Folsom's great little 7297 Chip Amp

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uncola

Re: Folsom's great little 7297 Chip Amp
« Reply #960 on: 22 Oct 2017, 10:37 pm »
it's the hammond ei core transformer from the BoM..  I'm asking because I don't have the math to calculate the right fuse size
is the formula..  80VA  so 80 divided by 120volts.. is 0.66666?   so I need a 666mA fuse or bigger?
Edit:. Oops 80va divided by 16V secondary winding equals 5 so with safety margin use a 6 amp fuse?
« Last Edit: 23 Oct 2017, 01:00 am by uncola »

Abszero

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Re: Folsom's great little 7297 Chip Amp
« Reply #961 on: 23 Oct 2017, 03:32 am »
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.
Hi Jeremy,
Yes, it is a NTC CL60 10 ohms @ 25C, and it is used to provide ground loop isolation between the
chassis, which is hardwired to the AC outlet ground, and the circuit ground. So the chassis is always grounded.

Abszero

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Re: Folsom's great little 7297 Chip Amp
« Reply #962 on: 23 Oct 2017, 05:21 pm »
it's the hammond ei core transformer from the BoM..  I'm asking because I don't have the math to calculate the right fuse size
is the formula..  80VA  so 80 divided by 120volts.. is 0.66666?   so I need a 666mA fuse or bigger?
Edit:. Oops 80va divided by 16V secondary winding equals 5 so with safety margin use a 6 amp fuse?
Hi James,
Choosing the right fuse is a tricky thing. You'll need a slow blow on the primary. This will protect the downstream of the transformer too. However, the sensitive solid state devices will not be protected.
See this : http://www.emerson.com/documents/automation/1276316.pdf for reference.

In your case, a 120VA transformer needs a 300% In primary which will be 3A. However, this transformer will never be loaded more than 50% anytime and has less inrush compared with toroidal, so you'll be fine with a 1.6A fuse.
Cheers,

drew_t

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Re: Folsom's great little 7297 Chip Amp
« Reply #963 on: 24 Oct 2017, 09:01 pm »
Radu, what fuse would you recommend for a toroidal like this: http://www.antekinc.com/as-1215/ ?

uncola

Re: Folsom's great little 7297 Chip Amp
« Reply #964 on: 29 Oct 2017, 09:22 am »
Vinyl decals are easy!  and much cheaper than mailing your frontplate to get cnc routed or laser etched hehe
Yes I realize now it's slightly crooked.  but hey that is part of the charm of diy or custom builds
I'm telling people that it's not crooked it's a dutch angle and my tribute to lars von trier

got it from this vinyl service, very low prices

poseidonsvoice

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• Science is not a democracy - Earl Geddes
Re: Folsom's great little 7297 Chip Amp
« Reply #965 on: 29 Oct 2017, 12:53 pm »
Uncola,

You totally get an A for effort man!

Best,
Anand.

Abszero

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Re: Folsom's great little 7297 Chip Amp
« Reply #966 on: 29 Oct 2017, 01:55 pm »
Radu, what fuse would you recommend for a toroidal like this: http://www.antekinc.com/as-1215/ ?
3A should work just fine. With toroidal transformers , most likely over 200VA, it'll exhibit up to 5x nominal at start up and will need NTCs to make it start soft. Not your case though.

Abszero

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Re: Folsom's great little 7297 Chip Amp
« Reply #967 on: 29 Oct 2017, 01:55 pm »
Vinyl decals are easy!  and much cheaper than mailing your frontplate to get cnc routed or laser etched hehe
Yes I realize now it's slightly crooked.  but hey that is part of the charm of diy or custom builds
I'm telling people that it's not crooked it's a dutch angle and my tribute to lars von trier

Awesome job.

got it from this vinyl service, very low prices

lacro

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• Posts: 601
Re: Folsom's great little 7297 Chip Amp
« Reply #968 on: 29 Oct 2017, 02:47 pm »
Vinyl decals are easy!  and much cheaper than mailing your frontplate to get cnc routed or laser etched hehe
Yes I realize now it's slightly crooked.  but hey that is part of the charm of diy or custom builds
I'm telling people that it's not crooked it's a dutch angle and my tribute to lars von trier
got it from this vinyl service, very low prices

Nice! I will have to save the link for future builds. I made my own decals on my first Folsom amp build.

mresseguie

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• D Sachs amp/pre + Daedalus Audio Speakers = HEAVEN
Re: Folsom's great little 7297 Chip Amp
« Reply #969 on: 18 Nov 2017, 08:28 am »
Hi, everyone.

Before I flew off to Taiwan, I managed to power two very different pairs of speakers with this amp. In the first effort I paired an old pair of AV123 two-way speakers (5.25"  midwoofers, ~86 dB) and a Nuprime DAC-9. The result was really ice sounding music that was a little on the warm side- almost tube-like sound. The next pairing was with my Daedalus Apollos (three-way, 96.5 dB). These are very resolving speakers. The resulting sound is very different. There's a noticeable brightness in female vocals, violin, and other higher frequency sounds. It's not a big issue but very noticeable after listening to the other speakers.

Now, let me point out that different rooms were used. The brighter room is nearly square and there are few soft surfaces. The Apollos are mere inches from the front wall whereas the small two-ways were placed in the middle of a large room.

Have any of you experienced brightness with your speaker pairings?
Do you think the room is generating some/much of the brightness?
Could it be that the amp had but a few hours' use and really just needs a solid 100 hours of burn in?

Folsom

Re: Folsom's great little 7297 Chip Amp
« Reply #970 on: 18 Nov 2017, 10:28 am »
What input caps are you using? Different ones take different amounts of time.

The amp takes at least a half hour before it really is up and going.

mresseguie

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• D Sachs amp/pre + Daedalus Audio Speakers = HEAVEN
Re: Folsom's great little 7297 Chip Amp
« Reply #971 on: 18 Nov 2017, 10:34 am »
It's got the Jantzen caps.

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #972 on: 18 Nov 2017, 10:37 am »
Hi, everyone.

Before I flew off to Taiwan, I managed to power two very different pairs of speakers with this amp. In the first effort I paired an old pair of AV123 two-way speakers (5.25"  midwoofers, ~86 dB) and a Nuprime DAC-9...

AV123 ELT525M Monitors

http://www.highfidelityreview.com/av123-elt525m.html

Quote
System: 2-way, 2-driver direct radiating vented enclosure with rear-firing flared ports.
Drivers: One (1) custom 5.25″ woofer and one (1) 1″ tweeter
Frequency Response: ± 3dB to 20KHz with -3dB at 60Hz
Crossover Point: 2200Hz Slope: 2nd order acoustic Impedance: 8 ohms Efficiency: 83dB @ 1w/1m Video Shielding: Yes

Other very data is the minimum impedance but few manufacturers tend to indicate it. In the rest of the speakers, through the measurements of frequency response, impedance and phase.

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #973 on: 18 Nov 2017, 10:43 am »
https://www.guru3d.com/articles-pages/av123-elt-525m-2-speaker-kit-review,3.html

Only the frequency and spectral graph.

ELT525M -> Mini monitors. Are there ELT525 monitors?

uncola

Re: Folsom's great little 7297 Chip Amp
« Reply #974 on: 18 Nov 2017, 10:54 am »
hmm I just tested it with the anne akiko meyers vivaldi four seasons and my max richter Leftovers soundtrack and the violin sounds very realistic and not unnaturally harsh..  this amp has totally replaced all my other amps for my "serious listening" 2 channel bedroom setup.. I really love it.  Folsom if you ever come out with some commercial stuff I'll definitely be interested!
edit:  I've got the jantzen z-superior input caps too..  mine is fully burned in by now though.  using philharmonic audio new philharmonitors bookshelf speakers

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #975 on: 18 Nov 2017, 11:08 am »
It was a good idea the RF/EMI inlect input filter. With this amp only you need the 1 A. I have a lot of Schaffner RF/EMI FN 9244B in my house, 3 A (and one 8 A).

And I use fuses + varistors in my DC blockers. Recently one fuse and the varistor burned down after joining phase and neutral and the old electric company cables was burned. 230 volts -> 400 volts.

I put one as you can find them in air conditioners.

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #976 on: 18 Nov 2017, 11:13 am »
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

Earth loop-breaker boards

-> https://hoppesbrain.com/2017/05/26/earth-loop-breaker-boards/

[IMG] http://hoppesbrain.files.wordpress.com/2017/05/diode-shunt-loop-breaker.png

The ARTICLE, by Rod Elliott (1999)

Earthing Your Hi-Fi – Tricks and Techniques

-> http://sound.whsites.net/earthing.htm

[IMG] http://sound.whsites.net/earth-f4.gif

uncola

Re: Folsom's great little 7297 Chip Amp
« Reply #977 on: 18 Nov 2017, 11:29 am »
Maty oh yes, since I said that Radu my builder corrected me and told me it Breaks earth ground from signal ground.  I have a delta 6A iec with emi/rfi filter in mine..  and I have it behind an atl hifi  dc blocker that you recommended.  But I understand EI core transformers such as the recommended Hammond in the BOM are not vulnerable to DC the way toroidal are

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #978 on: 18 Nov 2017, 11:40 am »
Maty oh yes, since I said that Radu my builder corrected me and told me it Breaks earth ground from signal ground.  I have a delta 6A iec with emi/rfi filter in mine..  and I have it behind an atl hifi  dc blocker that you recommended.  But I understand EI core transformers such as the recommended Hammond in the BOM are not vulnerable to DC the way toroidal are

6A is too much with only 15 watts amp!!!! It is better idea to use the lowest possible amperage because they attenuate much more.

Schaffner F2244B:

[IMG] http://maty.galeon.com/WP-imagenes/hard/IEC-inlet-filter-Schaffner-FN_9244-specs.png

The graphs: [IMG] http://maty.galeon.com/WP-imagenes/hard/IEC-inlet-filter-Schaffner-FN_9244-typical-filter-attenuation.png

[IMG] http://maty.galeon.com/WP-imagenes/hard/IEC-inlet-filter-Schaffner-FN_9244-cicuit.png

I can use Würth 150 kHz ferrites with the power cables (besides the RF/EMI filters). The usual problem in audio is in the RF < 1 MHz.

The ferrites (and very cheap) that are usually seen there are for EMI ( > 1 Mhz), so they are not very useful in audio. They are useful with video.

maty

Re: Folsom's great little 7297 Chip Amp
« Reply #979 on: 18 Nov 2017, 11:41 am »
But I understand EI core transformers such as the recommended Hammond in the BOM are not vulnerable to DC the way toroidal are

EI and toroidals are vulnerable with more 10-15 mV at AC, specially the BIG toroidals (400 VA). Your EI 80 AV is very small. I have problems -distorsion- with DC and the almost 400 VA of the EI transformer, but I do not have mVolts!

The small continuous not only may vibrates the toroids and the consequent noise, it also causes the ALL transformers (EI and toroidal) to stop working in the linear zone of the hysteresis curve, with which they add distortion.

The ARTICLE, by Rod Elliot (1989)

Blocking Mains DC Offset

http://sound.whsites.net/articles/xfmr-dc.htm

With amplifiers of such low power I do not think there will be problems with the small continuous at mains.