Hey, I've not bothered to check what config you are using on BrianGTs boards (2 devices, 6 devices), but an answer for you is likely buried in the "New Aleph Mini PCB" thread (use printer icon & dump all posts & search?)
I *knew* exactly which adjustment resistors on the black boards did what, but now that I'm done w/it, they've passed out of me🙂
Changes that worked for biasing for me are in my newer pos to that thread
I have a compilation of some Aleph info that is a bit disjointed & comes w/no promises (sorry for length & lack of attribution):
Aleph improvements
R12 750 PPC750XCT-ND * initial value, could be optimized for expected power/load conditions
R13 47.5K PPC47.5KXCT-ND * initial value, could be optimized for expected power/load conditions
R17 100 PPC100XCT-ND * initial value, could be optimized for expected power/load conditions
-With r13 at 47k I get .55v across the resistor (1.1a).
-With r13 lifted I get .68v across the resistor (1.36).
Keep in mind that you can jack up the bias by increasing R13. The stock value for the Mini-A is 47k. That gives you about an amp of bias. Just for fun, I tossed in a 220k resistor, and ramped up the bias to something like 1.6A.
On brians Pcb R12 is AC current gain, R13 Bias, R18 Dc offset.
I have one channel up and running, with standard values I get 20mv Dc on output, 4.58v across Q4 and 5, 0.588v across R35-46, Q1-2 are @ 60 C and my heatsinks are 24 C above ambient,
So yes the parts list that I posted works and I did not fit the A5 C6 that has no location (please don't mix this up with the C6 that is on brians pcb that is for a zenner bypass cap)
-------- Could be wrong component #s: --------
If you've studied the Aleph circuits at all, this circuit should be pretty much self-explanatory. The idle voltages will all read about the same as the real Alephs:
--About 4 or 5 volts across R4
--9V across D1
--Roughly +4 volts at the sources of the front end differential, relative to ground
--About 4 or 5 volts across R3
--About 4 or 5 volts across Q4
----------- Previously printed --------------
1. Crank the bias up as much as you can manage.
2. Use a better power supply than what is shown in the service manual.
3. Use non-polar caps for the two 220uF caps.
4. Use a silver mica cap (or something similar) for the feedback cap.
- Best coupling caps: expensive, huge foil types or – my reasonable tip – Panasonic FC Elkos 220UF 16V or 25V. They sound very fast, open and neutral. Spend an 10nF KP or MKP or FKP bypass and the loose last harshness. I compared them to 33UF MKP from Solen (the producer in France for almost all MKPs in Europe, like Mundorf, Audyn, …) – no chance for the fat monster. Somehow a bit intransparent and slow.
When I say R-19 I mean in the Aleph 2 and Aleph 5. Its a different R number in the 3 but the equivelent resistor in the 3 does the same thing. I think its alot higher value to begin with though. For the 2 or 5 I reccommend a 250K pot be inserted in place of R-19, and then you listen at different bias levels gradually working the bias up till you get the maximum drop across the source resistors. In my 2's thats just under .7 volts across the source resistors.
Regards,
Mark
--------------------------
Posted by Nelson Pass on 03-27-2003 09:57 PM:
My list of the most effective techniques for getting the best sound out of an Aleph:
1) measure the linearity of each output transistor in addition to matching and use the most linear
2) bias the hell out of it, with overkill heat sinking
3) substitute in combinations of diff pair devices, picking the best performing ones in terms of distortion, noise, and sound
4) a good pi filter on the supply
5) power transformer two feet away
6) filter cap on reference Zener
7) a glass of fine Cabernet
8) better caps
9) better connectors and wire
10) better resistors
------------------------
Posted by Nelson Pass on 03-28-2003 08:44 PM:
quote:
Originally posted by SuppersReady
[BAny prefered value for NP's filter cap[/B]
The cap is there to lower Zener noise. I usually use 1 to
4.7 uf, and type is not important. As you make the cap
larger, you tend toward a bigger turn-on thump.
-------
Run them between 25 and 50 watts at idle and keep them well heat sunk. Take my advice: don't ever exceed 50 watts on these 125+ wattage parts.
<I'm running about 18 watts per device>
quote:
Originally posted by Mark A. Gulbrandsen
[BI was wondering about a trimpot for R19 as a simple two connection variable resistor. Once I have found a value that appeals to me, I imagine it is best to replace the pot with a fixed resistor at that value.[/B]
Keep in mind that you can raise the bias above the figure where r19 is open by sending a high value resistor off to a decoupled negative rail voltage. Easy to do, and doesn't significantly adjust the gain of the current source. One of the nice things about the setup on the Aleph circuit as produced is the separation between DC and AC parameters. You can adjust one without screwing up the other.
-----------
Hi Mark,
I am still a bit confused here:
I have done the modification that WuffWaff did with his Aleph 5;
He wrote: "Since the last reports I changed the trimmers for R19 and R21 with resistors (49k and 390R) so now it runs at 2.4A bias and about 63% ac current gain (about 6.7A peak)."
Here is the thread: http://www.diyaudio.com/forums/show...77253#post77253
So all in all he changed R19 from 221 K in the original scheme down to 49 K while also changing R21 to 390R.
This should have made for a higher Bias, or am I wrong?
Now Mark suggests leaving R19 totally out, which makes R19 getting to an infinitely higher resistance, which should make the bias lower....????????
How can this be explained?
Hopefully Mark and WuffWaff can help me out on this....
Mark, to what total bias does you Aleph 5 go when leaving out R19 altogether? How much dissipation does this bring per channel / per mosfet? Can you describe the change in sound?
-------------
Posted by wuffwaff on 04-11-2003 01:25 PM:
Hello Lucas,
leaving R19 out will up the bias. Without it I get around 2.8A of bias.
R19 delivers a small current to the base of Q5. The bigger this current (R19 lower) the less the current through R20 has to be and the lower the value over R40-42. This way the bias is reduced.
hope this helps,
William
------------
Since my heatsinks do not get warmer than 47 degrees Celsius, I think I will soon try my Aleph 5 without R19.
Should I also change R21 then, or can I leave it at 390R?
---------------
everytime you change the bias you have to change R21 too, otherwise the ac-current-gain changes. (It gets lower if you only up the bias)
----------
I *knew* exactly which adjustment resistors on the black boards did what, but now that I'm done w/it, they've passed out of me🙂
Changes that worked for biasing for me are in my newer pos to that thread
I have a compilation of some Aleph info that is a bit disjointed & comes w/no promises (sorry for length & lack of attribution):
Aleph improvements
R12 750 PPC750XCT-ND * initial value, could be optimized for expected power/load conditions
R13 47.5K PPC47.5KXCT-ND * initial value, could be optimized for expected power/load conditions
R17 100 PPC100XCT-ND * initial value, could be optimized for expected power/load conditions
-With r13 at 47k I get .55v across the resistor (1.1a).
-With r13 lifted I get .68v across the resistor (1.36).
Keep in mind that you can jack up the bias by increasing R13. The stock value for the Mini-A is 47k. That gives you about an amp of bias. Just for fun, I tossed in a 220k resistor, and ramped up the bias to something like 1.6A.
On brians Pcb R12 is AC current gain, R13 Bias, R18 Dc offset.
I have one channel up and running, with standard values I get 20mv Dc on output, 4.58v across Q4 and 5, 0.588v across R35-46, Q1-2 are @ 60 C and my heatsinks are 24 C above ambient,
So yes the parts list that I posted works and I did not fit the A5 C6 that has no location (please don't mix this up with the C6 that is on brians pcb that is for a zenner bypass cap)
-------- Could be wrong component #s: --------
If you've studied the Aleph circuits at all, this circuit should be pretty much self-explanatory. The idle voltages will all read about the same as the real Alephs:
--About 4 or 5 volts across R4
--9V across D1
--Roughly +4 volts at the sources of the front end differential, relative to ground
--About 4 or 5 volts across R3
--About 4 or 5 volts across Q4
----------- Previously printed --------------
1. Crank the bias up as much as you can manage.
2. Use a better power supply than what is shown in the service manual.
3. Use non-polar caps for the two 220uF caps.
4. Use a silver mica cap (or something similar) for the feedback cap.
- Best coupling caps: expensive, huge foil types or – my reasonable tip – Panasonic FC Elkos 220UF 16V or 25V. They sound very fast, open and neutral. Spend an 10nF KP or MKP or FKP bypass and the loose last harshness. I compared them to 33UF MKP from Solen (the producer in France for almost all MKPs in Europe, like Mundorf, Audyn, …) – no chance for the fat monster. Somehow a bit intransparent and slow.
When I say R-19 I mean in the Aleph 2 and Aleph 5. Its a different R number in the 3 but the equivelent resistor in the 3 does the same thing. I think its alot higher value to begin with though. For the 2 or 5 I reccommend a 250K pot be inserted in place of R-19, and then you listen at different bias levels gradually working the bias up till you get the maximum drop across the source resistors. In my 2's thats just under .7 volts across the source resistors.
Regards,
Mark
--------------------------
Posted by Nelson Pass on 03-27-2003 09:57 PM:
My list of the most effective techniques for getting the best sound out of an Aleph:
1) measure the linearity of each output transistor in addition to matching and use the most linear
2) bias the hell out of it, with overkill heat sinking
3) substitute in combinations of diff pair devices, picking the best performing ones in terms of distortion, noise, and sound
4) a good pi filter on the supply
5) power transformer two feet away
6) filter cap on reference Zener
7) a glass of fine Cabernet
8) better caps
9) better connectors and wire
10) better resistors
------------------------
Posted by Nelson Pass on 03-28-2003 08:44 PM:
quote:
Originally posted by SuppersReady
[BAny prefered value for NP's filter cap[/B]
The cap is there to lower Zener noise. I usually use 1 to
4.7 uf, and type is not important. As you make the cap
larger, you tend toward a bigger turn-on thump.
-------
Run them between 25 and 50 watts at idle and keep them well heat sunk. Take my advice: don't ever exceed 50 watts on these 125+ wattage parts.
<I'm running about 18 watts per device>
quote:
Originally posted by Mark A. Gulbrandsen
[BI was wondering about a trimpot for R19 as a simple two connection variable resistor. Once I have found a value that appeals to me, I imagine it is best to replace the pot with a fixed resistor at that value.[/B]
Keep in mind that you can raise the bias above the figure where r19 is open by sending a high value resistor off to a decoupled negative rail voltage. Easy to do, and doesn't significantly adjust the gain of the current source. One of the nice things about the setup on the Aleph circuit as produced is the separation between DC and AC parameters. You can adjust one without screwing up the other.
-----------
Hi Mark,
I am still a bit confused here:
I have done the modification that WuffWaff did with his Aleph 5;
He wrote: "Since the last reports I changed the trimmers for R19 and R21 with resistors (49k and 390R) so now it runs at 2.4A bias and about 63% ac current gain (about 6.7A peak)."
Here is the thread: http://www.diyaudio.com/forums/show...77253#post77253
So all in all he changed R19 from 221 K in the original scheme down to 49 K while also changing R21 to 390R.
This should have made for a higher Bias, or am I wrong?
Now Mark suggests leaving R19 totally out, which makes R19 getting to an infinitely higher resistance, which should make the bias lower....????????
How can this be explained?
Hopefully Mark and WuffWaff can help me out on this....
Mark, to what total bias does you Aleph 5 go when leaving out R19 altogether? How much dissipation does this bring per channel / per mosfet? Can you describe the change in sound?
-------------
Posted by wuffwaff on 04-11-2003 01:25 PM:
Hello Lucas,
leaving R19 out will up the bias. Without it I get around 2.8A of bias.
R19 delivers a small current to the base of Q5. The bigger this current (R19 lower) the less the current through R20 has to be and the lower the value over R40-42. This way the bias is reduced.
hope this helps,
William
------------
Since my heatsinks do not get warmer than 47 degrees Celsius, I think I will soon try my Aleph 5 without R19.
Should I also change R21 then, or can I leave it at 390R?
---------------
everytime you change the bias you have to change R21 too, otherwise the ac-current-gain changes. (It gets lower if you only up the bias)
----------
Many thanks for that.
I think I've got it right that the R18+19 (grollins) are R27+28 (brianGT).
What I've got to figure now is do I need to change the other 0.47R ones too R20+21 (grollins); R20+21 (brianGT).
sure is confusing!
Fran
I think I've got it right that the R18+19 (grollins) are R27+28 (brianGT).
What I've got to figure now is do I need to change the other 0.47R ones too R20+21 (grollins); R20+21 (brianGT).
sure is confusing!
Fran
I don't have a schematic with me, but if you mean the series resistors at the output (which are the only other .47 Ohms resistors I can think of), then yes, they should match the MOSFET Source resistors.
Grey
Grey
- and a lifesaver too.
Fran,
The mini a is great little amp to play with, I have built 3 of them ( I keep giving them to graduating nephews) . I keep making them in different configurations to try altering components, the odd rub is the cheap ones sound as good as the more expensive ones. A testimony to a well engineered design does not require boutique components to sound good. Great work on Grey's part, as well as Mr Pass.
Bill
The mini a is great little amp to play with, I have built 3 of them ( I keep giving them to graduating nephews) . I keep making them in different configurations to try altering components, the odd rub is the cheap ones sound as good as the more expensive ones. A testimony to a well engineered design does not require boutique components to sound good. Great work on Grey's part, as well as Mr Pass.
Bill
bias resistors
Hi,
I have a question regarding Grey's schematic.
I've read through the posts. I understand R11(47K)
R18/R19(.47) sets the bias.
Digikey has no stock for the .47 3W. They do have a
.62 3W, I could double up for .33 but that would be more
costly.
What does R20/R21 do?
Does R20/R21 need to be the same value as R18/R19?
I also checked mouser, none of those values at 3W other than .5ohms.
So other than the 10pF across R8(10K). There is no other
major changes needed?
The Mini Aleph should should sound similiar to the Aleph 3,30?
Thx.
Hi,
I have a question regarding Grey's schematic.
I've read through the posts. I understand R11(47K)
R18/R19(.47) sets the bias.
Digikey has no stock for the .47 3W. They do have a
.62 3W, I could double up for .33 but that would be more
costly.
What does R20/R21 do?
Does R20/R21 need to be the same value as R18/R19?
I also checked mouser, none of those values at 3W other than .5ohms.
So other than the 10pF across R8(10K). There is no other
major changes needed?
The Mini Aleph should should sound similiar to the Aleph 3,30?
Thx.
Member
Joined 2002
Wow, after getting my new tweeters, thanks Planet10 for the 2gsi's. Now i have to finnish my chassis for my 2 stereo Mini a's.
Hi,
I went with mouser and got some .43. They were a lot cheaper
than the vishays.
I have the brian gt mini aleph boards and I'm going to use Grey's schematic for the mini.
What are the differences between the two other than bias?
I see some 9.1v zeners brian's schematic. The extra components
are for stability?
on brian's power supply board, there is an option to add
some resistors in series between the caps. does this
dramatically reduce noise by adding .47 3W resistors?
thanks.
I went with mouser and got some .43. They were a lot cheaper
than the vishays.
I have the brian gt mini aleph boards and I'm going to use Grey's schematic for the mini.
What are the differences between the two other than bias?
I see some 9.1v zeners brian's schematic. The extra components
are for stability?
on brian's power supply board, there is an option to add
some resistors in series between the caps. does this
dramatically reduce noise by adding .47 3W resistors?
thanks.
Bengali said:
humm. well there is a good reason why the Visahy Dales are expensive. It is what I supplied for all the Kits Jason did a few years back.
Anthony
I thought about the vishays but at $1.78 per resistor
vs. the KOA .43 3W 2% for $0.24, I decided to go cheap.
I've read through all of the Mini A posts. I'm still unclear
as to the difference between Grey's and Brian's mini-A.
Sorry, I know the question has been brought up before
but not really answered.
I ordered parts using Grey's schematic. However, I have
brian's mini-A board so will be using those.
Any enlightenment on the differences would help.
thanks!
vs. the KOA .43 3W 2% for $0.24, I decided to go cheap.
I've read through all of the Mini A posts. I'm still unclear
as to the difference between Grey's and Brian's mini-A.
Sorry, I know the question has been brought up before
but not really answered.
I ordered parts using Grey's schematic. However, I have
brian's mini-A board so will be using those.
Any enlightenment on the differences would help.
thanks!
Just a thought here, but why would you do that? There is a BOM for the brianGT boards with part numbering according to the silkscreen etc. It would be easy to get something mixed up otherwise....
Fran
Fran
based on the postings, there seems to be more info pertaining to grey's schematic. grey's has a smaller parts count.
It's confusing so I will do a point to point check on the pcb against grey's schematic, making sure I'm stuffing it correctly.
Since there are some that have built brian's per his bom, some have built grey's. I think some have built grey's using brian's pcb.
I'm asking since I really don't know the differences between the two and sticking to the one with fewer parts.
It's confusing so I will do a point to point check on the pcb against grey's schematic, making sure I'm stuffing it correctly.
Since there are some that have built brian's per his bom, some have built grey's. I think some have built grey's using brian's pcb.
I'm asking since I really don't know the differences between the two and sticking to the one with fewer parts.
It might be over simplified. Mini-A is an Aleph 30 with 2 pairs of fets cut off, lower rails, and a few parts changed. Brian's board can be used to build Aleph 30 as well as mini-A. Notice that Brian's parts numbers and Grey's are different, but if you put 2 schematics side by side, you should be able to map Grey's parts number into Brian's. You can use this spreadsheet for reference. I believe I downloaded it from Brian's website. I have a note on R14 and R16. I think they should be 750 instead 1.5K. You may want to do some research.
Thanks. There was some info on brian's website at one time but it's been removed. I will use what I got for now and hopefully can get it working. I could always go back to brian's bom.
Are those 9.1V zeners(Z1/Z2) on the input help keep it from oscillating?
Are those 9.1V zeners(Z1/Z2) on the input help keep it from oscillating?
Bengali said:
nope ;
help keep it from zapping - in case of excessive voltage or static charge/discharge on input
Grey: just to say thanks, I put in the 0.33R resistors today and she is back up and running. Heatsinks (subjectively) get warmer. I've only had it running out in the workshop so I can't comment on sonics yet (theres 2 sets of speakers and the small matter of a sabre DAC calling me!). When I get it back into the main rig I post.
I can't find my temperature probe for the DMM anywhere - so I'm reluctant to drop the R any more until I could get a reading off the heatsinks. I don't want to fry them. At a guess I'd say the heatsinks are at 60 degC (45-50 with the 0.47Rs in place).
Fran
I can't find my temperature probe for the DMM anywhere - so I'm reluctant to drop the R any more until I could get a reading off the heatsinks. I don't want to fry them. At a guess I'd say the heatsinks are at 60 degC (45-50 with the 0.47Rs in place).
Fran