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Folsom DIY7297 Amp & Antipole PSU

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Destroyer OS

Destroyer OS

Member
Joined 2005
pistollero said:
The heatsink get a bit hot after a few hours of playing...
But i think its normal..right?
Click to expand...

Well that just means it is working. As long as you're keeping decently under 70*C then everything is fine. If not you may need more airflow or a larger heatsink. Also, you could have some difficult to drive speakers which may ask more, which will make it operate warmer. Again it's no big deal so long as you're keeping it below 70*C.
 
pistollero

pistollero

Member
Joined 2016
Destroyer OS said:
The transformer, if you're using the Hammond 185, doesn't let as much noise through because it has higher loss in the RF range, so the lower voltage noise just doens't make it. So it can still get noise from the AC line going into it, but it transfers less than a toroid without a shield between the primary and secondary (and maybe still better than one with a shield, I don't know for sure).

The transformer doesn't emit RFI, but it does have a field that extends from it - which is comprised of 60hz. The field is there because it's what actually transfers power from one winding to the other, as the wires are not actually touching.

The boards themselves are going to get RFI from the air, since they are not in a metal, grounded, enclosure. But they are very specifically designed to reduce the amount that makes it to the signal. For example noise that does get in from the air or power is attenuated by the capacitors that are on a low inductance set of copper pours. As in they don't have traces, they have low inductance wide areas. Furthermore the section on the amplifier board that regulated voltage also rejects a lot of noise. Explaining that is a bit more complicated, but essentially to the circuit it looks like a big capacitor that doesn't like to feed noise through to the amplifier.

Neither board transmits much of anything. The amplifier board will have the largest fields from the speaker outputs if the wires are not twisted, because higher AC power will be going through them compared to the signal input which has small fields (real nice and small if they are twisted).

It's a good idea not to mix fields, which is why the layouts I've commended do a nice job of keeping wires separate, and keeping the transformers from being next to the amp board itself.
Click to expand...
Thank you very much for your explanation.
It is much clear to me now.
How big is the field of the transformer in inches?
 
pistollero

pistollero

Member
Joined 2016
Destroyer OS said:
Well that just means it is working. As long as you're keeping decently under 70*C then everything is fine. If not you may need more airflow or a larger heatsink. Also, you could have some difficult to drive speakers which may ask more, which will make it operate warmer. Again it's no big deal so long as you're keeping it below 70*C.
Click to expand...
It is bellow 70 degrees for shure. It gets warmer if the volume from the dac is louder. On lower volumes is always cold.
My speakers are jbl 3 way monitors 8ohlm.
The sound of the amp is very good. I have been switching input caps. And they all sound different.
Till now i used:
Audyn cap qs6 -2.2uf
Jantzen superior z -2.2uf
Russian ft3 -1.5uf
Wima mkp10- 2.2uf

Is there any benefit of using more than 2.2uf?

Regards
 
Destroyer OS

Destroyer OS

Member
Joined 2005
No, the corner frequency of 1.5uf is something like 4hz, and 2.2uf is lower. The reason for bigger capacitors is to have a lower corner frequency so you don't get bass roll off. 1uf had bass roll off, despite the corner frequency being a bit below 10hz.

I don't know the transformer field size in inches. There may be a way to approximate it but I'm not really acquainted. Sometimes you can hear it and wave the transformer back and forth from the signal lines to get an idea. But my approach is to just find ways to shield it if I'm worried or having problems. I'm not about to build an enclosure large enough to physically distance everything to guarantee they don't interact in the least.
 
S

soldersmoker

Member
Joined 2005
I just bought this amp from a member on audiocircle. While it shows promise (sounds great, really), my overall gain is way too high. I have a LTA MZ2 preamp and Omega high output alnico monitors (97dB). With my FW F6 inserted in my system, there's no problem with gain or noise. With the 7297 amp, when I turn the volume up just a hair (mm of volume pot movement), it gets pretty loud. With no sources playing and the volume at about 10 o'clock, there's a lot of noise, and the noise seems to be mostly from the preamp. I'm 99 percent certain that lower gain would be just what the doctor ordered. Is there any way to do this on the amp itself?

I've ordered some 12AU7s for the preamp to swap out the 12AT7s in order to hopefully reduce gain there (LTA says that both types work in their preamp though they are obviously very different tubes).

Here's a pic in case that's helpful:

7JrEb8m.jpg
 
S

soldersmoker

Member
Joined 2005
Destroyer OS said:
Sadly the amps gain is not adjustable. That has made it a poor pairing for several tube preamps.
Click to expand...

Thanks for letting me know. I should have done a better job of taking into account preamp/amp matching beforehand. But I can live with the sound as-is for now. It's actually a very satisfying amplifier in most aspects. Hopefully less gain in the replaced tubes of the preamp will solve the problem. I'll report back on how that works out.
 
Destroyer OS

Destroyer OS

Member
Joined 2005
32db

I recently tried something. I made a hole between my output binding posts. A slot would work too. NO reason to destroy existing binding hole posts or anything nutty; it just means that there is an open path between the two without the case fully blocking them. It does seem to help a bit with SQ.
 
D

dmy

Member
Joined 2009
Just received the amp board. Thanks

I am ordering the parts now from Mouser. They are out of the D45H11G bipolar transistor.
Is there a substitute for it?

On the pcb, there are 2 diodes (1n400x) shown but the part list does not include them, are these diodes required?

Many thanks
 
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