First Watt F5 vs Aleph 5

[a.wayne]

The value of the feedback resistors have to increase when paralleling outputs?
I did not realize that.

Up or down ?

 

[bobodioulasso]

Since adding additional outputs increases the open loop gain and I didn’t change the closed loop gain it had more feedback.

Does that means we need to decrease NFB and so increase the feedback resistors values in order to keep the stock close loop gain?

 

[Nelson Pass]

The value of the feedback resistors have to increase when paralleling outputs?
I did not realize that.

Neither did I.

 

[a.wayne]

 

[joho]

No zeners?

I think this would be the preferred topology.

Thank you Mr.Pass for your response.

I was thinking about 2 zeners to ground to keep a fixed voltage to the base of the cascode transistor. Bad idea?

My rail voltage is around 30 volts (at 225Vac) so I'm using a variac to make the primair AC voltage lower(24V rail).

Last Monday the man with the golden ears was in my listening room and we compared a F5 with an Aleph X (no parallel output fets).
He was impressed by both amps and his only comment on the F5 was;
- sometimes too detailled.
- mids a little bit too cold.

He preferred the Aleph X (more musical) mostly but it strongly depends of the recording you are playing.

Both are great amps.

 

[Nelson Pass]

I think your friend spotted the relative differences pretty
accurately, and of course one man's accuracy is another
man's "too detailed and cold midrange".

As to the Zener's, I don't think you need them, but they
won't hurt. probably.

 

[joho]

Yes, at this level it's a matter of taste (like good wine).

 

[lorienblack]

I don't know about the Aleph 5, but I built the Aleph3 as well as the F5. The aleph3 is much better in the mids and highs (like a good tube SET) and despite the fact that they have the same rating also seems to play louder into the same speakers (89db 4 ohms). The F5 is fuller in the lower end and probably goes deeper too. I would think that the sound of the Aleph3 would compare to the Aleph5 which looks like a more powerful version of it.

I use the A3 generally for small ensemble music, acoustic and vocals etc. and the F5 generally for larger scale music that needs to play loud. I have them both in the same enclosure using the same PS and heatsinks and switchable via several toggles for power and inputs and outputs etc.

Any chance of some pictures? I have been toying with the idea of building an Aleph J, and being able to put it in with my F5 is very interesting, and considerably cheaper as the heat sinks alone set me back £160. Many thanks for any advise or lessons you can offer on this.

 

[KatieandDad]

I've got the Aleph4 and the F5, the Aleph is just a much nicer sounding amplifier. The mids just seem to be much more vibrant leaving the F5 sounding dull and flat.

Some people might prefer the clinical sound of the F5 but to my ears the Aleph is much more pleasant to listen to.

 

[uvellani]

Any chance of some pictures? I have been toying with the idea of building an Aleph J, and being able to put it in with my F5 is very interesting, and considerably cheaper as the heat sinks alone set me back £160. Many thanks for any advise or lessons you can offer on this.

I seperated out the two amps since then in order to have two seperate systems in two rooms.
It was not very complicated to implement. I used seperate DPDT switches for each channel for the rails and output. I used just one input for both. You will need to size the transformer and heat sinks for the A3 which consumes more power. I have a 400va 18v transformer and each channel has a 12x10 sink with 2" fins, which gets pretty hot (5 sec rule).
As far as the sound is concerned, the aleph3 is warm and rich as many have noted. But I have discovered that if you drive the F5 with a good tube preamp, you get a lot of that liquidity in the midrange and none of the 'dryness'. Sort of best of both worlds. I think this is true for most class A amps.

 

[KatieandDad]

One thing that we have to pass on to new DIYers is the F5 is very easy to build. It can be built by a relatively novice DIYer.

The Aleph 3 (I think - the baby of the Alephs) is also not too difficult to build, the Aleph 4 and the Aleph 1 require some serious matching of components which make them very expensive.

I didn't build mine, it was inherited by my Son-in-Law, luckily some of the photos of it's build are still in existence.

A true Aleph 4 is absolutely immense. This one has 2 x 500VA transformers in it and is just one HUGE heatsink.

The F5 is a dwarf in comparison.

 

[lorienblack]

Thanks Uvellani - I have a toroidal 400va in the F5 and the heats sinks I used are BIG. On reflection, I will build the Aleph J and use it to replace the F5 boards for a trial spell. I love the F5 a great deal, but having played around with the EQ slightly I realize that I am open to a bit more "bloom" sometimes.

 

[KatieandDad]

Lori - be careful with the Aleph J. It's not an easy build. Good luck.

 

[lorienblack]

What aspect of the build is particularly harder than an F5? At a glance there are pcb's, the usual suspects for parts (+caps) and some fiddling with multimeters.

I haven't begun sourcing my bits yet, and had assumed that an Aleph would not be in a different league, re following the build post and standing on the shoulders of giants

 

[OllBoll]

I don't see why the Aleph J is harder to build, if you buy pre-matched devices from say someone here on the forum then it's easier than the F5 since you don't need to adjust anything.

 

[uvellani]

I don't see why the Aleph J is harder to build, if you buy pre-matched devices from say someone here on the forum then it's easier than the F5 since you don't need to adjust anything.

.

I couldn't agree more. I found the Aleph3 easier than the F5 to get up and running. True, the F5 has fewer parts, but it took me some trying to get the biasing to work.
If you can buy pre-matched parts and the PCB for the J from the diyaudio store there should not be any real complications. There is a great thread that has all the help you need - http://www.diyaudio.com/forums/pass-labs/241729-aleph-j-illustrated-build-guide.html

 

[AudioSan]

alephJ boards from the store also have pots for bias/offsett.
F5 circut is easier to understand then the aleph series. and a little more parts to solder. but if things DON'T work. then the aleph's are more difficult to fix.

 

[lorienblack]

Thanks guys.

Audiosan, I am an F5 user about to order the parts for the Aleph J, you have traveled this road and list the F5 as your Amp of choice. Would you share you impressions of the two amps with me?

I have the Version 1 of the F5 at the moment, but also have the third version built up on diyaudio boards with some spare resistors changes in order to "warm it up" I adore the F5, it's an amazing amp, but with my setup it lacks a certain musical seduction in the mids/lower mids.

Vlc media player - Havana DAC - F5 - Mark Audio Alpair 10.3 full range in QWTL.

Cheers

 

[Jean]

Interesting thread. I purchased Aleph J boards and currently have a borrowed Aleph F5.

In a box on a shelf I do have a fully populated Aleph 2, but don't have heat sinks big enough for it :/

 

[AudioSan]

Thanks guys.

Audiosan, I am an F5 user about to order the parts for the Aleph J, you have traveled this road and list the F5 as your Amp of choice. Would you share you impressions of the two amps with me?

I have the Version 1 of the F5 at the moment, but also have the third version built up on diyaudio boards with some spare resistors changes in order to "warm it up" I adore the F5, it's an amazing amp, but with my setup it lacks a certain musical seduction in the mids/lower mids.

Vlc media player - Havana DAC - F5 - Mark Audio Alpair 10.3 full range in QWTL.

Cheers

i used aleph2's for a while, but went for the F5. on my speakers the aleph was just too dark for my taste, compeared to the F5.
i used carbon composite resistors. so most F5's around probably are a bit brighter then mine. but it realy boils down to Your own taste, and the rest of the system.