Hagerman Bugle2 DIY Kit Phono Preamp

[LTig]

What is an "active" 47k load??

It's described in Douglas Self Small Signal Audio Design in the chapter Electronic Cartridge Loading for Lower Noise. You replace the physical 47 kOhm resistor by an op amp driven (electronic) load which creates less Johnson noise than the physical load.

 

[LTig]

Distortion is very much under control but one channel is a lot more noisy than the other. I tried different grounding schemes but did no good (red channel). That pushes the SINAD for that channel way low. The other channel has lower noise but major spike at mains 60 Hz which reduces its performance as well

These are the specs:

• 40 / 50 / 60 dB gain (1kHz)
• 47k / 680 / 100 ohm input impedance
• 330 ohm output impedance
• +/-0.5dB RIAA accuracy (30Hz to 30kHz)
• 10Hz to 1000kHz bandwidth (-3dB)
• 82dBA signal-to-noise (ref 5mV)

The measured unit is wired for 40 dB gain, but it does not meet them WRT S/N and RIAA accuracy. I wouldn't mind the latter because it's only at the frequency extremes while it's very flat between 50 Hz and 10 kHz.

Looking at the schematic this preamp uses a passive RIAA correction which is a typical audiophool implementation with problems (headroom) and nothing to gain. Nevertheless it does not explain the difference in S/N between the channels - it must be broken somehow. I remember when I bought my Mackie 1402 VLZ mixer one of the channels was noisier than the others and I got it fixed on warranty.

 

[audio_tony]

There seems to be a "rumble" filter to remove low frequencies which is probably wise.

This is probably the IEC amendment to the RIAA curve.

https://en.wikipedia.org/wiki/RIAA_equalization#IEC_RIAA_curve

 

[Nango]

Yeh, that is a major concern of mine.

First one to be tested: HD 800??

 

[mhardy6647]

I had one of these on loan for quite some time from a gracious & generous member of the Polk forums.
I was most favorably impressed with it.

Thanks for checking it out. I think it's hard to beat for the $

Heck, in a box here, someplace, I have a "Bugle 1" (so to speak), a (Hagerman) power supply for it, and Hagerman "Piccolo" MC head amp.

audioXpress, long ago, fairly raved over the original Bugle in a test of cheap phono preamps.

https://web.archive.org/web/20060626131832/https://audioxpress.com/reviews/media/403hansen2090.pdf

 

[Labjr]

I'd like to see the Pass Pearl 2 measured. However, they're all DIY so results could vary.

 

[mhardy6647]

I've gotta say -- when youse guyses talk about Johnson noise -- my inner twelve-year-old starts snickerin'.

 

[AudioTodd]

Yeh, that is a major concern of mine.

You‘re gonna have to beg for $$$ for full-time security!! LOL

 

[Digital Mastering System]

What is an "active" 47k load?? Amir's test rig has a nominal input load that shouldn't have caused any problems.
The Bugle2 has a 332 ohm build-out resistor, so I don't see issue. The noise performance is the noise performance.

The Bugle2 schematic is on the Hagerman website so it's easy to analyze. It's a straightforward setup with passive equalization. Nothing fancy and should be fine for most any phono application.

Dave.

Active 47k Load: See Doug Self "Small Signal Audio Design" 1st edition page 197. "Electronic Loading for Lower Noise".
With a SOA CMOS or FET opamp the predominate noise source in the circuit is the 47K resistor. Electronic loading uses a separate flat amp to keep the IV loading of the input the same but actually increasing the input resistor's value considerably. This rather counter intuitively reduces noise in the input circuit because the resistor noise source has the resistor's value as it's output impedance. As this resistor goes up in value the noise goes down because the other impedances in the input circuit shunt the noise away effectively. (The resistor is roughly 47K times the gain of the flat amp - Gain of 20 and R of 1 Meg seems common.) Put 1Meg as loading into your input circuit and calculate the noise - you'll see it it's much lower than the 47K by itself. From the point of view of the phono cartridge this amp and 1Meg still looks like 47K.

I have used this technique in tape head preamp designs and know it's very effective and easy to do. It works great. I consider it engineering malpractice not to use it in phone preamps frankly.

 

[patient_ot]

Curious what went wrong here. Hagerman seems like a bright guy but I never understood why he choose the cheap plastic cases. The only justification I could think of was to keep costs down. The noise level between channels is significantly different - I would wonder if the unit was broken. Would be interesting for someone to send in the current version of the Bugle and see if it is improved in any way.

I notice that Hagerman does not publish a THD spec, which is curious...I wonder what test equipment he used to come up with his stated specs.

 

[dachada]

With this phono design the noise change a lot depending the opamp used. Looks to me one of the opamp is out of specifications or a problem with one resistor

 

[theglobalelite]

I noticed my new Denon X4700H has an input labelled "Phono" and now I'm a bit curious vinyl-curious. I've never owned any vinyl or turntables and it looks like it might be fun endeavour (I promise not to go crazy). Would this device or any other phono-preamp be a upgrade to the Denon's phono-in, or is it for systems that don't have an AVR with that input?

 

[P_M]

Phono Stage Measurements
Here is our usual dashboard with 5 millivolt input:

View attachment 78084

Strange measurement, but unexpected nonetheless, its a fine preamp. What did you power it with ? AC ? DC ?
And if there are dip switches are they set identically for both channels ?

Or there's a defect in the power supply section on the board.

 

[AnalogSteph]

Could be as simple as a bad solder joint in the vicinity of R1 or R3.

I've gone through this design before. It's kind of neither fish nor flesh:

The LM4562 has higher input current noise than you'd really want in an MM preamp, so you're going to see higher than average high-frequency noise with a real MM cartridge, and feedback resistors R3/R4 are chosen higher than they would have to be for this opamp with fairly good output driving capabilities, compromising low-frequency noise.
Input filtering is basic, but at least you can install your own choice of input capacitor instead of R23 to match the cartridge / cable combo for best frequency response flatness.

At the same time, when configured for 60 dB the thing is at least 10 dB noisier than an average competent MC preamp (let alone a good one, at which point you can probably add another 6-10 dB). Neither opamp voltage noise level nor resistor values are terribly ideal for this usage. (Gain being spread evenly across all 3 stages does not help.) It probably would have been a good idea to expend an extra two transistors and a couple passives per channel for an (optional) MC prepre, the way a number of other designs are doing it.

It would be interesting to have a graph of maximum output level vs. frequency for both an amp like this and a regular "active EQ" design.

 

[audiopile]

Bought Bugle 2 board years ago off one of the used audio sites -these got lost in the future midden heap (aka office). Found and gave them to a buddy -he stuffed it and soldered the stuffed parts to the board and to my old nun handles - this thing is a absolute pleasure to listen thru. This is a "2" -I've never owned or listened to a 3 . I've run a Decca London Gold into it , some AT carts and at various times SUT's from AT ,Denon ,Ortofon and Sony - again- a pleasure to play music thru and that's all I can ask of anything that's part of the signal chain.

 

[milosz]

Does anybody here know why passive RIAA EQ has gained such admiration in audiophile circles? Is it because of the "negative feedback is always bad" superstition?

 

[Labjr]

What about a DSP phono stage? No noise, ruler flat EQ curve.

 

[audiopile]

You mean like the Parks Puffin - that came in Monday and I still haven't had time to set up and use . ARGHH

 

[Digital Mastering System]

Does anybody here know why passive RIAA EQ has gained such admiration in audiophile circles? Is it because of the "negative feedback is always bad" superstition?

As an engineer, I'd say that a single opamp stage can do the RIAA EQ with feedback. So a multistage ''passive" EQ has more feedback really. More GBW product. More stages, more feedback, less distortion. But as a practical matter, I suspect the passive approach is snake oil to some extent.
To me the topology doesn't matter. What matters is overload margin, noise, and distortion of the final design. Show me how a passive stage is better in any of these aspects and I'll consider it.
And to the Labjr comment about a DSP phono stage - yes great idea if your A/D was perfect and of exceptional dynamic range - but A/D are not great and typically much worse tham D/As so it's really best to do your RIAA EQ before the A/D/. The DSP post processing can of course fix any small EQ errors that you might be left with...

 

[Labjr]

You mean like the Parks Puffin - that came in Monday and I still haven't had time to set up and use . ARGHH

Not for purists, although most vinyl records are now being produced with digital masters. IMO, you're better off with Hi-Res files and a good DAC than all that A/D/A/D/A conversion.