• Disclaimer: This Vendor's Forum is a paid-for commercial area. Unlike the rest of diyAudio, the Vendor has complete control of what may or may not be posted in this forum. If you wish to discuss technical matters outside the bounds of what is permitted by the Vendor, please use the non-commercial areas of diyAudio to do so.

Swordfishy/ASPEN FETZILLA power amp

Status
Not open for further replies.
Jump to Latest
#728
I need some advice. My boards (2sk1058 2sj162) are populated and attached to their heatsinks. It came time to start testing and I got one board adjusted perfectly.

I hooked up the other board and started to adjust P1. The current was high to begin with and I started to adjust P1. Unfortunately, my hand was shaking so much (sweaty armpit syndrome), that as I started to adjust, my screw driver slid off the adjustment screw. I did not think it really hit anything significant, but it is possible that I did. My impression is that if I hit anything, I knocked the side of C8. I turned off immediately so that I could get the screw driver back in position but when I turn on, my main fuse blows.

I am using a single 115 : 24+24 300 va toroid to power both boards. So far I have only hooked up one board at a time to the toroid. The power receptacle has an internal fuse holder where I am using a 3 amp slow blow fuse. It is this fuse that blows.

The on board fuses have not blown. I have re-checked all the resistors with my multimeter and all are the correct values. I can't see any obvious sign of damage.

The toroid itself appears to be ok with the expected low resistance in each winding. The electrolytic caps are correctly inserted with positive and negative.

I've re-connected the first board and it is still fine. No fuse blows.

Any ideas on how to proceed?

ray
 
#729
Hi Ray,

I'm pretty sure you can rest easy......

A 3A fuse for 110-120Vac mains is not adequate for a 300VA transformer.

The switch on surge is powerful; typically around 10 times rated current. This heats the fuse, and the subsequent high loading with high a high quiescent setting - say one amp, pretty much the design limit with the bias generator used in this design - took the fuse over the edge and it blew.

Simply replace with a 5A slow blow fuse and you should be cool bananas.....

Oh, one thing. Be sure that the secondaries of the single transformer are connected in identical sense to both boards, otherwise you will create an earthing conflict and effectively short the transformer output. That is, secondary #1 goes to the positive rails of BOTH modules, and secondary #2 goes to the negative rails of BOTH modules.

Take heart, spark warrior.....

Cheers,

Hugh
 
Last edited:
#730
Thanks for the response. So will 5A be enough for both channels, or should it be 10A?

I had already read the advice about wiring for both channels, but thanks for reminding me. Hopefully tomorrow it will all be working.

Spark warrior! I like it.

ray
 
#731
A 300VA transformer will need a T8A fuse to start reliably from 110/120Vac.
You may find that it starts with a slightly lower fuse value (T6.3A or T5A) and it's worth experimenting.

If you want to close rate the fuse then you must adopt a soft start. Then T3A, or just possibly T2.5A, will reliably start the 300VA transformer.
 
#734
It takes me a while to make up my mind about sound quality and I like things to break in for a while before I say too much. I've built a few amps, mostly tube, so solid state / transistor is a departure for me. However I did build a chip amp some years ago and I think I could say right now that Fetzilla is a definite improvement.

By the way, my 2sk1058 2sj162 Fetzilla is standard except for a single 300va (24 +24) toroid and I used an R15 value of 180 ohms. (see posts 685 - 686 - 687). The line voltage at my house is 123vac so that works out to be about 25+25 volts.

I also use russian MGB 2uf caps instead of the Auricaps. I've used these in some of my tube amps and I like their sound. They look like this:
0.5uF 500V PIO Capacitor MBGO-2 / MBG-2/ NOS Lot of 16 | eBay
Of course I have to mount them off the board but the distance is short.

The amp is disassembled already and I am putting it in a larger container. My old toroid buzzes and I am experiencing some hum so I am going to re-route the power and signal wires. I also suspect my toroid was too close to the boards. Somehow I suspect I will be sending off to Antek for a couple of new toroids. I've used their transformers before and I have been pleased with them. They also will work for 230vac as well as 115vac.
Antek - AN-2225

My four heatsinks are approximately 7" x 5" and 2 1/4" deep. I ran the amp for about three hours and they barely got warm. I had used these heat sinks in my first DIY amp which was a Pass Son of Zen and as somebody pointed out "you could roast a chicken in that thing". That amp was too hot to keep.

I've played the amp through some 6" Tannoys and they sounded very dynamic with lots of detail. Just to see what would happen, I tried the amp into the 4 ohm load of my old Apogee Stages and they did pretty well but it was a bit of a struggle when the music got loud. You really need a powerful amp to get those speakers moving.

The build went pretty easily for me with the circuit boards. The fuse holders were a pain but I cut them down and they then fitted ok. The holes for D1A and D2A were a bit small as well so I cut down the pins of the diodes to fit. I think these issues have been mentioned before. I used a spare inductor (18 gauge) to wind the L1 inductor which wasn't too difficult. Virtually all my parts came from Mouser and thanks to Swordfishy for the BOM.

I'll post in a week or so with an update on the sound.

So thanks to all involved who created this amp. I followed the discussion from the beginning and it was fascinating to see how the design evolved.

ray
 
#736
Just get your parts ordered. If you are used to soldering, populating the board goes fairly quickly except for the fuse holders and D1A and D2A. I printed out the list of parts and ticked them off as I went. Pretty simple, really.

The longest part seemed to be putting it all together in whatever case you are using.

Incidently, I used three multimeters to check the voltages. If you are in the US, use these from Harbor Freight at only $4.99 each. They are more than adequate. They come with probes and I use clip leads to get everything set up before I turn on. Then you can do your adjustments of P1, P3 and P2 without having to turn off the mains AC. I don't like poking around in an amp with probes or screw drivers any more than I have to. Take a look at this for more ideas on multimeter use.

My amp is back in working state and I have got rid of the hum and a most of the mechanical buzzing from the toroid transformer. I have it resting on a piece of foam.

I suspect this is going to be a very good sounding amp.

ray
 
#737
I'm not really worried about soldering. This is the fun and easy part but since I'm already working on many projects I have to wait for this one...

Sad thing since this is one of the projects that I really want to get going soon... 🙁

I have all parts already so it makes it even more tempting to put the other stuff on hold... 😀

I actually found some really nice fuse holders that fit perfectly. It uses 5x20 type fuses. If anyone needs that part number, please let me know.

Ciao!
Do
 
Last edited:
Status
Not open for further replies.
Top Bottom