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.


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almarg's avatar
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almarg
8,673 posts
 
Hi Ian (Ieales),

Surely you realize that pi squared, rounded off slightly, equals:

3.14 x 3.14 = 9.86

Best regards,
-- Al
geoffkait's avatar
geoffkait
14,147 posts
 
The real question left unanswered is what is pi squared factorial? 😳
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jdjohn
5 posts
 
@jdjohn   Any thoughts on kits like this modeled after the Dynaco ST-70?  http://www.tubes4hifi.com/bob.htm#ST70  This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.


Looks good. I like to see the 3 tube driver board. Do they have a schematic?

The original single 7199 tube driver was flawed by tube to tube variations. Some good 7199 would bias up in a region that actually produced a lot of distortion and reduced power. There are many 3 tube drivers. I would like to know more about theirs.

The kit looks good and priced well.
Here's a schematic of the ST-120 version (sans values for resistors and capacitors), which is apparently the same schematic as the ST-70 except for resistor sets.
https://drive.google.com/open?id=1IMaAaaWRuIU8v-_OZ3jfrcQCI5a0gpP8 
pryso
1,501 posts
 
And I thought the unanswered question was who wants the last piece of pie?
clio09
2,978 posts
 
We get requests from folks who want their old RM-9s refurbished. One of the common side requests we get is to put in an IEC inlet in place of the captive power cord, which from Roger’s perspective is more than adequate for the job, of reasonable length, and quite flexible. We try to talk folks out of this as there is just not enough room between the transformer cover and the edge of the frame to add an IEC inlet. In addition, the RM-9 frame makes this task rather difficult as you have to cut into the wood and there is risk of damage if not done properly. So for those who insist we advise them we will chop the stock cord about 6" from the top plate strain relief, attach a male IEC, and finish it off with shrink wrap and the customer gets to choose the power cord of their choice. Now the signal comes from the Romex in the wall, through the designer power cord, then that last 6" through the original stock power cord into the power supply.

However, some may not be aware that Roger does acknowledge a power cord can make a difference in the system. In this case, a power cord that addresses hum caused by having DC on the line, which can be a hard problem to fix. So he designed a power cord rated at 5 amps that removes DC and will quiet troubled transformers.
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