Folsom's great little 7297 Chip Amp

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S Clark

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Folsom's great little 7297 Chip Amp
« on: 27 Oct 2015, 01:44 pm »
A year of so back, many of us were singing the praises of the $6 Chinese 7297 amp available on ebay.  Non sang louder than our own Folsom.  I bought several, modded them, used them, gave them away, and raved about them a bit myself. 
Fast forward to a few months back when Folsom offered a handful of boards of his own design with a recommended parts list.  I picked one up, ordered the list from Mouser, and got to work with the soldering gun.
Understand that in Texas summers, you really don't want to use a large tube amp like my Dodd, so I needed a better option, and this little amp fit the bill perfectly.  Driving a set of 93 dB efficient speakers, 10-15 watts was all I needed.
So I've had this little amp in the system for a couple of months and decided to write my impressions.

First, board and parts clearly qualify as Cheap and Cheerful, coming in well less than $100, but how does it sound. 
Clear, clear, clear.  Details abound, instruments are defined and placed precisely, even soundstage widens beyond the speakers well.  With efficient speakers, there is very solid dynamics.  In short, it held it's own with the much more expensive amp it replaced.  Bass was solid and most of all very clean.  Voices are natural but still clear in their enunciation.  This little guy is serious. 

How does it compare to the Chinese amp?  Better bass, a couple of more watts, better dynamics ( and the $6 had good dynamics).  Now that the weather has cooled, does it replace the Dodd?  No, the Dodd still has a fluidity and weight that I like.... but at 15X the price.  One more interesting comparison to note is with the much ballyhooed Crown amp that I had for a week.  No comparison. The Folsom was far superior on every front except pure power. 
These boards are a great way to build a high quality amp for peanuts.  I got one of the first batch, but they are about to be available on https://www.indiegogo.com/projects/diy7297-pcb-board#/
For what it's worth, my opinion is that they are a steal. 

Almost forgot to mention.  I built the amp from the basic parts list.  Cap upgrades to follow.   :thumb:

Odal3

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Re: Folsom's great little 7297 Chip Amp
« Reply #1 on: 27 Oct 2015, 03:48 pm »
I was hoping he would put up these for sale again. What power supply do you use it with?

This review is what made me more than curious where the reviewer used the Folsom chip amp to evaluate Vapor's  Perfect Storm speakers.
http://www.hometheatershack.com/forums/speaker-subwoofer-reviews/127042-vapor-audio-perfect-storm-speaker-review.html#/forumsite/20818/topics/127042?page=1

I just need to practice my soldering skills before getting one.

S Clark

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Re: Folsom's great little 7297 Chip Amp
« Reply #2 on: 27 Oct 2015, 06:25 pm »
I've used 18.5V from a variable regulated supply (a Hy1803D).  Folsom told me that a couple of more volts more hits the sweet spot and strengthens the bass.  I've got batteries ordered with the intent to put two 12v's in series to get 24V (that the US Post Office lost yesterday in shipping-althought the torn and crushed box was delivered sans batteries :cuss:).  I have to call after 4PM today to get their official runaround about why it's not their fault.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #3 on: 27 Oct 2015, 06:34 pm »
Yup, the "infinite capacitor" only activates with enough voltage (listed on my IndieGoGo). S Clark is going to get a very nice improvement soon switching to 24v input (gets regulated to 17.8-18v on amplifier board).

The PSU used in the review with The Perfect Storm is my Antipole, also now up as an IndieGoGo. It needs a transformer with it, 16v works best at 80va+. I prefer dual bobbin design for the best noise performance. The Hammond 185 series is what I used.


S Clark

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Re: Folsom's great little 7297 Chip Amp
« Reply #4 on: 27 Oct 2015, 10:21 pm »
I figured what the hey, I can always use another amp somewhere, so I got the Indiegogo started.  Hope you sell it out soon.  Thirty bucks down, 470 left to go.   :thumb:

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #5 on: 29 Oct 2015, 07:09 am »
Here's a word from my friend whom I made a full amplifier for

"I’m not convinced that critical listening of one audio product versus another is worth anyone’s time, unless you have a whole lot of it.  I therefore don’t understand those who are reviewers for all or part of their living, appears to take the fun right out of it.  The differences (in my experience) are generally minor and it’s difficult, if not impossible, to absolutely decide which one is better.  It ends up like choosing which flavor of ice cream to eat before bed, there is no wrong way to go.  However, audio equipment is expensive and ice cream is not.  Weigh in that cost factor and it’s no wonder my system has not changed in many years.  I require a rather large benefit per expenditure and a clear winner.

Nevertheless, every now and again I am compelled to purchase, the cost overcome by the improvement.  In late 2008, a friend of mine from the stereo shop contacted me to demo a power conditioner he had on loan.   The conditioner was custom-made by a young fellow named Jeremy Hood, right here in Missoula, and I really needed to “listen” to it in my room.  I’d demoed several power conditioners over the years from the local stereo shop and online vendors and had not thought any on them really improved the sound.  They all went back to where they came from.  This was different and after a few days, I begged to rent the unit until Jeremy could build a conditioner for me.  I suffered for weeks in silence as the rental option was not really an option (nobody in their right mind would be without this conditioner once it’s in their possession) and I had little interest in listening without it.

That was my last improvement until just recently.  Sure, I replaced my Bel Canto cd player in 2014 with a new one from the same manufacturer after the transport started acting up. It didn’t change the sound any, at least after the new unit broke in a bit.  I’ve considered my system complete since 2009 and I spent my money elsewhere.  That doesn’t mean Jeremy and others weren’t trying to tempt me with other “upgrades”.  They would bring the upgrade to the house and we’d listen to the change in sound.  In 6 years I bought nothing but more music.

That changed this summer when Jeremy hooked up his new chip amplifier in my rig.  He had already brought several previous amps to me for demonstration.  He trusts my ears, my system and my listening room. Plus I am likely his toughest critic, at least in person as it’s easy to be unimpressed over social media.  None of the previous amps were nearly as competent as my already broken in and paid for Bryston 3B-SST.  The rather expensive Bryston is powerful yet refined, quiet as a mouse and a great match for my Bel Canto CD transport and DAC as all appreciate a balanced connection.

After a few hours to let the demo amp settle in, I was pretty sure this was going to cost me as the Bryston was suddenly muffled and slow by comparison.  After a day, I had to have the new amp.  My daughter’s wedding would have to wait (kidding).  I once again suffered without much music during the build process.  A few days of burn-in time, a quick yet convincing A/B test of the two amps and the Bryston went into the closet.  Jeremy’s amp provides gloriously articulate, colorless gain.  I have so much music to relisten to.

For those who care and have inquiring minds, my system:
Piega Premium 5.2 speakers         Bel Canto transport 3 and DAC 3        Jeremy Hood Amplifier and Power Conditioner
Analysis Plus speaker cables         Zenwave Audio IC's, Nordost XLR and Heavens Gate AES/EBU
Shunyata and Cardas  AC cables        Oyaide power outlet"

ebag4

Re: Folsom's great little 7297 Chip Amp
« Reply #6 on: 1 Nov 2015, 04:56 am »
I finally picked up a couple of these (now $8.) eBay amps.  Powered it up from a 12v battery and fed it via an iFi iTube preamp, it sounds pretty great.  So I decided to pick up one of the Folsom amps, should be an excellent cool running backup to my Bottlehead, the extra power doesn't hurt either.  Anxious to give the Folsom amp a try.

Does anyone know what the input impedance is for these little amps?

Best,
Ed

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #7 on: 1 Nov 2015, 05:07 am »
I finally picked up a couple of these (now $8.) eBay amps.  Powered it up from a 12v battery and fed it via an iFi iTube preamp, it sounds pretty great.  So I decided to pick up one of the Folsom amps, should be an excellent cool running backup to my Bottlehead, the extra power doesn't hurt either.  Anxious to give the Folsom amp a try.

Does anyone know what the input impedance is for these little amps?

Best,
Ed

25-30kohm

That's why I recommend 1.5uf input cap for best bass.

Tyson

Re: Folsom's great little 7297 Chip Amp
« Reply #8 on: 1 Nov 2015, 06:03 pm »
I got a chance to demo the amp a few weeks ago and I thought it sounded better than the Pass First Watt F5 I'd built a while back - more forward, more dynamic, clean and clear but not sterile.  The F5 in fact sounded somewhat sterile in comparison. 

OzarkTom

Re: Folsom's great little 7297 Chip Amp
« Reply #9 on: 1 Nov 2015, 07:36 pm »
With so many very expensive components out there, it is very nice to see these chip amps, IFI components, and the new Andrew Jones speakers. My buddy Rex is going to order a pair of those from Music Direct and he might order the Auralic mini music streamer for $575. He owns several chip amps now. Rex was sad to see the Auralic go from $395 to $575, I guess that does include a one year subscription to Tidal. According to the Auralic Faceook page, German dealers are now receiving them.

For around $1500, this system with IFI Itube and a chip amp will come very close to the mega buck systems. A person does not need to rob a bank to get high SQ these days.

Odal3

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Re: Folsom's great little 7297 Chip Amp
« Reply #10 on: 5 Nov 2015, 04:04 am »
I'm assuming the parts list and instructions are included? Would this be a good first time project for someone like me who has never built up an amp from a board before?

What's the approx price for the parts?

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #11 on: 5 Nov 2015, 05:46 am »
Yes a BOM (bill of materials) is available.

Parts price depends, just the amp board it's about $35 worth of parts including a heatsink. The Antipole parts are about $42. The transformer I recommend can be had for $26/35 (depending on what's available).

So far I've found it doesn't really take instructions. The board is well labeled with very few parts. But I have a few notes like making sure the large transistor has long enough legs to get the heatsink on (best to put on heatsink and then solder it in last). Also the output for speakers doesn't have a "ground" because it's balanced, so no forms of ground can make contact with them. Thermal paste is recommended for the chip to heatsink. And most important is not to connect the amplifier while the power supply has any power in it's capacitors.

All of that makes it a pretty good first build option for an amplifier. It's also a nice choice because it's hard to screw it up since the chip has many fail safes and is the last line in the parts before your speakers.

I'll be taking a few more photos when the boards are printed up, to illustrate the few things you need to know.

GentleBender

Re: Folsom's great little 7297 Chip Amp
« Reply #12 on: 5 Nov 2015, 10:31 am »
I've been checking out this interesting thread, but am unable to find many details about this amp. This would be my first project of this type and the indiegogo page does not contain much info for a newbie such as myself. What additional parts would I need to order for the DIY7297 and the Antipole PSU?

Would this work as a headphone amp? What type of connections, input/output? So many questions... :oops:

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #13 on: 5 Nov 2015, 02:39 pm »
Yes a BOM (bill of materials) is available.

Parts price depends, just the amp board it's about $35 worth of parts including a heatsink. The Antipole parts are about $42. The transformer I recommend can be had for $26/35 (depending on what's available).

So far I've found it doesn't really take instructions. The board is well labeled with very few parts. But I have a few notes like making sure the large transistor has long enough legs to get the heatsink on (best to put on heatsink and then solder it in last). Also the output for speakers doesn't have a "ground" because it's balanced, so no forms of ground can make contact with them. Thermal paste is recommended for the chip to heatsink. And most important is not to connect the amplifier while the power supply has any power in it's capacitors.

All of that makes it a pretty good first build option for an amplifier. It's also a nice choice because it's hard to screw it up since the chip has many fail safes and is the last line in the parts before your speakers.

I'll be taking a few more photos when the boards are printed up, to illustrate the few things you need to know.

Does the BOM just state part values or actual part numbers from Digi-Key and Mouser? Actual PN's would really make life easier. Also, when do you expect the boards will be available, assuming you reach your goal.

DaveC113

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Re: Folsom's great little 7297 Chip Amp
« Reply #14 on: 5 Nov 2015, 03:19 pm »
I just got the amp yesterday, thanks Jeremy!  :thumb:

I have a few amps and a couple of speakers in the house. Pioneer S-1EX which are an Andrew Jones TAD design, and Omega Super 3 XRS. Amps are my own EL34 SET which is used with the Omegas, Crown XLS 1500 with Pomona posts and a top end Odyssey Stratos stereo amplifier. My preamp is an Aikido running 6SN7s and soon (hopefully) a zero-gain pre using Tortuga LDR + Aikido tube buffer.

The chip amp also came with a volume control and I'll also use my Aikido, which may have too much gain at 20 dB, and my zero-gain pre which should be done within 2 weeks, I hope...




Odal3

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Re: Folsom's great little 7297 Chip Amp
« Reply #15 on: 5 Nov 2015, 04:07 pm »
Dave, I'm already sold on it, but I'm still curious to hear your impression of it compared to the other amps.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #16 on: 5 Nov 2015, 05:17 pm »
Does the BOM just state part values or actual part numbers from Digi-Key and Mouser? Actual PN's would really make life easier. Also, when do you expect the boards will be available, assuming you reach your goal.

Yes it does! I'll show you. Here's the parts for just the amplifier section (not including the capacitor multiplier, voltage regulator section)

Amp parts: Mouser      # of parts
TDA7297                                    511-TDA7297   1
330uf                                    667-25SEPF330M   12
47kohm                                    CFR16J47K   2
Vishay/Sprague 10uf                    75-515D106M035JA6AE3   1
input cap recommended            80-PHE426KF7150JR6L2    2
input bypass cap recommended   MKP1837322161G     2


I've been checking out this interesting thread, but am unable to find many details about this amp. This would be my first project of this type and the indiegogo page does not contain much info for a newbie such as myself. What additional parts would I need to order for the DIY7297 and the Antipole PSU?

Would this work as a headphone amp? What type of connections, input/output? So many questions... :oops:

What kind of details are you looking for? The datasheet for the chip will tell you many. It uses singled ended connections. That means RCA phono jacks are used. The speaker outputs are whatever binding posts you'd like to use. I've used Ponoma's and Furutech Torq's, two different amps. The wire is your choice, and enclosure. I like Landfall systems enclosures; they'll CNC panels for what you want as well. I recommend a heatsink from Heatsink USA. And as stated above I have a recommended transformer, but you can use anything 80va+ that's 16v output for transformers or two 12v batteries, or a SMPS that can do 21v.

As far as a headphone amp I haven't tried, mainly because you have to either add a lot of resistance to the input or output. Other amps that get used for a headphone amp often control the power going in by modifying the feedback network to lower the signal strength greatly. This is uncharted territory thus far, but I can say if it did work I'd expect it to drive difficult loads effortlessly.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #17 on: 5 Nov 2015, 05:42 pm »
It seems that there's a lot of newbies to amp building that are interested. That's good :thumb:. It's a bit different than over on the DIYaudio website because half those guys are like gimmie a PCB, I'll figure it out! When the boards are released I'll make a thread just for showing some pictures, and answering some questions as well.

Peter J

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Re: Folsom's great little 7297 Chip Amp
« Reply #18 on: 5 Nov 2015, 06:08 pm »
It seems that there's a lot of newbies to amp building that are interested. That's good :thumb:. It's a bit different than over on the DIYaudio website because half those guys are like gimmie a PCB, I'll figure it out! When the boards are released I'll make a thread just for showing some pictures, and answering some questions as well.

That newbie moniker would certainly apply to me. I know my way around a soldering iron, but way outside my element on something like this. Some handholding would be appreciated and most probably a necessity.

I'll jump on both Indiegogo offerings out of curiosity more than need. Compared to almost anything else in the audio world, it seems like an inexpensive way to learn something new.

Edited to add: Top prove how green I am, I have to ask about the optional inclusion of a transistor in the Indiegogo offer. Do I need that? What would be the option for the neophyte?

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #19 on: 5 Nov 2015, 07:18 pm »
Peter, you can buy several thousands of them from another place that carries NOS.

You have to have the transistor. I include it for free! Maybe I should check because I mean for it to not sound optional. It's from my personal stash (I have a lot, maybe 1000 or so). There's lots of replacements, but the one I have has better specifications.

I hope the future holds more DIY, for those that can't lay down real big stacks of cash on gear, but want to have something truly good.