So far there has been no real “direct” reviews of the QED, in effect just innuendo clouded by politics, which is not helpful.
With the help of a friend I've just finished some testing of the QED and want to share our impressions here in the hopes of getting the ball rolling for some quality discussions (but maybe this is being too optimistic?) We hope and believe our tests were rigorously objective, the QED was used for general gold hunting and also comprehensively tested on buried real gold pieces of various sizes in a variety of soils, considerable care was taken to ensure no placebo/bias.*
We deliberately tested on only frequently detected but historically very productive public fields, not private property in which it can be relatively easy to find gold using any technology due to only ever seeing a few detectorists.
First and foremost, important details of the QED's method of operation that are different to other detectors which needs to be clearly understood:
Unlike Minelab detectors, the QED has a “dead zone” that can be varied using the Volume control. The threshold is set using the Bias control and has 2 different audio threshold settings, an upper and a lower value. When the Bias is turned down in number below the threshold lower value, OR, turned up in number above the upper threshold value, the “Threshold” audio increases as per usual.
Suppose for example, the lower audio threshold bias value of the Bias control happens to be 50 and the upper threshold bias number happens to be 60. Then if the Bias is turned down below 50 OR turned up above 60, the audio “threshold” level increases as per usual. For these threshold examples, 50 and 60, small gold (fast time constant targets) “in effect” produce signals less than 55 (half way between 50 and 60), and larger gold “in effect” produce signals more than 55.
If the Bias is set at the lower threshold limit, 50 for example, then the detection of small gold will give the usual INCREASE in audio level response, and larger gold will give a BELOW threshold level response,
If Bias is set at the higher threshold limit, 60 for example, then the detection of larger gold will give the usual INCREASE in audio level response, and smaller gold will give a BELOW audio threshold level response.
Similarly with ground noise; some ground noise will in effect produce signals below 55, so that if the Bias is set at 50, this ground noise will give an increase in audio sound, but if the Bias is set at 60, this ground noise will give a below threshold audio response. Conversely, if the ground noise is in effect above 55, then if the Bias is set at 50, this ground noise will give a below threshold audio, but if Bias is set at 60, this ground noise will give an increase in audio level.
Signals in effect BETWEEN 50 and 60 are in the “dead-zone,” for which the audio is below threshold. Signals in effect below 50 OR above 60 give an increase in audio.
So if threshold is set at the lower threshold of 50, then faint signals from small gold will give an above threshold audio, and large targets a below threshold audio. Whereas its the opposite for the upper threshold of 60, faint signals from large gold will give an above threshold audio, and small targets below threshold audio. So for shallow small gold select the lower threshold limit, for big deeper gold select the upper threshold limit. Bigger target signals will produce above threshold signals regardless of whether they are small or larger targets.
However the Volume control controls the dead-zone width; the gap between the upper and lower threshold Bias settings, that is, the dead zone gap is increased by turning the Volume down, or decreased by turning the Volume up.
In fact the QED can be set to operate with NO dead-zone (like the usual Minelab PI audio).
To do this:
a. Vary the Bias between the upper and lower threshold. Note the gap.
b. Increase volume a bit.
c. Re-do a. and note the decrease in the gap.
d. Continue to repeat a, b, c until there is no gap.
(This will allow some feel for true ground noise etc.)
However the QED audio has a very low level signal EVEN if below threshold, This below threshold faint audio signal is just the pitch signal only, and detects all signals, ground noise, target signals, whether long time constant or short, and EMI. But this below threshold pitch sensitivity is not as acute as the audio set at threshold per point 2 below, and it is very soft.
Yet even further, if a target or ground noise (or EMI) does drive the audio below threshold, the nature of the audio is that it has the usual “re-bound” response once the coil has moved over and past the target or ground noise. I refer to the lower pitch audio following the initial target higher pitch audio (“high-low”) or the opposite; the higher pitch audio following the initial target lower pitch audio (“low-high”) effect known from Minelab PI's. So for moderately weak target signals that cause the audio to dip below threshold once the coil moves beyond the target and the audio then rebounds above threshold. To recap; for these targets, as the coil passes over the target the audio goes first below threshold THEN above the threshold.
However for the fainter of these target signals (the important signals one listens for in thrashed ground), this rebound signal is hard to discern compared to the same signal that would occur if the Bias had been set at the alternative threshold setting for which the audio signal then would have given an initial increase in threshold as the coil passes over it and then a below threshold rebound. Therefore, it is important to understand that you EITHER need to set the Bias to chase the faint small targets in shallow ground (Bias at the lower number setting), but lose out a bit on the faint large target signals OR set the Bias to chase the faint larger targets in deeper ground (Bias at the higher number threshold setting) but lose out a bit on the smaller targets.
The QED has a “motion” audio response; meaning the coil has to be moved to hear a signal. It can be operated both quickly, and also, remarkably slowly. If the coil is moved “remarkably” slowly it is possible to hear the average audio detect a very faint target above the audio “background random chatter”, considerably more readily than if the coil was moved at a typical realistic operational speed. When depth testing and when you know where the target is, beware that you do not slow down the coil swing to an artificial unnatural swing speed to enable the detection of a deep target at its known location.*
1. It's very important to get the threshold (Bias) spot on for optimal results, If the threshold level is too high, then faint signals get drowned out, but if the audio threshold level is too low then only the residual very faint pitch signal remains, but this faint pitch only signal is less sensitive to target signals than the audio set optimally as per point 2 immediately following.
2. The threshold must be set so that it is just audible; in effect just immediately below the “real” audio threshold signal, so that what you are hearing is just between only the pitch signal and actual above threshold audio.
3. Note that the effective principal threshold control (Bias) is temperature dependent and requires reasonably frequent adjustment over time as the ambient temperature changes to get best results. Therefore there is NO actual specific optimal Bias number setting, rather it entirely depends on temperature. It can be as high as 70 in very hot conditions
4. Once 2. and 3. are optimally achieved, you will find that the GB setting has to be spot on for best results. If you find that it is not critical, you really need to re-address points 2. and 3.
5. The QED does produce ground noise that sounds on occasion like a target. If you aren't digging some ground noise you do not have it set up properly, especially in variable soils. With ANY detector (automatic GB or Manual) altering the GB setting slightly to eliminate a faint “deep target-like signal” will result in eliminating the faint signal whether it is ground noise OR in fact a deep real metal target.
6. You need to listen to the soft “subliminal” threshold of the QED very carefully, quality headphones are a must.
7. “Gain” acts as a sensitivity control as you would expect.
I suggest that the QED is best used as a specialist very fine (Small) gold detector. It produced a reasonably clear but quiet response to the extreme small gold (of the order of 0.1 g), we managed to find 5 tiny pieces in well-worked ground in all totaling 1 gram, although the SDC would have picked 5 of the 5, but not so well in one location due to power line noise (This could be remedied somewhat by lowering the Gain of the SDC and using minimal threshold). However, we purposely went over exactly the same ground with the SDC with the SDC set at a lower threshold and 3 on the gain, and then found 3 more pieces of gold; we are 100% sure we had already passed the QED exactly over the target locations so we put this down to QED ground noise masking targets. The QED struggles compared to the SDC in the more mineralised soils, however the QED does seem superior to the ATX.
To get the most out of the QED, use a small coil such as an 8” Commander mono, and set the Mode as low as possible so long as the ground signals do not become too intrusive. Usually 1 or 2 is OK for Minelab coils, but some other coils may produce too much ground noise at this setting so you may need to increase the Mode to 3 or above dependent on the ground.
Further, we got some very thin aluminium foil and very gradually trimmed it down until the SDC could no longer detect it. This represents particularly fast time constant targets (“extremely” small gold), and found that the QED did still detect it, but only within several mm of the coil surface, not further. But this does mean that the QED will detect extremely small shallow pieces that the SDC will not.
Alternatively we suggest the QED is also a suitable lightweight low-cost patch hunter when used with a large coil with the Mode turned up so that there is less ground noise.
For the sake of completion, to answer questions posed of the QED depth for an Australian 5 cent piece compared to the Zed both using the same sized coils. We measured this carefully and we are not prepared to give exact figures to avoid any trivial arguments, other than to say that the QED detected between 60% to 2/3rd of the depth of the Z.
The QED susceptibility to EMI in areas remote from mains compared to the 5k on EMI noisy days? In one word: “Good.
The QED susceptibility to mains in urban areas compared to the SDC or Zed? In two words: “Typically Bad.”
The QED’s main strength is its cost, light weight, ergonomics, and simplicity of use, and yes it IS definitely simple to use, but a bit “fiddly.” It has no “magic settings” once you understand exactly how it operates as described above. Going back to the SDC really highlighted the difference a light weight detector can have on general comfort and enjoyment of detecting, and our experiences with the QED underscored Minelab's poor ergonomics.
In our opinion the QED fits a market where people are looking for a cheap detector capable of finding small gold in thrashed areas, and are wanting more coil choices without the specialised "one size fits all" approach of the SDC. Good value for money.
Its main weakness is its underlying ground noise, which although having the advantage of being “hidden” in the dead zone, nevertheless limits depth compared to lower ground noise capable detectors, for targets other than the very fast time constant targets. In summary it works relatively best in the less mineralised soils for small gold.
Beyond the scope of the above suggested prospecting (very small gold & patch hunting mainly in relatively unmineralised soils), I choose not to comment further, other than we will not be using the QED for purposes other than secondary activities, and still intend to use other well-known detectors for primary prospecting activities because of their other advantages.
No doubt others with QED's will disagree with us. We welcome this, and would be happy to be proved wrong.
Ultimately, time tells the truth by substantial gold finds or lack thereof in well-worked ground.
*Note: because of the subtle audio, it is easy to imagine you are “hearing” a target above the general background ground noise when you know where it is. We endeavoured to avoid this tendency.