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chip amps: Almost everything you ever wanted to know


DizRotus

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If you intend to upgrade or modify this amp, use caution to not overheat the board while de-soldering and soldering. Some of these printed circuit boards aren't the best quality for re-working. The thru-holes and eyelets are less than 1mm diameter, so you have to be careful about capacitor leads properly fitting into the thru-holes.

I received my 0.22uF Mundorf Supreme caps the other day and installed them in the TDA7297 amp the same evening. Using the Panasonic Polypropylene film and foil caps made a vast improvement in sound quality over the cheap stock Polyester film caps. Switching to the Mundorfs wasn't a quantum leap like the last change, but it was more a refinement of sound. Where the Panasonic caps addressed tonality, the Mundorfs maintained the warmth and rich tonality, but added a large degree of transparency. The timbre detail coming through along with a more focused image give more life to the music. My friend who recommended that I try the Mundorfs best describes these caps as having an organic presentation. Some may call it more life-like. I've gone through many capacitors in my DIY projects: Auricaps, Sonicaps, Sprague Orange Drops, Wimas, Obbligatos, Illinois Capacitor MPWs and the Panasonics, and these Mundorfs are very impressive. I have Sonicaps in my Klipsch Forte II crossovers that I purchased from Bob Crites as part of his crossover cap upgrade kit, but I might have to replace these with some Mundorf Supreme caps.

The TDA7297, in stock form, is better than the SMSL SA-S1 TA2020 T-amp, but these cap upgrades really take this amp to a higher level of performance. The circuit is so simple, it only takes changing these three caps.

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Rich-

More details about the Panasonic caps used please. Where did you get them?

I like to modify electronics, but, I confess my understanding of the EE aspects is limited. I can solder and read a schematic, but I don't fully understand what the various components accomplish in the circuit. That said, instead of just replacing the stock 2,200 uf 25v electrolytic with the Panasonic counterpart, is there any advantage to increasing the capacity of that component?

I haven't tried the new arrival yet, but I just ordered a second amp. I plan to try one as a substitute for the SMSL SA-S1 now in my "iPod" dock on steroids. Then I can hot rod the other and apply the successful modifications to both amps.

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Edited by DizRotus
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Nice portable system there. The TDA7297 ought to work in that rig very nicely. I'd like to make a portable system using some highly efficient single drivers. I have a pair of small speakers using Fostex FX120 drivers and I'm thinking of designing some new bass reflex enclosures that will house a small amp like the TDA7297 to make the stereo pair more portable. Here's a photo showing these speakers sitting on top of my Forte II's driven by the TDA7297. It sounds very nice.

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I just met one of my son's classmate's dad, and he has a pair of Klipschorns that I would like to try with this amp. The Klipschorns are not portable, but they'll make the most of this flea-powered amp's first watt.

For the power supply filter cap (the 2,200uF / 25V electrolytic), you can add higher capacitance if you want. You need to consider the size (diameter and height) and the voltage rating. The board you ordered may or may not accommodate a cap with a diameter larger than the stock cap, which is 12.5mm diameter. You have to consider the height of the capacitor based on the enclosure you want to place the amplifier in. As for the capacitor's voltage rating, use a cap with 25V up to 50V rating. Anything larger is unnecessary. I happened to use a Panasonic FM cap from Mouser Electronics since these caps are suitable for this type of application. Panasonic FC caps are also good choices.

Edited by rhing
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Rich-

Thanks.

The boombox has 2 Radio Shack 40-1197 (labeled FE-103 and rumored to have been made for RS by Fostex) drivers. The bass reflex enclosure is ~ .5 cu. ft. with a single port to the rear. Having the drivers share the enclosure and port is a compromise, but it's worth it for the portability (see https://community.klipsch.com/index.php?/topic/144722-bluetooth-ipod-dock-on-steroids/ from the old forum. The photo attachments had to be stripped from that thread so that I could attach files in the new platform). People are always amazed by the sound. Labor Day weekend my brother and his spouse felt it sounded better than their Bose iPod dock, which it does.

I've done some searching on Parts Express and Mouser for the Panasonic caps, so far without success. If you could provide sources, descriptions, values, prices, etc., I'd be very grateful. I'm shameless when it comes to profiting from someone else's experience and efforts. I don't feel compelled to re-invent the wheel.

BTW, I got impatient and hooked up the TDA7297, even without the inbound phono preamp. For now, I'm using a Motorola 12v 3A phone charger as the power supply. I'll try others eventually.

Unable to play vinyl, I'm relegated to listening to Pandora or mp3s via iPad or LG smart phone, each via Bluetooth. It sounds darn good. My immediate impression is that the bass is better than the Lepai TA2020, the SMSL SA-S1 or the SMSL SA-50. I'm eager to hear it play vinyl.

The plan is to await the arrival of the second TDA7297 prior to beginning surgery on this one. I'd like to hear them both after some burn-in to compare the stock units to each other. Then I'll keep one stock to compare it to the "improvements." Eventually, I'll probably modify them both.

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Edited by DizRotus
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Nice portable system there. The TDA7297 ought to work in that rig very nicely. I'd like to make a portable system using some highly efficient single drivers. I have a pair of small speakers using Fostex FX120 drivers and I'm thinking of designing some new bass reflex enclosures that will house a small amp like the TDA7297 to make the stereo pair more portable. Here's a photo showing these speakers sitting on top of my Forte II's driven by the TDA7297. It sounds very nice.

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I just met one of my son's classmate's dad, and he has a pair of Klipschorns that I would like to try with this amp. The Klipschorns are not portable, but they'll make the most of this flea-powered amp's first watt.

For the power supply filter cap (the 2,200uF / 25V electrolytic), you can add higher capacitance if you want. You need to consider the size (diameter and height) and the voltage rating. The board you ordered may or may not accommodate a cap with a diameter larger than the stock cap, which is 12.5mm diameter. You have to consider the height of the capacitor based on the enclosure you want to place the amplifier in. As for the capacitor's voltage rating, use a cap with 25V up to 50V rating. Anything larger is unnecessary. I happened to use a Panasonic FM cap from Mouser Electronics since these caps are suitable for this type of application. Panasonic FC caps are also good choices.

Rich-

I see now that you edited your post and answered some of my questions before I asked them.

Is there any reason a power supply filter cap can't be attached remotely to avoid the space issues on the board? If I install this inside the boombox there is plenty of space.

Neil

Edited by DizRotus
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You can mount the power supply cap off board, but keep it as close as possible to the DC input, and keep the polarity correct. I wish some of these Chinese manufacturers would make these boards a bit larger to accommodate upgrades and mods. Oh well. I can tell you that vinyl sounds good through this amp. You might as well let the amp burn in before you get your phono preamp.

If you want to keep the amp compact for your portable system, you can use compact box-type capacitors like Wima MKP2 0.22uF / 250V metallized Polypropylene film caps from Mouser. Just make shire you get the caps with the 5mm lead spacing. These will fit on the board. I got the Mundorf Supreme caps, because I want really high quality caps, but the Wimas will sound much better than the stock Polyester caps.

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The more I listen to this amp the better it sounds. I can't wait to begin the mods.

The left photo a few posts back shows the inside of the boombox, as well as the inside of the rear panel next to it. You can see the port and the power supply for the amp attached to the inside of the rear. The Lepai in the photo has since been replaced by the SA-S1 mounted to the underside of the enclosure. There's plenty of room inside the boombox.

The Bluetooth adapter will stay mounted to the underside of the exterior, for better reception, but the TDA7297 would be better protected inside. I'll probably remove the volume pot before hiding it away in the boombox.

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Rich-

I'm not ashamed to broadcast my ignorance. What's the difference between FC and FM. I'm guessing FM means Film Metalic and FC means Film Carbon, but I've really no clue.

Finding suitable components at Mouser's site is daunting. I ordered these. Will they work? I checked out Mundorf, but couldn't bring myself to put $20 worth of caps in a $6 amp.

Neil

Order_6680005.pdf

Edited by DizRotus
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I'm glad you're enjoying the TDA7297. I don't know the significance of FM or FC. Both are excellent and can be used. The FM caps have a bit lower Equivalent Series Resistance (ESR) compared to the FC caps. This is preferable for power supply filtering. Both are rated for long life. I just happened to have some Panasonic FM caps on hand for modifying power supplies in Sony Playstations for CD playback. There is only one Panasonic FM cap that has the 2,200uF / 25V rating. This will fit right on the board, and is more than adequate for the application. An investment in a better power supply would go a lot further than going for a slightly larger cap.

I'm not sure about the Panasonic ECQ-E Polyester film caps for the input coupling caps. I'm just not a fan of Polyester caps for audio signals. You can try them and see if you like them. I recommend the Wima MKP2 metallized Polypropylene caps (Mouser PN 505-MKP20.22/250/5). They should fit on the board without any problems.

Edited by rhing
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Rich-

As I type, I'm listening to the stock TDA7297 powered by the 12v jump-start box shown in the attached photo. It sounds very good. Am I correct that "a better power supply" will improve the sound to a point where it will sound like a 12v battery? If so, there seems to be a diminishing return factor, It sounds very good, but not significantly better than the 12v 3A Motorla phone charger.

What input coupling caps are shown in the pic attached to the post several posts back?

Perhaps I can still modify my order from Mouser. I see now that I mistakenly ordered four 2,200 uf, when I only need 1 per amp.

Thanks for taking the time to teach this old dog new tricks,

BTW, just because this is directed to Rich, doesn't mean input from others isn't welcomed, because it is.

My comment about not wanting to put $20 worth of Mundorf Supremes into a $6 amp isn't just because I'm cheap--which I am--but because part of the challenge for me is to get the most out of the least. When my old (redundant) college friends hear the sound from my DIY Radio Shack speakers, their jaws drop and they wonder why the spent many thousands on systems that don't sound as good. I can't wait to get their reactions to this Rube Goldberg setup.

Best,

Neil

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Edited by DizRotus
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Rich-

As I type, I'm listening to the stock TDA7297 powered by the 12v jump-start box shown in the attached photo. It sounds very good. Am I correct that "a better power supply" will improve the sound to a point where it will sound like a 12v battery? If so, there seems to be a diminishing return factor, It sounds very good, but not significantly better than the 12v 3A Motorla phone charger.

What input coupling caps are shown in the pic attached to the post several posts back?

Perhaps I can still modify my order from Mouser. I see now that I mistakenly ordered four 2,200 uf, when I only need 1 per amp.

Thanks for taking the time to teach this old dog new tricks,

BTW, just because this is directed to Rich, doesn't mean input from others isn't welcomed, because it is.

My comment about not wanting to put $20 worth of Mundorf Supremes into a $6 amp isn't just because I'm cheap--which I am--but because part of the challenge for me is to get the most out of the least. When my old college friends (redundant) hear the sound from my DIY Radio Shack speakers, their jaws drop and they wonder why the spent many thousand on systems that don't sound as good.

Best,

Neil

Hi Neil,

I like your experimental setup. I like the raw amp look.

The TDA7297 seems to like 12V plus current. My modified SMPS, which I used with my SMSL SA-S1 T-amp puts out 12V and 4-5A. An audio buddy of mine who lives in the South purchased a Mean Well RS-100-12 SMPS that outs out 12V and around 7A. I have to take his word that he gets deep bass and plenty of slam. Like me, he owns a pair of Klipsch Forte II's.

I tried my little black box SMPS that came with my Sonic Impact Gen 2 T-amp (Model 5065) that puts out 12V and 2A, the recommended power from the TDA7297 amp module manufacturer. It sounds okay, but it is anemic compared to my higher current modified SMPS: weakened bass, thinner sound and less detail. To get the most out of this amp, I would recommend something like the Astron RS-7A regulated linear power supply or the Pyramid PS9KX 13.8 VDC 5A regulated linear power supply. I'll probably get the Astron from a local marine radio and electronics dealer.

I'm not sure what photo you are referring to, but I posted a photo of my amp with the Panasonic 0.22uF / 400V ECQP Polypropylene film and foil caps (the largish rust-colored epoxy coated caps). You can only get these from Jim McShane, a well known vacuum tube dealer. He's the only person I know that has NOS inventory of these caps. They cost $3.50 each, and a little extra if you want Jim McShane to match them. The more recent photo of my TDA7297 amp shows the Mundorf Supreme 0.22uF / 1200V metallized Polypropylene film caps. These caps are awesome, and I'm glad my buddy turned me onto them. The Panasonic ECQP caps are a tremendous value, but these Mundorf Supremes are definitely higher end audio caps. Mundorf makes even more expensive Supreme caps that use Silver and Silver/Gold.

For your boombox needs, try the Wima MKP2 caps. They're good value and they work well. I used them in my rebuild and modification of my Dynaco SCA-35 tube integrated amp, and they worked very well in the phono stage and amplifier driver stage as coupling caps. They're compact, inexpensive and they look neat. My Audio Research LS7 line stage and PH5 phono stage preamps have a bunch of the little red Wima MKP caps in the power supply as bypass filter caps.

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That's the photo I was referring to. So those caps are not the same as in the previously attached Mouser order. Are they better than the Wima caps?

I too have a modified SCA-35 that I use to amaze my audio challenged friends. The TDA7297 will flabbergast them.

The booster puts out 12.65v at an unknown amp rating. Given it's ability to crank a car, it must be way more than the 2 - 6A of the available bricks. I'll try the TDA7297 with the 12v 6A brick now powering the SA-S1. I doubt it'll sound better than the jump-starter.

Edited by DizRotus
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I think so, but opinions may vary. To my ears, the Panasonic caps are warmer and reproduce fuller notes, but I'm probably splitting hairs here.

A friend of mine restored a Dynaco Stereo 35 power amp that duplicated my own Stereo 35 rebuild, except he used Polyester caps where I used the Panasonic ECQP Polypropylene caps. We did blindfolded listening tests comparing each other's Stereo 35's, and my amp came out on top when we auditioned different types of music--same tracks with each amp. This was an experiment among three listeners. Afterwards, he bought the same Panasonic ECQP caps from Jim McShane, and he's a happy man now. You can try the Sprague 716P Orange Drops, which are similar, but my personal preference are the Panasonic ECQP's.

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I ordered 4 of the Wima coupling caps from Mouser and 4 of the Panasonic ECQP caps from Jim McShane. That should give me plenty of ammunition to hot-rod the TDA7297s for now.

I'm still curious about whether the 12.65 volt/high amp battery booster is an inherently superior power supply for the TDA7297, as compared to power supplies with >12volts at >2 amps. I've got several to try, but I don't expect an improvement over the 12.65 volt battery. As an experiment, I'm, going to let the booster's voltage drop below 12 volts (I'll monitor it with a DVM) to see if I can perceive any degradation in performance.

For reasons beyond the scope of this post, and through no fault of billybob, the phono preamp I purchased has been bounced back to Florida. It'll be a few more days before I can mate a turntable to any of the chip amps. I'm eager to experience analog from the TDA7297.

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For reasons beyond the scope of this post, and through no fault of billybob, the phono preamp I purchased has been bounced back to Florida. It'll be a few more days before I can mate a turntable to any of the chip amps. I'm eager to experience analog from the TDA7297.

Got to hate it when that happens. I had an order frm Mouser that got to Atlanta and then sent back somewhere in Texas. Messed up plans to work on a project over Christmas a few years ago.

I'm enjoying this thread. I may have to dive into this soon, but our upcoming move is taking precedence over the hobby for some reason. :rolleyes:

Bruce

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I ordered 4 of the Wima coupling caps from Mouser and 4 of the Panasonic ECQP caps from Jim McShane. That should give me plenty of ammunition to hot-rod the TDA7297s for now.

I'm still curious about whether the 12.65 volt/high amp battery booster is an inherently superior power supply for the TDA7297, as compared to power supplies with >12volts at >2 amps. I've got several to try, but I don't expect an improvement over the 12.65 volt battery. As an experiment, I'm, going to let the booster's voltage drop below 12 volts (I'll monitor it with a DVM) to see if I can perceive any degradation in performance.

I'd like to know if you can hear the difference between the Wima and Panasonic caps with this amp. The Panasonics are no longer manufactured, so if the Wima's work fine, that would be great for others who want to try the amp.

According to a description of your car starter battery unit, it is capable of providing "900 peak amps and 225 cranking amps of jump starting power." Is the amp chip smoking or getting warm when you have it connected to the amp? I am curious what sound quality differences you hear when you use this battery.

That could very well be a very good power supply for this amp, especially for those of us who are on a dirty utility grid. I'm not sure what speakers you use in your home, but please share what kind of bass response you get from the TDA7297 amp, especially when you are possibly feeding 225-900A through the amp.

Edited by rhing
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