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-   -   PAssive preamplifier (volume attenuator) with Aleph 2? (http://www.diyaudio.com/forums/pass-labs/5197-passive-preamplifier-volume-attenuator-aleph-2-a.html)

vmajor 12th August 2002 09:39 PM

PAssive preamplifier (volume attenuator) with Aleph 2?
 
Hello all,

I am reading up on Pass amplifiers (have been for a while, but only recently seriously).

I would like to build an Aleph 2.

Can this amplifier be used with a passive 10 kOhm attenuator? (I have a DACT CT-2)

Has anyone found a chasis supplier that will supply premade chassis for Aleph 2?

Are there full instructions somewhere on how to hook everything up and construct/assemble the entire amplifier (chasis and all)? Or is there a list of FAQs?

I am getting pretty confident that I can solder the required components onto the PCBs that I will buy/make somewhere, but I am not at all certain that I will be able to buy or build an appropriate chasis.

Is the www.thlaudio.com PWAD-A100 sufficient case for the Aleph 2 (heat removal, solidity, size etc.)

I got my passive preamp components from there so I am very comfortable with using them (service was very good, everything arrived as specified and fast - best of all the chasis I got was of really high quality - unfortunately I desacrated it by drilling without stabilising the drill :rolleyes:

Thanks for your help,

Victor

wuffwaff 13th August 2002 07:32 AM

Hello Victor,

I donīt think a passive volume control would suit an Aleph2 wich has an input impedance of 10k with an unbalanced source. The gain is also not too high at 26dB so (depending on your speakers) this could also be a bit too low.

When you want to use a passive preamp youīll have to raise the input impedance (look at an Aleph3 or the Volksamps) and make shure that 26dB of gain is enough.

As far as I know there are no pre made Alephs out there. Most 19" cases with heatsinks are way too small. You need heatsinking with ca. 0,06°K/W per mono :eek:
The construction isnīt that difficult cause thereīs not a lot in it;) but if you havenīt build a power amp before I wouldnīt start with an Aleph2.

william

Peter Daniel 13th August 2002 01:43 PM

It depends on your speakers. If they efficient enough, you'll be OK with passive volume.
I'm using my Aleph 5 with a passive volume control. The input resistors are according to Volksamp schematic, the volume is inside my DAC and the maximum resistance is 500 ohm. My speakers are 93dB and I never found myself needing more power.

You shouldn't be afraid to start building Aleph 2, all the PCBs are available and in good quality, and there is so much info on the forum that you can't go wrong. If you won't make mistake with components on your board the amp will be workink fine. Don't even think about building something else.;)

Studley 5th February 2005 11:17 AM

Victor

Did you ever get to try a passive with a pair of Aleph 2s?

I have A2s and am thinking of making a passive preamp based on the TX102 transformers (like the Bent Audio NOH) because this type doesn't suffer from the impedance matching problems associated with traditional passives. However I'd like to know what the input sensitivity is of the A2s - none of the specs I've seen mention it. My CD player's output is 1.9 volts. My guess is that would be enough to produce full gain from the A2s, but it would be nice to know for certain!

jh6you 5th February 2005 12:41 PM

I would like to assume this way:

The A2 service manual informs that it has 20dB gain (i.e. x10) and maximum output of 40 volts. If so, the full gain requires about 4-volt input, which is greater than your CD output of 1.9 volts.

Pan 5th February 2005 06:03 PM

Using a 10k (or less) passive with a 10k input imp. amp. is no problem at all if you look at the resitive part of it. What can be problematic except obvious things as spl, is the high capacitance of the input on Aleph amps.

A high series resistance into a capacitive FET will increase HF distortion and will lower the roll off.

So iow. a passive solution may be better with a BJT input stage with low impedance like 2-5k (emitter resitors) and low capacitance.

I used a 10k attenuator with Aleph5 and it was extremly nice sounding but could possibly have had better performance yet with a lower impedance and balanced ontop of that.

/Peter


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