Folsom's great little 7297 Chip Amp

snake69fast · « **Reply #360 on:** 13 Jun 2016, 11:07 pm »

What part number is the transformer from your build? Thank you!

Folsom · « **Reply #361 on:** 14 Jun 2016, 12:19 am »

Hammond 185F16 but E and G can work as well.

shadowlight · « **Reply #362 on:** 14 Jun 2016, 05:38 pm »

Is it better to get a G instead of E in case F is not available?

Folsom · « **Reply #363 on:** 14 Jun 2016, 06:15 pm »

I would go with the highest letter available, yes. I prefer a robust PSU, but all of them will sound good.

shadowlight · « **Reply #364 on:** 18 Jun 2016, 01:09 am »

Anyone interested in soldering the parts on the board for me?

lacro · « **Reply #365 on:** 18 Jun 2016, 02:53 am »

Quote from: shadowlight on 18 Jun 2016, 01:09 am

Anyone interested in soldering the parts on the board for me?

I'll do it for ya! Send me a PM.

S Clark · « **Reply #366 on:** 18 Jun 2016, 03:44 am »

Thank goodness for Lacro. I was thinking about volunteering, but I've already fried one 7297 chip and did my best to ruin a board. Not sure I'm the guy to trust with someone else's project.

shadowlight · « **Reply #367 on:** 18 Jun 2016, 08:14 pm »

Lacro, S Clark,

I realized that I want to use the amp as my primary amp with either a Dodd Audio unity gain preamp or a 4P1L based preamp driving a Zu Audio Druid V so do not want to use my amateur soldering skills and screw it up.

I have couple of the original 5 dollar Chinese amps around which I will use to practice my soldering skills on

Lacro, thanks for helping with the build.

S Clark · « **Reply #368 on:** 18 Jun 2016, 09:05 pm »

It should work very well with your Dodd. If you go back to the first post in this thread, the review I wrote was with it connected to one of the original Dodd battery preamps, and it was a nice match.
It's really not difficult to build this amp, and the problems that I ran into were in trying to put it in too small of a case- shorting the chip and having to resolder several wires. That said, you might note that I'm not the only one that's fried the chip on this amp.
Mine hasn't been hooked up for a while, but with hot weather arriving in Texas, it's nearly time to put the tubes up until Oct.

BRN · « **Reply #369 on:** 19 Jun 2016, 04:23 am »

I had a mechanical noise coming from the amp that was caused by the power transformer. I did not think that I was going to have an issue when building the amp into such a solid chassis, but the noise was there. It was not a big deal since the amp is located in a cabinet, but I knew that I was going to have to take care of it. I took the advice Jeremy posted, about using rubber washer with the transfer, and I'm happy to report that the transformer is silent.

I'm really enjoying the amp. It has broken-in nicely, and has good controlled bass, smooth mids, and extended highs. I was not getting the extension from my tube amp that I get from the Folsom, and having the extra power helps as well.

KR500 · « **Reply #370 on:** 21 Jun 2016, 09:22 pm »

Finally got some time and began construction using Folsom's helpful illustrated and well written guidelines. I purchased a 4-40 tap for the heat sink mounting bolt from Lowes made by Irwin which quickly broke confirming similar reviews of it on the Lowes site . I used the insulating washers on both sides of the bolt mounting to isolate the chip from the heat sink metal.
Using my multimeter set to Ohms I get a reading of 1 with the probes on the chip tab and heat sink at all of the different ohm settings.
Is this correct ?

limits · « **Reply #371 on:** 21 Jun 2016, 09:27 pm »

Hi KR500...if that is the reading you get when you touch the two probe tips together, then it is not correct (this would indicate you have continuity between the chip tab and the heatsink).

limits

KR500 · « **Reply #372 on:** 21 Jun 2016, 10:14 pm »

Hi , thanks for your post . I get a reading of zero when touching the 2 probe tips together
When touching 1 probe tip to the chip tab and 1 probe to the heat sink per the instruction I get a reading of 1

Folsom · « **Reply #373 on:** 21 Jun 2016, 10:37 pm »

That would indicate that the screw is touching the chip tab. It should be 1000ohm to infinite.

lacro · « **Reply #374 on:** 21 Jun 2016, 11:26 pm »

Or - the thermal grease used was electrically conductive?

Folsom · « **Reply #375 on:** 22 Jun 2016, 12:57 am »

I guess that's possible.

BRN · « **Reply #376 on:** 22 Jun 2016, 02:39 am »

KR500,

Does your volt meter have a continuity tester? If so you can double check with that setting to see if there is a electrical connection.

KR500 · « **Reply #377 on:** 22 Jun 2016, 01:31 pm »

Thank you for your help ,
I used the continuity check on the Multi Meter and get a reading of "1" ,which the MM manual states indicates an open circuit . This is what is desired ?
If I change one probe from the chip tab to the bolt itself I then get an audible sound from the meter and the reading changes to "0.00"
Using the 200K through 2000K Ohm setting with one probe on the chip tab and one probe on the heat sink I get a reading of "1" ( just to be clear, a number 1 on the left side of the display , not 1.0 , 1.1 , 0.1 or 0.01 )
I'm using Radio Shack thermal grease which I used successfully last year to replace a burnt out power chip on a Samson Amp (which is still working fine )

Folsom · « **Reply #378 on:** 22 Jun 2016, 06:24 pm »

If it indicates an open circuit you're fine.

KR500 · « **Reply #379 on:** 22 Jun 2016, 07:47 pm »

okey-doke , thanks for confirming .
A dumb question I guess is if the heat sink dissipates heat and the chip is isolated by the mica and insulating washers from it is the heat transfer taking place by radiant transfer?
When I changed the power chip last year in a Samson amp it was bolted directly to the heat sink with only thermal grease between the 2 . It was a much larger chip