Folsom's great little 7297 Chip Amp

BRN · « **Reply #800 on:** 26 Apr 2017, 10:20 pm »

Quote from: KR500 on 26 Apr 2017, 06:48 pm

Just tried putting my Little Dot MkII+ tube headphone/preamp in front of the Folsom amp .
Not really any improvement and clicking sounds when turning the DACT so ...test over . Out it comes
The Little Dot does improve the sound of my modded Audio Source Amp 100 though !

KR500,

What do you normally use to control the volume on your Folsom?

Brad

KR500 · « **Reply #801 on:** 27 Apr 2017, 12:39 am »

The DACT that Jeremy initially recommended. It works well .
I Just got clicking sounds with each detent of the knob being turned using the Little Dot as a preamp .
This is in my exercise room on the same circuit as the HVAC and I've had clicking issues there with the Little Dot before .
But the LD didn't really make the chip amp sound any better anyway which I was curious about .

Odal3 · « **Reply #802 on:** 27 Apr 2017, 03:45 am »

I tried to put the Little bear P3 6N3 6Z4 tube preamp in front of the Folsom amp. This is a cheap preamp that used to be popular choice for the the TPA 3116 amps. I liked it a lot with my TPA amps since it added some tube character to the sound, but it didn't work well at all with the Folsom amp. It really degraded the sound (noise), so out it went after just a couple of minutes, and it's been collecting dust since. Perhaps I could swap out the tubes for better ones, but don't think it will help much.

I have tried to add a cheap buffer between my source and the Folsom amp and that made a nice positive difference. I still need to get around to buy the parts for the buffer recommended earlier in the thread. It's my understanding that it will take it to the next level.

KR500 · « **Reply #803 on:** 27 Apr 2017, 11:53 am »

I use the PASS B1 buffer in front of the 7297.
The B1 board and matched jfets are at PASS audio for $40 .

lacro · « **Reply #804 on:** 27 Apr 2017, 01:55 pm »

Quote from: Odal3 on 27 Apr 2017, 03:45 am

I still need to get around to buy the parts for the buffer recommended earlier in the thread. It's my understanding that it will take it to the next level.

That's the Kuartlotron Simple Error Correction Super Buffer: http://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-70.html#post4834519

It definitely does take the Folsom amp to the next level. Highly recommend it. I am currently using a passive shunt type (Haler style) volume control with a 10K Alps Blue Valvet pot, and 2 resistors that works very well. I do have one of the DACT pots that Folsom recommended, but haven't tried it yet.

S Clark · « **Reply #805 on:** 27 Apr 2017, 02:03 pm »

I've been running the Folsom amp from a Dodd battery pre from the beginning of this thread (wow, 41 pages ago!). It's a great pre driving an excellent amp. What's not to like?

BRN · « **Reply #806 on:** 27 Apr 2017, 03:54 pm »

I'm running a BH battery powered Quickie with my Folsom. I also have all the parts to build a new Kuartlotron buffer for it.

I had a Kuartlotron buffer, but sold it, but want to give it another try, because I made a build mistake wiht the first that could have affected the sound. Going to take my time and triple check everything this time.

KR500 · « **Reply #807 on:** 1 May 2017, 07:14 pm »

Finally got some time and brought the 7297 amp up out of the basement to my listening room where I have a dedicated electrical circuit for audio .

sources are TASCAM CD player > Schitt Uber DAC > quality IC's > PASS B1 > Folsom 7297 > Seas 8 inch full range speakers with the Seas contour circuit , no crossover.

Listening material is Paul Desmond and Gerry Mulligan on "Out Of Nowhere" RCA CD , ( The Desmond/Mulligan CD is really well recorded and the Folsom amp just reproduces each instrument beautifully , turning the volume up just sounds even better. )
Simon & Garfunkel "Bookends" CD , Juan Esquivel "Space Age Bachelor Pad Music" RCA CD and Colosseums' " Walking In The Park " from the Sanctuary CD of their debut album.

The amp has nice low end and treble extension , upright bass and drums sound really nice, the top end is not etched,but gets right up there on brassy material . If your room or speakers are bright sounding, this might not be the amp for you.
The amplifier really puts out some good sound. I wish my construction skills were past the beginner level to give the amp it's due when I was putting it together .
The transformer hum is an issue I'll have to address although it isn't audible when music is playing . It is about as much of an issue as the refrigerator cycling on or traffic sounds from outside . The NABU case I used just doesn't have enough clearance to really use much dampening on the transformer . I have some room on the case top to add a thin layer of something above the transformer but that's about it .
The soundstage on the amp just isn't as good as my tube SET amp though . The sound seems pretty directional and narrow although I didn't try toeing the speakers in or using different speakers so ......YMMV.
My tube amp doesn't reproduce the low or high end as well as the 7297 though and it seems a tad less focused although pleasing in it's own way . Tradeoffs .

The Folsom 7297 is a winner , holding it's own compared to an amp that costs much more.
Thanks to the designer for sharing it with us

Folsom · « **Reply #808 on:** 1 May 2017, 09:15 pm »

How many hours do you have on that amp?

KR500 · « **Reply #809 on:** 1 May 2017, 09:48 pm »

not a lot yet , with fall classes and work Jan through late April this year unfortunately I didn't have much listening time.
Probably 20 hours max so far on the 7297 amp

Folsom · « **Reply #810 on:** 1 May 2017, 09:56 pm »

It'll sound better with more time than that! You've got the basic amount that's needed for the OSCON's to shine, but not nearly enough for the input caps.

Maybe now with summer coming up you'll have some free time? I'm excited for trails and such to turn from mud to dirt.

KR500 · « **Reply #811 on:** 2 May 2017, 10:44 pm »

Would it speed up the cap hours burn in by putting a CD on repeat for a couple of days playing through the amp with the volume down ?

Folsom · « **Reply #812 on:** 2 May 2017, 11:25 pm »

Yes. Anything helps.

KR500 · « **Reply #813 on:** 3 May 2017, 05:11 pm »

I need an 8 hour governor before my posts are posted , there's no such thing as a dumb question until I ask one .
I have a cd playing on continuous repeat into the amp with the volume down until Saturday or Sunday.
It will help get the input caps on the PASs B1 buffer I just built get broken in too.
I'll give it a re-listen on Monday

KR500 · « **Reply #814 on:** 11 May 2017, 02:43 pm »

just an update after 150 hours continous CD repeat play of my 7297 amp .
The soundstage is not as directional and has gotten wider and deeper
Listening to Paul Desmond and Segovia sounds fine as wine, really draws you in to the music .
I'll have to listen to some more Pop music on it, but with that material it is not quite as engaging as my SET amp.
The amp is on the workbench so I can add some sound damping material to the area the transformer is in .

indosmokejon · « **Reply #815 on:** 12 May 2017, 06:13 pm »

So I got my first of two Folsom's built out and so far I am very impressed. I am not completely finished as I don't even have an on/off switch yet, and no faceplate but it will get there. I got tired of waiting for my heat sinks to come in from China and just sandwiched the two that came with the Nabu cases with some thermal grease and it seems to work fine with the heat. The nabu case is unfortunately a little large for my tastes but it has a lot of positives as well, like the built in divider as well as the power cord, it's also very heavy duty. I used the Antek As-1215 toroidal and I am very happy with it, no buzzing or noise of any kind, the amp is dead quiet. I will update my thoughts after some break in time. So far I find it bright, but in a very revealing way, not shrilly or with simblance. It was easy build too, with great instructions and BOM. Maybe not recommended, but I did no quality or DMM checks, just plugged it in and it fired right up. I am currently listening on some modded DCM time window 1A's and once broken in a bit I can't wait to see how it pushes around my Vandersten sig 2ce's. Eventually I will finish the second and try vertically biamping with the pair to increase power delivery.

KR500 · « **Reply #816 on:** 19 May 2017, 10:46 pm »

I opened the NABU case up and noticed I had installed 4 rubber washers between the transformer and chassis base, but only 2 on the tops of the 4 transformer legs before the nuts .
There must have been only 6 rubber washers on hand when I originally finished assembling the case .
A quick trip to Lowe's to get 2 more rubber washers to install and the hum is definitely diminished . Yay !
The vinyl damping material arrived from PE so I placed a layer on the case top panel above the transformer side.
The little stepped DACT volume Control is nice for making small adjustments and works well .

indosmokejon · « **Reply #817 on:** 11 Jun 2017, 04:41 am »

So I finished up my second Folsom, first one was fine, worked right out of the gate, this one unfortunately doesn't, so I am hoping for a little help. I am getting 16V AC to the antipole, but when I fire it up, the 300v 16A rectifiers start smoking? The antipole is pretty simple, everything on it is non polarity besides the capacitors. Any suggestions?

Folsom · « **Reply #818 on:** 11 Jun 2017, 05:19 am »

It looks like you drilled out the PCB board holes, probably causing a dead short.

Folsom · « **Reply #819 on:** 11 Jun 2017, 05:41 am »

The transformer might cook and weld itself before you trip the breaker, I guess... but something else should be failing before long if you leave it on. Sooo you need to use insulated mounts, basically, and replace diodes; maybe transformer if it is having heat issues, hopefully you didn't get that far.