Thank you everyone for your feedback, I have started a file with suggested mods for this amp. I am going to use it as is for a week or so while I regain dining table space 
and cleanup the mess left by construction. I am certain the sound will improve as the listening hours accrue, and I will leave it on for the next week or so.
I like the thought of on-board PS caps, I was thinking of putting some on while I was building but thought I would start with it stock, I also wasn't thinking that big but will add some onto my next parts order. Also EB, I was thinking the same thing about the 5pF cap, I have made small caps like you described for several of my RF projects, again, thought I would start out with the original BOM so that I had a baseline with known good sound. I hadn't heard about SILMIC problems, what have you experienced with them? I thought they were well regarded? As for the wiring, I am still not convinced that larger wire will make any difference in an amp this size, but I do have lots to choose from and if I tear this apart again, it wouldn't take much to simply remove the current harness and build a new one.
Power entry module, well, the back panel was machined to accept these and I have lots of them, I could dissect one as an experiment and bypass all the RFI stuff but why wouldn't an AC filter be a good thing? And yes, bias was checked and adjusted about 20 times as the amp warmed up and finally stabilized. I settled at 1.85A per channel, AC draw is right at 210W.
I already have my next project ready to start though when I get the house cleaned up....I am going to rebuild my old Threshold Stasis II which has been apart for 8 years or so. Needs complete restoration, mod removal and output xstrs replaced. It's been heavily modded and circuit changes have been made, want to restore to stock and get it back on it's feet, then upgrade as require.
Thanks again all.
Cheers
and cleanup the mess left by construction. I am certain the sound will improve as the listening hours accrue, and I will leave it on for the next week or so.I like the thought of on-board PS caps, I was thinking of putting some on while I was building but thought I would start with it stock, I also wasn't thinking that big but will add some onto my next parts order. Also EB, I was thinking the same thing about the 5pF cap, I have made small caps like you described for several of my RF projects, again, thought I would start out with the original BOM so that I had a baseline with known good sound. I hadn't heard about SILMIC problems, what have you experienced with them? I thought they were well regarded? As for the wiring, I am still not convinced that larger wire will make any difference in an amp this size, but I do have lots to choose from and if I tear this apart again, it wouldn't take much to simply remove the current harness and build a new one.
Power entry module, well, the back panel was machined to accept these and I have lots of them, I could dissect one as an experiment and bypass all the RFI stuff but why wouldn't an AC filter be a good thing? And yes, bias was checked and adjusted about 20 times as the amp warmed up and finally stabilized. I settled at 1.85A per channel, AC draw is right at 210W.
I already have my next project ready to start though when I get the house cleaned up....I am going to rebuild my old Threshold Stasis II which has been apart for 8 years or so. Needs complete restoration, mod removal and output xstrs replaced. It's been heavily modded and circuit changes have been made, want to restore to stock and get it back on it's feet, then upgrade as require.
Thanks again all.
Cheers
It's on the agenda for tomorrow...I'm still fiddling with bias,
Updates tomorrow.
Cheers
I built my F5 Chassis from aluminum in a similar manner, and had more heat once top was buttoned down. I was fearing a bad look from attempting to drill vent holes in the top plate. Bottom plate not so concerning.
A member contacted me and suggested instead of drilling holes, to use spacers to slightly raise the top plate. He indicated his math showed this small amount (1/4 inch or less) equaled more vent space than the holes would.
I dont know if this was accurate, but cost was nothing to try. I did and problem solved. I never needed to drill the holes in the bottom either. I was using the bottom plate to sink 16 high performance diodes, each with own silpad as well.
I think your spacer idea will work, if not well enough, try spacing the top as well. In the end no holes drilled and temps were fine. The solid case also housed two 300 VA transformers as well.
Russellc
Thanks, it did work. I used fiber washers and it's only spaced about 1/16" but it's enough to decouple the base plate and keep the heat out of the chassis. I was worried about the xfmr heating up and also heating the big caps, it would really shorten their life. The sinks now run at 53C and the bottom plate is 42C at the rear, and 46C at the front near the rectifiers. The xfmr runs at 45C now. Front and back are about 45C so they are helping as well. I also drilled about 40 new holes in the bottom just to be safe. Belt and suspenders.
I don't have a lid for it yet, working on that.
Cheers
Well, that did it.
The transformation is quite stunning. The sound is now properly laid in front of me, with a much better perspective. It is much easier to hear everything; the sound is less in your face. The whole stage also opened a lot, the highs gained the most, i.e. the height of the soundstage improved a lot. The bass is a bit softer, but definitely present.
I will try a simple IEC connector, without the RF filter. I know from my experience the sound may lose finesse, but it will also gain in definition.
THANK YOU!
Regards,
Nick
I use two small Noctua fans to cool the two Meanwell power supplies that I use. Using the low-speed adapter included with the fans, they are dead silent, unless I put my head inside the chassis.
Using the low-speed adapter included with the fans, they are dead silent, unless I put my head inside the chassis.
In which case you may become dead silent.
Dual mono power supply upgrade
Is there a target value for the voltage drop between the 1st and 2nd stage of a CRC power supply that would indicate that you have sufficient decoupling? It seems that the R value recommendations I'm seeing for dual mono are the same or even less than my original supply even though the current requirement are cut in half. I understand a tight supply is a good thing but at some point don't you loose decoupling?
Is there a target value for the voltage drop between the 1st and 2nd stage of a CRC power supply that would indicate that you have sufficient decoupling? It seems that the R value recommendations I'm seeing for dual mono are the same or even less than my original supply even though the current requirement are cut in half. I understand a tight supply is a good thing but at some point don't you loose decoupling?
As I have quite a lot of space inside the amp, I would like to know what the sonic benefit is of adding motor start caps to this? Could you let me know what values you plan to use and why? Is there a certain construction type preferred, or composition?
Thanks
Motor run caps
in this neck of wood , Icar and Ducati are the brands
don't use Chinese ones ...... not because there are not good Chinese ones , but simply because I don't have a knowledge which to recommend ; so - only well known and established brands
say 40uF and up
sole important thing is that you distinguish ( while ordering/buying) motor-run vs. motor-start caps
first one are for permanent use, second one are for momentary use
in this neck of wood , Icar and Ducati are the brands
don't use Chinese ones ...... not because there are not good Chinese ones , but simply because I don't have a knowledge which to recommend ; so - only well known and established brands
say 40uF and up
sole important thing is that you distinguish ( while ordering/buying) motor-run vs. motor-start caps
first one are for permanent use, second one are for momentary use
When I used motor run caps in my M2x, the only amp I've built recently with a shared PSU, they helped improve the stereo separation and spatial content of the music. I used a pair for each channel, placed next to the channel boards. These were only 40 uF due to size limitations of that chassis, but the effect was definitely noticeable. They were fairly standard oil-filled polypropylene, cheap compared to the 'audiophile' brands of the same construction.
I'm used to appreciate proper industrial quality , much more than audiophool quality
especially when best of audiophool parts aren't anything else than industrial quality parts in different skin
I remember, years ago , we evaluated different electrolytics in Babelfish J Aleph CCS modulating path ( that 220uF seen on all schmtcs) ; after trying plenty of them (all proper caps) , good industrial Elna (470uF/35Vdc/125C) bypassed with MKC was sounding as any other , bypassed with same MKC ; bypassing declared as being extremely beneficial ; 470uF Black Gate was simply thrown out , after painful 3 weeks of burning in ....... we simply couldn't wait longer to get it finally sing
your mileage may and must vary, of course
especially when best of audiophool parts aren't anything else than industrial quality parts in different skin
I remember, years ago , we evaluated different electrolytics in Babelfish J Aleph CCS modulating path ( that 220uF seen on all schmtcs) ; after trying plenty of them (all proper caps) , good industrial Elna (470uF/35Vdc/125C) bypassed with MKC was sounding as any other , bypassed with same MKC ; bypassing declared as being extremely beneficial ; 470uF Black Gate was simply thrown out , after painful 3 weeks of burning in ....... we simply couldn't wait longer to get it finally sing
your mileage may and must vary, of course