Hifi Preamps for your Record Player

By: skrodahl | November 23, 2017

Background

To see if the Burson V6 operational amplifiers are viable in the Muffsy Phono Preamp, I went ahead and bought the dual version of both the V6 Classic and V6 Vivid (*). They don't come cheap, about 20x the price of an OPA2134. Getting two of these instead of 40 OPAs for my kit stock was quite a difficult decision...

The Burson V6 Classic and Vivid (dual op amps)
The Burson V6 Classic and Vivid (dual op amps)

The op amps from Burson were delivered with cable ties. I have not been able to figure out why... ;)

I have both feet firmly planted in the objective side of things, so I decided to get the Burson's to do some measurements. I did listen to them in the gain stage of my headphone amp, comparing them with both NJM2068 and LM4562. They sounded pretty damn good (as in more or less indistinguishable from the others) in that scenario (both 2.5 and 6.5X gain), so I really don't feel fooled or anything.

The Burson V6 Classic in NwAvGuy's Objective2 headphone amp
The Burson V6 Classic in NwAvGuy's Objective2 headphone amp. A tower of DIL sockets were required to make the op amp fit.

JFET inputs are best suited for moving magnet cartridges. The Bursons do have JFET inputs. I would like my op amps to be able to run on +/-15 volts. The Bursons handle up to +/- 16.5 volts. The basics are covered, let's see what they're capable of.

(*) Yes, I did by them myself. They were not given to me by Burson.

Preparations

In my quest to measure the Burson V6 discrete operational amplifiers, I've established the measurement baseline and used the OPA2134 as reference.

I'll start with the Burson V6 Classic, and I'll have to visit the Burson V6 Vivid later. The V6 Vivid that I received appears to be defective. Burson kindly agreed to send me a new one.

I have shown that I can measure THD down to -117.5 dB / 0.00013%, Here's how the Burson V6 Classic fares.

The op amp is placed in a test rig with 1.36 dB gain. There is no filtering circuitry in the test rig. The input signal is -10.33 dBV, which is the level at which my audio analyzer performs the best.

Op amp test rig
Op amp test rig - A modified Muffsy PP-3

The plastic around the Bursons gets comfortably warm (not hot, but they would be perfect for warming my hands now that it's winter), and they need a minute or so to warm up before the measurements stabilize. This is taken into account when performing the measurement below.

THD Measurements

Burson V6 Classic - THD
Burson V6 Classic - THD

As it turns out, the V6 Classic is within the measurement limits of my QA401. Barely. The THD shows up at -115.8 dB / 0.00016 %

While the OPA2134 performed beyond the abilities of the audio analyzer, the Burson didn't. This shows that the V6 Classic can't compete with the OPA2134 when it comes to THD at low gain. Still, this is pretty respectable.


Based on the THD alone, they should be virtually indistinguishable from most "normal" op amps in the gain stage of a DAC, headphone amp, CD player and similar line level equipment. I won't be testing their output capabilities, but they're probably not suited for output directly to a headphone (and neither are more than 99% of the IC op amps).

By: skrodahl | November 23, 2017

Measurements on their own are no good unless they can be seen in relation to something. Having established the measurements baseline, I want to get an idea on how the preferred OPA2134 performs.

The conditions are the same as they were with the baseline setup, and the op amp is placed in a test rig without any filter circuitry. The gain is 1.36 dB.

I did actually get a better result than the loopback test, which has to do with the OPA2134's noise rejection. It shows a THD of -117.5 dB / 0.00013%.

This is obviously beyond what the QA401 can measure, and Texas Instruments claims that the OPA2134 has a THD of 0.00008%. It does show what the audio analyzer is capable of, which is very useful for the next measurements.

Measuring the OPA2134
Measuring the OPA2134

By: skrodahl | November 23, 2017

I've been asked about how the Burson V6 discrete operational amplifiers would perform in the Muffsy Phono Preamp quite a few times. They don't seem to have many published measurements, so I thought I'd give it a go.

To perform the measurements, I have a QuantAsylum QA401 audio analyzer. This will obviously not be measurements of datasheet quality, but I still hope I can find out if these op amps will work for the low signal levels from an MM cartridge. They have JFET inputs and work with up to +/- 16.5V power, which are two of the basic requirements.

QA401
The QuantAsylum QA401 Audio Analyzer

To get the very best results from the QA401, I followed the tips in this blog article. Using the R- output and the R+ input gives the best measurements. I tested signal levels to find what gave the cleanest output signal and the very best THD measurements, which was -10.33 dBV.

A loopback test on the QA401 shows that I get a THD of -116.5 dB / 0.00015%. Operational amplifiers have great noise rejection, so I might get somewhat better measurement results. It shouldn't be by much though, this is basically as good as it gets.

QA401 Loopback Measurement
QA401 Loopback Measurement

By: skrodahl | October 16, 2017

I've been getting my new hobby room ready, and I knew I needed some kind of stereo system in there. Preferably one that didn't annoy others in the house, so I ended up ordering PCBs from Nwavguy's gerber files. Yup, I'm gonna use headphones. :)

White o2 headphone amp PCBs

The components that I didn't have at home were ordered from DigiKey, and I ended up doing quite a few component substitutions. The cabinet + front and back panels were ordered from Headnhifi.

O2 headphone amp components from DigiKey
Empty O2 cabinet and panels from Headnhifi

I did spend a lot of time identifying the right components. There are a lot of different resistor values, and they have to be cross referenced with the BoM. Of course, it didn't help that I have a box with all E24 resistor values that aren't sorted in any way.


Once the sorting of components was done, it didn't actually take long to solder the thing. I'm really happy I got the recommended enclosure and panels. This thing looks really great.

O2 headphone amp, soldering done
Completed O2 headphone amplifier

Initial impressions are really good. My main problem (until the Sennheiser HD 600 headphones arrive) is that I only have an old pair of Koss PortaPro available. The foam around the earpieces is really old, and creates a cloud of tiny black dust...

Koss PortaPro headphones

By: skrodahl | August 31, 2017

YouTube user Blake G has posted a couple of vinyl-rips using the Muffsy Phono Preamp onto the video site. Although YouTube probably alters the bitrate, you can still get an idea on how the Muffsy Phono Preamp performs in his setup. His setup, btw, is:


    • Turntable: Sony PS-X500
    • Cartridge: Empire 999ve/x
    • Phono Stage: Muffsy PP-3
    • Line In: Behringer UCA202

Muffsy Vinyl-rip on YouTube

Here are the links to Blake G's two rips:

 
 

Category: News 

Tags: muffsy, phonostage, vinyl, youtube, rip 

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