Top ten ways to a better Aleph?

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#81
Originally posted by Nelson Pass (Post 18 on Page 2)
My list ... 3) substitute in combinations of diff pair devices, picking the best performing ones in terms of distortion, noise, and sound
Click to expand...

With respect to the Aleph-X, what about using a dual MOSFET, rather than worrying about matching discrete pieces.

You can get the Philips PHP225 ("Dual P-Chanel Enhancement Mode MOS transister) in Aus for around US$0.40 - it seems to have sufficient voltage/current/power rating. Compared with the recommended IRF9610, key diffs seem to be:

V_GS(th):
IRF9610: -2 to -4 Volts
PHP225: -1.0 to -2.8 Volts

Forward Transconductance (g_fs):
IRF9610: 0.9S (min)
Forward Transfer Admittance (Yfs):
PHP225: 2.0S (typ)

I assume that "Forward Transconductance" is equivalent to "Forward Transfer Admittancy" - any views on this?

Also, does any know why the smaller ZVP3310A is recommended in the Aleph-X BOM as an alternate to the IRF9610 for the current source, but nothing is said about using this for the diff pair?

BTW, I calculated that the current source and each of the diff pairs have a power dissipation of around 200 to 300mW each, so a low power device should be fine.

All the best
Nix
 

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#82
Exact matching of the diff pair does not necessarily result in the best amplifier. If you are willing to take the enormous amount of time and effort to substitute devices into a circuit and evaluate them after warm up you can do better.

If you aren't willing to go to those extremes, matching is the next best approach.

You can use the ZVP3310 for both current source and diff pair if you want. You need to keep an eye on dissipation, and keep in mind that the device has a lower transconductance.
 
#83
Nelson Pass said:
My list of the most effective techniques for getting the best sound out of an Aleph:

6) filter cap on reference Zener
Click to expand...

For my new Aleph5 monos I'm going to implement this with a 1uF, but I was wondering what's best; right across the zener, or from top of the zener to ground?
:dodgy:
 
#86
Hello Dan,

Yes, the diode is marked as D3 on the Aleph 5 PCB.

Use film capacitor (non-electrolytic).


Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
 

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#88
Bypassing zener

Keep the bypass cap on the zener a pretty small value. Larger value caps will cause the current for the front end to come up more slowly and the output will pull towards the positive rail until the bypass cap becomes charged. I lost a set of tweeters when biamping this way by not including a coupling caps for the tweeters and using 680 uF caps. I now use five series green LEDs biased by a jfet. This has better power supply rejection and lower noise than the original zener resistor combination.
 
#92
Re: Bypassing zener

Fred Dieckmann said:
.... I now use five series green LEDs biased by a jfet. This has better power supply rejection and lower noise than the original zener resistor combination.
Click to expand...

Fred,

Do you like the sound of this CCS over the LM329 CCS (HHCCS)? How would you say they differ in their performance?

Thanks,
Rodd Yamashita
 
#93
Has any one tried Shinkoh metal film resistors in the signal path?

I know Waveglength uses them in their amps after thousands of hours of listening. I recall a discussion he had with Stereophile magazine about them. I remember the way they were described. Lack of harshness, completely grainless, beautifully transparent. He preferred them to them to Vishay, Holco etc.

I know Gordon Rankin of Wavelength has a golden ear, 'cause my amps have imaging that pours out like liquid into the room.

I know tubes amps are different, but mine are single-ended. Passive components may have similar effects on the sound in the Alephs
 
#94
Coulomb said:

To put into numbers what I mean here is one example.
a FET measure 3.163 volts initially, after 30 minutes it measured 3.143 volts, after being off for an hour it came back on at 3.202 volts and gradually dropped to 3.170 volts. When I came back to lable it the next day and measured it for "one last time" it read 2.995 volts!!!:scratch:

I thought it an irregularity and put it aside and built a Device to test many FET's at one time. Well wouldn't you know it they all do the same thing regardless of type of FET or datecode!:cannotbe:

I checked my circuits for errors and my component values, everything is working within specified parameters.

Any feedback? Is this usefull or useless?

Anthony
Click to expand...

I match the mosfets for the temperature also. The voltage goes down as temperature rises. I think that's the reason you measure differently in different days, the ambient temperature is different. I match them for the temperature they will (hopefully?) have once heatsink mounted, around 45c°.

I mount them on a small copper heatsink with a temperature sensor inside. When the temperature hits 45c° I record the reading. It takes a couple of minutes each... and the day after if you do it again, the reading is the same :nod:

ciao,
Roberto Amato
 
#96
For parallel output stages, equal dissipation is pretty much it. For differential pairs, it yields lower DC offset.

Matching per se doesn't necessarily give the best specs or best sound. This is usually achieved by substituting parts in and out until you get what you want. This is not a very practical approach because:

a) If you're a manufacturer you have the part quantities but not the time.

b) If you're a DIYer you might have the time but probably not the quantities.

c) It assumes you really know what you want.
 
#98
How about Aleph 5?

The cap is there to lower Zener noise. I usually use 1 to 4.7 uf, and type is not important. As you make the cap larger, you tend toward a bigger turn-on thump.
Click to expand...

Since Aleph 5's output is less, should I still use 1 uf to 4.7 uf? or less than this?

Also, is there any tweak I can improve Aleph 5's bass?

Thanks,

Thomas
 
#100
IRFP044 in Aleph5

One quick question:

I happen to be able to find a good supply of IRFP044. The question is: can I substitute IRFP240s as prescribed in the Aleph5 with IRFP044s? Would this improve the sound? Any harm I need to watch out?

Anybody?

Thanks.
-Sean
 
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