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Old 10th September 2007, 09:59 PM   #1
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Default Few Really Quick Pass Amp Questions

I know I just posted here not to long ago, but I have a few more really quick questions. I am building lots at the moment, and have big plans for a future theater build (really really big plans).

This will be for movie watching, some music listening, and gaming. The "listening system will be in a separate room/different setup. What I am wondering is whether the Pass amps I am considering are good for this style setup, or if I should look elsewhere. Here are my consideration for amps.

Mains: Aleph-X, I was thinking somewhere between 150-250watts. I know it is a lot!!! I also know that it will be expensive!!!

Center: Aleph-X (undetermined wattage) or Aleph 5

Surrounds: Aleph 5

Sub: unknown, but leaning towards the X350 or something like it.

This is a very future and very slow going project, so expect anything soon. I have other projects right now...Aleph Mini and Aleph-X Mini currently to get my feet wet. Then some Aleph-3's for my room, along with JLH tweaks, addicted to this amp for some reason (sorry Mr. Pass...well I guess variety is the spice of life).

Comments, suggestions, it's all very welcome. Yes like I mentioned I know it is very big undertaking. Keep in mind I am new to audio and audio circuits, but am learning quickly. However I am very experienced with building electronics for/with my dad for his business, designing is not my strong suit, but I can build all day.

Another question though. I have looked a little at the JFET Aleph's, and I am curious, are the sonics better than the traditional IRF9610 input? Would the sonics benefit from a UGS style input, or has anyone tried this?

One more, I have been reading a lot recently about the SuSy setup, documents, studying circuits, reading patent info, what not. I have also been reading a lot about the XA's, but little about the straight X's. I know the Xxxx.5's are different at the input, are the regular X's just a pair of cascodes, or are they a cascoded differential pair? I did see a post somewhere a while back in the Pass forum where Mr. Pass mentioned the use of a current mirror with a cascode (I think) at the input on I believe the X1000? I don't know if you can comment on it or not, I have seen the X100 back-engineered thread, but is it different for the X350,600,1000?

Thanks in advance to all for the so far kind responses and help to a new Pass DIYer

BTW I apologize for my last thread where I was being a little thick about the unbalanced source to a balanced preamp or amp. I got it all straight, and much thanks to all who helped.
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Old 10th September 2007, 10:10 PM   #2
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Default Re: Few Really Quick Pass Amp Questions

Quote:
Originally posted by JPeitzman
I know the Xxxx.5's are different at the input, are the regular X's just a pair of cascodes, or are they a cascoded differential pair? I did see a post somewhere a while back in the Pass forum where Mr. Pass mentioned the use of a current mirror with a cascode (I think) at the input on I believe the X1000? I don't know if you can comment on it or not, I have seen the X100 back-engineered thread, but is it different for the X350,600,1000?
The earliest X amplifiers had a single differential pair which was
cascoded and then fold-cascoded which formed the VAS.

Later the design was altered to a single differential pair which
was cascoded and then level-shifted with a low gain common-
source pair forming the VAS.

The more recent circuits have dual differential pairs which are
cascoded and level-shifted with low gain common-source pairs
forming the VAS.

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Old 10th September 2007, 10:38 PM   #3
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Default Re: Re: Few Really Quick Pass Amp Questions

Quote:
Originally posted by Nelson Pass

The more recent circuits have dual differential pairs...
Is this as preached by Mr. Curl (complementary differential)?
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Old 10th September 2007, 10:48 PM   #4
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Default Re: Re: Re: Few Really Quick Pass Amp Questions

Quote:
Originally posted by Blues


Is this as preached by Mr. Curl (complementary differential)?
And X'ed! (Can't believe I'll forget that!)
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Old 11th September 2007, 02:20 AM   #5
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Quote:
The more recent circuits have dual differential pairs which are cascoded and level-shifted with low gain common-source pairs
forming the VAS
Somehow I imagined they would be fold-cascoded as well.

All these recent discussions make me appreciate the A-75 even more......as does my recent listening experience while the aleph was on the bench....and I haven't even run the A-75 folded-cascode yet.

JJ
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Old 11th September 2007, 04:08 AM   #6
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Sounds ambitious, and expensive; I like it. Whichever company you decide to buy heat sinks from please let me know, I will be be purchasing stock in them soon thereafter. Build 5 Aleph 5's at 5 amps with 12 outputs and huge heat sinks, and you will be the king.
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Old 11th September 2007, 08:16 PM   #7
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Quote:
Originally posted by jupiterjune
Somehow I imagined they would be fold-cascoded as well.
I love folded cascodes (done properly), but the transconductance
of the input jfets vs the original Mosfets is lower by a factor of
about 5, and I can't get enough gain coming out of the cascode,
so I made up the difference and did my level shifting with a low
gain common-source device.

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Old 11th September 2007, 08:56 PM   #8
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interesting.... so the later Xamps with the jfet inputs are actually 3 stages (I guess not that much different, depending on if you consider a folded cascode a stage or not).
Would pairs of jfets work to make up the difference, or would this hurt the sound?
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Old 11th September 2007, 11:21 PM   #9
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Quote:
Originally posted by nobody special
interesting.... so the later Xamps with the jfet inputs are actually 3 stages (I guess not that much different, depending on if you consider a folded cascode a stage or not).
Would pairs of jfets work to make up the difference, or would this hurt the sound?
All depends on what you call a gain stage. My working definition
is, "Does it contribute substantially to the gain?" A cascode
would not qualify (although it does increase gain slightly as a
general rule). A level shifter can be set to unity, and when that
occurs I would think of it as not a gain stage.

I could parallel 5 sets of JFETs to make up the transconductance,
but I run into bandwidth vs input impedance trade-offs, and
besides, 2SK389's and 2SJ109's have become unobtainium
and my stock keeps getting smaller.

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Old 11th September 2007, 11:49 PM   #10
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Quote:
Originally posted by Nelson Pass


................. and
besides, 2SK389's and 2SJ109's have become unobtainium
and my stock keeps getting smaller.


knowing that , Papa's offer from this post

http://www.diyaudio.com/forums/showt...33#post1224133

was even more generous

hehe

there are numerous ways to even more spoil greedy boyz.........




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