Firstwatt F5: Why some people should not DIY

[Duggeh]

Nice to know that box of shite has been made into something worth a damn. Mini F5 would seem the way, because if you lower the power you could always stick a TRS socket on it for all of your dynamic headphones.

...wait.

[n_maher]

I don't see a way out of it without either lowering the cooling load (lowering the rail voltage or something like that ) or increasing the cooling capacity with new heatsinks. My vote is for lowering the load, for now, to see if you can get it to the point where it's stable without the use of a fan.

[spritzer]

Ahh that would mean it would power the RS-2's sitting on my desk now or the K1000 that is 5 minutes away?

Nate is right though, no way around this except increase cooling capacity or dialing back the 120W of heat this thing gives off. I'm going to see if there are any cheap sinks available locally that I could just bolt onto the inside to add surface area and if that doesn't do it, look figure out how low I need to go. There was somebody in DIYA working on a mini amp but his posts are a bit of a mess.

[Pars]

I thought digger had a larger hifi2000 case for sale, maybe a 4U or 5U... not sure if he sold it already or not.

[spritzer]

That would work but the issue isn't really about using a larger chassis. I'm going to build a second F5 with all the trimmings and my usual level of insanity so I just want to convert this one into something useful. You can see the heatsinks I'm going to use in the upper left corner of the above picture. That plus solid aluminum panels all around should be more than enough.

[luvdunhill]

Only one option. Same rail voltage lower bias. It won't be the end of the world.

[guzziguy]

How about buying a small refrigerator and running it in there? Of course you'll have to figure out how to run the cables while keeping the door closed.

On a slightly more serious note, would running it on a laptop cooling mat solve the problem in a reasonable manner?

[spritzer]

Only one option. Same rail voltage lower bias. It won't be the end of the world.

Yeah you are right but I'm still going to try and add some internal sinks just in case. There is really no such thing as too much metal...

How about buying a small refrigerator and running it in there? Of course you'll have to figure out how to run the cables while keeping the door closed.

On a slightly more serious note, would running it on a laptop cooling mat solve the problem in a reasonable manner?

I could always just store it outside. It's pretty warm now at 7

[mrarroyo]

How about buying a small refrigerator and running it in there? Of course you'll have to figure out how to run the cables while keeping the door closed.

On a slightly more serious note, would running it on a laptop cooling mat solve the problem in a reasonable manner?

Or how about a PC water cooling system?

[spritzer]

That would work but the chassis is pretty small. There is also the issue of all PC coolers being pretty small (since the processors are so small) so it would have to be modified. There is also the noise of the fan and pump to think about.

[Dusty Chalk]

I could always just store it outside. It's pretty warm now at 7

[spritzer]

Nope.

[spritzer]

I've been adjusting the bias for the last few hours and at just over 1A it is around 70

[spritzer]

Time to close this case once and for all, here is the finished article sitting on its new rubber feet:

The back panel is pretty nasty and somebody really should have told the original builder about the magic of masking tape when doing chassis work. Still, it's not like anybody can see it or the truly horrific bottom panel.

[guzziguy]

I've been adjusting the bias for the last few hours and at just over 1A it is around 70

[Jon L]

No sound quality impressions?

When I had a F5 clone, I personally thought it sounded quite uninvolving and sterile. I actually preferred my gainclone for a more organic, involving presentation, not to mention my 2A3 SET and EL84 SEP.

[luvdunhill]

I think the issue is many people prefer lots of distortion so when they're given a simple DC coupled amp they're a bit underwhelmed. Sort of the same story that we see every day around here when people get into 'stats.

[spritzer]

I've been running it with purely my testing components (Pioneer DV-525 DVD player, Noble 10k pot as a passive preamp and Tannoy R2 speakers) but it is very good indeed. Far better than my Gainclone but the true test will be firing up the new Lundahl transformer boxes.

I'm with Marc though, lack of distortion is so often misunderstood.

[fishski13]

No sound quality impressions?

When I had a F5 clone, I personally thought it sounded quite uninvolving and sterile. I actually preferred my gainclone for a more organic, involving presentation, not to mention my 2A3 SET and EL84 SEP.

any specifics on the F5 build? what speakers? i think the F5 has much better groove and dynamics compared to the LM3875 Gainclone driving FR Fostex.

nice re-build spritzer!

[swt61]

For the short period of time my F5 was driving my K1000, I found it anything but sterile. In fact I thought it would be a nice compliment to the very neutral

[kevin gilmore]

First watt is a current source. Sounds absolutely fantastic with some speakers and headphones.

Sounds horrible with lots of other stuff. Highly inductive speakers for example typically blow the

fuses.

[luvdunhill]

It's a DC-coupled 2-stage current source amp with a complementary MOSFET common source output stage with feedback. What would you suggest that it would do bad with?

[Voltron]

First watt is a current source. Sounds absolutely fantastic with some speakers and headphones.

Sounds horrible with lots of other stuff. Highly inductive speakers for example typically blow the

fuses.

It's a push pull amp with feedback.

Saturday Night Live - Shimmer Floor Wax - Video - NBC.com

[spritzer]

It's a DC-coupled 2-stage current source amp with a complementary MOSFET common source output stage with feedback. What would you suggest that it would do bad with?

People who like distortion and SET amps? While some of them are good, some are truly horrible designs. The same crap recycled over and over again...

[luvdunhill]

Highly inductive speakers for example typically blow the

fuses.

I thought more about this. I doubt this would happen. Do you feel the thermal compensation and current limiting in the design is some how inadequate?

Also, are you aware that there are, what, 7 First Watt designs? Not all of them are current sources.