Valhalla - GK1

PSP · « **Reply #40 on:** 26 Sep 2003, 08:23 pm »

Ginger,
Thank you for your many knowledgable and interesting posts.

Regarding bypassing PS caps, any thoughts (or experience) on whether it is best to mount the bypass caps across the main filter cap leads or (in the case of the AKSA) would it be better to mount the bypass caps to the AKSA power supply spades (i.e., mounted between power supply negative and earth and between positive and earth on the AKSA pcb)?

I have some spare 47uf Nichicon Muse caps that I could use, and perhaps I could bypass those with 0.47uf MITs?

Thoughts?

Peter

andyr · « **Reply #41 on:** 27 Sep 2003, 02:27 am »

Ginger, you gave us a good explanation on why it is good to parallel large caps with smaller ones (value/100). However, you were talking in terms of frequency ... so I assume you were talking about signal caps?

Can you explain what the situation is with PS (electrolytic) caps? I presume the only frequency which is relevant to them is the 50Hz/60Hz mains frequency ... so do these benefit from having parallel film caps?

This will answer Peter's post as well.

Thanks,

Andy

ginger · « **Reply #42 on:** 29 Sep 2003, 11:34 pm »

The point that many people (even qualified engineer types) often miss is that as far as the signal is concerned - the power supply bypass caps are part of the signal flow loop. Some even draw up an equivalent AC circuit, to do a full mathematical analysis, and just leave the power supply capacitors out of the drawing - The power supply is AC ground - right. Well yes and no - the power supply lines are at AC ground ONLY because they are connected to the "real" ground via the Power Supply Capacitors. This means that everything we say about paralleling signal capacitors also applies to power supply filter capacitors. Because the capacitors are usually large electrolytics they will have a low "self resonant frequency" which may be well down into audio frequencies. Above these frequencies the power supply caps will look like inductors and the power supplies are no longer truely at "signal ground".

Conclusion: Yes - certainly apply the 1/100th rule of thunb to power supply caps as well as signal caps.
For the 55N - parallel the 4700uF caps with 47uF and possibly also a 0.47uF film capacitor. You might be surprised at the additional top end detail you suddenly hear.

Cheers,
Ginger

andyr · « **Reply #43 on:** 29 Sep 2003, 11:42 pm »

Thanks, Ginger, your knowledge is much appreciated.

Regards,

Andy

PSP · « **Reply #44 on:** 30 Sep 2003, 01:10 am »

Ginger,
Thanks... you are a good teacher. Much appreciated!

Peter

cmscott6 · « **Reply #45 on:** 30 Sep 2003, 01:19 pm »

Thank you Ginger! I greatly appreciate your posts. Things are actually starting to make sense here!

I paralleled (is this a real word?) the three Auricaps in my GK-1 with polystyrene and foil caps, and the difference is wonderful. That sense of "presence" in the top end is incredible. I guess by presence I mean that high frequency sounds like cymbals and upper register piano chords sound much more lifelike and real in the room - much more three-dimensional in their attack and decay. This is only after about ten hours, so I guess the effect may moderate a bit as the caps break in, but it still sounds great - made me forget about doing any more mods for a while.

The only annoying downside is that the turn-on thump is a little louder, and there is a hum right at turn-on. (Maybe because I mounted the parallel caps on the upper foil side of the pcb.) Hum disappears though after about ten seconds. Then everything is very quiet. Malcolm, this is definitely worth a try!

Malcolm Fear · « **Reply #46 on:** 30 Sep 2003, 09:00 pm »

Ahhh, just when I was about to weld the lids down on GK-1 and AKSA 55.

All of my Auricaps are mounted on the foil side. I think the 10 second turn on hum is a "feature" of the GK-1.
What brand of cap did you use to bypass the Auricaps?

AKSA · « **Reply #47 on:** 1 Oct 2003, 12:05 am »

Chris, Mal,

This is interesting....... Let me give a few of the design considerations here. I don't want to rain on anyone's parade, not at all, but some might be interested in the design brief on precisely this aspect of the GK-1.

There are three principle signal caps in the GK-1 - this number being a reflection of the tube circuitry used. They are the input cap to the preamp, C1 (MMK, Evox-Rifa), the input cap to the tube grid, C19 (Suflex, polystyrene), and the output coupler C21 (polypropylene/ps composite, 1uF Auricap).

These three caps were the subject of high anxiety discussion (HAD - now you know all about Cary) between Darl and me.

One of these caps has essentially no DC bias across it, C1. It has about 150-200mV, that's all. With no DC bias across a cap to stress the dielectric, it's tough going to extract good sonics, because the extreme dielectric plasticity at low voltages is rather non-linear, giving higher distortion (read 'mud'). With strain on the dielectric due to appreciable DC bias, the mechanical behaviour of the plastic film is more linear, leading to less distortion, and most of it at a lower order, particularly at low AC levels. Generally speaking, an AC signal of 1Vrms passing through a cap with 0.1VDC across it will not sound as good as the same AC signal through the same cap with 10VDC across it. With music, of course, H2 and H3 are tolerable because they are relatively euphonic, and accord well with our intrinsic notions of musical harmony. H5, H6 and higher sound pretty non-musical, with the higher odd-orders sounding appalling, and at low levels below conscious perception, giving rise to marked listener fatigue.

Thus C1 had to perform well at low bias voltages. We tested a large number of caps and found that only the RTX polystyrene composite caps performed better than the Evox-Rifa in this role. Given the cost of these beasts, we decided to opt for the vastly less expensive Evox-Rifa. We also tried the Auricaps, but for some reason, with almost no DC bias across them, found they sounded dull and lifeless, a situation which did not prevail for C21, the output coupler role. Now, YMMV, and I'm not going to disagree with anyone because when it comes down to it this is a highly subjective opinion. Remember, I'm the good guy navigator, not the maniac fighter pilot!

C19 was different. Here there is about 45V across the cap, and thus the constraints are relaxed. However, this location calls for a very small capacitor, because the input impedance of the tube is very high, more than 1M. Knowing my dielectric theory, I opted for an industrial polystyrene, hard to source, but very, very good sonically. The cap need only be 10nF, with maximum size not exceeding 100nF, but polystyrene is probably the best dielectric shy of silver mica so it was our first choice, and remains so. I don't recall if Darl tried many others here, but my own experience over years tells me it's very difficult to best a tubular polystyrene sonically - just don't overheat them while soldering!

The output cap, a large value of 1uF, was a whole new ball game. With almost 50 volts across it, we needed something pretty damn good. Once again, the RTX tested very good but considering it's cost at this value we settled on the Auricap, which was significantly cheaper, available in 200V rating, and sounded very good indeed.

Knowing that the Auricap is not as good as the RTX, however, it does not surprise me that Chris found a little ps bypassing improved it. The GK-1 is redolent with bypass caps; C6, C7 and C18 all carry bypasses for precisely the reasons Ginger has explained. Not all caps are bypassed; there are always practical limits, and diminishing benefits, but the careful design of this preamp according to the conservative rules of engineering has definitely paid dividends. There is no magic in this design; just great care in component choice, operating points and implementation, and the wonderful sounds it makes are a result of plain vanilla engineering done right, a bit like a Chevy V8.

Chris, I despatched your AKSonics yesterday; you should have them within two weeks at the most.

Guys, thanks for all the interest and discussion. And a big thanks to Chris, Peter, Mal and Ginger for their valued input. Long may it continue!

Cheers,

Hugh

cmscott6 · « **Reply #48 on:** 1 Oct 2003, 01:00 am »

Hi Hugh and Malcolm,

Part of my tinkering is not knowing when to leave well enough alone...

I stumbled onto these surplus caps at a store across the streeet from my work http://safe.spsp.net/cgi-bin/debco/scan/st=sql/va=catgy%3dCapacitors/va=subcatgy%3dCap%2dPolystyrene/co=yes/sf=category/se=Capacitors/sg=0/os=yes/op=em/sf=subcategory/se=Cap%2dPolystyrene/os=yes/sg=1/op=em/tf=sku/ml=20/sp=results_list.html?id=xp5esdYm

One was labeled "TRW"; one was labeled "Diehl"; others weren't labeled at all. They looked enough like Hugh's original C19 and were cheap enough, so I took a chance - I definitely don't have the funds to insert RTX's in the same spots

Thank you Hugh for the insight into component choice; I'm looking back over the schematics of the GK-1 and 55N and finding all of the bypass/parallel caps. I feel like I'm in school again (and I studied political "science"

).

Some of this tinkering came about after installing the Auricaps/Rikens. Although I love the deeper bass extension (still there) and smoooooth mid's, the treble just wasn't where it should have been (perhaps the "muddiness" you described). Now the treble does sparkle and is balanced with the bass and midrange. Hope it doesn't fade as all the caps age.

By the way, would someone indulge me and tell me what the reasoning is behind the orientation of these film/foil caps, i.e. they have a red/green stripe on one end. I'm assuming you orient them so that the signal "exits" from the striped end? Thank you!

Jens · « **Reply #49 on:** 2 Oct 2003, 09:56 pm »

This is just one good thread, guys! It's a goldmine for those of us who are not all that technically (electronically) minded, but still want to get the best out of our amps. Keep it coming!

I was wondering whether any of you have tried tube dampeners on the GK-1?

Any experiences, anyone?

Cheers,

AKSA · « **Reply #50 on:** 2 Oct 2003, 11:45 pm »

Chris,

Usually the red or orange band indicates the higher DC potential. To my knowledge it's not related to the signal direction.

Cheers,

Hugh

EchiDna · « **Reply #51 on:** 2 Oct 2003, 11:51 pm »

after having read this entire thread a few times I'm gooing to grab a few BG's and the only really nice resistors I can get are Riken's - I'll try and see!

fred · « **Reply #52 on:** 18 Oct 2003, 08:59 pm »

Malcolm - Earlier in this thread you posted that you had used a 25V PK black gate at C4 in your GK-1. I ordered some of these to use in my initial build (now in progress).

The CAPS that come with the kit are rated 35V. Can you please confirm that the 25V are sufficient?

Malcolm Fear · « **Reply #53 on:** 18 Oct 2003, 10:15 pm »

Hi Fred
Yes, the 25 volt rating is ok. That is what I have installed. Works fine.

If you look at the circuit diagram, there is 19 volts runing around in this neck of the woods.

ginger · « **Reply #54 on:** 7 Nov 2003, 06:03 am »

I used 68uF/20V OSCON for C4.

Fantastic improvement to bottom end even over the Rubycon ZL I tried earlier.

NOTE: If you use the OSCONs be patient they take some time to run in and they seem to do it all of a sudden after about a week. You'll notice immediately it happens - there is suddenly a heap of really low bass.

Cheers,
Ginger

EDIT: 10 Nov
The OSCONS will be better than any "standard" electrolytic and will match standard Blackgate. HOWEVER it won't be as good as a Blackgate 'N' which in turn wont be as good as 2 off Blackgate N's wired as a "Super - E Cap" (2 Blackgate Ns or NXs wired in parallel BUT with one cap reversed with respect to the other" - performance of this arrangement is exceeded only by its cost).

OZ purchase of 68uF/20V OSCON - Try Rarefaction (do web search) - this is the new name for Scott Thomsons buisiness in Melbourne which used to be called Thomson Audio Design. He keeps a very limited range of high quality parts for Valve amps in particular BUT has this cap at about 70% of the price from Radiospares or Farnell.

cmscott6 · « **Reply #55 on:** 8 Nov 2003, 02:17 pm »

Thanks for the post, Ginger; I'm very curious to try out these OSCON's. Does anyone know of a source for these caps in the US? I've checked the usual suspects and, so far, no luck (Digikey, Mouser, Parts Connexion, Michael Percy, Reference Audio Mods...)

Occam · « **Reply #56 on:** 8 Nov 2003, 09:49 pm »

Quote from: cmscott6

Thanks for the post, Ginger; I'm very curious to try out these OSCON's. Does anyone know of a source for these caps in the US? I've checked the usual suspects and, so far, no luck (Digikey, Mouser, Parts Connexion, Michael Percy, Reference Audio Mods...)

Assuming the partsconexion sale is out of stock -
http://www.partsconnexion.com/econnexion/eflash_102502/eflash.html

Consided Vishay's OSCONs in the SP series, not specific for audio use, but spectacular specs and OFC leads -
http://www.newark.com/product-details/text/CD121/58878.html

Bdent.com carries the Sanyo OsCons but they're out of stock and overpriced.

andyr · « **Reply #57 on:** 12 Nov 2003, 05:16 am »

Silver Plated IEC connectors and fuse holders for your GK-1 ... and AKSAs, of course.

Yes, gentlemen ... here's the latest entrant in the "audio jewellery" stakes!

There has been some some posts recently on "Cable Asylum" to the effect that the silver-plating makes them sound so much better than your standard nickel-plated part from RS and other places.

Here's the supplier: http://www.acmeaudiolabs.com/

Actually, US$5 (less than A$7.50 at the current exchange rate) for a panel-mount IEC plug is not that much more than I've been paying at RS Components for an ordinary nickel-plated one ($6.10 incl GST).

And panel-mount silver-plated fuse holders are US$3 - which is in fact CHEAPER than RS ($9.67, incl GST)!!

You can even have them cryogenically treated if this tickles your fancy. More expensive, of course!

C'mon, who's gonna go for em?? You can't spend all that extra money on Black Gates, OSCONs and Riken Ohms without letting the full benefit of these upgrades come through!!

Regards,

Andy

Malcolm Fear · « **Reply #58 on:** 12 Nov 2003, 11:46 am »

Ahhhh, just when I welded the tops down on my AKSA gear.
Oh well, the bottom still unscrews.

andyr · « **Reply #59 on:** 14 Nov 2003, 11:07 pm »

Quote from: ginger

The OSCONS will be better than any "standard" electrolytic and will match standard Blackgate. HOWEVER it won't be as good as a Blackgate 'N' which in turn wont be as good as 2 off Blackgate N's wired as a "Super - E Cap" (2 Blackgate Ns or NXs wired in parallel BUT with one cap reversed with respect to the other" - performance of this arrangement is exceeded only by its cost...

Ginger, a coupla Qs if you don't mind:

1. if BG 'N/NX/NH' caps are non-polar ... how do you tell which terminal is which - ie. how do you make sure you have one 'N' cap reversed??

2. you are saying a pair of 68uF/350v BG 'NH' caps would be better than a 68uF OSCON ... is there "an even better" (cost-no-object) option?? EG: 68uF/400v Solen?

3. should this cap (whatever is used!) be parallelled by a 680nF cap of some sort? Like ... what?

Regards,

Andy