The Mini-A

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#141
The 30 is pretty much the same as the 3. There were some minor changes to the front end that meant it could accept a balanced input, as I recall.
Lowering the rail voltage will cause the capacitance of the MOSFETs to rise. In consequence, they're a little more difficult to drive and distortion rises a bit. I chose 15V rails for the Mini-A for a number of reasons, among them being 10W just sounded like a good, round number and that I didn't want to push things any lower voltage-wise due to changes in the MOSFET characteristics.
It's always a question of tradeoffs and you just have to juggle things back and forth to see what you can come up with.

Grey
 
#142
GRollins said:
The 30 is pretty much the same as the 3. There were some minor changes to the front end that meant it could accept a balanced input, as I recall.
Lowering the rail voltage will cause the capacitance of the MOSFETs to rise. In consequence, they're a little more difficult to drive and distortion rises a bit. I chose 15V rails for the Mini-A for a number of reasons, among them being 10W just sounded like a good, round number and that I didn't want to push things any lower voltage-wise due to changes in the MOSFET characteristics.
It's always a question of tradeoffs and you just have to juggle things back and forth to see what you can come up with.

Grey
Click to expand...

Here!Here!:c_flag:
 
#143
Years ago it was determined that wirewound power resistors were a distinct negative factor when used in audio circuits. Would'nt you know that I have ALOT of them in values less then 1 ohm. Some are even 1%.

Do I dare use them in THE MINI-A??? OR..must I resort to the DigiKey catalog and spend $$$ for the MO 3watters???

Also side note here ..Have been looking at output Mosfets suitable for The MINI-A and can with some certainty call out BUZ71A (will need lots of heatsink... 40W rating) or better yet IRF530...88W. Both have Gfs less than 10..Ciss well under 1000pf
..and Vgs typ 3.
 
#144
sandyhooker said:
Years ago it was determined that wirewound power resistors were a distinct negative factor when used in audio circuits. Would'nt you know that I have ALOT of them in values less then 1 ohm. Some are even 1%.

Do I dare use them in THE MINI-A??? OR..must I resort to the DigiKey catalog and spend $$$ for the MO 3watters???

Also side note here ..Have been looking at output Mosfets suitable for The MINI-A and can with some certainty call out BUZ71A (will need lots of heatsink... 40W rating) or better yet IRF530...88W. Both have Gfs less than 10..Ciss well under 1000pf
..and Vgs typ 3.
Click to expand...

There have been countless Alephs built with wirewounds - others certainly have dared

😉

Why not go with the IRF T0247 (or fairchild equiv) parts? - cheap as dirt especially because they don't need matching in the mini <and> you can't go wrong.
 
#147
The potential problem with wire wound resistors is inductance. If you wind the wire on the core in a continual spiral you'll end up with a bit of inductance to go along with your resistance. It's possible, though more difficult, to wind the wire so that it goes back and forth in a series of hairpin turns. This tends to cancel the inductance. It's up to the manufacturer as to which method they use--read the spec sheet.

Grey
 
#148
Unfortunately spec sheets are'nt available in most cases. Some are listed as complying with certain mil specs which may or not be an issue.

The level of inductance has to be quite small which would mean any effect on signal would be at very high frequencies. I think as I recall the issue was with noise.

I just have alot of these and would prefer to not have to buy somethting else if not necessary.

Anyway I will use what is available and hope for the best !

Your thoughts are always appreciated.
 
#149
Resistors do have several intrinsic noise mechanisms, but somehow I can't get all worked up over Source resistors in the output stage of a power amplifier being a big noise problem. If you hear noise in your system (and you probably will--even if you have to put your ear right next to the tweeter to hear it), I'd look elsewhere before blaming the Source resistors.

Grey
 
#151
Old trick from studio days, add high values of polycarb resistors across the wirewounds (ie 47R // 0.47R), silly as this may seem, and it helped control high level transient problems - todays equiptment is a lot better, so this may not be applicable, but so easy to try .......

Many wirewounds do, unfortunately, "resonate" (sorry!) near speakers, trannies, etc quite easily.

Hope this is of assistance.
 
#152
Hi GRollins,

I got so many Japan K405 and K135 in my drawer.
Do you think it can replace Q6 & Q7 ?
Is it good to use a trim pot 50K or 100K to replace R11 for adj. the "A" ?
If I want to adjust the DC offset, what #R to replace to a trim pot ?

Thank you for your advise !!!!!:cannotbe:
 
#153
mpmarino said:


There have been countless Alephs built with wirewounds - others certainly have dared

😉

Why not go with the IRF T0247 (or fairchild equiv) parts? - cheap as dirt especially because they don't need matching in the mini <and> you can't go wrong.
Click to expand...

I'm from the old school and tend to refrain from apparent overkill. I'm also very cheap and consequently my projects are slowed by search for bargains. I have a tube of IRF240's but compulsively wont use them on a Mini . Hard to change ones ways at 75. The wider the selection ,the greater opportunity to find a bargain.

Really wanted the Babo Zen5 but the power supply requirements are HUGE in cost.
 
#155
thomasfw,
I can't tell for certain from the datasheets I found for the 2SK405...is that a later MOSFET? If so, you're going to have problems making it work because it will be way overbiased.
The 2SK135 is, if my memory hasn't sprung a leak, one of the output devices used in the old Hafler amps. Those I'm pretty sure were lateral. The same problem applies.

Grey
 
#156
Hi Grey and All,

I found the attached schemetic in internet.
I have some questions (red in color) :

1) Is the R1 is missing, I saw some kit use a 100k Trim pot ?
is it correct without the R1 ?
2) The Rf is changed, why ? What is the adventges ?
3) Why they use 100k//10k and don't use one single resistor ?
4) What is the normal bais (A) when I use +-18V ?
It is because with the same document source, the PSU sheet showed use the transformer with AC 15V X 2 (150VA). I think they are wrong !
:smash: :whazzat:

Thomas
 

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#157
The only Aleph-based circuits I've started threads about are the Mini-A and the Aleph-X. Both those threads are here at diyAudio. To the best of my knowledge, I was first in both categories (speaking solely in terms of DIY--obviously Nelson was first with the circuit). All other offerings on the web came later and most if not all of them were derived from those two threads. They've proliferated to such an extent that I make no effort to keep track of them.
To the extent that others copy the Aleph circuit, I expect them to give Nelson credit for originating the Aleph (and X) concept(s). I do not insist, but I do appreciate it when people give me credit. I did not create either the Mini-A or the Aleph-X out of thin air. They were both derived from Nelson's work; all I did was play around with his ideas. He was gracious enough to let me do so. The Mini-A was done without Nelson's foreknowledge (he's never said anything to me about it). I was in touch with Nelson about the Aleph-X from the time I finished the first conceptual schematic to the beginning of the thread.
Asking me why someone else did something the way they did is not going to accomplish much, I'm afraid. I've misplaced my crystal ball. I suggest that you ask the person in question.
I will go so far as to say that I have grave reservations about the schematic you've posted and the person who drew it. Others are welcome to their own opinions. I've stated my position elsewhere and it remains unchanged.

Grey
 
#159
Hello,

During my research about the mini Aleph on the web I've found an article, the diagram, typon and part list of the ZEN 10 Watts a Single-Stage Single-Ended Class A wich is a Pass DIY project (a 1994 article).
What is the difference with the mini A: why a mini A when the Zen 10 watts exist? I imagine there's an advantage?

Thank you: David
 
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