Balanced Zen Line stage

[Luke]

Im building my first preamp and have a couple of questions.

I have 4 x 5uF MKPs and wondering if its safe to use this on the output. Seems like 5uF would block DC as well 10uF or not?
Which makes me wonder why the aleph p1.7 uses 30uF per side.
What role does the value play other than low end frequency response.

Secondly, about the gain, what is normal for a linestage, isnt unity gain all thats required for cd players?
Im going to use it to drive my aleph 2s in balanced mode, and think Ill get an extra 6db of gain going from single ended to balanced. Would that mean that unity gain is all I need?

Is the aleph p1.7 a better match for my alephs, and is performance far superior.

[Mad_K]

It is safe to use them. The DC will be blocked. The P1.7 uses 30uF because more is better. The value also plays a role in the low frequency phase-shift, which may or may not be audible to you.
If you make a XBZLS instead the 5uF will be more than enough into a nominal 10K load.

The gain setting depends on how much power you need to deliver into a given speaker (ie sensitivity of your speaker and the power rating of the power amp and the gain of the power amp).

Nelson said that there is not much difference between the two preamps. Maybe you like the P better, maybe you don't. The P makes a better phase-splitter/converter (when used with a unbalanced source), but if you intend to use it to drive an Aleph, I wouldn't loose any sleep over that matter.

I say; go for the BZLS, it's a wonderful amp, and comes with a really nice project desciption

[hifimaker]

Hi Luke,

I second that... go for the BOSOZ. I just built one and the sound is simply wonderful. I asked Nelson the same question and he recommended the BOSOZ to me over the Aleph P 1.7. The BOSOZ is simpler to make and the heart of both preamps is the same circuit. Try a pair of the cool ladder attenuators from Taiwan and you'll have have easy to build preamp that sounds great.

Mad's comment above bears merit. The BOSOZ has a great build guide published by Nelson that can make the difference based upon experience level.

The gain is higher in balanced use, and the sound is more detailed.

Good Luck,

-David

[Luke]

Hi Mad_K and David,

thanks for your help. What I may do is build it and order some bigger caps in the future.

The gain setting depends on how much power you need to deliver into a given speaker (ie sensitivity of your speaker and the power rating of the power amp and the gain of the power amp).

I guess I wasnt so clear about gain, what I want to know is what gain I need on my preamp to get a full 100 watts on my aleph 2s?

If you make a XBZLS instead the 5uF will be more than enough into a nominal 10K load.

I looked a circuit of the XBZLS and I didnt see how it was different Maybe I was looking at the wrong circuit?

Try a pair of the cool ladder attenuators from Taiwan and you'll have have easy to build preamp that sounds great.

Hadnt even thought about attenuators yet. Is that P1 and P2? Can I use a 50K pot there instead?

[Mad_K]

Originally posted by Luke

I guess I wasnt so clear about gain, what I want to know is what gain I need on my preamp to get a full 100 watts on my aleph 2s?



I looked a circuit of the XBZLS and I didnt see how it was different Maybe I was looking at the wrong circuit?


Hadnt even thought about attenuators yet. Is that P1 and P2? Can I use a 50K pot there instead?

10dB gain is a good starting point..

The XBZLS has the caps inside a feedbackloop, so they're effectively "amplified"..

You can use your 50K, but it isn't recommended to go above 20K because of the input capacitance of the MOSFETS creates a high-pass rolloff together with the input pot.

Look at the XBZLS some more, the added components are marked with a *.

[Luke]

Hi Mad_K,

Ive had a closer look and I got it, but I was an expecting additional pair diff input bridged to make it an X. Does the feedback give it additional gain too?
Thanks for your help, I may use what I have for now and maybe get some boutique parts and upgrade it at a later stage.

cheers arthur

[Mad_K]

The feedback cuts back the gain, but as the Sources of the MOSFETs are shorted, you have about 30dB open loop gain (and 20dB feedback) and you have 10dB gain.

The XBZLS also make a better phase converter when driven from a single ended source.

That's good plan; use what you have now and upgrade later when funds/time permits you. The conversion from regular to X linestage is trivial

[Luke]

The feedback cuts back the gain, but as the Sources of the MOSFETs are shorted, you have about 30dB open loop gain (and 20dB feedback) and you have 10dB gain.

I got it, so to increase the gain, I should increase R122 and R123 on your circuit, decrease it by making them smaller.

[Mad_K]

You got it, but be careful with gain changes via the feedbackresistor, as it also affects the frequency response. If you change the inputresistor instead you don't change the frequency response, but the inputimpedance (and the gain of course). The designer of the X-modifications is a diyadio member called Henrik, and I would talk to him before any gain changes are to be made. He can tell you what will happen, and what the best solution would be in your case. My guess is that if you use a CD player as a source and have "normal" speakers, 10dB is just right.

[Luke]

thanks for all your help Mad_K


One other thought i had was if the X version is happy with single ended input?