P1.7 / APOX completed

[Klaus]

Hi Andreas,

I understand your "fears" to leave Nelson Pass genius solutions by tweaking and destroy the hole thing.

But you got me wrong, I think. I am also EE and know very well what I do. I even measured some effects with best equipment at a lab at my job. Of cause the Pass circuits are perfect working stuff – but also of cause Pass is equipping devices with this budget limitations of OEMs. Exactly here we DIYer can be extremely happy – our main budget is not an exiting high end aluminum chassis for customers in hifi studios, it can be best material regarding electronic devices, too.

I had the chance to compare my Aleph4 monos blocks to original Aleph2 power stations. They, the pure OEM 2, had no chance. My 4 has almost three times more cap capacity, bypass impulse cap everywhere, soft recovery power diodes, best coupling caps, inductance free power resistors… The OEM 2 was really blown away, the perfect sound of them was improved strongly and lost nothing – it just wins. Tweaking destroys nothing; it just improves the things not given due to OEM budget limits. I had no chance to compare an OEM P1.7 with my clone, but the tendency should be the same. The story is always the same: additional impulse caps to stabilize the function of caps at impulse loads and suppress HF distortions. EE should not have fear, they should know and be open minded to check this up. Many OEMs create "special edition" versions for higher price and do exactly this stuff! Best example is the company AVM in Germany, they copied exactly the tweaks Mr. Hartwig at Thel uses for almost 10 years and which are discussed at audiomap.com forum for now many years. Why should this tweaks be not valid and helpful for the magic Nelson Pass solutions? So I have highest respect for Nelson Pass and also know how to improve the magic performance of his work at free budget.

How to describe the sonically improvements? Well, it is more focus, silence, transparency, dynamics, "freshness" and better saturation and colors of sound. Especially the heights are no longer a bit of soft. The extreme neutrality is combined with more precision. Test it – each step can be easily gone back! It is a pitty that you live far away from my, we could have a nice session – without winners or competition, just to open mind.

By the way, I do not love the M-Cap Supreme 0,1uF for its high price, it is simply the best impulse cap I have ever measured. NO additional inductance, extremely low ESR and neutral frequency behavior. Second best is the M-Cap tin (Zn) 0,1uF, sometimes a bit bright in sound. MKP10 0,1uF from WIMA is comparatively slow and tiered. Wrong bypass caps can destroy the complete harmony in sound, that is the only risk.

Enough tweaking stories from my side. I am a kind of irritated that not more guys and EEs just test tweaks. They would be astonished about the success. Of cause it just makes sense if the hole hifi set chain is already on e high level.

Regards

Klaus

[ARAD]

Rob,

I use a programmable remote control that can be programmed to use either Philips or Sony codes (as needed for the APOX system).
I purchased it locally in Germany (Conrad Elektronik).

Regards,
Andreas

[ARAD]

Klaus,

thanks again for your thoughts - as said earlier, I would consider 'tweaking' if a comparison of my P1.7 and a 'tweaked' version would clearly show 'significant' differences that could be verified via some sort of 'blind testing' in MY SYSTEM. I am certainly not afraid to tweak, nor am I afraid that I could 'ruin' my amplifier.
I do not want to go down this path before the rest of the system is to the same level of performance than my DIY-PASS components.

Regards,
Andreas

P.S.: We used decent quality components, matched Cs and Qs, good quality (matched) Rs but tried to stay away from exotic parts and snake oil.

[macka]

Klaus,

I like your experiments with the bypass caps and theory.

I am right in saying from your description that the head of the supply filter bank (initial filtering) benefits the most from the bypassing and then within the regulator itself, but no bypassing on the in board line stage decoupling caps?

Can you post a diagram to show your modifications?
I assume your mods would equally benefit the BOSOZ.

Whats do you use for the output coupling caps by the way?

Cheers

Ian

[PsykoK]

Hi,
I build a SOBOZ and want to upgrade my volume control!
For the moment I have a 4x10K log potentiometer and I have not a good result. the solution is maybe to switch for a digital volume control.

Do you think I can use the P1.7 volume control from APOX for my SOBOZ?

Regard,

Alex

[Klaus]

Originally posted by macka
Klaus,

I like your experiments with the bypass caps and theory.

I am right in saying from your description that the head of the supply filter bank (initial filtering) benefits the most from the bypassing and then within the regulator itself, but no bypassing on the in board line stage decoupling caps?

Can you post a diagram to show your modifications?
I assume your mods would equally benefit the BOSOZ.

Whats do you use for the output coupling caps by the way?

Cheers

Ian

Hi Ian,

I also like them, the open minded experiments – because the sonically improvements really astonish. I can "promise" Andreas not to need any direct A-B comparison with an OEM or untweaked DIY P1.7. – the differences are really easy to be accessed. Without snake oil and voodoo… Even best components benefit from improvements, especially bypass caps.

I totally agree upon your PSU experience, the initial filtering bank benefits most. All interferences which are shorten or not created here can not disturb the rest. The next level in the 1.7 PSU is the support of the Zener stack. Rests of Zener supply trash then to be cleaned on the PSU FET gate filter cap. And resulting from my tests the 2nd most important place to "help" is the buffer cap at the FET output. Here impulses are really demanded from the signal circuit. At that oversized circuits with 20mA bias current it is hard to argue this way, but… The remaining rest is the line stage cap behind the 3,3Ohms in line filter resistor. Here I found a strange effect like at many other tweaks at various devices before. If this at-front cap is impulse supported as well as the buffer cap at the FET output the sound is like "two pictures superposed". The sound is no longer homogeneous, it is disturbed. So two solutions are thinkable, to support just the cap in-front - or just the one right behind the FET. I found that the first solution increases stability and dynamics, but the sound suffers of saturation and substance somehow. As if the energy supply after "the first fast impulse" is not adequate. The second solution sounds just perfect! So my recipe, keep the in front cap "slow" and support as impulse capable as possible from the PSU cap side. These demands also inductance free resistor for the 3,3Ohms (dissipating less than 0,1W – so use normal metal film resistor) of cause as well as drilled cables for supply.

Sorry, I have no diagram, because there is no universal recipe which impulse bypass cap is the best for this or that electrolytic cap. Here in Central Europe a company called Mundorf has opened the market for better parts. I found that just their 0,1uF caps really sound good, bigger ones are to much. The tin caps have very low ESR and support very well, but somehow sound to sharp and bright sometimes. The Mundorf Supreme is the best cap I know and measured. Standard polyprop caps like WIMA MKP10 are nice, but far behind the lower ESR Mundorfs. They sound somewhat slower and more intransparent. But for first tests perfect. So my topology:

Filter bank behind rectifier: best available bypass cascade. I use 1uF Wima MKP10 to fill mids, 0,1uF M-Cap Supreme as "turbo" and small 10nF MKP ERO1837 63V as HF-cleaner. This cascade fits almost universal at not to fast bigger electrolytics. If smaller and faster ones are used the 1uF is obsolete. Bigger than 1uF often slowes down the sound.
Zener stack: the P1.7 PSU buffers the Zener supply at the gate so IMHO no bigger electrolytic is required. I just use a 0,1uF WIMA MKP10 as HF filter.
Gate buffer electrolytic: the most reasonable and one of the best caps I know is the FC series from Panasonic. Very dynamic and clear, a bit of sharp. A 0,1uF M-Cap tin bypass improves, a WIMA already is to slow and disturbs. A 10nF cleaner also helps much.
Buffer electrolytic behind FET: just the best I know – 1000uF Panasonic FC + 0,1uF Supreme + 10nF. This opens the sound of the P1.7 really immense! Just the FC sounds already very good, but check it out, guys, what you give away!!!!
In front buffer on the line stage PCB: 1000uF Fc without anything. Even a 10nF cleaner creates an inhomogeneous sound.

For coupling caps I tested many stuff: fat 33uF Solen MKP (= polyprop), some paralleled 4.7uF Solen MKPs, some paralleld WIMA MKP10 4,7uF, bypassed with everything like mentioned above. I was never satisfied, slow, rests of in transparency and so on. I never tested the Pass OEM BCs. I found low ESD electrolytics with 10nF MKP bypass the best. Like Elna, Pana FC, Black gate, … . Without 10nF cleaner they sound a bit aggressive and sharp and often bright. No go. BUT with the 10nF bypass everything is gone, really! Just extreme open, fresh and dynamic. Specially the deep bass is unbeleavable clear. I heard some weeks with this solution and then tested the fat foil caps again – it was like covering the clear room with something and retiring most of the musicians… The live like magic was strongly reduced. I can just give the tip to test electrolytics and not to waste room and money for fat foil cap monsters!
A small problem left: 10uF or 30uF Pana FC are almost not available, just bigger ones. With increased cap values the P1.7 circuit needs longer to start up due to the loading time of the bigger caps. At start up the amp should be muted. I delayed the mute from the volume set circuit to 15 seconds and cover the problem. So I use everywhere in my Pass clones exactly the same 220uF FC cap with 10nF bypass. One equal failure character everywere reduces the total failure amount.

So, some readers will have turned there eyes wile reading. But nobody is forced to tweak caps and explore the real performance capabilities of the genius Pass circuits. Isn't Peter denial also bypassing everything with enthusiasm?

Tweaky regards

Klaus

[macka]

Thanks Klaus,

Great bed time reading, kinda tickles my imagination:

I wonder if Karen our Pass Diy Diva would have any trinket Cap upgrade kits ever available after Mr Pass's secret capacitor experiments in the famous Zen Lab?


Ian

[joho]

Hallo Klaus,

I read about your tweakings with great interest and i have a few questions.

The 10nF MKP ERO1837 63V ??? is that old stock ?
I can only find Vishay MKP 1837 series 160V.
I hope it's almost the same.

What do you mean with "drilled cables for supply"? twisted?

By the way, Mundorf Supreme are really excellent. Did you alreaddy try the gold versions ?

Best regards,
Johan.

[Josep]

Hi Andreas,

Very good work !

Where do you buy the chasis ?

Regards

Josep

[ARAD]

Josep,

the chassis is a catalog item from Schroff and is called MULTIPAC. It was purchased from RS-components in Germany. It is a standard 19" chassis, in our case with 2 height units (2HE). You have to order the bottom plate and the cover separately. We used an additional 'subchassis' (2mm aluminum) to mount all the transformers, boards etc. etc.) - the bottom plate from Schroff is simply too thin to mount anything heavy onto it.

Regards,
Andreas