John Curl's Blowtorch preamplifier

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janneman said:



How about this. Some of us are of the opinion that casual, anecdotal, uncontrolled listening is just that, a personal experience, that is only valid for oneself, an experience that, because of the many perceptive factors involved, can be very different for someone else even with the same equipment and music. In that perspective, my or your listening experience is irrelevant for someone else, so why should it be discussed and analysed here, unless this is a thread about perception.
Does that make some sense?

Edit: corrected spelling

Jan Didden


G.Kleinschmidt said:



ROFL

1) You evidently haven’t the slightest interest in understanding what other people are either saying or thinking and are far to wrapped up in pontificating your own point of view and subjectivist baloney, partly buttressed with the erection of straw man arguments to define what others allegedly say and think.

2) That freaking headphone issue was put to rest two pages ago but you can’t see the forrest for the trees. The reality is relatively mundane and nothing special, but the pollywaffle production continues unabated. :rolleyes:

3) As for my ignoring of your vague request for subjective equipment evaluations on my part, it has nothing to do with being “afraid”. Refer to (1)


You guys would be funny except that you are serious.

Jan, if you don't listen, or can't perceive any "differences" or don't have an opinion as to what you believe sounds "good" or "bad" to your ears, what the heck is your purpose in doing audio in the first place? Tell me, please.

Is it all just specs and measurements for you?
If so, that's ok by me, but at least leave it there.

This is most certaintly a thread about perception, this is about the Blowtorch preamplifier. That preamplifier is/was built and designed the way it was almost entirely due to the perceptions of what sounded best. We are engaged in discussing THAT unit's merits or lack thereof - which by its very definition must include and not exclude the sonic perception of the circuit and implementation when listened through by people with ears (and maybe brains too...).

I know that it is not lost upon you, Jan or Glenn, that you can buy a unit that has virtually identical circuit design, pick the vintage one(s), the cloned one(s), a copy you can make, or else the Halo version. What then is the difference? Are there any differences? Are they audible? Have any differenced been measured? Etc.

Glenn, your responses are shall we say unworthy of a person of your obvious abilities and training. Trying to remain polite, I am.

But since you are so clear on the "headphone thing" - explain it to me in a logical fashion, and dispatch it for once and for all.

The question remains for anyone to answer - can you or have you heard (make it simple here) amplifiers or preamplifiers sound noticeably different, or "GOOD or BAD", when they have been "properly designed and implemented" (ie. no obvious electronic or electrical flaws)??

Stand up and be counted!!

I'll start it off.

I have.

Your turn.

(yes, this is not scientific, engineering, or the like - this is a statement of personal perceptions and experiences only - there is no right or wrong answer)

_-_-bear
 

GK

Disabled Account
Joined 2006
bear said:
Jan, if you don't listen, or can't perceive any "differences" or don't have an opinion as to what you believe sounds "good" or "bad" to your ears, what the heck is your purpose in doing audio in the first place? Tell me, please.

Is it all just specs and measurements for you?
If so, that's ok by me, but at least leave it there.


Gasp! Surprise! From beneath the Everest of polywaffle another straw man shall arise!
 
The question remains for anyone to answer - can you or have you heard (make it simple here) amplifiers or preamplifiers sound noticeably different, or "GOOD or BAD", when they have been "properly designed and implemented" (ie. no obvious electronic or electrical flaws)??

This has been a difficult Equation for me lately (perception +
knowledge / pride) :) . After being "around the block" I find
that the very fact that I DIY'ed a piece of equiptment biases
my perception to it's quality.

The pride of touching the components that are not :hot:
burning and listening to something not made in china
can make the comparison very subjective. Destroyer X
has the best technique.. let kids or a non-diy'er (not one
of us) do the comparison.

The "headphone thing" can be very useful , listening
to the driver stage with headphones before final OP hookup can be very valuable (power amp wise). I have heard the
actual differences between devices , compensation,and
topology.

Good or Bad is subjective... some circuits are better suited
for different purposes.. A triple darlington is better for a sealed
high power HT sub (didn't need the kids to discern that),
I absolutely can hear it (I can still hear/feel LF good)
and it is backed up by the topology.

With a "properly designed and implemented" (no magic smoke
for 4 months 24/7 ):D .. amp or preamp , there is a difference,
(even the kids say so... with their 18khz+ "human bandwidth").
My opinion is that loudspeaker dynamics far outweigh amp
configurations (except for power output).

I did a crossover distortion test and the younger listeners could
hear it (distortion) on the speakers where I had to see it on a scope.:bawling:
I can't/ won't let my ears Have the final say because they are not
"up to spec" and nothing can change that.

Perception must be a group experience. Any one person (or
reviewer) will most certainly be biased by the room, speakers,
source, or even the color /price/preconception(origin) of any given design or product.
OS
 
alansawyer said:


I can't see a reason to connect it to other than PWRGND, at the point of the red dot, along also with the caps that are shown connected to PWRGND. Do you have reason to connect to SIGGND ?

Actually, the method shown in the image is the best one, regarding PSU related noise suppression. If you connect load to PWRGND (red dot), and signal ground remains as is, you get the worst possible result, which is shown in my previous time domain measurement. Current ripple of 500uF board caps is then directly added to output signal, voltage drop on R+L of the wire between SIGGND and PWRGND. These spikes shown previously.

The second best method is to connect both signal ground and load to PWRGND, i.e. typical starr ground. However, it suffers from noise, also HF noise, on inductances of long wires connected to PSU GND terminal. This is a usual DIY method, but not the best one.

My image is valid in case that both channels have independent power supplies (dual-mono). Use of only one supply is inferior and always leads to problems; direct groundloop or 10R resistors.
 
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bear said:
[snip]Jan, if you don't listen, or can't perceive any "differences" or don't have an opinion as to what you believe sounds "good" or "bad" to your ears, what the heck is your purpose in doing audio in the first place? Tell me, please.[snip] _-_-bear

Bear,

It is pretty impossible to answer this, because it isn't true. I don't know why you ask me this? I didn't say those things you mention, why do you pretend I did? Did you somehow misunderstand my post?
I know that it seems to be accepted tactic in politics that if someone says A, pretend he says B and then attack him on B, but do we need that here?

I noted that several persons rushed to agree with you. Am I to believe that they TOO didn't understand my post? Or maybe even didn't read it? Funny....

Jan Didden
 
AX tech editor
Joined 2002
Paid Member
ostripper said:


This has been a difficult Equation for me lately (perception +
knowledge / pride) :) . After being "around the block" I find
that the very fact that I DIY'ed a piece of equiptment biases
my perception to it's quality.

The pride of touching the components that are not :hot:
burning and listening to something not made in china
can make the comparison very subjective. Destroyer X
has the best technique.. let kids or a non-diy'er (not one
of us) do the comparison.

The "headphone thing" can be very useful , listening
to the driver stage with headphones before final OP hookup can be very valuable (power amp wise). I have heard the
actual differences between devices , compensation,and
topology.

Good or Bad is subjective... some circuits are better suited
for different purposes.. A triple darlington is better for a sealed
high power HT sub (didn't need the kids to discern that),
I absolutely can hear it (I can still hear/feel LF good)
and it is backed up by the topology.

With a "properly designed and implemented" (no magic smoke
for 4 months 24/7 ):D .. amp or preamp , there is a difference,
(even the kids say so... with their 18khz+ "human bandwidth").
My opinion is that loudspeaker dynamics far outweigh amp
configurations (except for power output).

I did a crossover distortion test and the younger listeners could
hear it (distortion) on the speakers where I had to see it on a scope.:bawling:
I can't/ won't let my ears Have the final say because they are not
"up to spec" and nothing can change that.

Perception must be a group experience. Any one person (or
reviewer) will most certainly be biased by the room, speakers,
source, or even the color /price/preconception(origin) of any given design or product.
OS


I agree with that.

Jan Didden
 
AX tech editor
Joined 2002
Paid Member
PMA said:


Actually, the method shown in the image is the best one, regarding PSU related noise suppression. If you connect load to PWRGND (red dot), and signal ground remains as is, you get the worst possible result, which is shown in my previous time domain measurement. Current ripple of 500uF board caps is then directly added to output signal, voltage drop on R+L of the wire between SIGGND and PWRGND. These spikes shown previously.

The second best method is to connect both signal ground and load to PWRGND, i.e. typical starr ground. However, it suffers from noise, also HF noise, on inductances of long wires connected to PSU GND terminal. This is a usual DIY method, but not the best one.

My image is valid in case that both channels have independent power supplies (dual-mono). Use of only one supply is inferior and always leads to problems; direct groundloop or 10R resistors.


Pavel,

One comment again: there is no explicit indication of the internal signal grounds of the amp block. Assuming that these signal grounds are also connected to the junction of load and source return, we are in total agreement. But, if that is the case, the label 'siggnd' is somewhat misleading, because it isn't.

Another point is that if you use a stereo chassis, and if you connect both channels as shown, there is an implicit ground loop via both source cable ground wires if the supply is common. Therefor, I prefer totally separated supplies. (Common transformer but fully separated secondaries, rectifiers and capacitors.

Jan Didden
 
janneman said:
Another point is that if you use a stereo chassis, and if you connect both channels as shown, there is an implicit ground loop via both source cable ground wires if the supply is common. Therefor, I prefer totally separated supplies. (Common transformer but fully separated secondaries, rectifiers and capacitors.
yes, 4 secondaries with 4 rectifiers allowing two floating power grounds, each connected to their respective Audio Ground.
Add disconnecting networks from each Power Ground to Safety Earth.

But, I have never yet been able to make this arrangement work as well as a true monoblock.
What else needs to be done? Or what am I doing wrong?
 

GK

Disabled Account
Joined 2006
janneman said:
Another point is that if you use a stereo chassis, and if you connect both channels as shown, there is an implicit ground loop via both source cable ground wires if the supply is common. Therefor, I prefer totally separated supplies. (Common transformer but fully separated secondaries, rectifiers and capacitors.

Jan Didden



That still does not get around the ground loop formed by the mains earth and back through the signal lead shield (unless the power amplifier supply is floating WRT the its chassis).


Cheers,
Glen
 
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G.Kleinschmidt said:




That still does not get around the ground loop formed by the mains earth and back through the signal lead shield (unless the power amplifier supply is floating WRT the its chassis).


Cheers,
Glen

I've done that, floating from the chassis. It often works, but you sometimes have RFI. One solution that *sometimes* work is to connect the signal ground to chassis via a 1nF capacitor, sometimes with 10 ohms or so in parallel.
I never have discovered a firm rule for this, but I have a couple of tricks and so far there's always one that does work ;)

Jan Didden
 
jacco vermeulen said:
Any reason why it couldn't be ?

Safety standards (i.e. EN60065). unless you have a "double insulated (Class II)" transformer you will need to connect some part that is conductively coupled to the power supply transformer secondary to the chassis.

This seems to cater for the condition where the psu transformer develops a fault that conducts mains power to the secondary and could make accessible parts (speaker terminals, input connectors) carry hazardous voltages.

Plitron http://www.plitron.com/medical_schematics.asp offer isolation versions suitablr for Class II double insulation that should allow this. You still need to be careful to "double insulate" internal mains conductors to switches connectors fuse holder etc.

OK, for DIY we are not, I assume, selling these things, but the standard is a good way of keeping ourselves and loved ones safe.
 
janneman said:



JPV,

I think it's almost impossible to map ground loop issues directly to audibility. As I see it, the best we can come up with is to map ground loop issues to hum, noise, distortion, stability, EMI susceptability etc. That in itself will be a tall order. Then, the next step would be to map the, say, increased noise or distortion to audibility, and I think that will be easier than the first step.

BTW Did you get my email on the TM5000?

Jan Didden

I agree. Therefore I asked for the experience people would have with some specific options, all other things beeing equal.

I recieved your mail. I will answer directly but I have a momentary timing problem that I hoped to be solved before proposing an appointment; I'll mail you

Cheers

JPV
 
PMA said:
... Current ripple of 500uF board caps is then directly added to output signal, voltage drop on R+L of the wire between SIGGND and PWRGND.

The second best method is to connect both signal ground and load to PWRGND, i.e. typical starr ground. However, it suffers from noise, also HF noise, on inductances of long wires connected to PSU GND terminal.

Useful point PMA, thanks for that. I will review my wiring!

Does this beg the question as to what improvement we get from the local caps on the amp board? And perhaps what capacitance value they need to be?
 
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AndrewT said:
Hi,
there is significant advantage to on board decoupling.
Choosing the wrong value or omitting can give rise to instability.

On board decoupling must not be connected to Signal Ground. It must have it's own Power Ground connection to the Audio Ground.


Andrew,

What do you mean by 'audio ground'? Is that not the same as signal ground?

Jan Didden
 
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