In the frugalphile spirit, I'd like advice on an amplifier for my sister to build. (Yes, she (a woman!) is interested--how can we nurture this?!)
However, she brings no experience and little money to the table. Low total component cost and simplicity must be foremost. A kit would be OK, if cheap enough--say up to $100. I will help her, but since I am no electronics expert, the amplifier should be supported by a thorough how-to writup, if not a kit.
Power should be 40+ watts/ch. with as much audiophile mojo as budget allows.
Any suggestions?
Bill
However, she brings no experience and little money to the table. Low total component cost and simplicity must be foremost. A kit would be OK, if cheap enough--say up to $100. I will help her, but since I am no electronics expert, the amplifier should be supported by a thorough how-to writup, if not a kit.
Power should be 40+ watts/ch. with as much audiophile mojo as budget allows.
Any suggestions?
Bill
Bill F. said:
Only 25W per but in it beats the heart of a gainclone.
and cheap -- $12 CAD / ~$8 USD per board
Add a trafo & rectification/smoothing (they have a kit for the latter as well, but bridge & caps are a pretty simple p-to-p job.)
Should be well within the budget -- how much depends on how well you make out with the trafo and what kind of case & heatsinks you find/salvage (ApexJr has 120AV 18-0-18 toroids for $15 USD -- you could get away with one, but 2 gives a big push towards audio-philedom).
dave
How 'bout a gainclone based on either LM3875 or LM1875
LM3875 should be good for 50 odd Watt into 8 Ohms and is about as simple as they come (Power supply ends up costing you the most anyways). Freewiring would make this just about the cheapest amp around. Have a peek at http://pub4.ezboard.com/ffakeidsfrm1 and click on the banner ad look-alike to get to Thorsten's infamous inverted gainclode schematic. This user group would be more than willing to help you troubleshoot such a creation and I myself am about to embark on my LM1875 gainclone (cannot get my hands on 38xx series in South Africa)
Martin
LM3875 should be good for 50 odd Watt into 8 Ohms and is about as simple as they come (Power supply ends up costing you the most anyways). Freewiring would make this just about the cheapest amp around. Have a peek at http://pub4.ezboard.com/ffakeidsfrm1 and click on the banner ad look-alike to get to Thorsten's infamous inverted gainclode schematic. This user group would be more than willing to help you troubleshoot such a creation and I myself am about to embark on my LM1875 gainclone (cannot get my hands on 38xx series in South Africa)
Martin
Re: How 'bout a gainclone based on either LM3875 or LM1875
The Q-Kit i mentioned is an 1875 amp. These are actually optimum for driving real world speakers at 25W into 8 ohms. Above that the 4 ohm output goes flat.
These also are pretty good with 2 12V batteries in series.
With the buy all the bits in one bag + the ease of a circuit board with instructions i figure it might be better for a 1st amp. It can be modded into a Thorsten amp and a full p-to-p version built as a later project.
dave
mgoedeke said:
The Q-Kit i mentioned is an 1875 amp. These are actually optimum for driving real world speakers at 25W into 8 ohms. Above that the 4 ohm output goes flat.
These also are pretty good with 2 12V batteries in series.
With the buy all the bits in one bag + the ease of a circuit board with instructions i figure it might be better for a 1st amp. It can be modded into a Thorsten amp and a full p-to-p version built as a later project.
dave
i agree on the LM3886/76 as a great basis for a frugal-phile amp. as long as you heatsink them properly and don't let them use that "spike" protection they use.
there's a very good project amp based on them here and the guy who does the site sells pcb's for them. he's australian so all you u.s. people can take advantage of our really crap for us, good for you exchange rate on aussie$ vs. u.s.$. i've bought other pcb's from him and they're excellent quality. he's very approachable for help and when you buy a pcb he gives you access to a secure part of the site where there are very good detailed construction plans.
the expensive part of any amp based on this i.c. will be a +/-35v power supply for the rails. there's a good supplier here in australia called harbuch electronics that have really cheap toroidal transformers. you need two 25v ac secondaries. a cheap way of doing this may be using two separate 25v transformers rather than a dual secondary one, but i don't know know easy they are to find (or if they exist at all!). i know you can definitely get them at 24v and that'd be fine. you need to supply about 3-4 amps per rail.
one particular point about power supplies and making them cheaper is the reservoir capacitors, the big value ones i mean: it's cheaper to use multiple paralleled lower value ones (and you get a more reliable power supply) than single high value ones. for example, instead of using 2 10000uF caps, use 4 4700uF (meaning replace each 10000 one with two 4700's in parallel). just make sure they are voltage rated for the supply!
there's a very good project amp based on them here and the guy who does the site sells pcb's for them. he's australian so all you u.s. people can take advantage of our really crap for us, good for you exchange rate on aussie$ vs. u.s.$. i've bought other pcb's from him and they're excellent quality. he's very approachable for help and when you buy a pcb he gives you access to a secure part of the site where there are very good detailed construction plans.
the expensive part of any amp based on this i.c. will be a +/-35v power supply for the rails. there's a good supplier here in australia called harbuch electronics that have really cheap toroidal transformers. you need two 25v ac secondaries. a cheap way of doing this may be using two separate 25v transformers rather than a dual secondary one, but i don't know know easy they are to find (or if they exist at all!). i know you can definitely get them at 24v and that'd be fine. you need to supply about 3-4 amps per rail.
one particular point about power supplies and making them cheaper is the reservoir capacitors, the big value ones i mean: it's cheaper to use multiple paralleled lower value ones (and you get a more reliable power supply) than single high value ones. for example, instead of using 2 10000uF caps, use 4 4700uF (meaning replace each 10000 one with two 4700's in parallel). just make sure they are voltage rated for the supply!
Re: Frugal-cap(tm)
The dynamics and transparency start to go out the window for a start. Hugh found that for his amp too much C was also detrimental and settled on 4,700 uF as optimal.
Here is a post from the ampchipDIY board on why.
------------
blip blip blip
This is the sound of your power supply working. Twice a cycle, the diodes conduct, and a pulse of current recharges the capacitors.
The bigger the capacitor, the shorter the current pulse and the larger the instantaneous current demand placed on the diodes and transformer. Further, the voltage ripple, while smaller, will have a sharper risetime.
So there are some good enough reasons why large capacitance is a bad thing. But don't you need the energy storage to handle music transient peaks?
Well, yes, but only to the extent that the ripple (voltage droop between charge cycles) isn't excessive. Excessive is a subjective term, but for the LM3875 it can be a couple of volts without much effect.
More important, I think, is the ability of the transformer and diodes to fully charge the capacitor in a small period of time. This requires a surprisingly large peak current, and corresponding powerful transformers.
A big transformer, working into small capacitors, provides a low stress power supply.
rjm
-------------------------------
dave
mrfeedback said:
The dynamics and transparency start to go out the window for a start. Hugh found that for his amp too much C was also detrimental and settled on 4,700 uF as optimal.
Here is a post from the ampchipDIY board on why.
------------
blip blip blip
This is the sound of your power supply working. Twice a cycle, the diodes conduct, and a pulse of current recharges the capacitors.
The bigger the capacitor, the shorter the current pulse and the larger the instantaneous current demand placed on the diodes and transformer. Further, the voltage ripple, while smaller, will have a sharper risetime.
So there are some good enough reasons why large capacitance is a bad thing. But don't you need the energy storage to handle music transient peaks?
Well, yes, but only to the extent that the ripple (voltage droop between charge cycles) isn't excessive. Excessive is a subjective term, but for the LM3875 it can be a couple of volts without much effect.
More important, I think, is the ability of the transformer and diodes to fully charge the capacitor in a small period of time. This requires a surprisingly large peak current, and corresponding powerful transformers.
A big transformer, working into small capacitors, provides a low stress power supply.
rjm
-------------------------------
dave
Budget Tweeters
i have been threatening for sometime to do some cone tweeter mods to see how good i could get an almost no cost tweeter. I have a number of 2" alnico "thimble-magnet" tweeters that even stock have quite impressive performance despite their modest value (i've sold a couple pr for $2 USD/pr).
1st mod was to do a dustcapectomy and add a phase plug. I discovered that my earplugs were just right for this job. I have only been able to find 3M ones so far and they are a bit fatter so i had to shorten them (next ones i'll try to do a better job). A washer is glued to the base and they are held magnetically. More pictures on my BD-Pipes page.
I'll listen to them for a while, then treat the paper with either damar or puzzlecoat. This should make the cone more acoustically opaque. And a proper covering of ductseal as opposed to just the blob holding them onto the top of the speaker.
dave
i have been threatening for sometime to do some cone tweeter mods to see how good i could get an almost no cost tweeter. I have a number of 2" alnico "thimble-magnet" tweeters that even stock have quite impressive performance despite their modest value (i've sold a couple pr for $2 USD/pr).
1st mod was to do a dustcapectomy and add a phase plug. I discovered that my earplugs were just right for this job. I have only been able to find 3M ones so far and they are a bit fatter so i had to shorten them (next ones i'll try to do a better job). A washer is glued to the base and they are held magnetically. More pictures on my BD-Pipes page.
I'll listen to them for a while, then treat the paper with either damar or puzzlecoat. This should make the cone more acoustically opaque. And a proper covering of ductseal as opposed to just the blob holding them onto the top of the speaker.
dave
Attachments
A frugal-phile classic speaker
Hey guys,
Haven't had a chance to do a long post of Frugal-phile(tm) amps yet but some of that has been covered off in a couple gain-klone threads-- here is one for a start:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=7419
But ChrisB and i have been working away and have built one of the classic FE103 backhorns -- the Buschorn MkII -- to use as a reference for the development of our own horn.
Sounds amazing for the cost (<$100 USD). The RS 40-1197s need help above 10k and here we are using some MG horns 1st order at a nominal 10k. You can pick out the ripple from the fore-shortened horn on occasion, but it isn't at all objectionable.
If one were to find a set of 1197s at clearout in the US ($4 USD/pr vrs $20 CAD each for the only regular stocks), wired the drivers straight to the amp, used a less expensive tweeter (ie the $2/pr as above -- currently w purple instead of orange phase-plugs), the cost would be on the order of box material + $10 USD.
Chris grabbed a set of FE103A to try in them next ...
dave
Hey guys,
Haven't had a chance to do a long post of Frugal-phile(tm) amps yet but some of that has been covered off in a couple gain-klone threads-- here is one for a start:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=7419
But ChrisB and i have been working away and have built one of the classic FE103 backhorns -- the Buschorn MkII -- to use as a reference for the development of our own horn.
Sounds amazing for the cost (<$100 USD). The RS 40-1197s need help above 10k and here we are using some MG horns 1st order at a nominal 10k. You can pick out the ripple from the fore-shortened horn on occasion, but it isn't at all objectionable.
If one were to find a set of 1197s at clearout in the US ($4 USD/pr vrs $20 CAD each for the only regular stocks), wired the drivers straight to the amp, used a less expensive tweeter (ie the $2/pr as above -- currently w purple instead of orange phase-plugs), the cost would be on the order of box material + $10 USD.
Chris grabbed a set of FE103A to try in them next ...
dave
I may have to try some cheap speakers and an amp for my computer.
I though about how cheap I could build a pair of zens.
$7.95 7A 24V trans apexjr
$3.95 4x10x1.5 inch heatsink surplus from bgmicro
$2.50 25A bridge apexjr
$20 fets - digikey
$9 6x 10000uF 50V apexjr
$5 other pieces
$0.50 2x rca in
$1 cheap speaker connectors
old computer power cord
board to mount it all on
$50 total.
Mine aren't that cheap, but they are close.
Darrell Harmon
I though about how cheap I could build a pair of zens.
$7.95 7A 24V trans apexjr
$3.95 4x10x1.5 inch heatsink surplus from bgmicro
$2.50 25A bridge apexjr
$20 fets - digikey
$9 6x 10000uF 50V apexjr
$5 other pieces
$0.50 2x rca in
$1 cheap speaker connectors
old computer power cord
board to mount it all on
$50 total.
Mine aren't that cheap, but they are close.
Darrell Harmon
dlharmon said:
So we could have speakers & amps for on the order of $100. Add a passive-pre (will that work w the Zen?) and one of the new cheap SACD players (source is the most important) and you could have a serious hifi for <$500 (and a budget one with a used CD for <$200). Phono would push the price up a bit -- but Hagtech has a phono stage for cheap that looks well thot out.
I wonder if this would drive a passive pre?
dave
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