ChrisMmm said:
dunno where latest schematic is , but at this drawing :
http://choky.on.neobee.net/images/Babelfish J bal.gif
gain is set with ratio of R9/R8 ;
principle is the same
Thanks agen Zen!
I was working from the scematic in post 1059 which matches the PCB I believe. Yours is a lot easier to read! Yeah, thats how I unserstood the gain to be calculated. Your scematic mentions removing some parts for unbalanced use so I will do the corresponding on the PCB as well.
I am using an autoformer as a pre-amp which has no gain. I need to bump up the gain to 15-20, hopefuly that won't have any adverse affect. I have seen other Aleph builders bump the gain up to 20 or so.
Cheers
I was working from the scematic in post 1059 which matches the PCB I believe. Yours is a lot easier to read! Yeah, thats how I unserstood the gain to be calculated. Your scematic mentions removing some parts for unbalanced use so I will do the corresponding on the PCB as well.
I am using an autoformer as a pre-amp which has no gain. I need to bump up the gain to 15-20, hopefuly that won't have any adverse affect. I have seen other Aleph builders bump the gain up to 20 or so.
Cheers
Completed my Mini-A using Brian GT boards, after leaving it to "burn in" for 100+ hours have done some critical listening and very pleased with the results. I am comparing with my most recent amp which is a single ended EL84 (http://www.tubeaudio.8m.com/RH84/rh84.html) the Mini-A clearly has much cleaner bass yet retaining the clean smooth mid/tops without any of the glare I have heard with other transistor amps. Ultimately the RH84 may win in terms of its detailed yet silky smooth presentation but the Aleph is better balanced. I have yet to decide my preference! Speakers are Fostex 208ESigma/T90 in BIB cabs, fairly efficient.
Briefly, I am using a 18v-0-18v toroid 225VA, rails sit at 22 to 23V. The PS uses 6 18kuf caps in a CRCRC config (I cut the track on Brian's board between the first and second caps), resistors are 4 @ 1ohm 3watt and drop about 0.58 volts each set. Current draw per MOSFET is 1.12A so gives approx 25-26Watt. DC offset starts around 50mv each channel but drops to below 10mv after 1 hour. I am using 2 Conrad MF30-75 (0.37 C/watt) hear sinks per channel, they are bolted together with piece of solid brass to which the power mosfets are attached (I had 6 of these sink sitting around for an A75 project that never got built, that also provided the power mosfets!). After an hour they are sitting on 40C which is a 21C temp rise. More than adequate heat sink then.
In noticed after about 3 hours running you can still hold the heat sinks continually without much discomfort however the transformer is hotter than the heat sinks. I would guess its sitting around 50C. I know they get hot running class A (my RH84 traffo gets fairly hot) but is this too hot and reason for concern? It wasn't so hot before I put it all together in the chassis with the heat sinks - I have drilled holes in the base and the top is an open mesh for airflow.
Will post some picks later.
Usual thanks to Nelson, Grey for the design and Brian for the great boards.
Cheers
Briefly, I am using a 18v-0-18v toroid 225VA, rails sit at 22 to 23V. The PS uses 6 18kuf caps in a CRCRC config (I cut the track on Brian's board between the first and second caps), resistors are 4 @ 1ohm 3watt and drop about 0.58 volts each set. Current draw per MOSFET is 1.12A so gives approx 25-26Watt. DC offset starts around 50mv each channel but drops to below 10mv after 1 hour. I am using 2 Conrad MF30-75 (0.37 C/watt) hear sinks per channel, they are bolted together with piece of solid brass to which the power mosfets are attached (I had 6 of these sink sitting around for an A75 project that never got built, that also provided the power mosfets!). After an hour they are sitting on 40C which is a 21C temp rise. More than adequate heat sink then.
In noticed after about 3 hours running you can still hold the heat sinks continually without much discomfort however the transformer is hotter than the heat sinks. I would guess its sitting around 50C. I know they get hot running class A (my RH84 traffo gets fairly hot) but is this too hot and reason for concern? It wasn't so hot before I put it all together in the chassis with the heat sinks - I have drilled holes in the base and the top is an open mesh for airflow.
Will post some picks later.
Usual thanks to Nelson, Grey for the design and Brian for the great boards.
Cheers
ChrisMmm said:
using a 1/4 sheet palm sander , take all the scratches out of the surface , finishing with 320 grit silicon carbide paper.
wash surface well.
on a sanding block load up 80 grit silicon carbide paper .
using straight linear strokes sand the surface, you may want to clamp a straight edge on the panel to guide your strokes (be sure to pad the clamp so it does not marr your work).
Every few strokes blow off the surface preferrably with compressed air to remove particles of grit. move straight edge to next position till you reach the other edge of panel.
this method has given me some beautiful looking panels, after anodizing they look as good as any commercial products.
on further note 80 grit may give a courser finish than you are after so by all means try this first on a scrap.
happy diy'ing
It's almost guaranteed that a novice with a sander will round down the corners (because it's unavoidable to maintain even pressure as the sander moves over the corners). Depending on the depth of the scratches, you may find it more fool proof (but more work) to use only coarse (maroon) Scotch-Brite. Rinse with soapy water and dry it off and judge how the finish is turning out. (The S-B will wear out and become fine S-B, which is also useful. Wash it out periodically.) Best to practice on a piece of scrap first.amp-guy said:
Just a quick report.
A while back I built a mini aleph using some of the brian GT boards. I used a 12V supply also from briangt.
Now sounds was pretty good on startup - in fact it was very good! I lived with it for a while, and one night when I had a few friends over I put back in my EL84 amp and have to say it sounded a lot sweeter. The EL84 stayed. I reported here and Grey (grollins) mentionedthat upping the bias a bit could help. 0.47R resistors came in the boards, so I fitted some 0.33R - and yes it did improive things.
So eventually I found the temperature probe for my DMM and decided to up the bias a bit more. I paralleled the 0.47 and 0.33 giving me 0.19 or thereabouts. Current draw from the mains went up from 0.5A to 1A (240V) and yes, there was heat.
But having listened now for a night with this amp, I can't draw myself away form it. It sounds great. Really great. Did I say it sounded really great? Well it does.
Its not perfect - I think that there is a little bit less treble "sparkle" compared to the EL84, but boy what it does to midrange and vocals is amazing. Soundstage depth and width is very impressive. And its a major improvement from the earlier incarnation with the lower bias. It snot that anything was missing as such with less current, its just that it all pops into life so much more now.
But, But there is a problem. There is heat - lots of it and I'm not sure if I'm pushing it too far..... I hope I'm not.
So here are the measurments: TO220 diodes on heatsinks get to 70-75 deg C. Body of the PS caps are at 45 deg C. Bodies of the power transistors are at 75-80 deg C and the heatsinks hover about 60 deg C. Air measurements inside the (closed) case work out about 55 deg C. All these temps are stable over a few hours of use.
Here are pics of the amp:
There is reasonably good airflow through the amp with holes drilled top and bottom along the heatsinks....
What do you guys think? Am I OK? Am I doing harm?
Fran
A while back I built a mini aleph using some of the brian GT boards. I used a 12V supply also from briangt.
Now sounds was pretty good on startup - in fact it was very good! I lived with it for a while, and one night when I had a few friends over I put back in my EL84 amp and have to say it sounded a lot sweeter. The EL84 stayed. I reported here and Grey (grollins) mentionedthat upping the bias a bit could help. 0.47R resistors came in the boards, so I fitted some 0.33R - and yes it did improive things.
So eventually I found the temperature probe for my DMM and decided to up the bias a bit more. I paralleled the 0.47 and 0.33 giving me 0.19 or thereabouts. Current draw from the mains went up from 0.5A to 1A (240V) and yes, there was heat.
But having listened now for a night with this amp, I can't draw myself away form it. It sounds great. Really great. Did I say it sounded really great? Well it does.
Its not perfect - I think that there is a little bit less treble "sparkle" compared to the EL84, but boy what it does to midrange and vocals is amazing. Soundstage depth and width is very impressive. And its a major improvement from the earlier incarnation with the lower bias. It snot that anything was missing as such with less current, its just that it all pops into life so much more now.
But, But there is a problem. There is heat - lots of it and I'm not sure if I'm pushing it too far..... I hope I'm not.
So here are the measurments: TO220 diodes on heatsinks get to 70-75 deg C. Body of the PS caps are at 45 deg C. Bodies of the power transistors are at 75-80 deg C and the heatsinks hover about 60 deg C. Air measurements inside the (closed) case work out about 55 deg C. All these temps are stable over a few hours of use.
Here are pics of the amp:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
There is reasonably good airflow through the amp with holes drilled top and bottom along the heatsinks....
What do you guys think? Am I OK? Am I doing harm?
Fran
Hi Fran,
Similar findings here comparing EL84 amp to the Mini-A.
On temp - how hot is your mains toroid? Thats the hotest part of my amp as things stand at the moment. I will measure it tonite. What is your current draw for the power Mosfets? (Voltage oaccross your 0.19ohm resistors divided by their resistance). Oh, and what is the ambient temp? I would think 60C on the sinks is as far as you would want to go so if the ambient temp is likely to go say another 10C higher in summer that could be a problem.
Cheers
Similar findings here comparing EL84 amp to the Mini-A.
On temp - how hot is your mains toroid? Thats the hotest part of my amp as things stand at the moment. I will measure it tonite. What is your current draw for the power Mosfets? (Voltage oaccross your 0.19ohm resistors divided by their resistance). Oh, and what is the ambient temp? I would think 60C on the sinks is as far as you would want to go so if the ambient temp is likely to go say another 10C higher in summer that could be a problem.
Cheers
OK:
Mains toroid measures 50 deg C. I think its 300VA... Its ages since I bought it so I can't remember off hand. Its big anyway....
Will have to open the amp to measure the current draw... would these be the R27 and R28 on the brianGT boards? Sorry I seem so ignorant, but I actually bought these built so I never really read the whole thread and studied the schematic.... (link to a pic of the board here linky
Ambient temp is 20deg C mostly year round. Might get to 25 in summer but thats it. Never drops below 19 even in winter due to climate control in the house. Its not really a worry - I live in Ireland so hot summers are not something to worry about!
After my last post, I went back and listened again. That little worry I had about the treble seems to have gone - maybe it just needed a little more time to warm up. Definitely it didn't sound its best until at least 30 mins after turn on. One thing that really jumps out is how dynamic this amp is. Real punchy - and I'm using some nearing-40-year-old quads. I'm sorry now I didn't play with this amp more when I built it first. Can't believe I've been missing this.....
Fran
Mains toroid measures 50 deg C. I think its 300VA... Its ages since I bought it so I can't remember off hand. Its big anyway....
Will have to open the amp to measure the current draw... would these be the R27 and R28 on the brianGT boards? Sorry I seem so ignorant, but I actually bought these built so I never really read the whole thread and studied the schematic.... (link to a pic of the board here linky
Ambient temp is 20deg C mostly year round. Might get to 25 in summer but thats it. Never drops below 19 even in winter due to climate control in the house. Its not really a worry - I live in Ireland so hot summers are not something to worry about!
After my last post, I went back and listened again. That little worry I had about the treble seems to have gone - maybe it just needed a little more time to warm up. Definitely it didn't sound its best until at least 30 mins after turn on. One thing that really jumps out is how dynamic this amp is. Real punchy - and I'm using some nearing-40-year-old quads. I'm sorry now I didn't play with this amp more when I built it first. Can't believe I've been missing this.....
Fran
Well your trafo isn't getting too hot at least.
Yes R27 and R28 are the ones to measure. Get the voltage accross them and divide by the resistance for current. Multiply current by line voltage and you have the watts that the Mosfets are dissipating.
I did a lot of reading about heatsinking when I built my mini-A (I like to think I learn something new each amp I build!). Grey has a good explanation of dissipation and heatsink rating here http://www.diyaudio.com/forums/showthread.php?s=&threadid=2001&perpage=25&highlight=&pagenumber=9 Post #212 (you may well have read it already). The aim is usually a max rise of 25C, I am managing 21C so quite happy and may even increase the current draw sometime.
This site http://www.conradheatsinks.com/technical-details.html also has some good info on heatsink temp rise and derating.
I am not answering your question here as to if things are too hot but these are the tools i used to work that out for my build. Others may disagree but I would not feel comfortable with a 40C temp rise (your 60C temp less 20C ambient).
Cheers
Yes R27 and R28 are the ones to measure. Get the voltage accross them and divide by the resistance for current. Multiply current by line voltage and you have the watts that the Mosfets are dissipating.
I did a lot of reading about heatsinking when I built my mini-A (I like to think I learn something new each amp I build!). Grey has a good explanation of dissipation and heatsink rating here http://www.diyaudio.com/forums/showthread.php?s=&threadid=2001&perpage=25&highlight=&pagenumber=9 Post #212 (you may well have read it already). The aim is usually a max rise of 25C, I am managing 21C so quite happy and may even increase the current draw sometime.
This site http://www.conradheatsinks.com/technical-details.html also has some good info on heatsink temp rise and derating.
I am not answering your question here as to if things are too hot but these are the tools i used to work that out for my build. Others may disagree but I would not feel comfortable with a 40C temp rise (your 60C temp less 20C ambient).
Cheers
OK, will measure that tonight and report back. Funny the first post you linked to actually refers back to an earlier post I made with pics to this amp. In a way the guy is asking a similar question - are these heatsinks big enough.....
So I measure for each resistor and so the maths and then add together the values for the 2 devices per channel, right?
**************************
So from reading Greys analysis, it would seem just on my readings so far that I am too hot - he is talking degress farenhiet too, not celcius as I am (max temp he accepts on the heatsinks is 45 compared to my 60deg C). Problem is, no way can I go back to not having it sound as good. Greys quote is "Nelson likes to cook on his"......
Even just looking at it from a laymans point of view it probably is too hot. If I fitted a small fan into the back of the case sucking air from outside and blowing it through the inside of the case would that solve the problem do you think?
Fran
So I measure for each resistor and so the maths and then add together the values for the 2 devices per channel, right?
**************************
So from reading Greys analysis, it would seem just on my readings so far that I am too hot - he is talking degress farenhiet too, not celcius as I am (max temp he accepts on the heatsinks is 45 compared to my 60deg C). Problem is, no way can I go back to not having it sound as good. Greys quote is "Nelson likes to cook on his"......
Even just looking at it from a laymans point of view it probably is too hot. If I fitted a small fan into the back of the case sucking air from outside and blowing it through the inside of the case would that solve the problem do you think?
Fran
"5) Decide how hot you will allow your heatsink to get. Nelson cooks on his. I'm more conservative in this area, preferring to be able to leave my hand on the heatsink indefinitely."
Please note that Grey says DECIDE, not "This is the 11th commandment". The calculations are for his CONSERVATIVE temperature rise.
Remember that the Alephs had a 75decC temperature switch mounted on the heat sinks, so anything up to that point was within normal operating parameters. I'd be looking at 60degC as being 15degC BELOW the maximum recommended operating temperature rather than being 15degC ABOVE a rather conservative maximum heatsink temperature.
Please note that Grey says DECIDE, not "This is the 11th commandment". The calculations are for his CONSERVATIVE temperature rise.
Remember that the Alephs had a 75decC temperature switch mounted on the heat sinks, so anything up to that point was within normal operating parameters. I'd be looking at 60degC as being 15degC BELOW the maximum recommended operating temperature rather than being 15degC ABOVE a rather conservative maximum heatsink temperature.
OK, thats good news!!
I do have a little 12V fan that I could use (and some bigger 5" ones), but naturally don't want to use it if I don't have to. Don't like the idea of the fan noise and also the vibration. However, I will use it rather than back down on the bias given the sonic benefits of the bias....
Opinions welcome here .......
Fran
I do have a little 12V fan that I could use (and some bigger 5" ones), but naturally don't want to use it if I don't have to. Don't like the idea of the fan noise and also the vibration. However, I will use it rather than back down on the bias given the sonic benefits of the bias....
Opinions welcome here .......
Fran
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