Author Topic: gainclones diy anyone? (Read 384760 times)

JojoD818 · « **Reply #180 on:** Oct 27, 2003 at 12:00 AM »

Hi guys,

Just finished a 2 channel OPA549 and got it connected to my 48dB LPF and powered my 12" dual voice coil Targa sub. I used an 800VA transformer and lots of filter caps. These chips are really good, they rock! No problems encountered at all.

Since my sub has dual 4 ohm coils, I plan to series it to get 8 ohms and use a simple bridging converter (currently working on) so that I can bridge the 2 channel amp. The bridging converter is nothing more than 2 opamps with one as a non-inverting and the other in an inverting mode.

I'll post my findings asap. BTW, I will try to upload pics and link it here.

Cheers,
JojoD

joan2 · « **Reply #181 on:** Oct 27, 2003 at 10:17 AM »

if you like to color your aluminum parts, this is for you:http://t6aluminum.tripod.com/Anodizing.htm

joan2 · « **Reply #182 on:** Oct 29, 2003 at 09:27 AM »

those of you who missed this, this is a nice read:http://www.decdun.fsnet.co.uk/buildingyourown.html#casework

Garp · « **Reply #183 on:** Oct 29, 2003 at 10:09 AM »

Grrr...was finally doing my hybrid gainclone when I accidentally clipped pin 7 on my LM3875. Probably the most stupid mistake any newbie can make. I sawed off a portion of the chip near the edge so I can resoldier the pin. I hope this will work.

joan2 · « **Reply #184 on:** Oct 29, 2003 at 10:32 AM »

lesson learned, leave off about 1/8 inch, so in case of mistakes, you can still easily salvage the situation....hey i found an 8fq7 in my junk box!!!!

JojoD818 · « **Reply #185 on:** Oct 29, 2003 at 11:01 AM »

Garp,

That's one of the "accidents" I am talking about.

It should work if only the plastic part of the chip was sawed off.

JojoD

Garp · « **Reply #186 on:** Oct 29, 2003 at 11:44 AM »

Yes I think its only the plastic chip I sawed off. I saw someone do it on a LM1875 (pic below) so I thought maybe it should work with LM3875. I'll let you guys know when I've completed the circuit.

Craig Fraiser's webpage

joan2 · « **Reply #187 on:** Oct 29, 2003 at 01:20 PM »

yes, the die is probably 1/16 of an inch away!!! but it should work...

JojoD818 · « **Reply #188 on:** Oct 29, 2003 at 10:08 PM »

Garp,

I hope your chip still works, the die is really close...

JojoD

joan2 · « **Reply #189 on:** Oct 30, 2003 at 07:01 AM »

garp,
after verifying that it works, you put a few drops of mighty bond around the leads and on the sawed off encapsulation part just to seal it, a little precaution would not hurt!!!

Garp · « **Reply #190 on:** Oct 30, 2003 at 08:03 AM »

Joan2, Jojod818

Thanks for the tip Joan2--will do that. Hopefully I'll have my tube GC working by weekend! That is if I don't run into grounding issues, oscillation etc. I've actually finished the power supply already and measured DC voltages at the output are just right. I did my measurements with the PS not connected to my amp circuit which is still in the works.

I'm puzzled however that when I put my el-cheapo meter to AC I get a high voltage. So I have an 18-0-18 secondary with one bridge per rail, rectified that's about 25VDC per rail which is ok but when I measure using AC I get something like 65V per rail? I don't get it. I did the same for the filament which is at 5.9 volts and I get a AC of 12+ something. For the tube supply at 33V I get something like 75V AC. And the AC volts I get on one rail is equal to the other rail for all power modules I did. I hope I'm making sense.

And one more question, for my tube supply I'm using EI core 12-0-12v secondaries 3 amp but dual primaries 110v and 220v. To get 24V I instead used the 110v tap instead of the 220. Are there any issues here aside from the mechanical hum I get? I intend to replace it with a better one when I have time to go to Raon but for the moment I'll make do with it.

Thanks.

JojoD818 · « **Reply #191 on:** Oct 30, 2003 at 10:12 AM »

Garp,

First, shoudn't your meter be set to DC rather than AC? I think I also experienced that measuring DC with the setting on AC and getting a high voltage reading.

Second, I would suggest that you replace that 12-0-12 with the proper rated trafo. However, all things being equal (which is not) you should be able to use that but it is not designed that way. I mean, 220v is 220V and 110V is 110V, and that's it.

Safety first,
JojoD

Garp · « **Reply #192 on:** Oct 30, 2003 at 11:01 AM »

Quote from: JojoD818 on Oct 30, 2003 at 10:12 AM

Garp,

First, shoudn't your meter be set to DC rather than AC? I think I also experienced that measuring DC with the setting on AC and getting a high voltage reading.

Second, I would suggest that you replace that 12-0-12 with the proper rated trafo. However, all things being equal (which is not) you should be able to use that but it is not designed that way. I mean, 220v is 220V and 110V is 110V, and that's it.

Safety first,
JojoD

Yes I did measure using DC and the voltages are right and equal on all rails but I read from Joe Rasmussen that you can measure the ripple by setting your meter to AC so I thought maybe that should work. Joe said that one way to troubleshoot the IGC is to measure the ripple on the rails by setting your meter to AC--he quoted a figure at 2-5mv as acceptable. I don't know however if he meant measuring the ripple WHEN the PS is connected to the amp circuit or if you can do that to the standalone PS. I just have this notion--not having a backgrounds in electronics--that when AC has been rectified you shouldn't get AC on the rails.

I agree. Iwill replace the tranny soon but I'll be using it this weekend just to test my circuit. Thanks for your inputs.

joan2 · « **Reply #193 on:** Oct 30, 2003 at 05:29 PM »

garp,
you are lucky the traffo did not burn-out on you, a 110volt winding fed with 220volts draws a lot of current, that is why the humming, the transformer gets very hot in no time and smoke follows..so as jojo said, safety first!!!!

kinyo · « **Reply #194 on:** Oct 30, 2003 at 08:32 PM »

Garp,

Your multitester do not have a DC blocking capacitor on its AC setting, which explains the anomalous readouts. Try a not-so-el-cheapo digital multitester.

I have an el-cheapo digital multitester and find it lacking DC blocking capacitor and therefore reads incorrectly, similar to what you observed. It simply half-rectifies the signal so that reversing the tester leads would read zero. But my Radio-Shack multitester correctly reads ripples.

And yes, your notion is correct, after AC has been rectified and filtered by a capacitor, there will be pure DC at the capacitor terminals if and only if there is no load at all, i.e., there is nothing to discharge the capacitor. As soon as a load is connected, ripples will appear at the rails.

JojoD818 · « **Reply #195 on:** Oct 30, 2003 at 08:50 PM »

Guys,

I think that PSU ripple is something that we guys must live with. I once read an article (can't remember from where) saying that lots of capacitors and proper decoupling minimizes (not eliminate) ripple.

Maybe our design goal (for the psu at least) should be aimed at having the best psu that we can build for a better sounding amp without blowing our pockets apart!

Cheers,
JojoD

JojoD818 · « **Reply #196 on:** Oct 30, 2003 at 08:53 PM »

Forgot to mention that chipamps "usually" have excellent PSRR ratings.

garp,

I think your psu would work just fine.

JojoD

arnoldc · « **Reply #197 on:** Oct 30, 2003 at 10:46 PM »

Quote from: joan2 on Oct 06, 2003 at 10:59 PM

gem metals in makati is one such shop...

may i know the address?

Mika · « **Reply #198 on:** Oct 31, 2003 at 04:51 AM »

got my opa541am, surprised how fast the delivery was

. the chips came from malaysia, delivered by ups at our office. no payment made, taxes whatsoever.

too excited ordering, i got the to-3

(halata bang newbie). what to do?

what's next?... gainclone building EB

JojoD818 · « **Reply #199 on:** Oct 31, 2003 at 11:44 AM »

Mika,

The datasheet says nothing about the metal part of the to-3 opa541 to be connected to any pins so I suppose it is safe to install it directly to the heatsink. Be careful though because the datasheet seems to be top-view!

You might accidentally interchange the pins.

Wiring it should be the same as p2p wiring a zip11 plastic package.

What's next? Buy the remaining parts needed and do some exciting work.

Then fire it up! (Not literally!)

Good hunting,
JojoD

JojoD818 · « **Reply #200 on:** Oct 31, 2003 at 01:20 PM »

My OPA541 pcb.

http://www.geocities.com/jojod818/OPA541_Power_Amp.gif

JojoD

JojoD818 · « **Reply #201 on:** Oct 31, 2003 at 01:23 PM »

My OPA549 pcb. I hope it shows up though.

http://www.geocities.com/jojod818/OPA549_Power_Amp.gif

JojoD

joan2 · « **Reply #202 on:** Oct 31, 2003 at 01:45 PM »

Quote from: arnoldc on Oct 30, 2003 at 10:46 PM

may i know the address?

the last time i had anodizing job done was in 1993, in 1994 i went to work overseas(algeria, then singapore) and was back to manila 2001. i have lost my contact numbers, but i know "gem metals" is in makati, i used to request our purchaser to bring my items for anodizing there, there is another one, Echo Metals which is in Hulong duhat in malabon, there is also onother shop here in Pasig, but when i checked them after my return, they have already closed down...that is why i am considering doing it on my own....sorry i could not be much help at this time.....

joan2 · « **Reply #203 on:** Oct 31, 2003 at 02:00 PM »

Quote from: Mika on Oct 31, 2003 at 04:51 AM

got my opa541am, surprised how fast the delivery was . the chips came from malaysia, delivered by ups at our office. no payment made, taxes whatsoever.

too excited ordering, i got the to-3 (halata bang newbie). what to do?

what's next?... gainclone building EB

best deal in town, congrats!!! the metal types, to3 hermetic is more rugged and i would say have higher package dissipation capability, very rugged, and can last longer than the plastic versions...although harder to mount...did you say gainclone building eb? magandang idea, say mo jojo?

JojoD818 · « **Reply #204 on:** Oct 31, 2003 at 07:07 PM »

Ganda nga idea yan! Go go go...

Back to the to-3, If I can just have a technical drawing of the package, maybe I can make a template for a center punch prior to drilling the heatsink.

Yan na talaga best deal in town! gainclone metal madness!!!

JojoD

JojoD818 · « **Reply #205 on:** Oct 31, 2003 at 07:09 PM »

Ignore the pcb links, they don't work!

JojoD

arnoldc · « **Reply #206 on:** Oct 31, 2003 at 08:24 PM »

hi joan2, thanks for the heads up. i'll look around

Mika · « **Reply #207 on:** Oct 31, 2003 at 11:06 PM »

nice work jojod

click to enlarge

sir posted your pcb, hope it's ok with you.

Mika · « **Reply #208 on:** Nov 01, 2003 at 02:08 AM »

Quote from: JojoD818 on Oct 31, 2003 at 07:07 PM

Ganda nga idea yan! Go go go...

Back to the to-3, If I can just have a technical drawing of the package, maybe I can make a template for a center punch prior to drilling the heatsink.

Yan na talaga best deal in town! gainclone metal madness!!!

JojoD

eb! eb!

one afternoon maybe, in sir joan2 or jojod's place?

we can mount the circuit in a breadboard(?), experiment in replacing different values of resistor, caps, power supply, etc. how they will affect sound quality.

help a newbie

joan2 · « **Reply #209 on:** Nov 01, 2003 at 12:33 PM »

Quote from: arnoldc on Oct 31, 2003 at 08:24 PM

hi joan2, thanks for the heads up. i'll look around

hi arnoldc, i am also looking for one, even the machine shop thati used to go to for machining my aluminum parts in now gone, i used to own a bench drilling machine but i sold it just before i went to work overseas, that decision i now regret...

mika,
these gainclones are no different to plastic lm301 or lf351 opamps except they can deliver more power, so that analysis of opamps also apply to gainclones....my place? i would love to but i have actually turned our living room into a bodega of sorts...lots of computer parts, monitors etc, but anybody is welcome to go to my place, most number of peple i can accomodate will be three or four....because of the clutters...

Quote

The datasheet says nothing about the metal part of the to-3 opa541 to be connected to any pins so I suppose it is safe to install it directly to the heatsink. Be careful though because the datasheet seems to be top-view!

yes, i verified this with my dmm set to read 2k and there is really nothing connected to the case, a real improvement over lm12 i would say....