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The best phono preamp under $1000 (aka the Hagerman Bugle upgrade thread)

Actually, my advice was wrong- or at least unnecessary. Generally I use a second or higher order roll off to deal with potential RF problems, staggering the poles over 100s of KHz to not significantly effect the RIAA compliance
The Hagerman design is not as egregious as many others and an extra pole is not really necessary. (At least if OPA2210s with their lower gain bandwidth product are used. The high closed loop gain of the three stages acts as de facto causes of frequency roll off in the amplification stages)
 
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wyn palmer said:
Using opa1612s will extend the bandwidth to several MHz and extra roll off should be provided, in my opinion.
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I know this doesn’t make sense but something is telling my ears that 3 1612s don’t “sound “ as pleasing as 1 1612 with 2 2210s.

Similar to what is said w Acrux White paper?
 
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desertrat748 said:
Honest question; does the Neumann design cause problems? I don’t know anything about design but wondering why Jim would use it if it was a bad idea?

What happens when you make your suggestions as to the performance of the bugle2?

DR
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In real world listening tests it may or may not be noticeable. It might be worth experimenting to see if you notice a difference.

Jim Hagerman is or at least used to be a fan of the Neumann or Allen Wright pole.
http://www.hagtech.com/pdf/riaa.pdf

Many of the articles I've read on the subject conclude that it's just not necessary to implement.

Here's Douglas Self's thoughts on the subject from his book Small Signal Audio Design:
The ‘Neumann pole’
The RIAA curve is only defined to 20 kHz, but by implication carries on down at 6 dB/octave forever. This implies a recording characteristic rising at 6 dB/octave forever, which could clearly endanger the cutting head if ultrasonic signals were allowed through. From 1995 a belief began to circulate that record lathes incorporated an extra unofficial pole at 3.18 μs (50.0 kHz) to limit HF gain. This would cause a loss of 0.17 dB at 10 kHz and 0.64 dB at 20 kHz, and would require compensation if an accurate replay response was to be obtained. The name of Neumann became attached to this concept simply because they are the best known manufacturers of record lathes.

The main problem with this story is that it is not true. The most popular cutting amplifier is the Neumann SAL 74B which has no such pole. For protection against ultrasonics and RF it has instead a rather more effective second-order low-pass filter with a corner frequency of 49.9 kHz and a Q of 0.72 [19], giving a Butterworth (maximally flat) response rolling-off at 12 dB/octave. Combined with the RIAA equalisation this gives a 6 dB/octave roll-off above 50 kHz. The loss from this filter at 20 kHz is less than -0.1 dB, so there is little point in trying to compensate for it, particularly because other cutting amplifiers are unlikely to have identical filters.
 
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wyn palmer said:
The simulations agree with this,
View attachment 2710575

the bump at the end is the "Neumann pole" which assumes a characteristic for the lathe cut off filter (order, type and frequency) which is rarely followed in practice and is usually chosen to not be implemented these days- for good reason. I don't include it.
However, implementing the 75us has to take into account the shunt resistance that is R12 plus R13 in series, and is actually maximally flat with a value of c. 8.82k (NOT 7.5k) with the other Rs nominal.


View attachment 2710581
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Just to clarify, is the second graph with R10 = 8.82K and R11 shorted or swapped for a jumper?
 
WizardWG4 said:
Thanks. The reason I ask is based on my RIAA calcs, 8.82K with 10nf works out to 1,804Hz for f3.

Baxandall used a similar approach for the 75us time constant with 750 ohm and 100nf.

View attachment 2710799
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As I tried to point out the effective resistor in series with the shunt cap is NOT the 8.82K but the 8.82k in parallel with 47.5k in series with 332ohms.
Are you a EE? Are you familiar with the concept of superposition?
That's why the sims turn out to be correct.
 
wyn palmer said:
As I tried to point out the effective resistor in series with the shunt cap is NOT the 8.82K but the 8.82k in parallel with 47.5k in series with 332ohms.
Are you a EE? Are you familiar with the concept of superposition?
That's why the sims turn out to be correct.
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I think I'm following you now thank you.

I'm not an EE. Just a guy who studied way too many phono preamp schematics during quarantine. I guess I found it more interesting than baking sour dough bread or watching Tiger King.

I'll definitely read up on superpostion. Thanks!
 
WizardWG4 said:
I think I'm following you now thank you.

I'm not an EE. Just a guy who studied way too many phono preamp schematics during quarantine. I guess I found it more interesting than baking sour dough bread or watching Tiger King.

I'll definitely read up on superpostion. Thanks!
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You got me at “watching Tiger King” ! Well played sir. Well played indeed!
 
WizardWG4 said:
I think I'm following you now thank you.

I'm not an EE. Just a guy who studied way too many phono preamp schematics during quarantine. I guess I found it more interesting than baking sour dough bread or watching Tiger King.

I'll definitely read up on superpostion. Thanks!
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All it really means is that there are, in effect, two voltage sources (well, actually three as the branch with the cap to ground is also effectively a voltage source) that combine at a node, each of which has its own output impedance. As a result the output impedances are in parallel and the output voltage is the combination of the two sources each of which is ratiod by the source impedances. One just happens to be zero volts, which makes it easy.
 
Is anyone going to try the mods on the B2? I’m sure hoping that someone has one that are willing to try. Obviously it’s going to take a minute but it’s possible that some have an old Bugle2 laying around and perhaps a few caps too.

From however my ears are tricked, I really believe that c5 with silver mica, and perhaps a Vishay 1822 220nF at c4? will make some heard changes. Dare I mention adding the Vishay 10nF 1837 in parallel at c4? I don’t want anyone’s blood pressure to get as bad as mine.

I don’t know what outcome will happen with the stock op amps and c4, c5, c6 changes. I am partial to not doing anything much else to c6 other than a Vishay 1822. Oranda did the XO swap there I believe and if I remember correctly, wasn’t a bad idea but I defer to him for proper reporting.

Looking forward to those who try some of suggestions are whatever they find.

DR
 
WizardWG4 said:
I think I'm following you now thank you.

I'm not an EE. Just a guy who studied way too many phono preamp schematics during quarantine. I guess I found it more interesting than baking sour dough bread or watching Tiger King.

I'll definitely read up on superpostion. Thanks!
Click to expand...
https://www.dropbox.com/s/qlqwoalnysuxysb/whitepaper (2).pdf?dl=0
You might find the above interesting reading as a not too technical description of a different phono stage approach, unless you have developed a taste for sourdough.
 
desertrat748 said:
Is anyone going to try the mods on the B2? I’m sure hoping that someone has one that are willing to try. Obviously it’s going to take a minute but it’s possible that some have an old Bugle2 laying around and perhaps a few caps too.

From however my ears are tricked, I really believe that c5 with silver mica, and perhaps a Vishay 1822 220nF at c4? will make some heard changes. Dare I mention adding the Vishay 10nF 1837 in parallel at c4? I don’t want anyone’s blood pressure to get as bad as mine.

I don’t know what outcome will happen with the stock op amps and c4, c5, c6 changes. I am partial to not doing anything much else to c6 other than a Vishay 1822. Oranda did the XO swap there I believe and if I remember correctly, wasn’t a bad idea but I defer to him for proper reporting.

Looking forward to those who try some of suggestions are whatever they find.

DR
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I recently picked up an AudioWind A300 clone of the Bugle which I have yet to hook up and try.

I'll eventually mod and report back but it could take awhile. Too many other projects in the mix right now
 
WizardWG4 said:
I recently picked up an AudioWind A300 clone of the Bugle which I have yet to hook up and try.

I'll eventually mod and report back but it could take awhile. Too many other projects in the mix right now
Click to expand...

I’m with you. Outside stuff today Building doors, from scratch. This one is harder than I thought.
 
wyn palmer said:
One other thing, the WP design- which uses these metrics to guide the design choices- has been extensively tested in comparative listening sessions versus many different phono stages, including some extremely expensive ones, and has performed well, generally being preferred- at least by those who are not wedded to tube designs where the odds are 50-50 at best. It seems that having extremely tight RIAA compliance and distortion that is below the audibility threshold over the entire audio range together with very low noise does seem to provide a neutral presentation and extremely good retrieval of detail without false brightness.
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You've been working overtime to let us know how great your phono preamp is, but I have yet to see a link or website where I can:
A. Find specs and background info on it, and
B. Order it (completed, as a kit, whatever you offer.)

I'm sure people would be interested in reading about and possibly ordering it.
 
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