Folsom's great little 7297 Chip Amp

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mlundy57

Re: Folsom's great little 7297 Chip Amp
« Reply #500 on: 25 Aug 2016, 04:59 am »
Mike some switches run on 12v, some have resistors in them for 120v. Here's one that doesn't require you to mess around dropping the voltage to 12v. It's my go to for projects that don't have to be overly pretty.

Jeremy,

Thanks. I thought Radio Shack was out of business

Mike

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #501 on: 25 Aug 2016, 05:15 am »
Lots of local stores closed, but no, they are not online or locally to me (yet).

poseidonsvoice

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Re: Folsom's great little 7297 Chip Amp
« Reply #502 on: 25 Aug 2016, 11:58 am »
Quote
Founded in 1921, at its peak in 1999, it operated stores in the United States, Mexico, United Kingdom, Australia, and Canada. On February 5, 2015, the company filed for Chapter 11 protection under United States bankruptcy law after 11 consecutive quarterly losses.[4][5] By then it was operating only in the United States and Mexico. On March 31, 2015, the United States Bankruptcy Court for the Northern District of Texas approved a $160 million offer by General Wireless, which gained ownership of 1,743 RadioShack locations, and immediately leased them to Sprint

More info @ Wikipedia.

Best,
Anand.

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #503 on: 25 Aug 2016, 02:09 pm »
Larry,

The light is built into the rocker switch, I guess it is an LED.
Mike

Mike, You should probably get a switch like Jeremy suggests, or use a separate switch, and LED as I did. That way you switch the AC mains, and pull LED power from the 24V output of the PS. You could have the switch on the back, and the LED on the front panel.

You can use this calculator to find the correct resistor:
http://led.linear1.org/1led.wiz

 I used this LED:
http://www.digikey.com/product-search/en/optoelectronics/led-indication-discrete/524729?k=p563-nd

 and this resistor:
 http://www.digikey.com/product-detail/en/vishay-bc-components/PR01000101501JR500/PPC1.5KW-1CT-ND/597203




KR500

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Re: Folsom's great little 7297 Chip Amp
« Reply #504 on: 25 Aug 2016, 03:03 pm »
I received my case from Surplus Sales and took out the insides ,saving all bolts washers etc and tossed the circuit boards . I popped the plastic legend for the LED functions off the front panel which will be the access for the front panel switch and DACT . Probably will spray paint the plastic cover to cover the industrial brown look of it .Steel wooled off some type of corrosion from something on the divider panel seam .
Home Depot has bags of 3/16" and 1/4" rubber washers so I grabbed one of each . I thought about trying to mount the transformer sideways to the divider panel to save a tad of space, but it's pretty heavy iron balancing on those brackets, so I'm staying upright with installation of it. The Antipole board will be mounted on the divider panel in the larger compartment.
There is a nice paddle SPST toggle switch ( Digi-Key 679-1246 ) in my parts drawer marked 15 amp 125 V, so I filed out one of the 4 LED cutouts on the front panel a little and the switch fits in perfectly. I'll run an LED to the adjacent hole. Thank you Lacro for posting the illustration for us in the previous post on the wiring of this . I will use the 3rd original LED hole for the 10K DACT pot and then have the remaining hole available if I add a buffer or something in the future.
I'm going to mount the reccommended heat sink from Heatsink USA inside and will drill vent holes for it top and bottom in the case. Now I just have to decide if I should use the existing power cord or go with a Furutech IEC . Convenience or upgrade ? I would have to use an insulated adaptor to get the power wire to the on/off switch to reach the front panel .

walkern

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Re: Folsom's great little 7297 Chip Amp
« Reply #505 on: 25 Aug 2016, 04:49 pm »
I mounted the amp board with the heatsink right next to the back center of the chassis, and drilled lots of spaced out holes in the back of the chassis and the under side immediately below the heatsink (so no holes in the top).  This has been more than sufficient cooling / ventilation for the amp/heatsink.  Just saying you may not need to drill holes in the top.
And I used a Furutech IEC AC inlet rather than the stock AC cord that came with the chassis, and I'm very pleased with the result.  Don't know how good that AC cord is that comes with the chassis.

N

mlundy57

Re: Folsom's great little 7297 Chip Amp
« Reply #506 on: 26 Aug 2016, 03:00 am »
More info @ Wikipedia.

Best,
Anand.
Lots of local stores closed, but no, they are not online or locally to me (yet).

Thanks. The store close to me closed last year.

Mike, You should probably get a switch like Jeremy suggests, or use a separate switch, and LED as I did. That way you switch the AC mains, and pull LED power from the 24V output of the PS. You could have the switch on the back, and the LED on the front panel.

You can use this calculator to find the correct resistor:
http://led.linear1.org/1led.wiz

 I used this LED:
http://www.digikey.com/product-search/en/optoelectronics/led-indication-discrete/524729?k=p563-nd

 and this resistor:
 http://www.digikey.com/product-detail/en/vishay-bc-components/PR01000101501JR500/PPC1.5KW-1CT-ND/597203





Larry,

Thanks. I have two different red LEDs on hand. One says it is 1.7Vdc-2.2Vdc @ 15mA-25mA and the other is 1.7Vdc-2.2Vdc @ 20-30mA. 

When I run the four permutations of this through the calculator I get four different resistors: 820 Ohm, 2W; 1.0 kOhm, 2W; 1.2 kOhm,1W; and 1.5 kOhm, 1W.

How do I know which one to use?

Also, I have ordered in some of the switches Jeremy recommended so I have options.

Mike

nik.d

Re: Folsom's great little 7297 Chip Amp
« Reply #507 on: 26 Aug 2016, 07:15 am »
Hi Mike,

You can use resistor in range of 10K to 15K (KiloOhm) 1/4W, whichever you have on hand. With such resistor
value your LED will not shine like car's head light but softly indicate the amp is switched / powered on :)

Brgds
George

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #508 on: 26 Aug 2016, 01:41 pm »
Thanks. The store close to me closed last year.

Larry,

Thanks. I have two different red LEDs on hand. One says it is 1.7Vdc-2.2Vdc @ 15mA-25mA and the other is 1.7Vdc-2.2Vdc @ 20-30mA. 

When I run the four permutations of this through the calculator I get four different resistors: 820 Ohm, 2W; 1.0 kOhm, 2W; 1.2 kOhm,1W; and 1.5 kOhm, 1W.

How do I know which one to use?

Also, I have ordered in some of the switches Jeremy recommended so I have options.

Mike

The specs for the LED's you have are probably a usable range for using a battery to power the LED. If your LED lists 2.2 forward voltage then it is the same as I used, so a 1.5K ohm 1 watt resistor should work fine. On mine the illumination is about perfect, not too dim, and not too bright. a 1 watt resistor is probably overkill, I think 1/2 Watt is closer to the formula calculation, but the calculator makes this statement: Resistor power ratings are chosen based on operating within 60% of the rated value. for best heat dissipation 1 Watt is probably a better choice as the calculator suggests.

 

KR500

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Re: Folsom's great little 7297 Chip Amp
« Reply #509 on: 26 Aug 2016, 08:48 pm »
The built in power cord of the Surplus NABU case is pretty good although plug end  is molded plastic.... but I decided to go with the Furutech IEC socket.
Seems a better interface plus I won't have to use an inline disconnect to get the power wire to reach the switch like I would have with the built in OEM cord
The Furutech Jeremy suggests are on sale at Sonic Craft but shipping priority is $12

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #510 on: 26 Aug 2016, 09:12 pm »
Yup, and there's the new NCF version that's not too expensive either!

mlundy57

Re: Folsom's great little 7297 Chip Amp
« Reply #511 on: 26 Aug 2016, 09:47 pm »
The specs for the LED's you have are probably a usable range for using a battery to power the LED. If your LED lists 2.2 forward voltage then it is the same as I used, so a 1.5K ohm 1 watt resistor should work fine. On mine the illumination is about perfect, not too dim, and not too bright. a 1 watt resistor is probably overkill, I think 1/2 Watt is closer to the formula calculation, but the calculator makes this statement: Resistor power ratings are chosen based on operating within 60% of the rated value. for best heat dissipation 1 Watt is probably a better choice as the calculator suggests.

Larry.

Thanks. How did you secure the LED into the wood face plate?. I have some plastic grommet type devices that are designed to secure an LED to the thin metal of a chassis but I'm unsure how it would work with wood. I have my eye on a nice piece of spalted Tamarind for the front.

Mike

lacro

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Re: Folsom's great little 7297 Chip Amp
« Reply #512 on: 27 Aug 2016, 01:06 pm »
Larry.

Thanks. How did you secure the LED into the wood face plate?. I have some plastic grommet type devices that are designed to secure an LED to the thin metal of a chassis but I'm unsure how it would work with wood. I have my eye on a nice piece of spalted Tamarind for the front.

Mike

Mike,

I opted not to use an LED panel mount holder, instead I just drilled a 3mm through hole, and a larger counter bore to control the amount of protrusion of the LED. The LED has a slight taper so it's just a nice friction fit in the hole. A dab of hot glue would work if the fit was loose.










walkern

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Re: Folsom's great little 7297 Chip Amp
« Reply #513 on: 27 Aug 2016, 03:36 pm »
I've been listening to this amp for a few weeks now (long enough to be certain that it's fully run in) and I wanted to post my impressions.  Here they are in a long winded nutshell:

Treble: best I've ever heard from any amp I've ever owned (includes an assortment of Class A and Class A/B solid state amps, 2 other types of chip amps, two different class D amps, and a few different tube amps).  Instruments with lots of harmonics and overtones have a clarity that is outstanding, while completely lacking any extra distortion products.  Assuming a good recording, there is no 'honk' or 'clank' in the upper range of the piano, no spit or sizzle (but plenty of shimmer) with cymbals, no grit in the upper ranges of the violin, and no glare in higher notes from trumpets or soprano singers.   There is plenty of 'air' around instruments, and the amp does ambiance recovery beautifully (you can hear the bounce and echoes off walls and ceilings in the recording venue).  High frequency transients are fast without having any extra emphasis, and treble extension seems excellent (note that I'm an older guy, so my hearing doesn't extend as well into the extreme highs as it used to).

Midrange: wonderfully balanced and even.  It is very revealing of subtle details without shoving anything untoward in your face.  Vocals are very convincing (female and male) and instruments with plenty of midrange energy sound like the 'real thing' (please note that I attend classical music concerts on a regular basis, and played a modest assortment of instruments in my youth).  Again, no trace of any sort of emphasis anywhere in the mids, but the amp sounds energetic / lively and has good pace and rhythm.

Bass: seemed a little tight and reticent at first, but as the amp settled in this tendency vanished.  Currently I am using bookshelf speakers and a self-powered subwoofer, so I can't judge the deep bass capability of the amp.  I can however say that the bass down to about 50 hz or so sounds powerful, controlled and articulate.  No 'one note' humps anywhere, and bass transients and harmonics seem beautifully balanced.  The transition from my standpoint speakers to the sub is as seamless as I've ever heard.

Imaging: With a decent recording, this amp has palpable presence on par with the best tube amps I've heard (owned a SET 300B amp, as well as tried and pentode based amps with more oomph - up to 100 wpc).  The amp is almost spooky in how well it captures placements of people and instruments within space.  I would describe it as corporeal.  Images are not enlarged or diminished (as best I can tell), and the overall imaging leans toward precision rather than vagueness.

Dynamics and power: Subtle shifts (micro dynamic changes) are very well captured and articulated.  For me this effect tends to draw me into a performance and lends to the appreciation of the emotional character of the music.  I can't speak to macro dynamics well because I don't listen to music very loud (occasional 95 db peaks maybe), but I can say that when I have cranked up the volume a bit (Pink Floyd's 'Comfortably Numb" sounds best to me when LOUD) the amp has not audibly clipped or run out of gas.  My speakers are not rated as high sensitivity, so I'm pleased that the little bugger doesn't shy away from an occasional crank on the volume control.

Overall impressions: This is an amp that compels me to listen to the music.  I find myself drawn into recordings no matter how familiar they are.  I also find myself listening to the whole disc and enjoying songs or segments that I'd previously ignored or found boring or lackluster.  This amp will clearly convey those occasions when different cuts on an album where recorded in different studios/venues, or by different mixing engineers.  I've been able to make out lyrics that I've never before been able to hear or understand, yet this is not due to some emphasis or highlighting of the singer's range.  The amp just seems to dig out a bit more detail, while still sounding very refined and composed.

As far as I'm concerned, this amp is an absolute triumph.  My hat is off to Jeremy for all of his efforts to bring out the best in the 7297 amp chip.  Consider me not only impressed, but completely enamored.  FAR and away the best 'bang for the buck' amp I've ever owned (I currently have 4 amps sitting around), and one of the best amps I've ever heard at any price.

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #514 on: 27 Aug 2016, 04:44 pm »
Thats a great review! Thank you.


limits

Re: Folsom's great little 7297 Chip Amp
« Reply #515 on: 27 Aug 2016, 09:41 pm »
walkern...Are you sure you aren't a professional writer?  :lol:

Nice review--you pretty much nailed every aspect of this amp.

I have three systems. The other two are 2.0 and 5.1 channel setups. Both of these systems cost much more than the one with my Folsom amp, yet I have been using my Folsom setup for probably 80 percent of the time...

The imaging on this thing can be startling at times  :thumb:


zek

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Re: Folsom's great little 7297 Chip Amp
« Reply #516 on: 27 Aug 2016, 11:31 pm »
@walkern
Did you use a preamp with Folsom amp, and which one?

BRN

Re: Folsom's great little 7297 Chip Amp
« Reply #517 on: 28 Aug 2016, 03:33 am »
walkern,

That was a great review and I have had the same experience with the Folsom amp. I'm using it with bookshelf speakers and a powered sub as well with great results. I'm not using a preamp, just a passive with a 4 pole 3 position switch and 10k ebay DACT stepped attenuator.

I ordered a Bottlehead Eros phono preamp which has a high output impedance and does not like 10k input impedance of my passive, so I'm going to build the Kuartlotron  buffer and use a 100k DACT.

poseidonsvoice

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Re: Folsom's great little 7297 Chip Amp
« Reply #518 on: 28 Aug 2016, 11:33 am »
Walkern,

Thank you for the review.

Please list your system in some detail.

Which amplifier(s) specifically did you compare them to? Did you have them on hand or did you compare them from memory?

Can you list some of the recordings you listen to and format?

Thank you,

Anand.

KR500

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Re: Folsom's great little 7297 Chip Amp
« Reply #519 on: 28 Aug 2016, 03:35 pm »
Thanks for the excellent review walker .