TDA7297 Build Guide

devinkato · « **Reply #20 on:** 9 Jan 2014, 11:14 pm »

Quote from: Salis Audio on 15 Dec 2013, 09:27 pm

Use only DC power supply after removing the diode.

Firstly, thanks so much for taking the time to put this together.

Secondly, when it comes to removing the diode - do you mean that we need to use only a standalone dc power source (12v battery), or can we use a 12v dc switching supply like a laptop brick, or Meanwell?

Folsom · « **Reply #21 on:** 9 Jan 2014, 11:44 pm »

Anything that doesn't get near 18v and is DC will work.

With the diode you can run AC, but it's not going to sound great.

devinkato · « **Reply #22 on:** 16 Jan 2014, 08:19 pm »

Looks like there's another revision running around. Note the "-002" label on the left side. Looks like some components are in different places. Is there any way to verify that replacing by using the labels (C2, C3, etc) will still work? Or do we need to come up with a separate guide?

mboxler · « **Reply #23 on:** 16 Jan 2014, 08:37 pm »

Looks like they removed the LED and it's current limiting resistor. Is there still a diode behind the big power capacitor?
Seems like the mustard colored caps are the coupling capacitors, but a view from the bottom (to see the traces) would help.

Mike

devinkato · « **Reply #24 on:** 16 Jan 2014, 08:59 pm »

Quote from: mboxler on 16 Jan 2014, 08:37 pm

Looks like they removed the LED and it's current limiting resistor. Is there still a diode behind the big power capacitor?
Seems like the mustard colored caps are the coupling capacitors, but a view from the bottom (to see the traces) would help.

Mike

View from the bottom added above to post #22.

mboxler · « **Reply #25 on:** 16 Jan 2014, 09:45 pm »

Judging by the traces, the diode must still be there (hidden behing the big capacitor). But, WOW! Looks like they beefed up the power and speaker traces with a silver (?) coating.

The coupling caps (the mustard ones connected to the middle pins of the volume control) could be easily replaced, but removing/replacing any other component will be tricky. Anyone else agree?

Mike

Edit: Google "conductive ink pen".

Folsom · « **Reply #26 on:** 16 Jan 2014, 10:21 pm »

You are correct, the capacitor names did change.

Remove C2, the little yellow bypass cap. You can wiggle it off if you want.

C3 and C5 appear to be the input caps, replace those with the 4 Nichicon ES or anything .47uf-2.2uf in size (.22uf rolls off prematurely in the 20-30hz range, when a larger cap allows -3db at 20hz)

C1 looks like the big power cap, replace with the other big 2,200uf of choice.

C4 can be changed if you please, it doesn't matter.

The resistors are fine how they are, they're insignificant to sound.

Also, yeah, I'd remove the diode and bridge it still.

The inputs are identical if you want to remove the 1/8th jack.

I don't know why it has tinned tracing... Silver solder wouldn't really do anything. But I've been skeptical as to whether or not these have copper or steel tracing. Maybe cutting tracings for signal and just running wire would be better.

elb · « **Reply #27 on:** 23 Jan 2014, 08:08 am »

I bought this fantastic amplifier and did all the suggested Salis mods.

Only one issue,when I touch the case that I mounted the amp in I get a hum through the speakers.

All input & output sockets are isolated from the case.

At this stage I am using a volume pot,not the one supplied but an Alps.
Mounted on the front face of the case and connected via wire to the pcb.

Suggestions would be most welcome.

Thank you in advance.

mboxler · « **Reply #28 on:** 23 Jan 2014, 03:17 pm »

Quote from: elb on 23 Jan 2014, 08:08 am

At this stage I am using a volume pot,not the one supplied but an Alps.
Mounted on the front face of the case and connected via wire to the pcb.

If this is a metal case, it may help to solder a thin wire from the volume pot case to the chassis.

Mike

elb · « **Reply #29 on:** 23 Jan 2014, 04:07 pm »

Hi mboxler,

I was thinking of doing that but dismissed the idea because the front panel is wood.

Thank you.

Folsom · « **Reply #30 on:** 23 Jan 2014, 10:18 pm »

I'd connect the ground of the amplifier to the case via a .1uf and 100-150ohm resistor (in parallel). Also maybe try connecting the case to earth ground at the same time. You might have to play a bit for this, as I can't predict what'll work for certain, because I don't know your other equipment.

elb · « **Reply #31 on:** 24 Jan 2014, 09:01 am »

Problem solved.

I put in 2.2 uF Janzten superior z caps for the inputs.

Because I had to mount them off the board I extend the leads,insulated wire.
Talk about a hum magnet.

I replaced the Jantzen caps with 1.0 uF Wima's that fitted nicely on the board.
They were the only caps I had on hand.

Once again,Thank you.

rhing · « **Reply #32 on:** 24 Jan 2014, 04:08 pm »

Quote from: elb on 24 Jan 2014, 09:01 am

Problem solved.

I put in 2.2 uF Janzten superior z caps for the inputs.

Because I had to mount them off the board I extend the leads,insulated wire.
Talk about a hum magnet.

I replaced the Jantzen caps with 1.0 uF Wima's that fitted nicely on the board.
They were the only caps I had on hand.

Once again,Thank you.

Glad you were able to fix the problem, but I have Mundorf Supreme film caps off board on my amp too with an Alps Blue Velvet volume pot in an Aluminum case, and I did not have have any grounding or hum issues. I always check to insure there is no continuity between connectors and the case before I wire everything up. Sometimes, I use Teflon plumbers tape around the connector bodies to insure there is no ground path through the chassis. Are you sure the ground connections were properly wired and soldered between the RCA jacks, volume pot and PCB?

elb · « **Reply #33 on:** 24 Jan 2014, 07:34 pm »

The case has served duties for other amplifier experiments without issues.

Good point about using Teflon tape,I do this as a matter of course.

Thank you.

Folsom · « **Reply #34 on:** 24 Jan 2014, 08:25 pm »

The cap and resistor I recommended makes your case less of an inductor, and not an antenna. But also doing this can match ground potential through your power strip, through safety ground, if your source has safety ground connected (to signal in some way, phono preamps usually do if they run on AC).

When you touch parts and get noise you are often inducting a change in ground potential. As you know induction doesn't explicitly require connectivity.

Well anyway, glad you like it.

elb · « **Reply #35 on:** 24 Jan 2014, 09:06 pm »

I just love Audiocircle,lots of good people so generous with advice.Not like that other forum(diy*****)where some people,not all, derive pleasure from treating people like fools.

Folsom · « **Reply #36 on:** 24 Jan 2014, 10:06 pm »

As often a fool myself, I love it too

seaverd · « **Reply #37 on:** 29 Jan 2014, 04:57 pm »

So since you are so friendly, I would like to ask a stupid question. Could this amp be used in a car to boost the signal from a DAC to a headphone 3.5mm aux input on the vehicles head unit? I assume that these amps are too powerful, but wanted to see what you think. Maybe what I need is just a small headphone amp. I am intrigued by a simple DIY and cost effective solution, but don't want to damage my existing vehicle head unit.

Thanks,

Dan

Folsom · « **Reply #38 on:** 29 Jan 2014, 06:36 pm »

It's much too powerful. You be putting in lots of resistance to get it down. I think a headphone amp is a great idea. They also often have a form factor that fits in convient cases too.

devinkato · « **Reply #39 on:** 29 Jan 2014, 07:11 pm »

Speaking of the car - I think an awesome application for these could be tweeter or midrange amplifiers for an active setup. Wondering if direct power from the car battery/alternator would be clean enough for these amps or if it'd have to be filtered.