Folsom's great little 7297 Chip Amp

Folsom · « **Reply #180 on:** 27 Feb 2016, 11:38 pm »

Length will be the height when you order. I suggest sizing it to the enclosure or so. As far as heat goes 3" is very good.

KR500 · « **Reply #181 on:** 28 Feb 2016, 03:39 pm »

Thanks J.
I'm ordering the 3 inch length from Heat Sink USA.
Would the Glassware Aikido Buffer PCB work with the 7297 amp ?
I've been eyeing their kit for a while .Here's the description from their website.

Octal Aikido Cathode Follower
"The Aikido cathode follower PCB/kit is a modest affair, consisting of one tube per channel (two triodes per tube envelope) and a handful of capacitors and resistors. This unity-gain buffer, using a modified cathode follower, offers a high input impedance, a low output impedance, low distortion, and a great PSRR figure. In addition, the ACF does not invert the phase. The ACF use is not limited to line-stages, as the ACF can be used in creating an active crossover or even a headphone driver, if the headphone's impedance is high enough and the tube robust enough.
$24.00"
I just noticed they have a resistor stepped attenuator on sale there for $10.
Is this better than the 10K DACT ?

shadowlight · « **Reply #182 on:** 28 Feb 2016, 04:21 pm »

PCB holder similar to what Lacro posted but not as good looking - Amazon

Anyone have good link for good cheap magnifying glass?

Folsom · « **Reply #183 on:** 28 Feb 2016, 07:49 pm »

Quote from: KR500 on 28 Feb 2016, 03:39 pm

Thanks J.
I'm ordering the 3 inch length from Heat Sink USA.
Would the Glassware Aikido Buffer PCB work with the 7297 amp ?
I've been eyeing their kit for a while .Here's the description from their website.

Octal Aikido Cathode Follower
"The Aikido cathode follower PCB/kit is a modest affair, consisting of one tube per channel (two triodes per tube envelope) and a handful of capacitors and resistors. This unity-gain buffer, using a modified cathode follower, offers a high input impedance, a low output impedance, low distortion, and a great PSRR figure. In addition, the ACF does not invert the phase. The ACF use is not limited to line-stages, as the ACF can be used in creating an active crossover or even a headphone driver, if the headphone's impedance is high enough and the tube robust enough.
$24.00"
I just noticed they have a resistor stepped attenuator on sale there for $10.
Is this better than the 10K DACT ?

The Aikido adds gain so it's not my favorite choice. But tube selection can keep the gain down and it'll work. DaveC used one with the amp. I prefer no gain line stages with an amp that has 32db gain.

Their stepped attenuator is mono only. That too me is a big pain, so I would never rock it. I doubt it sounds as good either.

shadowlight · « **Reply #184 on:** 28 Feb 2016, 07:55 pm »

Can you change the gain on the amp from 32 to say 26db or 20db, if you plan to use it with preamp that has gain?

Folsom · « **Reply #185 on:** 28 Feb 2016, 08:54 pm »

No, the amp gain doesn't change.

Odal3 · « **Reply #186 on:** 28 Feb 2016, 09:55 pm »

Is the heat sink supposed to just hang off the chip?

Lacro - that looks nice!

Btw - Where do you buy those nylon (?) standoffs?

Mmaxed · « **Reply #187 on:** 28 Feb 2016, 11:03 pm »

Please refer to the transformer diagram for wiring of it, if you’re using one. You need 16v out of the transformer before rectification (and 80+va). SMPS 21v min, and batteries 24v.

I assume the above quote from the construction notes PDF means that I can use 2 SLA batteries wired for 24 volts to power the amp.

I may get the amp board together and would like to get it powered up this way.

Will need some instruction later on wiring the trans in the PS.

Folsom · « **Reply #188 on:** 28 Feb 2016, 11:09 pm »

Quote from: Mmaxed on 28 Feb 2016, 11:03 pm

Please refer to the transformer diagram for wiring of it, if you’re using one. You need 16v out of the transformer before rectification (and 80+va). SMPS 21v min, and batteries 24v.

I assume the above quote from the construction notes PDF means that I can use 2 SLA batteries wired for 24 volts to power the amp.

I may get the amp board together and would like to get it powered up this way.

Will need some instruction later on wiring the trans in the PS.

That's correct, you can use two 12v batteries wired in series.

I'll post some photos on the transformer soon.

lacro · « **Reply #189 on:** 29 Feb 2016, 12:44 am »

Quote from: Odal3 on 28 Feb 2016, 09:55 pm

Is the heat sink supposed to just hang off the chip?

Lacro - that looks nice!

Btw - Where do you buy those nylon (?) standoffs?

I mounted (drilled/tapped) mine so the heat sink will support it's own weigh, not hanging off the chip. The one on the transistor is one I salvaged from an old PC, and cut down to size. It's really light, and it is hanging off the Transistor.

I got the stand-offs from the "bay" Lot's of choices from China.

Here's a kit with black ones that I just ordered:

http://www.ebay.com/itm/180-Pcs-Black-M3-Nylon-Hex-Spacers-Screw-Nut-Stand-off-Plastic-Assortment-Kit-/381537029579?hash=item58d5610dcb:g:x1MAAOSwvUlWsbdG

Folsom · « **Reply #190 on:** 29 Feb 2016, 01:09 am »

If you're worried about the transistor and the rather light heatsink you can add a little solder to the legs of the transistor to coat them top to bottom. But the one I recommend doesn't seem to budge at all during shipping.

lacro · « **Reply #191 on:** 29 Feb 2016, 02:33 pm »

Jeremy,
Are the 47K resistors, and the 10uF cap part of a mute/standby circuit to prevent on/off pop? Also, are signal grd. and power grd. isolated from each other or shared?

Folsom · « **Reply #192 on:** 29 Feb 2016, 06:45 pm »

Quote from: lacro on 29 Feb 2016, 02:33 pm

Jeremy,
Are the 47K resistors, and the 10uF cap part of a mute/standby circuit to prevent on/off pop? Also, are signal grd. and power grd. isolated from each other or shared?

Correct on the mute/standby circuit. SG and PG are connected at the point that proved to be the best sounding. They cannot be isolated because if they are they amp will never turn on. Believe me, the first PCB board was very frustrating trying to figure that one out!

Folsom · « **Reply #193 on:** 1 Mar 2016, 06:47 pm »

The datasheet for the transformer shows all you need. I don't think I'm going to draw anything better. The connections for 115/230v are your hot and neutral from your power inlet, hot being the one you'd put a switch on. To achieve 16v output you use the series configuration.

Odal3 · « **Reply #194 on:** 2 Mar 2016, 06:17 am »

Finally there is some progress to report and got the first few things soldered to the board. Since I'm pretty much a newbie to soldering it was a little bit tricky to get the chip on. Fortunately I remembered I had a finer tip for the iron which made it so much easier. Think one hole didn't really fully fill up with the solder so will retouch tomorrow.

Also realized I forgot to buy a bolt to actually attach the hit sink with. Hoping they have something I can use at Home Depot. Fun project and I'm learning a lot.

Folsom · « **Reply #195 on:** 2 Mar 2016, 06:22 am »

#4 fits the isolation to-220 washer. (4-40 or 4-48)

Markvdv · « **Reply #196 on:** 2 Mar 2016, 09:27 am »

Quote from: Folsom on 28 Feb 2016, 07:49 pm

The Aikido adds gain so it's not my favorite choice. But tube selection can keep the gain down and it'll work. DaveC used one with the amp. I prefer no gain line stages with an amp that has 32db gain.

ACF is (close to) unity gain, it slighly attenuates input, post you react to has the information.

Odal3 · « **Reply #197 on:** 3 Mar 2016, 06:39 am »

Almost there! Just need to put on the heat sink and connect the wires.

shadowlight · « **Reply #198 on:** 3 Mar 2016, 04:28 pm »

What is everyone using for case? Are there in pre-drilled cases available?

Folsom · « **Reply #199 on:** 3 Mar 2016, 06:51 pm »

Quote from: shadowlight on 3 Mar 2016, 04:28 pm

What is everyone using for case? Are there in pre-drilled cases available?

Landfall systems will CNC whatever you want.