[shadowlight]

For folks who are totally removing the pot what are you replacing it with?

[rhing]

I choose Muse ES caps for this next build, cheap enough it's cheaper to order 10 than 2! They are considered bass oriented (good for this amp) and know to be more transparent than many caps at higher prices, to naturally show of the extreme detail in this amp. My experience is they are pretty smooth to. It's going to be good; and docmented. Sometime next week..

Along with the Black Gate N non-polar caps, I've had really good experience with the Elna Silmic II electrolytic caps in signal coupling applications. Nelson Pass recommended them when I met him at a Burning Amp Festival in San Francisco a few years ago. I am very interested in how the Nichicon Muse ES caps work with this amp.

Yea...both units I received had damaged pots.  The "mummy" wrapping was so tight it bent both pots.

On the bright side, my de-soldering skills are improving  .

That's unfortunate that you received damaged goods. These stock volume pots and should be replaced with something like these:

http://www.ebay.com/itm/190844814249?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_sacat%3D0%26_from%3DR40%26_nkw%3D190844814249%26_rdc%3D1

I recommend that you use a good solder sucking tool to remove the solder when you remove the stock volume pot. You'll need to use some solid core wire like 20AWG Silver-plated Copper solid core wire or leftover capacitor lead wire, and use needle nose pliers to fabricate some pins to solder into the thru holes of the base of the stepped attenuator. After that, you can just plug the stepped attenuator right into the TDA7297 amp board, and solder that in place.

I've also tried a 100k Alps Blue Velvet and like it as well, but this will not fit into the small space on the amp board.

[randytsuch]

Along with the Black Gate N non-polar caps, I've had really good experience with the Elna Silmic II electrolytic caps in signal coupling applications. Nelson Pass recommended them when I met him at a Burning Amp Festival in San Francisco a few years ago.

I also like Silmics, and you can buy them from Digikey.

[rhing]

I also like Silmics, and you can buy them from Digikey.

Mouser carries them now along with the Nichicon Muse ES and Wima MKP2 Polypropylene film caps:

• Elna RFS 1uF 50V 20% Audio SILMIC II (RFS-50V010MF3#5)
• Nichicon Muse ES 1uF 50 V 85c 5x11 2LS (UES1H010MDM)
• Wima MKP2 Film Capacitor 250V .22uF 5% (MKP2F032201K00JSSD)

Looks like some cap-rolling fun.

[Folsom]

The solder on these is very easy to work with. The through holes are fairly tough too.

However for all work done I love these things. They don't last forever, but if you aren't professionally working on circuit boards they are the bomb.

[mboxler]

For folks who are totally removing the pot what are you replacing it with?

I replaced my pots with ones from a fried LP-2020A+ (the two tones control pots were the exact same pots, albeit still cheap).

However, I'm curious as well.  If I were to use a preamp, would I run a straight wire from 2 and 3, and a 50K resistor from 1 and 2?  To cut the gain to 80%, use a 10k resistor from 2 and 3, and a 40K resistor from 1 and 2.  The resistance from 1 to 3 should always be 50k.

Mike

[Folsom]

You don't have to replace the pot with anything necessarily. The chip itself has 25-30k input resistance.

[rhing]

I took my first prototype TDA7297 chip amp with the Mundorf Supreme coupling caps and installed it in a nice black anodized, brushed Aluminum enclosure that I picked up at a Fry's Electronics store. Fry's is a chain of electronic superstores out in the West Coast. Each store is about the size of a Walmart and they carry everything electronic under the sun. Anyway, the Context Engineering extruded Aluminum case cost me $25 including tax. I spent most of the morning drilling all the holes for the connectors, ventilation and Alps Blue Velvet volume pot. Eventually, I will design a thick Silver brushed Aluminum faceplate that will match my ARC gear and order it from Front Panel Express. I also installed a mini toggle SPST on/off switch that I picked up from Radio Shack. The knob is from a Chinese eBay seller. It's no longer a $6 bargain chip amp, but for about $125, I have a nice sounding little black box.

 

[Folsom]

Are you running a shaft for volume?

[rhing]

I mounted the volume pot on the front faceplate and ran wires from the RCA jacks to the volume pot. The Mundorfs are directly wired to the volume pot and to the board.

[Folsom]

I Believe my intuition about using diodes as a filter for DC source may have been a good idea. I'm not testing with this amp since I am waiting on replacement, but my class D seems to be presenting an enhanced focus and harmonics.

It would make since that a reduction of tiny AC flowing the wrong direction through a device only using forward current, would enhance accuracy of inlay or switching.

[shadowlight]

Question for the folks who understand the spec sheet.  Do I need to make sure that the power volts listed on the PS is between 12V and 18V, with max of 4.5 amps?  Assuming that if I go over 18V I am going to blow the amp but what happens if I go over 4.5amps?  I am planning to run the amp with battery and just want o make sure that I purchase the correct battery.


TIA

[wushuliu]

I Believe my intuition about using diodes as a filter for DC source may have been a good idea. I'm not testing with this amp since I am waiting on replacement, but my class D seems to be presenting an enhanced focus and harmonics.

It would make since that a reduction of tiny AC flowing the wrong direction through a device only using forward current, would enhance accuracy of inlay or switching.

Hm, got a schematic?

[mboxler]

Question for the folks who understand the spec sheet.  Do I need to make sure that the power volts listed on the PS is between 12V and 18V, with max of 4.5 amps?  Assuming that if I go over 18V I am going to blow the amp but what happens if I go over 4.5amps?  I am planning to run the amp with battery and just want o make sure that I purchase the correct battery.


TIA

Your PS should be a minimum of 4.5 amps, although the amplifier will seldom draw that much current.  Anything larger than that would be overkill, but okay.

I run mine from a battery similar to this

http://www.amazon.com/18Ah-Sealed-Lead-Battery-Terminals/dp/B001C20T9C/ref=sr_1_7?ie=UTF8&qid=1386720425&sr=8-7&keywords=ub12180+battery

I use a CTEK 3300 to recharge the battery.  A battery of this size will power one of these amps for hours.

Mike

[rhing]

Question for the folks who understand the spec sheet.  Do I need to make sure that the power volts listed on the PS is between 12V and 18V, with max of 4.5 amps?  Assuming that if I go over 18V I am going to blow the amp but what happens if I go over 4.5amps?  I am planning to run the amp with battery and just want o make sure that I purchase the correct battery.


TIA

I am not sure there is a maximum limit on current for your power supply. A friend of mine is using a Mean Well RS-100-12 100W SMPS with a 7A current and 12V DC voltage with his TDA7297 amp. What seems to be most important is that the power supply doesn't exceed 18V DC, or else your amp will fry. The battery that mboxler is using should be just fine.

[Folsom]

Hm, got a schematic?

Yeah. Here's a couple options. I'm not sure how the TDA7297 will respond to multiple diodes, but it might be worth it to stack them, (parallel) just like with stacking a few not-too-big caps; it does work, just not sure of level of affect yet. It creates a dividing network. The more diodes the less AC that'll be flowing the opposite direction of the DC source through the amp itself because you're passing more through the diodes with each added. Unfortunately SMPS's and many other power supplies we use tend to generate a tiny bit of AC, or catch it on the line, so this seems to work. Even if the diodes generated some sort of noise, my first test indicates that it'd be like trading a locomotive for a neighbor with a Prius.

I'm sure shortly someone will recommend using different types of filters that include series elements. You can play with them, but I'm not into it. A lot of people prefer to go minimalist, I am one of them. Many designs I like have very few parts, and are very uninhibited for current and voltage. When I want to filter I try to retain that. Hence I'm not recommending any inductors or whatever. Let the ears talk.

The TDA7297 is a chip amp, so it's not as responsive as class D/T to power supply capacitance in the same way, but it can still be good. You might have to play with it yourself. Generally they seem to act well once you hit as much capacitance as they are going to use. Transparency, subtlety, speed, is not affected as much like with class D/T, but dynamics certainly need some juice in a chip amp. SO in this case I think it's appropriate to be more concerned with using a few diodes.

For the record I'm using MUR860's (preferably not Fairchild version).

[Folsom]

I'm not so sure that 18+v "fries" the amplifier. In fact I think what it does is bridge one of the mute/protection switches permanently.

Why? Because a regular chip-amp has the burden of heat to deal with, not voltage. In fact I wonder if there is a TDA7297 that's identical, but lacks those two features. It'd probably be able to put out more power with cooling. Oh well, 15w gets my Horn's rocking loud enough anyhow!

[randytsuch]

Unfortunately SMPS's and many other power supplies we use tend to generate a tiny bit of AC

Are you talking about ripple voltage riding on the DC voltage?

I'm really not sure what AC current you are referring to.  As long as the voltage stays positive, there would be no AC current.  The ripple in the voltage would change the current draw, but it would not create an AC current.

The diode may create a filter, and reduce the ripple, especially when paired with a cap.  My guess is it would create something like a RC filter, but not quite.

Randy

[Folsom]

Put your meter on it, ripple, leakage, inducted, doesn't matter, it's there.

The output inductors on SMPS's can generate AC by the way. It's low, and ideally shouldn't except under heavy load, but.....

[jkelly]

Do you see any advantage to running two boards - just with one channel running on each?

Jeff