# Personal Review: Zapco ST-5X Amplifier



## llebcire (Nov 17, 2016)

*Personal Review: Zapco ST-5X II Amplifier*

This is my personal and non-professional review of the Zapco ST-5X II amplifier.

Zapco states the Studio Series were designed to deliver legendary Zapco sound quality while keeping the price low enough to fit in any budget and have incorporated the same caps, op-amps and outputs used in the C2K and Reference series.

I purchased this amp last November to drive a simple system with front stage and a sub running on the factory HU. This amp has high-level inputs and a basic crossover (50 – 250 Hz) so it is very flexible for a system like mine.

Currently I have this amp driving a pair of Morel Maximo 6s on channels 1 & 2 and a single 12” Alpine Type R as a 4-ohm load to the sub channel. Channels 3 & 4 aren’t being used and I’m running the Morels at the lowest crossover frequency, 50 Hz, with the sub around 70 Hz. I listen to a wide variety of music and this amp hasn’t let me down. It’s loud and clean without being harsh, never sounds strained and often I don’t realize how loud the system is as it is so clean. The amp does what it should – disappear and let the music play. Whether it’s jazz, rock, rap, dubstep or Focal test discs the amp is a pleasure to listen to. As it isn’t heavily loaded and I typically drive less than 30 minutes (often less than 15) I’ve never had issues with the amp getting hot and I wouldn’t expect it too under these conditions. 

Initially, I thought I was getting 350 watts to the sub but recently found out it’s only doing 200 watts – I haven’t (won’t) clamp it but I’m confident the amp is doing at least rated power. I have been impressed with the bass output, especially given its only 200 watts, as the Alpine is in a small (0.9 cubic foot) sealed enclosure however this is the older (gray) Type R where 200 – 500 watts was the recommended range.

Amp is class A/B (all channels)
100 watts x 4 into 4 ohms plus 200 watts x 1 into 4 ohm sub
150 watts x 4 into 2 ohms plus 300 watts x 1 into 2 ohm sub
300 watts x 2 into 4 ohms plus sub channel

I haven’t found a bench test for any of the newer Zapco amps and it doesn’t come with a birth sheet but am comfortable it’s producing at least rated power. While the specs don’t indicate whether the numbers are on 12V or 14, I did a simple test with a VOM. Playing bass heavy Sail by Awolnation (Omega Remix) at normal listening volume I got 36.1 volts (AC) at the sub. Of course this isn’t clamped or controlled like other tests, and I don’t know the speaker’s impedance at this voltage. If I could find the impedance curve for the driver in a sealed enclosure I could test using sine wave for a better idea, however I wouldn’t know if the amp was clipping so it still would be an estimate. 36.12 / 4 = 325 watts, even figuring that 32v is cleaner that would still be 256 watts so I’m confident it’s doing rated power. I didn’t test the main channels but certainly could and while it would be easier to hear clipping it might be 2 – 3% before I hear it.

*Pros:*
*Sound quality* – transparent, handles bass well without taxing and doesn’t struggle with wind instruments and female voices. In my experience, many amps can run out of headroom and sound terrible with this type of material at high volumes.

*Build quality* – Amp feels solid inside and out. Quality components and beefy RCA connectors. Power and ground easily accept 4 gauge but anything larger would be a challenge.

*Price* – Woofers Etc. sells this amp for $299.95 indicating full retail is $549.99 – not sure if this retail is realistic or not. I remember Kicker used to provide dealers with a “retail” and a selling price so who knows. However, Woofers Etc. often sells this on Amazon for $269.99 and when I bought it was on sale for a week at $199.99. $269.99 is a great deal on this amp and worth every penny in my opinion.

*Speaker level inputs* – Channels 1, 2, 3, and 4 have high-level inputs although the sub channel does not. The amp has the ability to monitor for signal on the high-level to initiate turn on without a dedicated remote lead.
Built in crossovers – Channels 1/2 and 3/4 can be electronically crossed, either over high-pass or low-pass from 50Hz to 250Hz.


*Cons:*
Published specs (power? Crossover parameters?) - As I mentioned above, the actual specs on the amp are not what I initially thought and working with Zapco there was a disconnect between marketing and engineering when the amp was revised (this is the second iteration). Published specs are still varied, even on Zapco’s site, and I know that the company has been going through changes in ownership and distribution so this may be expected. Also – I assume the crossovers are 12 Db Linkwitz-Riley but I’m waiting on confirmation.

*Customer Service* – more from John on forums than company as I’ve sent several e-mails to Zapco that haven’t been acknowledged. Also seems that their phone number isn’t published and known numbers were disconnected when I called last year.

*Limited crossover* – Built-in crossover is nice but the high-end is limited to 250 Hz (no multiplier) and there’s not a band-pass option. If I wanted to go active I would need to purchase an external crossover.
No bass control – Not a deal breaker but remote volume for the sub would be nice. I’m adding an AudioControl OEM integration unit to get this functionality.

*Speaker sensing turn-on* – While this works >90% of the time, it has some quirks: once in a great while when I put my vehicle in reverse the amp will shut down until I restart the car. Also – I sometimes need to start the car to get the amp turned on then I can kill the engine – this isn’t a big deal as I always have the engine running but it’s a quirk.
AM alternator noise – This may very well be the HU’s fault – I have no engine noise unless listening to AM radio.

-Eric

*Pictures:*


----------



## jijivs (Mar 26, 2016)

Thanks for the nice review. Infact the model us st5x ii, which is second generation. I'm using st5x, the previous generation model. As you had put and pos, I would like to add few cons. 
1. The amp sub channel can't drive 2 ohms continously. So the effective output is 220w to 240w at 4 ohms.
2. The rating for channel 1 to 4 will be under 80w per channel (it is around 65w in st5x). Zapco power specified in portal, manual ate all confusing. 
3. Subwoofer wired remote provision could have made it a complete package. Especially for customers like me who uses factory head unit, where there in no way to adjust sub level on the go.

Sent from my E6553 using Tapatalk


----------



## llebcire (Nov 17, 2016)

jijivs said:


> Thanks for the nice review. Infact the model us st5x ii, which is second generation. I'm using st5x, the previous generation model. As you had put and pos, I would like to add few cons.
> 1. The amp sub channel can't drive 2 ohms continously. So the effective output is 220w to 240w at 4 ohms.
> 2. The rating for channel 1 to 4 will be under 80w per channel (it is around 65w in st5x). Zapco power specified in portal, manual ate all confusing.
> 3. Subwoofer wired remote provision could have made it a complete package. Especially for customers like me who uses factory head unit, where there in no way to adjust sub level on the go.
> ...


Thanks for your input!

I agree that Zapco's website, retailers' websites and the actual owner's manual are confusing for this amplifier. I worked directly with Zapco for the specs on the second generation ST-5X II and was told the power supply was beefed up and the new amp does 100 x 4 into 4 ohms (150 x 4, 300 x 2) and the sub channel is 2 ohm stable at 300 watts continuous power. 

I also updated my original post calling out the amp is a series II - thanks for pointing that out!

-Eric


----------



## TxHouse (Nov 7, 2010)

This review couldn't have come at a better time. I am researching for my next build and this amp is one of the one's I am considering but like you I hadn't heard anything on it. It is nice to know that it appears to do above published specs. 

Well written review.


----------



## llebcire (Nov 17, 2016)

TxHouse said:


> This review couldn't have come at a better time. I am researching for my next build and this amp is one of the one's I am considering but like you I hadn't heard anything on it. It is nice to know that it appears to do above published specs.
> 
> Well written review.


Thank you!

I would purchase again as I'm that impressed with the amp. Take my experience with a grain of salt as I'm not driving the amp very hard and as always your results may vary ☺.

-Eric

Sent from my SM-G930R4 using Tapatalk


----------



## Mic10is (Aug 20, 2007)

Ive been very impressed with the STX amps. Some of them actually use 5532 Opamps which are quite nice audio opamps used in much much more expensive "high end" amps.

compact size and decent power. 

hard to beat for the money or even more


----------



## jijivs (Mar 26, 2016)

*Re: Personal Review: Zapco ST-5X II Amplifier*

Yes, the amp has got decent sq, and will satisfy as long as you are not a power hungry.

Sent from my E6553 using Tapatalk


----------



## makinsparks (Feb 17, 2017)

I bought one of these a few months ago when it was $199. I haven't hooked it up yet. I have emailed Zapco twice, both times with very quick response from John. Yes, the 5xII is 2 ohm stable @350w sub channel. And, no x-over multiplier. He said it was designed for use in a 4 channel passive component system. I am going to use it as a 2 way active with mini DSP 2x4. Remote bass knob would be nice.


----------



## jijivs (Mar 26, 2016)

makinsparks said:


> I bought one of these a few months ago when it was $199. I haven't hooked it up yet. I have emailed Zapco twice, both times with very quick response from John. Yes, the 5xII is 2 ohm stable @350w sub channel. And, no x-over multiplier. He said it was designed for use in a 4 channel passive component system. I am going to use it as a 2 way active with mini DSP 2x4. Remote bass knob would be nice.


The prev gen st5x is not stable at 2ohms for sub. The installer, who is the official importer too clearly told me to go for 4 ohms at sub. That was the only small let down. A sub level control in the form of wired remote could have been icing on cake!


Sent from my E6553 using Tapatalk


----------



## bassfreak85 (Jul 26, 2009)

very nice layout. looks like a STEAL at that price..


----------



## llebcire (Nov 17, 2016)

makinsparks said:


> I bought one of these a few months ago when it was $199. I haven't hooked it up yet. I have emailed Zapco twice, both times with very quick response from John. Yes, the 5xII is 2 ohm stable @350w sub channel. And, no x-over multiplier.  He said it was designed for use in a 4 channel passive component system. I am going to use it as a 2 way active with mini DSP 2x4. Remote bass knob would be nice.


When I bought the amp it was $199 as well - and Amazon was offering $70 credit to sign up for their credit card so it was under $130.

My information is from John as well stating 200 watts into 4 ohm and 300 into 2.

-Eric


----------



## llebcire (Nov 17, 2016)

jijivs said:


> The prev gen st5x is not stable at 2ohms for sub. The installer, who is the official importer too clearly told me to go for 4 ohms at sub. That was the only small let down. A sub level control in the form of wired remote could have been icing on cake!
> 
> 
> Sent from my E6553 using Tapatalk


Once I learned it wasn't 350 watts I started thinking about finding a dual 4 ohm version of my sub to get the extra power. I'm not sure it would be worth it as going from 200 to 300 watts (rated) might be slightly audible, however I think the gain would be in the overall power of the sub and not volume, at the expense of more heat and wear and tear on the amp. As it sits now the sub can overpower my mids/highs so unless I find a deal on a replacement sub I'll stick to 4 ohm.

-Eric


----------



## jijivs (Mar 26, 2016)

*Re: Personal Review: Zapco ST-5X II Amplifier*

I'm using audiofrog g12 (dual 2 ohms in 4 ohm wiring), so far so good. 

Sent from my E6553 using Tapatalk


----------



## llebcire (Nov 17, 2016)

*Re: Personal Review: Zapco ST-5X II Amplifier*

This thread is short enough I'm uploading pics through Tapatalk after they were broken by Photobucket's change.

-Eric









































































Sent from my SM-G930R4 using Tapatalk


----------



## Victor_inox (Apr 27, 2012)

That is well build amplifier for 270 bucks.


----------



## Civicx (Sep 15, 2017)

I recently purchased this amp and I am getting a slight hissing in my tweeters and mids when the amp is on, regardless of the car being on or off. It has to be the amp because I did a direct swap from a PHD 4060 amp that had a bad rca. You couldn't hear any hiss- noise through the speakers when that amp was on what so ever. The Hiss is not variant with head unit volume and the gains are set to 0 for each channel. Does anyone think the amp could be faulty? Or if it's just the way it is.


----------



## Civicx (Sep 15, 2017)

I had recently purchased this amp that replaced a PDH 4060 amp with a bad rca. It was a direct swap. My concern is, the Zapco amp has a hissing noise through the speakers when on, and the phd amp was silent. The car does not have to be running for the noise to be present. The hiss is at a constant volume, not variable by headunit volume. Does anyone think this amp could be bad, or is that just the way it is?


----------

