The Truth Pre Amp Review

[KSTR]

The only real point of objection is the safety stuff, the high risk of something really going wrong here. Pretending touch safety with a 3-prong connector and metal chassis is really the worst thing you can do.

 

[Francis Vaughan]

A few other odd thoughts about this device.

The amp is DC coupled end to end. Users should perhaps at least be warned this is the case.
The buffer amps are a single device. As in there are no passive devices other than the power supply bypass caps. The entire buffer circuit is inside the IC. A quick search brings up the Calogic LH0002 as the likely integrated circuit chosen. The bypass caps are badly chosen. In the usual ignorant audiophile manner very large capacitors have been chosen. This misses the point about why the data sheet will have suggested a much lower value. The inductance of big electrolytic caps will basically make then useless at high frequencies, and these buffers are good to 50MHz. There is a very real danger that the buffers will be unstable at RF. With the various bits of interconnections flapping in the breeze* and zero care taken on layout there is a good chance there is potential for RF instability.

Now to the value proposition. The buffer chips might run you change out of $10 each. So $40.
The power supplies are basic Meanwell. Even if you option out dual supplies you are not up for much more than $40.
The connectors are panel mount, but otherwise nothing special. Lets be generous and allow $20.
LDRs and regulator for volume control $5
The knobs are parts bin. $2.
The case is a cheap extrusion parts bin. $20 tops.
The pots are Alpha brand cheap but OK. $3 maybe.
Wire, $2 and that is being generous.
IEC socket and ground lift switch another $3.
PCBs, $5, and that is really generous.

I get a BOM of about $140.
These are the sorts of prices a hobby builder would pay, there is no volume discount or the like. Anyone could build one for this money. A volume builder would be doing significantly better. Given the hand-build and volumes likely, these are the prices I expect are actually paid.

If it took anyone more than 2 hours to assemble that I would worry. Given the appalling quality you would wonder how anyone would have the sheer effrontery to charge for that. I'm going to value labour as zero. Given the device has no distribution channel, the profit is totally with the vendor. So I'll let him pay himself out of the profit whatever he thinks he is worth.

By my arithmetic there is $900 made on each device.
A few forum comments claim that the rationale for the cheap knobs and lack of labelling is to keep costs down. There is one born any minute.

* since we are doing Dave Jones references

 

[manisandher]

Want to send those cables to Amir for testing so we can get more pictures of the headless panther?

I just picked the shortest cables I had in my cables bin to make up into XLR-RCA adaptors. If they're so bad, it should make identifying the Truth between the three tracks even easier .

Mani.

 

[egellings]

Why a switchmode power supply in a low current app like a preamp?

 

[GDK]

but also probably not going to hurt anyone

This may be the very definition of damning with faint praise...

 

[EchoChamber]

This pre amp is a joke, right? And that price tag!!?? Did you guys noticed how the front knobs and rear RCA inputs are not even horizontally aligned? I think everything is eye balled... LOL

For much less one can get a DAC/Pre with superb SINAD...

 

[Sir Sanders Zingmore]

@amirm it would be great if you could post them.
One of the usual objections raised is that these devices are never run at full volume so measurements done at full volume are irrelevant.
The claim is always that the measurements would be much better at lower levels. These claims are of course, never backed up by measurements, so it would be good if you could post them and put that myth to bed

@amirm any chance you could post those measurements?

 

[Jmudrick]

I don't imagine that Ed sells more than a couple of these a year. It's not exactly a current product, I bought one 11 years ago. At that time most all of his customers were listening to vinyl, most on his Hornshoppe Horns speakers with tubes, not exactly studio monitors but enjoyed by me for many years. Don't remember what I paid but not $1,000.

 

[amirm]

@amirm it would be great if you could post them.
One of the usual objections raised is that these devices are never run at full volume so measurements done at full volume are irrelevant.

I did post the SNR at two volume levels/positions:

But yes, I I have time I will do another measurement.

 

[Highvolt60]

Wait a minute this is June 1st not April 1st ?
Thought it was a joke when I saw it.
Looks like a poorly made home brew preamp.
Note the input and volume knobs are not at the same height.

 

[gvl]

Wait a minute this is June 1st not April 1st ?
Thought it was a joke when I saw it.
Looks like a poorly made home brew preamp.
Note the input and volume knobs are not at the same height.

The ugly truth, now we know the origin of this expression.

 

[H-713]

Why a switchmode power supply in a low current app like a preamp?

Those Meanwell power supplies are a simple and easy solution. A linear power supply would require the builder to design / build their own, or buy an off-the-shelf linear supply. Commercially available linear supplies (like the Power One products) tend to be rather pricey, so this solution makes sense.

 

[H-713]

This may be the very definition of damning with faint praise...

Pretty much. As I mentioned, it's not great, but "standard practice" from 50 years ago was probably worse.

 

[manisandher]

I was surprised that crosstalk was not frequency sensitive and not that good:

Seems like there is some coupling on purpose between the channels??? Strange.

I've used @pkane 's Deltawave to look at the difference the Truth makes in the loopback signal path... and it's not pretty:

Notice here that the PK Metric is 25dB worse with the Truth in the signal path.

The crosstalk is clearly evident in the difference files. Here they are (amplified by 30dB) for anyone interested in hearing how much further the Truth takes the signal from the truth:

https://drive.google.com/file/d/1bl5a04Y-EVWMbYCH7n3w3v3Mk0W2AWvb/view?usp=sharing

https://drive.google.com/file/d/1r9lIdSHTiCLJRnl3uaVfVhPA3N_kQuDM/view?usp=sharing

Mani.

 

[PipHelix]

I wonder why someone would make the decision to buy this at all. It’s not like there‘s some nice marketing page for it http://www.thehornshoppe.com/the_truth_pre_amp.html

Yikes! That website would’ve looked very impressive in ‘97 or ‘98. As a place to drop $1k in 2021, not so much.

 

[manisandher]

Hadn't looked at the website for a while, but just took a look now and noticed this:

"The Truth has a balance control that is not in circuit and the balance does not shift with volume changes ."

This is patently false. Setting the balance control to equal at -20dB attentuation, here's the difference between the right and left channels at varying degrees of attenuation on my Truth:

Att: Diff
0dB: +0.1dB
10dB: +0.3dB
20dB: 0dB
30dB: -0.6dB
40dB: -1.4dB

Something else caught my eye:

"As far as I know there is nothing like it available for any price.....I could be wrong but I doubt it."

Finally, some truth!

Mani.

 

[Francis Vaughan]

"The Truth has a balance control that is not in circuit and the balance does not shift with volume changes ." This is patently false.

Indeed. What is even more disingenuous is that it nullifies any claimed advantage of the LDR volume control. Looking at the device it is clear that the volume control is effected as an LDR in series with one leg of the balance potentiometer, with the wiper of the potentiometer grounded. The other channel is the same with its LDR going to the other leg of the balance potentiometer. For each channel the volume control output is taken from the junction of the LDR and pot. Varying either the pot or the light on the LDR will change the output volume. Easy. Except that there is a conventional cheap potentiometer in the volume control circuit. So much for the purity of the LDR volume control.

 

[KSTR]

Looking at the device it is clear that the volume control is effected as an LDR in series with one leg of the balance potentiometer, with the wiper of the potentiometer grounded. The other channel is the same with its LDR going to the other leg of the balance potentiometer.

That's how I see as well now you've pointed it out.

 

[manisandher]

Looking at the device it is clear that the volume control is effected as an LDR in series with one leg of the balance potentiometer, with the wiper of the potentiometer grounded. The other channel is the same with its LDR going to the other leg of the balance potentiometer. For each channel the volume control output is taken from the junction of the LDR and pot. Varying either the pot or the light on the LDR will change the output volume.

Does this explain the high channel crosstalk?

Mani.

 

[Francis Vaughan]

Does this explain the high channel crosstalk?

No. The only common point is the ground.

The crosstalk is possibly just due to the really high impedances likely to be found with the volume control and the high impedance input of the output buffer, all allowing the terrible layout to crosstalk. Just an idea, there is only so much one can guess. The whole thing is just a trainwreck of poor design.