Douk Audio L1

This product does exactly what it says it does, it will boost your audio line signal by around 20 decibels. My own measurement put this at 17.2 DB louder from 15 feet away before you start to get distortion. It can go up to around 19 DB or so but you get distortion. Even 15 db is plenty to make a stock stereo in a car really loud, but be warned you won't be pumping mass bass as the power output isn't there to drive your Fosgate 12s for example, obviously anyone installing quality equipment like that won't be using this thing.The product is cheap and has multiple inputs and outputs available (see pro tips below). It also comes with a USB-A power cable so you'll need a USB-A port available or otherwise supply your own power.Many of the complaints about this product seem to be curable but do require extra work and or parts.Pro Tips on how to get this to work great:1. Take into account where you will be installing this. If you are installing this around unshielded cable, high voltage etc, because of its cheap nature, it will pick up a hum, this thing is not insulated at all really. It is best to keep it away from other devices and power it cleanly off a dedicated USB or power supply. See below for ideas how to fix if you get a hum.2. The 3.5MM input will be priority and no other inputs will work at the same time if you use the 3.5MM input, however, if you use RCAs and the 5-Din this thing will take in both and mix them evenly (There is no way to to mix or boost one more than the other). The output is both 5-Din and RCA, you can use either or both at the same time.3. Since this thing isn't driving that much power, I found even the cheapest cables work fine. Normally you want to use higher quality cables for the best sound with the least leakage but in this case we are going cheap, so even cheap cables will work.4. If you are installing this in a car, you're probably like me and installing it on an old or stock in-dash stereo and those are horrible for grounding and will usually pick up a hum because of ground issues so here is:How to fix the dreaded hum that people complain about:First, you can try to ground your stereo better if you can. This can help, but if you are just hoping to plug it in and not mess around try a Ground Loop Isolator like this: https://www.amazon.com/dp/B06XQYN77L?psc=1&ref=ppx_yo2ov_dt_b_product_detailsThe linked isolator uses the 3.5MM input on the amp and takes in a 3.5MM connection. An over simplified explanation is that by using an inductor that then creates a magnetic field, a ground loop isolator can essentially force any differences in current (caused by a bad or different resistance ground) to be nullified because this is what causes the hum. Please realize you'll need to get the correct kind of isolator for your inputs and outputs. Just search Ground Loop Isolator here on amazon and you'll find many. Since this isn't putting out that much power, cheap ones usually do the trick.Also keep in mind that there are two schools of thought and which one works for you depends on your situation:1. Place the isolator between the head unit (a stereo for example) and the amp. In other words place the isolator on the input side of this amp. This is the typical way of doing things and works for the vast majority of cases in car audio although not all.2. Place the isolator after the amp but right before the speakers if there are other components in the system like a game console, or another stereo component etc. This case is more specialized but you can pick up hum caused by the amplifier itself and it bleeds on the output side but this is less likely. The amp usually get's hum fed into it and you can eliminate that on the input side and the amp will output a clean signal.3. Place an isolator on the input AND the output side. This is really rare and only happens in extreme instances where there are a lot of electronics at play causing problems for one another OR there are powered devices after the amp that are picking up hum from the combination of sources. In this case you'd add one on the input side as close to the amp as possible, and then one on the output side as close the speakers as possible.Good luck! This thing is a steal at the price for what you can do with it using a little know how.

If you own an Yamaha MX49 or MX61 synth, then you know how wimpy the output levels are. Yamaha bumped up the output in the newest firmware, v1.01, by 6db. I have this version (see pic), but the levels are still so wimpy that a decent output level is only attainable by cranking the synth's volume knob, and the mixer's gain and all EQs to max. This is simply not acceptable, and it shocks me that Yamaha would release a product with such an issue.The fix = Douk line level preamp :: I connect the MX49's stereo outs to "Priority IN" using a shorty dual 1/4" TS (mono) to stereo 3.5mm (TRS) cable ... then ... connect "To Amp" RCA outputs to a stereo line level channel on the mixer via stereo RCA to dual 1/4" TS (mono) cable. I set the Douk volume knob to MAX.This affords adequate levels with overall sane settings :: synth's volume knob = 50%, mixer gain = 50%, all EQs = 0db. The sonic properties are great! All the synth voices sound every bit as good!Powering the Douk preamp is a little weird. It states "5 - 24V", but that CANNOT true. I initially used a 19V PC supply and the preamp went into some bizarre flashing mode and sent popping spikes to the board. Now I'm using a "smart" USB wall wart that can deliver 5-15 Volts at 2.4 Amps. Operation is perfect.

I purchased this item to use between my componet CD player and a Stereo Tube Power Amplifier. Because my componet Preamplifier is awaiting shipment of a new power switch. I thought this would be a good inturn solution allowing me to still listen to my CDs. The not so good. The unit has a set of RCA inputs and a stereo 3.5mm input jack. The signal chain goes from the RCA jacks through the 3.5mm input jack. Unfortunately the RCA jacks did'n't work on my unit meaning the internal contacts in the jack were not connecting properly. The 3.5mm jack did work and with the proper adapter cable and I was able to get it working in my system. It is a pretty cool little device. I did remove the covers to investigate the problem. I was surprised to see this. It will run from single 5Vdc USB power supply. Inside the unit is a small power inverter that takes that 5Vdc and generates a +/- 12Vdc isolated power supply to power the NE5532 Dual OpAmp. It provides 20 db of gain ( voltage gain of 10). It has a slight rolloff of -3db @40Hz which is not quite ideal. Otherwise the unit has excellent fidelity and for my purpose it works fine.

Why did you pick this product vs others?:Really disappointing. Had wanted to use this as a signal boost for an older powered subwoofer. Unfortunately it Introduced a ton of line noise to the system. Also the knob serves as more of a binary switch than an analog volume control.Value for money:Too good to be true, the low cost correlates with low build and sound quality. I returned the item after testing for a couple days.

works perfectly so far. clean signal, easy to use.

First connected with RCA cables. Load pulsing hum. Used 3.5 m connector and made separate chassis GND cable to main stereo preamplifier . Humming stopped. Works fine now.