[lacro]

 Looks like you were able to stuff a bunch of  parts into that smallish chassis. interesting how you did the top Curious what the single gang electrical box is for?

[absolutk]

Yeah, the top is just a piece of maple plywood that I had stained a few years ago, sitting on top! The electrical box was intended to include an outlet so I could easily mess around with various sources (The Raspberry Pi and the isolator HAT both need 5v, for example). I didn't do it because then the components would be too tall to put a cover on top. 

[Folsom]

I'm relieved that the issue is resolved, undertowogt1! You will not be disappointed in what you hear.

TL;DR: This amplifier is incredible... IF your speakers are not insanely hard to drive. If you've been debating, do it now.

And not just sound - a sound that got me close enough to the Devialets to make me sell them.

Here are the characteristics that stand out the most:

* Impeccable control on the sub-100 Hz range
* I'm not sure if I'm using this correctly, but the 'dynamic range' is fantastic. Its ability to deliver a bass punch to the gut and simultaneously rustling leaves in your ears is pretty neat.
* The background is black as ink. Though, when I get closer there's a mild 120 Hz hum that I need to trace down.
* The soundstage was wide when I used the standard Kemet + Vishay caps in the input stage. When I replaced those with Jantzen Superior, it became W I D E. The Jantzen took about 3-4 days to break in.
* Micro details/voice texture could be more pronounced, but then again, the entire source is <$150, so that's likely the bottleneck

This weekend I took the amp to my friend's place who also has a Devialet 400, but with a pair of Magico Q1 (4~5 Ohms, 86 dB/w/m). Listening to it at medium volume (baby was sleeping), we couldn't hear any bass from 5-6 ft away. Swapped back to the Devialet and more music seemed to emanate at the same listening level. My speakers are supposedly 91 db/w/m sensitive, and simply rock at all volumes.

The boards are really thoughtfully laid out and their quality is fantastic. As you can see, Jeremy is enthusiastic about helping and teaching. Super kudos to him. This is a wonderful and simple opportunity for one to create something of beauty *and* value.

Thank you for kind words.

The Magico speakers have elliptical filters and without very special treatment that, frankly, Magico and 99.999% of speaker makers are unfamiliar with, they drain current and have a bigger reactive load in general. Basically even in a two way speaker or theirs the crossovers have at least a dozen more parts than the average speaker. That combination with low efficiency simply is going to need more power.



Btw, I really like that the chip has such awesome protection that it won't turn on unless the speaker binding posts are not shorted.

[undertowogt1]

Hi AC members and Folsom Builders,

After almost a week with my DIY Folsom Amp I just wanted to share my impressions of the amp.

A little background. I used to listen with mediocre powered monitors so I really have no listening experience with Hi quality "audiophile" amps. Once I purchased my Spatial M3 Turbos S' I moved on and started using an old integrated amp that my father did not want any more, it is a YAMAHA CR 1020. I was bypassing the preamp in the Yamaha and using my Promitheus Audio TVC  before the amp. Over all this combo worked pretty good. The sound stage was deep, the sound formed a deep "U" behind the speakers, very laid back listening actually. I did lack slam in the bass department. Even though it sounded pretty good and the bass was ok it was not very detailed. This is why I was wanting another amp option. 

So now with the Folsom Audio Amp I am completely satisfied (for now ). I have all the Bass I need with "slam" as well as the detail I want. I am hearing more air around instruments, more reverb within tracks. I have noticed that instruments are more dynamic, especially with drums and strings.  The sound stage is not as deep as my last amp, but I now have more sound infront and side to side of my speakers .  The timbre of all the instruments has improved. Everything sounds great so far with this amp

So thank Folsom for a great sounding amp and your help during my build.

[rtate]

Hi Folsom, I plan on using a Felix conditioner on my amplifier and in your "construction recommendations"
you say to use x-caps on both sides of the cmc but earlier in this thread you stated to use the caps only in front of the cmc and not post.
I am just looking for some clarification before I order the parts for the pcb.

Also are the values stated : 1.8k/3watt resistors , 1uf.,.1uf., and .01uf. x-caps and Bourns 8120 cmc optimized for the 7297 amplifier
For the resistors would you use wire wound or metal film ?

Thanks
Robert

[limits]

Hi Folsom, I plan on using a Felix conditioner on my amplifier and in your "construction recommendations"
you say to use x-caps on both sides of the cmc but earlier in this thread you stated to use the caps only in front of the cmc and not post.
I am just looking for some clarification before I order the parts for the pcb.

Also are the values stated : 1.8k/3watt resistors , 1uf.,.1uf., and .01uf. x-caps and Bourns 8120 cmc optimized for the 7297 amplifier
For the resistors would you use wire wound or metal film ?

Thanks
Robert

Hi Robert:

On my latest build, I wired a felix inside the case of the amp. For the resistor that bypasses each coil winding on the CMC, I used http://www.mouser.com/search/ProductDetail.aspx?r=588-23J1K8E. You can kind-of see the resistor, shiny brown at the base of the CMC. The other values you list (for the X caps and the Bourns CMC) are also what I used --> 1 uf .1 uf .01 uf CMC .01 uf .1 uf 1 uf. I put the felix in front of the transformer primaries. This picture is a little busy, but might give you an idea of what I did. I really love this amp! I should hook up my other build and compare, but haven't yet...

limits

[Folsom]

Hi Folsom, I plan on using a Felix conditioner on my amplifier and in your "construction recommendations"
you say to use x-caps on both sides of the cmc but earlier in this thread you stated to use the caps only in front of the cmc and not post.
I am just looking for some clarification before I order the parts for the pcb.

Also are the values stated : 1.8k/3watt resistors , 1uf.,.1uf., and .01uf. x-caps and Bourns 8120 cmc optimized for the 7297 amplifier
For the resistors would you use wire wound or metal film ?

Thanks
Robert

I guess I better look at construction notes. I do prefer only on the side away from the amp.

[uncola]

I, too had Radu Tarta at simpletubepleasures construct my amp from parts I had collected.. since I chickened out on making this my first diy amp build.  Just arrived an hour ago, sounds incredible with scary big and realistic soundstage
I'm using it with new philharmonitors 85db sensitive in near field at my computer setup with a ps audio gain cell dac/pre with 12db gain and it's working out great.. I was worried I'd have to switch to my other preamp with 0/6/12/db gain settings or that I'd get hiss but nope!

[shadowlight]

@uncola, any pointers on where you got your case from?

[uncola]

this is the case I have, Radu said he had to flip the EI core transformer sideways so it would fit.  it's 80mm tall
https://www.modushop.biz/site/index.php?route=product/product&product_id=449&search=1NGXA388

this one is 120mm tall but otherwise the same, might allow you to use a giant transformer
https://www.modushop.biz/site/index.php?route=product/product&path=67_195_200&product_id=642

in other news..  this amp hasn't even been burned in more than 24 hours but it's sounding amazeballs..  I have firstwatt f7, odyssey kismet monoblocks, digital amplifier company inline maraschinos..  and this amp holds it's own with all of them in my near field setup
I did end up switching to my preamp with gain settings so I could use 0db gain..  the 12db gain preamp was useable but not good for very quiet listening, got loud fast

Is there an official name for this amp other than Folsom TDA7297?  I'm thinking about having my friend create an applique sticker thing for the frontplate of the amp with the name

[pocomo]

Looks great @uncola.  I too am quite taken with the sound.  The value prop on this amp (even using a hired gun) is out of this world.

Glad you had a good experience with Radu.  He is a truly nice guy who does quality work at very reasonable prices.

[rtate]

@ uncola, what is the varistor used for in your set up ?

[pocomo]

@rtate - I think you are referring to the little standalone black disk in the photos? 

My amp has the same thing - it's a PTC thermistor in the chassis ground connection.  It serves as a secondary fuse and an easily removable connection when debugging ground loops.

[Folsom]

I bet it's an NTC, because that would conduct very little until it needs to be wide open. Basically you can reduce ground noise with it, but when the juice starts to move it'll heat up and act like an open wire. That would be much safer than a PTC... which conducts all the time but would trigger like a fuse and leave you with a deadly hot chassis.

[pocomo]

I stand corrected 

Thanks Jeremy, and congratulations on such a successful project.

[drew_t]

What is the little part between the thermistor and the AC connector/switch unit?

[uncola]

I believe that's just a chassis ground screw.  When I asked radu for more information about the thermistor he said it's commonly used in many nelson pass amps to break signal ground from earth ground.  This amp is insanely good.. I can't believe how cool it runs.. it's literally cold to the touch but sounds so powerful.  The soundstage is massive

Theory:  you know how in GI Joe, Cobra create their ultimate evil leader by combining the dna of hitler, ghenghis khan, atilla the hun, alexander the great, stalin and hannibal of carthage into one ultimate guy?  I think Harmon International must have done something similar using the dna of Nelson Pass, John Curl, Douglas Self and Bruno Putzy to create Jeremy Folsom

[lacro]

Theory:  you know how in GI Joe, Cobra create their ultimate evil leader by combining the dna of hitler, ghenghis khan, atilla the hun, alexander the great, stalin and hannibal of carthage into one ultimate guy?  I think Harmon International must have done something similar using the dna of Nelson Pass, John Curl, Douglas Self and Bruno Putzy to create Jeremy Folsom

 +1 

[uncola]

I have some leftover 1 amp slow blow fuses, is that rating ok for this amp?  They are fancy ceramic not glass

[Folsom]

What size is the PSU/transformer? There is no reason why you can't use whatever fuse you wish, so long as it is sized right.