 12V DC 2.5A, then you also double the dissipation through the fet.

If you go from 12V DC 1.25A to 24V DC 2.5A, then you quadruple the dissipation through the fet.

[Jamier]

So based on Mike's numbers, I'm going to get about 50% more dissipation, which means probably yes to at least some fan assistance( my idle current is 1.7 A @ 19V ) Thanks PB.

Jamie

[Paul Birkeland]

Also note that my power estimates are presuming that whatever voltage coming into the amp can be swung successfully by the MoFo.  Personally I would use the 193V if your budget allows.

[Jamier]

Derek,  who did you buy those fans from? Amazon?

Jamie

[Deke609]

Derek,  who did you buy those fans from? Amazon?

Yup. I got the non-"PWM" version.  I'm not tech-savvy, but I think PWM involves powering stuff from the motherboard.  My fans came with a 3-wire/3-pin socket. I cut off the socket. Somewhat frustratingly, the wires are not color coded, so I had to experiment by process of elimination to figure out which was DC+ and which was DC-. It will only work one way. Reversing + and - makes the fan whir and sputter. I think the third wire is for a sensor or something - connecting it to power does nothing.  But you could just as well google the 3pin socket to figure out which is which. But then you'll have to take the socket apart to keep track of which identical looking black wire is attached to which pin.  Worst case scenario: it will tkae you 10 min to figure out which is which.

And note the fans are pretty big - 140mm. They also come in a 120mm version. And you could always get smaller fans from another manufacturer. I hit on the "Silent Wings" after a quick google search for "quietest computer fan" - there are other really quiet fans out there. But I didn;t feel like fussing for hours just to get 1 or 2 less dB.

cheers, Derek

[Jamier]

Derek, How will you power the fans? Battery, or some simple PS? 140mm is probably about right. the heatsink measures around 5 1/2 or 6 inches square, more or less. Actually it's about that tall too, so think of a 6 inch cube shape with fins, sharp, hot fins. I think the fan will be a good upgrade as long as it's not too noisy!

Jamie

[Deke609]

I haven't decided yet. I am going to mock up the BeePre rebuild using plywood to play around with layout to eliminate/minimize noise. I'll test various options then. Battery is obviously the safest bet noise-wise, since the power supply wouldn't be connected to either the amp wiring or mains. But some folks on DiyAudio who've used fans report no injection of noise running the fans off the amp filament supply. B/c I'm installing separate filament supply transformers, the existing 6.3V secondaries can be repurposed - so I'll try running the fans off of those (after doubling/rectifying and smoothing) and compare with battery power. If I can't hear or measure any additional noise, I'll go with using the 6.3V windings. But if that proves noisy, I'll try a separate trafo (10 or 12V).  I might even try (being the crazy guy that I am) using a C4S in from of them to isolate them - but this assumes that isolation of the C4S (which I assume is function of impedance to AC - but don;t know) works both ways: PS and load each isolated from each other. Not sure if it does work that way or is instead one-directional.

I think I may also install a pot to control dc voltage/fan speed.  To be even fancier, one can install a temp sensor or thermistor that controls fan speed. I'm thinking about that, but will probably leave it as something fun to play with in the future.

cheers, Derek

[Jamier]

PB,

     I pulled the trigger on the Mainline, figuring that it can serve a multitude of purposes for me.
 Will it have the same input clipping issue (1V) like the crack?

Jamie