Hm, some of the links have disappeared since I last checked this thread and I've been stupid enough not to save the content.
I've BriantGT's boards and I'm trying to collect all info about:
- The right components
- Bias adjustment
- DC offset adjustment
Especially about the latest, there are at least 3 different comments on how to adjust it in this thread, which greatly confuses me. When it comes to Brian's boards, what exactly should I be doing to fine-tune the DC offset? I'll have matched transistors, but I like to try to get those down to zero.
When it comes to the PSU - I've found some nice Air-core inductors at about 1.2 mH. Will those be a good choice? I could go bigger, but size and cost start getting a bit prohibitive at that point.
I've BriantGT's boards and I'm trying to collect all info about:
- The right components
- Bias adjustment
- DC offset adjustment
Especially about the latest, there are at least 3 different comments on how to adjust it in this thread, which greatly confuses me. When it comes to Brian's boards, what exactly should I be doing to fine-tune the DC offset? I'll have matched transistors, but I like to try to get those down to zero.
When it comes to the PSU - I've found some nice Air-core inductors at about 1.2 mH. Will those be a good choice? I could go bigger, but size and cost start getting a bit prohibitive at that point.
Replace the resistor feeding the first Mosfet on the input with 100R resistor in series with a 220R trimpot adjusted to about 100R before installation.
Bias adjustments are done by replaceing the 56k resistor with other values or a trimpot, (I am useing 100k trims).
What is the resistance of the inductors?
Bias adjustments are done by replaceing the 56k resistor with other values or a trimpot, (I am useing 100k trims).
What is the resistance of the inductors?
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Thanks for the clarification, I'll introduce those trimpots to the design.
The inductors have 0.45ohm of DC resistance. I was thinking they should be ok. I'll use them in Brian's PSU board, btw, which will power both channels.
The inductors have 0.45ohm of DC resistance. I was thinking they should be ok. I'll use them in Brian's PSU board, btw, which will power both channels.
Transformer voltage and VA rateing? also what do you plan to use for caps? Be as specific as you can then I'll put it through Duncan's PSUD for you.
with a 225VA 12V transformer, 1x 22000uf ( reccommend paralleling caps here to share the current ripple) and 1 x 10000uf seperated by your inductor gives an RMS voltage of 14.75V with a 128mV peak to peak ripple, useing some values of the parts in my PSU...
Doubling up on the 22000uf caps will bring the voltage up to 14.8V and ripple down to 64mV at 2A draw. This creates a near perfect looking sine 🙂
with a 225VA 12V transformer, 1x 22000uf ( reccommend paralleling caps here to share the current ripple) and 1 x 10000uf seperated by your inductor gives an RMS voltage of 14.75V with a 128mV peak to peak ripple, useing some values of the parts in my PSU...
Doubling up on the 22000uf caps will bring the voltage up to 14.8V and ripple down to 64mV at 2A draw. This creates a near perfect looking sine 🙂
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Right, sorry, here come the full details:
Transformer - I'm planning on:
+/-12V CT or dual-secondary, at about .. say 250VA
PSU board:
2x 15 000 uF, 30k total - Inductor - 15 000 uF , that is per-rail.
Transformer - I'm planning on:
+/-12V CT or dual-secondary, at about .. say 250VA
PSU board:
2x 15 000 uF, 30k total - Inductor - 15 000 uF , that is per-rail.
OK, it should still run about 14.8V...if you add another set of caps infront of the inductor, this also halves the ripple.
Thanks, I'm on Mac now so I can't use PSUD. 14.8 is good enough, I believe, what would the value be if I used 15V, 250VA trafo? Maybe too high for a Mini-Aleph?
Its fine if your sinks are big enough. You could always use another RC stage after or before if it is too hot, to drop it a bit. I am actualy sorry that I didn't go for a 15V transformer, importing inductors is expensive (relatively) to just getting a higer voltage transformer and useing some power resistors between banks of capacitors... (PS you want to keep the First C bigger than the one after it or you produce a nasty triangle type output.
I've no chance of changing the Caps on the board, as I've already stuffed it 🙂. I think this will do, and the price and size will determine whether I use 12 or 15V trafo. I'll be using some really powerful forced-air heatsinks, 1 per channel so I should be able to keep it cool in both cases.
Alright, so I'm left with figuring out which is the right schematic for a Mini-A, Brian's boards then. Pass ALEPH-M DIY Class-A amplifier PCB perhaps? Although its bipolars are different, but still a good replacement.
Alright, so I'm left with figuring out which is the right schematic for a Mini-A, Brian's boards then. Pass ALEPH-M DIY Class-A amplifier PCB perhaps? Although its bipolars are different, but still a good replacement.
Member
Joined 2002
If you are building a mini a' and nothing else you don't really need a HUGE beefy psu, but anything more than the Mini needs a nicer beefier psu.
The mini' has about 10mv dc off set when left on for 20 min after warm up, and some times it goes down to about 1-2mv power up the amp and test it first don't rush or get all hyped up on setting the bias, probably won't even need to touch it. Mine i didn't touch and after it settled down and was at operating temp was around 4-10mv MAX.
Anyone got a copy of the schematic for Brian's *black* boards? The ones with the non-smd components. I'd like to know what goes where without having to trace every item on the PCB.
I think I've got 5-6 schematics saved now, all except the one I'm looking for 😉
I think I've got 5-6 schematics saved now, all except the one I'm looking for 😉
Member
Joined 2002
Bom, bom ... I've got one Excel file with 2 pages - one for Aleph30, second page for Mini-A, from this thread. Is that the right one? There are some resistors that look suspicious to me in that BOM 🙂
Digits, can you send me the PSUID file of the thing you used? I'm not sure I'm doing my simulation right.
I accidentally connect wrong polarity from the power supply to the circuit.
And as usual, "the smoke came up".
Which components possibly been fried due to smoke?
The circuit still fired up but the heatsink stays cool. No heat from the transistor.
And as usual, "the smoke came up".
Which components possibly been fried due to smoke?
The circuit still fired up but the heatsink stays cool. No heat from the transistor.
There is still sound comes out from that circuit but it's so awfully distorted. Is it possible for the circuit to work if the FETs failed?
I think so, they may just be slightly damaged, especialy considering how far from their max abilities we use them at... These amps are pretty tough and I have created a whole range of error conditions, none of which destryed any parts yet, (have not reversed rails though, nor crowbarred the outputs, as those methods would kill something). Also check that the zener is still producing the right voltage as you may have exceeded its reverse voltage ability. Check electrolytics for bulgeing too
OK, I don't have data for a 250VA transformer, the one I used is 225VA.
capacitors are 2x15000uf then L then 1X22000. To increase voltage you would need a thicker guage inductor with lower resistance... also any fuses placed between PSU and amp will further reduce voltage like a 150m ohm resistor.
I must emphasise that the amp works pretty much flawlesly with just 4 10000uf caps paralleled, and I guess it would still work nicely with just one pair of something much lower.
capacitors are 2x15000uf then L then 1X22000. To increase voltage you would need a thicker guage inductor with lower resistance... also any fuses placed between PSU and amp will further reduce voltage like a 150m ohm resistor.
I must emphasise that the amp works pretty much flawlesly with just 4 10000uf caps paralleled, and I guess it would still work nicely with just one pair of something much lower.
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