2. amps-preamps
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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.


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ramtubes's avatar
ramtubes OP
460 posts
 
@prof  And if burn in occurs in cabling, why don’t we see people producing these measurable results between a new and burned in cable? The suspicious thing is that when most cable manufacturers are hyping either the technical reasons why their cables produce better sound, or telling you the cables need burn in, they are always appealing to some objective, technical phenomena whose existence is known because it was measurable. "Here’s a technical problem with cables you need to know about, that we have solved via our manufacturing process!"



Nicely done all of it. To the part quoted the reason we dont see measurable changes is that there arent any. Of course the people who believe in burn in and such will just go to the default "well you cant measure everything".  If you measure the things we can measure they will stay the same. 

We all need decent cables, thats fine. Decent cables need not cost much and are very easy to make. Up until Monster came on the scene most people made their own speaker cables out of zip cord, which is an excellent choice, very low capacitance, resistance as low as you want just buy more copper. High capacitance speakers have been known to blow up SS amps as they cause the amplifier to go into oscillation. Ive seen a Levinson smoke.


ramtubes's avatar
ramtubes OP
460 posts
 
@grannyring  I have a technical question regarding a PP EL86 tube amp I am modifying. I would like to upgrade the power supply. The current power supply is very, very simple and while simplicity is good I think a more robust supply could help sound quality.

A couple of questions and these should also have application for many others here.

1) All filaments are AC heated! Not DC. No filtering, no rectifier....Love you hear your comments on this. Would converting to a CLC filter with possible voltage regulation be worth doing?

2) 5U4 rectifier Tube receives 350 VAC and post tube VDC of 476 with no load. The plate supply is a simple RC only. 100 ohm resistor followed by two 680uf electrolytic caps in series. This feeds the vintage Scott output trannys. If I wanted to add a choke where should it be placed and how do I determine the value correctly. Like to know how you would design the plate supply for this simple PP el84 amp.

I ask your opinion of SS voltage regulation on both filament and plate supplies. Is it something you regard as very important?

EL 86 is an interesting tube. I think of it as an EL84 with half the screen voltage so Ultralinear is generally out. What is the circuit like? Most people dont realize the screen supply is more important than the plate for hum. So how are the screens connected?

No need to DC heat power tube filaments, better not to. If you have hum in the front end DC heaters may fix that. 

The 5U4 is a good rectifier but does have a larger voltage drop than a cathode tube like a 5AR4. They put the 100 ohm resistor to reduce the plate peak current. Even a 5AR4 doesnt like to see more than 40 uF. All that information is on the data sheet. Tube rectifiers were useful in their day, I see no need for them now.

As to filtering, you really have only one cap and thus a fair amount of ripple. C L C filtering is the best and make the last C large so the bass can draw on it and not sag. There are lots of power supply emulator programs out there. Duncan Amps has a nice one. 

Regulation for filaments is easy so use a 3 terminal regulator for that. B+ regulation is difficult. Dont try to do too much too soon in the learning process.


ramtubes's avatar
ramtubes OP
460 posts
 
@ieales  More than once I've rejuvenated a system by re-plugging ALL connectors, both internal and external.

YES, YES, YES.  Ive fixed so many things just doing that. Flat screen TVs, my Sony ES player many times, Its used up 6 of its 9 lives. 

Its sad how many components, expecially CD players end up on the scrap heap that could be fixed in 10 minutes. Dont forget the ribbon running to the laser head. That one needs the most attention. Use some logic. If the player cant read a CD go for that one. If some of the display is out or buttons dont work go for the one going to the front panel. Its really simple and you have nothing to lose. CD players cannot shock you. Do unplug them however. (I dont). 

When I open a unit with lots of those ribbon connectors inside I know it has limited life. All connectors oxidize. Oxides also form rectifiers in the signal chain and distortion.  
bdp24's avatar
bdp24
9,874 posts
 
The old Polk Audio Cobra cables were a very high capacitance design, and caused some amps to become unstable.
krelldreams
128 posts
 
@ramtubes. 

   It is very likely that what I’m hearing with this preamp vs passive thing is a less than perfect passive, against preamp distortions which “smooth” the sound. I’d like to know more about your suggested solution to this issue, but contact outside of this discussion is probably best.

   I do have technical questions regarding cabling and AC outlet use though! I’m not excited about super expensive cables (I’ve tried many with very little in the way of difference), but there are electrical differences (capacitance, inductance) in wire. Also, there are different metals and connectors used. What should one look for in terms of material (copper, silver, etc), and electrical properties (capacitance, etc) when choosing wire?
 
  Regarding AC outlet use, how does one best work out the unavoidable need to plug various components into a two outlet wall plate? I had an electrician run a dedicated 30A, 10AWG line to the duplex behind my system location to isolate the stereo components, and to provide enough amperage for the amplifier’s initial turn on draw (it was tripping the 20A breaker). I have seven components that need power. I plug my power amp into one of the outlets, and a “high end” six outlet power bar to the other outlet. Is there something special, and necessary about power strips for stereo components? If so, what does one look for when choosing between them?
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