Nelson Pass First Watt F4 clone

TomS · « **on:** 6 Mar 2008, 04:42 am »

I've been on a deep dive over the last couple weeks to build a pair of Nelson Pass First Watt F4 clones. I built this as the "mule" before I start swapping out the stocker parts for boutique goodies as well as develop a prettier case option.

It is a unity gain current amplifier (yes, no voltage gain), ideally front ended by a nice tube voltage stage like the Aikido which I'm also building. It's 25wpc stereo or bridgeable to be balanced monoblocks at about 100wpc (class A), and since it's a current source, you can parallel the inputs AND the outputs to get 100w into 2 ohms single ended.

Heat sinks are Conrad MF35-151.5, dual Plitron 300va toroids, Peter Daniels PCB's for power supplies and signal boards, wiring is whatever was laying around (and looks it), general purpose bridges. I did splurge and used some Cardas Patented Binding Posts that I like so much from my Merlins (a bear to install though). I found these little 6 position push-in electrical connectors in the electrical section at Menards that were absolutely great for temporarily testing grounding schemes. You can see all the black wires going to those little plastic thingies.

Heat sinks are only running about 41 degrees C so I will probably crank the bias a little harder to see how they sound. I'm a sucker for Class A amps though, even if they double as room heaters.

So far it sounds great driving the 100db efficient HF of my Emerald Physics CS2's and is dead quiet. Lots of mods to come. Here are a few pix, with more in my gallery

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=1378

Tom

mgalusha · « **Reply #1 on:** 6 Mar 2008, 04:49 am »

Very nice Tom! You made it sound ugly, I think you've done a very nice job, neat and organized.

Love the dual power supplies.

TomS · « **Reply #2 on:** 6 Mar 2008, 12:56 pm »

Quote from: mgalusha on 6 Mar 2008, 04:49 am

Very nice Tom! You made it sound ugly, I think you've done a very nice job, neat and organized.

Love the dual power supplies.

Thanks Mike!

In the next non "mule" iteration, I'll get around to direct soldering the bridges (though they probably become IXYS FRED discretes) and grounds, shortening up everything, and dressing all the wires and stuff. I have some Cardas, Vampire, and Jena Labs cryo wire I was saving for just such an occasion

It's just a pain to solder correctly without a pot. Those Vishay S102 resistors I am eying for the front end are about $12 a pop

Geez it adds up fast.

Tom

sts9fan · « **Reply #3 on:** 6 Mar 2008, 01:35 pm »

You are in for a treat. I really like this amp. I do wish the one I was using looked like your though...

JoshK · « **Reply #4 on:** 6 Mar 2008, 03:15 pm »

I like the look of this as is. I was planning to build a pair someday (have all the boards/heatsinks/parts). I was planning a chassis just like you built.

gbeard · « **Reply #5 on:** 6 Mar 2008, 03:34 pm »

Nice Job TomS!!

I have about half of the parts to start mine in the coming weeks. I snarfed a heatsink from a big ol ups system and cut it in half. The two halves are about 11" x 9" each. I have the PD boards, the MOSFETS and JFETS, and the power supply caps (although I purchased the Nichicon KG caps for the power supplies and they are HUGE). I still have to buy a lot of other stuff though. Your chassis looks very good. I am thinking of something similar. I am still undecided about whether to use a dual primary Piltron to save money, or go with two like you did. Btw, what model number are the Piltrons you used?

Thanks,
Gary

anubisgrau · « **Reply #6 on:** 6 Mar 2008, 03:58 pm »

how much is it in all the parts so far?

Occam · « **Reply #7 on:** 6 Mar 2008, 04:02 pm »

Very slick! Not only dual mono supplies, but dual bridges for each. I really like the way you mounted the bridges on the heatsinks.

So how does it sound?

sts9fan · « **Reply #8 on:** 6 Mar 2008, 04:37 pm »

Quote

I really like the way you mounted the bridges on the heatsinks.

I saw that and insantly decided to do that on my Zv9

TomS · « **Reply #9 on:** 6 Mar 2008, 07:00 pm »

Quote from: gbeard on 6 Mar 2008, 03:34 pm

Nice Job TomS!!

I have about half of the parts to start mine in the coming weeks. I snarfed a heatsink from a big ol ups system and cut it in half. The two halves are about 11" x 9" each. I have the PD boards, the MOSFETS and JFETS, and the power supply caps (although I purchased the Nichicon KG caps for the power supplies and they are HUGE). I still have to buy a lot of other stuff though. Your chassis looks very good. I am thinking of something similar. I am still undecided about whether to use a dual primary Piltron to save money, or go with two like you did. Btw, what model number are the Piltrons you used?

Thanks,
Gary

The Plitron # is 077014201 300va 2x18vac windings (not CT). I originally planned one per amp, but ended up using both in this mule, based on some of Hugh Dean's thoughts on dual smaller transformers in the AKSA's. I believe there is also some magic on not going too far, so the 180va ones might even be fine for this application. Unfortunately, they are still very expensive to buy new, but they are dead quiet mechanically since they're potted in the middle.

My sheet metal job is one of those things that when you see in person you realize it's pretty cobbed together, as in don't turn the lights too high or you'll see what she really looks like. I don't have the tools or expertise to do this right myself. I found a local Metal Supermarket franchise store here (GREAT service by the way). I had them cut a 5052 12x14 sheet of .125 aluminum for the pan (~$10), 12x6 .125 for the back (~$7), and 12x14 perf steel .080 on top (~$12). The front is 12x6 0.250 5052 (~$15). The angles are all 1 x 1 x.125 (~$1/ft). I have around $50 in all that, but then there's the 2 or 3 6-32 taps I broke hand threading all of them

That took by far more time than anything. I just don't have access to small job machine shop or friends with those tools. Oh, and a Unibit is worth every penny for the back panel.

And for those who asked about sound. For VERY basic parts quality (PRP resistors, Panasonic FC coupling caps, IR bridges, Panasonic TSHA PS caps, etc.) and automotive connecting wire, it sounds really good. That is where the fun begins IMHO. I still don't have enough gain from my Burson Buffer on HF to match with the Odyssey SE's on LF, so until the Aikido gives me the extra 20db I want, it's too early to really say a lot. At the lower levels available, it is very open and yet organic in a non-tubey sort of way. I am comparing to the Bella Extreme 3205 which is also extremely good, but unfortunately my sample, at least, is not dead quiet like the F4.

I need to take a breath from the anxiety of turning all the sheet metal and tapping before starting on the second monoblock, but I'm really looking forward to getting that one together to see what a pair (or maybe Aikido/quad biamped!) sounds like.

It was a fun project and best of luck with yours!

gbeard · « **Reply #10 on:** 6 Mar 2008, 10:12 pm »

Tom,

Thanks for the detailed reply. As I get closer to starting (some time yet) I may ask you a few more questions if you don't mind. I am not in the machine shop biz either, but homemade is something we can be proud of!

I just finished (sort of--still have a little buzz) my first diy project--and 845 amp--but I had a lot of help. More on that in an upcoming article on PFO. I have been working on it for quite a while and I am taking a short break while I enjoy the fruits of my labor.

I am very hopeful the F4 clone will be a perfect complement to my big ol' honkin' tube amp!!

JoshK · « **Reply #11 on:** 6 Mar 2008, 10:18 pm »

An 845 amp isn't something most people cut their teeth on.

That is deadly voltage!

TomS · « **Reply #12 on:** 6 Mar 2008, 11:31 pm »

Quote from: gbeard on 6 Mar 2008, 10:12 pm

Tom,

Thanks for the detailed reply. As I get closer to starting (some time yet) I may ask you a few more questions if you don't mind. I am not in the machine shop biz either, but homemade is something we can be proud of!

I just finished (sort of--still have a little buzz) my first diy project--and 845 amp--but I had a lot of help. More on that in an upcoming article on PFO. I have been working on it for quite a while and I am taking a short break while I enjoy the fruits of my labor.

I am very hopeful the F4 clone will be a perfect complement to my big ol' honkin' tube amp!!

Perhaps you already were thinking this, but one cool thing about the F4 is you can run the speaker output of the 845 directly into the F4 and take advantage of the added current output it provides while retaining the sonics you like about the 845 amp. This thing is incredibly versatile if you think outside the box a bit. Nelson Pass truly went a different road just by releasing this to the market IMHO.

gbeard · « **Reply #13 on:** 6 Mar 2008, 11:45 pm »

Oh yeah mon...I 'twas definitely tinkin' 'bout it!!!!!! aa

g

gbeard · « **Reply #14 on:** 6 Mar 2008, 11:56 pm »

Quote

An 845 amp isn't something most people cut their teeth on. That is deadly voltage!

Hey Josh,

You're right, what was I thinking!

Really though, you are right, not for the faint hearted I suppose. Larry Moore provided me with the design, held my hand and anwered all my silly questions, but I did all the assembly myself. I don't have a clue about a lot of the design, but in another life I was an electrician. I currently (heh Bevis, he said "current-ly" !

) work for a large electrical contracting company, so I have a healthy respect for all voltages. Believe me, testing the thing made my boys hide for a minute or two!!

It is a wonderful amplifier. It isn't broken in yet and still needs a little tweaking for noise, but I believe it is the finest I've owned by fair margin and I've owned some good ones.

Cheers,
Gary

poseidonsvoice · « **Reply #15 on:** 7 Mar 2008, 02:11 am »

Cool Thread fellas.

I have one F4 which will have the Black Gate NX caps in the circuit section and Jensen 4 pole caps for the power supply. Single Plitron Transformer. The second F4 will have dual mono power supplies, dual transformers and standard issue capacitors and resistors. The first F4 will be for the satellites while the second one will be for the subs.

A very versatile design. I'm glad others are using the Aikido as the front end which is what I am planning. You can have your 6SN7 bliss with rock solid bass too.

Best,
Anand.

TomS · « **Reply #16 on:** 7 Mar 2008, 02:12 am »

Quote from: poseidonsvoice on 7 Mar 2008, 02:11 am

Cool Thread fellas.

I have one F4 which will have the Black Gate NX caps in the circuit section and Jensen 4 pole caps for the power supply. Single Plitron Transformer. The second F4 will have dual mono power supplies, dual transformers and standard issue capacitors and resistors. The first F4 will be for the satellites while the second one will be for the subs.

A very versatile design. I'm glad others are using the Aikido as the front end which is what I am planning. You can have your 6SN7 bliss with rock solid bass too.

Best,
Anand.

I've long admired those beautiful cases and faceplates in your gallery. Where do you get all that stuff done - FPE?

poseidonsvoice · « **Reply #17 on:** 7 Mar 2008, 02:19 am »

Tom,

Yes, FPE. Some of the enclosures are from www.diyenclosures.com. The wooden types are my premium designs as wood can be expensive. However, all the panels are FPE designs. I have a ton of them. I have more than half a dozen designs on my bench including the F4. For every one design I'm working on, I think of three more! Currently I'm finishing the active crossover to my cardiod U-frame subwoofer. The subs will be in tiger maple. All of it will be documented in my gallery. In addition I have an SB3 power supply, two Greg Ball amplifier designs, Two F4 designs, another RAKK dac with active tube output stage, the Aikido, a parafeed based phono stage, a push pull KT88 design, and even the Aleph 30 design on my bench.

Enjoy your work!

Anand.

TomS · « **Reply #18 on:** 7 Mar 2008, 02:25 am »

Quote from: poseidonsvoice on 7 Mar 2008, 02:19 am

Tom,

Yes, FPE. Some of the enclosures are from www.diyenclosures.com. The wooden types are my premium designs as wood can be expensive. However, all the panels are FPE designs. I have a ton of them. I have more than half a dozen designs on my bench including the F4. For every one design I'm working on, I think of three more! Currently I'm finishing the active crossover to my cardiod U-frame subwoofer. The subs will be in tiger maple. All of it will be documented in my gallery. In addition I have an SB3 power supply, two Greg Ball amplifier designs, Two F4 designs, another RAKK dac with active tube output stage, the Aikido, a parafeed based phono stage, a push pull KT88 design, and even the Aleph 30 design on my bench.

Enjoy your work!

Anand.

I thought about using them for this project, among others, but I can't get past the fact that all the edges of anodized panels get machined back to raw aluminum. I noodled that around a bit and I never could work it out so they didn't all show. I suppose with silver it works out ok though.

poseidonsvoice · « **Reply #19 on:** 7 Mar 2008, 02:30 am »

Tom,

Yes, that is why I use wood in some of my designs. For the others, I just ship the panels to FPE, and they do the rest. Learning the software is easy. What took four hours, now takes me about 30 minutes to design on FPE. I've had quite a few fellas ask me if they are for sale. Maybe in the future I'll consider it, but for now I'm just having fun. I'm just one of the those guys that needs it to sound and look good.

Best,
Anand.