2. amps-preamps
  3. 140029-80294

Does anyone care to ask an amplifier designer a technical question? My door is open.

I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.

I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer.
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Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.

I like to tell true stories of my experience with others in this industry.

I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.

On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.

I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.

Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.


128x128ramtubes
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almarg
9,670 posts
 
Ramtubes 12-26-2018

daveyf:
first the swapped polarity from amp to speaker does no harm and most will not hear any difference as long as the swap is the same on both sides. All you have done is invert absolute phase which has been a point of contention for many years.

As to one speaker not playing. probably just a loose wire.

Roger, see my lengthy response to Davey dated 12-22-2018, as well as Davey’s original statement of the question on the previous day. I believe that he did not simply invert absolute phase, but instead he caused the high and low frequency sections of the speaker to be driven with opposite polarities. On the speaker that was producing sound, that is. That would of course have adverse sonic consequences, while not causing any damage.

On the speaker that was not producing sound a loose connection is one possibility, but another possibility (which I cited in my post) is that he was applying the + output of the amp to both the + and - terminals of one section of that speaker, and the - output of the amp to both the + and - terminals of the other section of that speaker. Which of course would result in no sound (and no damage), since no voltage difference would be present between the + and - terminals of each section of the speaker.

Regards,
-- Al
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almarg
9,670 posts
 
@Jafox, to add to the responses Roger and Ralph have provided to your question, fyi I believe that as a special order item Cardas can supply XLR-female to RCA-male adapters that leave pin 3 unconnected, rather than shorting it to ground (pin 1) as is done by most such adapters.

Regards,
-- Al
ieales's avatar
ieales
1,201 posts
 
@ramtubes
preamp is balanced via electronic buffers. We don’t want to short those.
Depends on the circuit design. A lot of pro gear has IC balanced outputs that can short either leg to Gnd and the output acts single ended, driving no current into the shorted leg.

However, as Roger said, if you don’t know the output is single ended capable, only use one leg.

AND if using balance lines, only connect the screen at the driven end. A shield grounded only at the receiver forms pair of low-pass filters for common-mode noise
atmasphere's avatar
atmasphere
11,901 posts
 
Ralph, couldn't he use a Jensen transformer to make he XLR to RCA change? Would it still offer the proper grounding?

Yes.

Okay, does atmasphere believe that power cables can make huge differences in an amplifier’s sonic performance and why?
I don't use the word 'believe' because I made the measurements which showed that the power cord **without question** can affect the amplifier's performance. The measurement is easy- the voltage drop from one end of the power cord to the other. Its not rocket science and its not mumbo jumbo woo. Anyone with a 3 1/2 digit DVM can do it. After you know what the voltage drop across the cord is, then measure the resulting differences in the amplifier: output power, distortion and output impedance. You will find that they all change. So by this simple means you have a tool to correlate with what you hear.
So in a nutshell, I don't believe it, I **know** it.
jetter
3,043 posts
 
Hi Ralph, please put your statement above into perspective for us non electrical savvy persons.  Would a "normal" power cord supplied with a piece of gear have enough excess power passing capacity so that any drop in voltage due to the cord, is from one satisfactory voltage to a lesser, yet still satisfactory voltage to power the unit?  Or are you saying that the power cords supplied with a piece of gear could be starving the unit for power and maximum performance?
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