Folsom's great little 7297 Chip Amp

DaveC113 · « **Reply #60 on:** 24 Nov 2015, 04:23 pm »

I've had this amp for a while and have enjoyed it.

I have Omega Super3 XRS (94.5 dB single drivers) and Pioneer S-1EX (3-way 89.5 dB floorstanders), surprisingly enough the amp worked great with both of them. It's overall character is refined and laid-back but it doesn't smooth out all the detail. It's a very refined, relaxed and easy to listen to amp.

On the Pioneers the Folsom amp is a bit less damped than my other amps (an Odyssey Stratos with upgrades and a Crown XLS 1500), which worked pretty well as the Pioneer's bass is a bit overdamped. The XLS accentuates the overdamped bass but has great control over the woofer, with the Folsom amp the bass was a bit more free sounding, not boomy/uncontrolled as that's probably not possible with these speakers. Overall it felt a bit more natural and musical with the Folsom amp vs the XLS. The Odyssey amp is more damped but not as much as the XLS, it's a very good match with the Pioneers and the mids/highs are very precise. In comparison the Folsom amp is more relaxed sounding, a bit more romantic, a bit softer and more forgiving. It's not an amp you'd normally pair with these speakers yet it did really well, I was surprised how good it sounded. Of course it can't go past moderate volumes but it did fine up until clipping.

Where the Folsom amp really shined was with my Omegas... I have a DIY EL34 SET that's close to as good as it gets for low-powered tube gear, the driver is a 6SN7 Aikido with it's own power supply, Jupiter copper caps, Clarity TC power supply caps, pure copper connectors, James OPTs, etc... It has over $2k in parts invested. The Folsom amp came darn close, way too close for the kind of money it costs, a small fraction of the cost of my SET amp. Interestingly enough if you listened to the 2 amps blind you'd probably guess the Folsom amp is the tube amp and the EL34 amp solid-state. The Folsom amp was smoother and more laid-back vs my amp, but with the Omegas it controlled the bass really well and it also has plenty of power for them too. This is an amazingly good combination... My SET otoh was clearer, more detailed, slightly more controlled. Overall it's a better amp but it's so many multiples of the Folsom amp's price it's hard for me to believe the Folsom amp comes so close.

In conclusion, the value for the money you get with the Folsom amp is the best I've ever seen. It has a smooth, refined, tube-like presentation that is musical and non-fatiguing... a perfect set of characteristics for the speakers and sources it's likely to be paired with. This amp would be my top recommendation before spending a lot of cash on a high end tube amp. Yes, it is possible to do better but it's going to cost you a lot of cash. This kind of amp would also be great for a DIY active speaker powering mids and tweeters.

Odal3 · « **Reply #61 on:** 24 Nov 2015, 05:09 pm »

Dave - what a great review. Did you use the Folsom power supply as well, and was this with the
1uf input capacitors or the 1.5?

DaveC113 · « **Reply #62 on:** 24 Nov 2015, 05:21 pm »

Quote from: Odal3 on 24 Nov 2015, 05:09 pm

Dave - what a great review. Did you use the Folsom power supply as well, and was this with the
1uf input capacitors or the 1.5?

The PS is built into the amp so I'd guess yes. Not sure which caps are in there... I didn't notice any bass roll off but my speakers don't get down to 20 Hz without rolling off themselves. The difference in damping factor was apparent but I really didn't notice any lack of bass from the Folsom amp.

Folsom · « **Reply #63 on:** 24 Nov 2015, 05:45 pm »

It has the 1.5uf.

The input RCA's are not copper on the demo. They work fine, but I've used copper ones on another build and it does very good things.

Dave's capacitors, probably just the input capacitors, cost more than the parts for the 7297. One could always upgrade the input capacitors on the 7297 if they wanted. His amp with chassis and labor would probably run $10k as a commercial product, maybe more. Lamm amplifiers don't use more expensive parts, but they have more parts overall and probably better transformers.

Also a buffered signal would get the amp much closer to more expensive amplifiers, as volume controls steal a bit of refinement on their own. And we have yet to find out what Nichicon capacitors for the DC side of the amplifier will do.

Odal3 · « **Reply #64 on:** 24 Nov 2015, 05:57 pm »

Thanks for the input.
Can you please expand a bit what you mean by "buffered signal."

Folsom · « **Reply #65 on:** 24 Nov 2015, 06:02 pm »

Buffered means it doesn't have trouble driving the amplifier due to impedance mismatch.

A 1:10 ratio is often desired. But that would mean you'd need a 2-3kohm volume device and there is no such thing.

So a buffer in front of it helps such as a Pass B1/DCB1 or Kuartlotron, or some sources are buffered on their output such as a Bel Canto DAC3.7, that uses a digital volume control.

mboxler · « **Reply #66 on:** 27 Nov 2015, 07:55 pm »

Quote from: Folsom on 24 Nov 2015, 06:02 pm

So a buffer in front of it helps such as a Pass B1...

The Pass B1 has capacitors on its outputs. Might this eliminate the need for the input caps to pins 4 and 12?

Mike

Folsom · « **Reply #67 on:** 27 Nov 2015, 08:27 pm »

They're big enough on the B1, so I suppose you could give it a try. The amplifier does tend to bias electrolytic input caps, so it may have undesirable affects without it's own capacitors.

Markvdv · « **Reply #68 on:** 28 Nov 2015, 02:41 pm »

Quote from: Folsom on 24 Nov 2015, 06:02 pm

Buffered means it doesn't have trouble driving the amplifier due to impedance mismatch.

A 1:10 ratio is often desired. But that would mean you'd need a 2-3kohm volume device and there is no such thing.

So a buffer in front of it helps such as a Pass B1/DCB1 or Kuartlotron, or some sources are buffered on their output such as a Bel Canto DAC3.7, that uses a digital volume control.

Standard 10k pot is exactly that at maximum 2500 ohm ????

Folsom · « **Reply #69 on:** 28 Nov 2015, 04:34 pm »

I don't understand what you're saying/asking.

Markvdv · « **Reply #70 on:** 28 Nov 2015, 07:42 pm »

I assume you want 1/10th of tda7297 inputimpedance at most, the 1 to 10 ratio. Max outputside impedance 10k pot is 2500 ohm I believe, not 10k, so very common and ordinary pots exist that gives you 1 to 10 ratio.

Folsom · « **Reply #71 on:** 28 Nov 2015, 07:49 pm »

I use a 10k stepped attenuator, and it works quite good. But it's not as good as with a buffer, even if it fits the ratio. However that's true with most amplifiers to begin with.

Markvdv · « **Reply #72 on:** 28 Nov 2015, 08:33 pm »

So question could be: why not include buffer on pcb ? You paid a lot of attention to power and that probably makes bigger difference, your anticipated answer:)

Folsom · « **Reply #73 on:** 28 Nov 2015, 08:53 pm »

Some day, when I've got one thoroughly tested out. But I'd actually prefer a separate board, maybe with the same footprint.

I don't use a buffer in my own stereo yet, btw, and I don't feel like I'm pinged on needing one.

ronu9400 · « **Reply #74 on:** 29 Nov 2015, 07:19 pm »

Hi, Folsom & all the rest

I've been a lurker for a good while, but just had to join today - so that I could continue the discussion from posts #49 & #50 (etc.) about the Antipole PSU (for Folsom's 7297).

I sent my $ for the Antipole & 7297 boards early on in those offers, and I have continuously checked on how close the Antipole is getting to the IndieGoGo target...hopefully it gets there. However, if the Indiegogo route doesn't work out, i would still be interested in getting the Antipole pcb (c/r post #50).

I could have probably covered this via e-mail, but it was also a good opportunity to bump the thread.

Thanks again, Folsom

Folsom · « **Reply #75 on:** 4 Dec 2015, 06:34 am »

Don't worry, I'll contact everyone and collect enough to print the Antipole if IndieGoGo isn't going to work out.

shadowlight · « **Reply #76 on:** 4 Dec 2015, 03:21 pm »

How do you go about ordering multiple Antipole? I did not see an option to do that.

Folsom · « **Reply #77 on:** 4 Dec 2015, 04:47 pm »

Click here.

Odal3 · « **Reply #78 on:** 9 Dec 2015, 07:06 am »

Been practicing my soldering skills on one of the cheap generic boards. Against all odds, I manage to get it to make sound... actually very good sound thanks to the great instructions and help from Folsom. I'm now excited to get the Folsom board.

BTW: these 7297 amps may be a great way to split the signal and send it to both main speakers as well as balanced inputs on a crown xls amp for active or subwoofer duties. I'm ordering the XLR connectors now and will hopefully try it out this weekend.

I'm still going back and forth on the psu - more on the fact that I'm not yet comfortable with the A/C.

If you haven't purchased yet, you better hurry up since it's just about to expire.

Folsom · « **Reply #79 on:** 9 Dec 2015, 07:09 am »

Boards will be available after, many boards.