Yung Plate Amp - Initial Impressions - Page 3

Marty, is that the non-boost version? If so, any chance you can measure a couple of resistors for us? Look over this thread, it has pics to guide if you are able.

Sounds good. I noticed PE still has the 300W for a good price, and I'm tempted. But with two extra 500W BASH's, a Yung 200W-6, a 300W BASH, and a CSS 500W Yung, do I really need another plate amp? Plus I have a PE SA-1000 waiting to be used too! And that's not counting the old Keiga sitting in an enclosure that I can always use if needed. Sounds like I need more woofers, not amps!

The old style 280W? that Madisound sells. It's been solid, and very well built. Mine induced a bad hum in my system, due to a protection filter of sorts on the preamp inputs (filtering to earth gnd). I didn't see any other amp doing this, so I removed the filter and now it's dead quiet. May have just been caps going bad, but I removed it to isolate the audio circuitry completely from earth ground.

Well, I got a little ambitious and ran some plots.

Here are two graphs showing the FR of a Yung 200-6 plate amp. One with and one without modification to the hpf. Notice there is still a boost even when the hpf is modified. The hpf was modified to have an Fc of about 13Hz, and a Q of .6. There should be NO boost at all, and FR should actually sag down low. There is some recovery in the frequencies below 30Hz, but not what I'd expect. Educational for me, as I now suspect I will have to learn about active boost filters. When I reassembled my 200-6, I did note another pair of matching caps, and they were configured in a way I haven't seen in any other plate amp schematic. I'm suspecting that is the stage providing the boost, in addition to the stock hpf.

I just noticed someone had plotted the fr of their 500-6 (borrowed from a gent on the PE forum). It does have the bass boost as spec'd, and achieves this in spite of having the 30Hz HPF as noted here. So there appears to be a seperate boost circuit in the signal chain. I will trace the fr along the way, and see if I can find a way to mod/defeat the bass boost.

Do you at least get the red power led when you plug it in? If so, do you hear a slight click when you feed it an audio signal? Have you checked to see if the fuse is blown?

Not enough experience with these yet to see if there are common problems with any of these models. I did order a 300W model after all, so I hope they don't suffer from some design defect. Keep us posted.

Yes, something is definitely wrong. Give the amp a good visual inspection to make sure there is nothing touching that shouldn't be, like a couple of components leads shorted, or something touching the metal plate. It's about all you can do. Hope it's something as simple as that.

Yes, measure the resistors if you can. Make sure the amp is completely unplugged before you do to avoid accidentally shocking yourself. No power necessary to measure them. Thanks.

So here is a wrap up regarding the frequency response of this line of amps. We know that all the boost models share the same HPF (subsonic, rumble filter, etc), and it is set at 30Hz with a little boost above that. We also know that there is a seperate bass boost circuit to give the boost that is spec'd for each model. The HPF and boost are summed (combined) to give the overall frequency response (plus the phase and low-pass adjustments of course). So for those still interested in these, and having the desire to modify/customize the response, here are a couple of pics to help. Best thing to do is to defeat the boost circuit altogether, then tweak the HPF as desired, and as is common with other plate amps.

This pic points to the two resistors that need to be changed to tweak the HPF. They are located close enough to the edge of the pcd (near the led) that it shouldn't be too difficult.



This next pic is the back of the preamp pcb, and shows the two jumpers needed to defeat the bass boost circuit.



Here is the frequency response of my 200-6, after defeating the bass boost circuit, and modifying the HPF to an Fc of 13Hz, Q = 0.6.



We haven't had any user feedback about the non-boost models, but my suspicion is that they share the 30Hz HPF, but their boost circuit is configured for no boost. I will try to confirm this when my backordered 300W model arrives.

They are .22uF.

The two resistors are for modifying the HPF.

The jumpers bypass (short across) the capacitors that are on the SEPERATE bass boost circuit, to defeat the boost. Placing the jumpers on the back side is easier than having to remove the caps and install jumpers in their place. Also, one may actually like the bass boost, in which case they can simply remove the jumpers to re-enable the boost. The major drawback to this boost circuit is that it really hurts the low-end frequency response of these amps, especially if one is looking for output below 20Hz.

These amps actually have a little boost configured into the HPF and also have a seperate circuit that provides the bass boost that is spec'd for each model. The outputs of these two circuits is summed together (combined) right before the signal hits the 'phase adjustment' circuit, then on to the 'low-pass adjustment' circuit. So I identified the components for tweaking the HPF, and also identified a way to defeat completely the bass boost. It would be nice to find a way to modify the bass boost circuit, but its components are located such that it would require removing the board, which is quite a pain and not worth the trouble. Better to just defeat it completely, and incorporate any desired boost at the HPF stage.