These questions may have been better split, but since they are both simple questions I figure I'll ask them both in the same thread.
Is it wise/typical to run an input buffer with a gain higher than 1 to boost the line level input before it hits the power amp stage?
When mounting a toroidial transformer, is it normal to have the mounting bolt on the bottom(outside) of the chassis? Avel documentation also says the mounting bolt must be insulated from the case, how is that normally done?
Guess that was 3 questions, thanks for any help though.
-Adam
Is it wise/typical to run an input buffer with a gain higher than 1 to boost the line level input before it hits the power amp stage?
When mounting a toroidial transformer, is it normal to have the mounting bolt on the bottom(outside) of the chassis? Avel documentation also says the mounting bolt must be insulated from the case, how is that normally done?
Guess that was 3 questions, thanks for any help though.
-Adam
Adam M. said:
If you need more gain, that can be had from the gianclone chip - indeed I run mine at 30dB plus, mainly because my SACD/CD Player is 11dB down from the usual standard 2V RMS (I need the extra gain). In fact I believe it sounds better that way, even if using normal CD Players. More gain = less feedback. Actually measures higher THD, typically 0.1% vs 0.03%, but that means nothing as it is often the case that amps which relies on feedback for low THD often sounds worse than those that don't rely on it, even if they measure worse. I call it "Hiraga's Law."
So in conclusion, there is really not much need for gain in the buffer. BTW, the conventional term 'Buffer" usually describes a Unity Gain stage.
Joe R.
A timely reminder (I hope) that you can have too much gain! (This is an all too common problem with many systems assembled from commercial components)
If you want to use a stepped attenuator rather than a pot, and you want an affordable 12 step version, the more gain that you have, the larger your attenuation steps will be!
If you want to use a stepped attenuator rather than a pot, and you want an affordable 12 step version, the more gain that you have, the larger your attenuation steps will be!
That's a 'how long is a piece of string' type of question Adam.
It depends on how many sources you use and the range of their output levels. Also, on the efficiency of your speakers.
Basically, I would say don't go above a gain of 30 for your GC and if you use a preamp/buffer make it unity gain.
If you want to use a 12 step attenuator (which I recommend over any pot), it is really a question of a bit of experimenting to find the range of attenuation that works best in your system; ie it gives you enough attenuation without each step being too big.
Nuuk said:
You guys are yet to taste the delights of a "silver-carbon" pot, the pot you must have if you must use a pot!!!
I sourced some from an obscure source (not audiophile) and use them in my JLTi.
I had an interesting experience, this guy phoned me from Germany and he said that it intrigued him that the website said I used a "silver-carbon" pot. We ended up chatting for an hour (he was paying - not sure what Germany to Australia call costs are). He said he had come across an 'audiophile' pot on a German website and in his translation were called "silver-coal" - getit? Coal is the same as carbon - in german. I looked and found it on the site and it was a stereo pot but did not look like the one I used. Can anyone of you guys help me, I recall this company which sold audio parts and modules, including switched attenuators. Thiele or Thiel?
To continue: My german friend called them and asked about this strange pot and got an admission:
At a fraction of the price it wasn't far behind their switched brothers in sonic excellence. Hey, that's what my silver-carbon pots sounds like too.
These pots, unlike 'conductive plastics' which are all colured, are so clean and transparent, they don't sound like a pot.
I did this A-B test on a local friend, he was coming over to pick up some gear I'd been working on. I told him on the phone he was going to be my guinea pig. Between my SACD player and my RTP preamp (uses DACT) I inserted a pair of resistors forming a voltage devider, approx -10dB. I also inserted the s-c pot and a high quality gold plated toggle was able to switch between the two. The pot was adjusted so the output terminals I had the exact same levels with 0.05dB of each other.
Now Nick, do you follow me? I am comparing a pot against a refence pair of decent high quality resistors, not gainst another pot. This is near the ultimate test for a pot.
My friend Les arrived. Sat down in the hotspot seat. I told him I would play A first as a reference, and then when he was ready for it I would switch to B and after a while, would like to see if B showed any deterioration against A.
Les didn't have a clue what I was doing, didn't know this was a pot test.
Les, after about 40 minutes, switching back and forward, sometimes even when the track was playing: "B is ever so slightly soft against A and also slightly less focus." I asked if there were any colourations induced such as midbass plumminess of mid or treble changing any tonal character? "Absolutely none!"
Try this test with any conductive plastics and the colourations stand out like a sore thumb! I mean Alps Black or Blue, or the Noble pot, any conductive plastic pot.
I have tried to find this German website again and no luck. It is called Thiel or Thiele (not the loudspeaker) and I think it was entirely in german. I tried Googling it, but no luck. Too many with that name or similar.
Joe R.
Nuuk said:If you are worried about the transformer bolt issue, use a nylon nut and bolt or cable ties instead of the metal bolt.
But if used properly, there is no problem with the metal bolt and it can be used in either direction.
I would advice strongly against using zip ties, as a transformer can become very hot (100c+). This is especially true for big trafos under heavy load.
Magura
Joe Rasmussen said:
After googling myself, I found out that the answer is inside this forum.
Check this, post #5:
http://www.diyaudio.com/forums/showthread.php?s=&postid=62927&highlight=#post62927
Those guys call it high-end pot, but my german is no good to read the rest:
http://www.thel-audioworld.de/bauteile/regler/Potis.htm
But it's enough to see the price: 22 Euros.
But but but... only 10k and 100k versions?
Well I'm always open to suggestion Joe and if I can find one of the 'carbon coal' jobbies, I will try it and report back.
At the prices reported by our erstwhile Portuguese bloodhound, it compares well against the cost of a DIY attenuator and won't have the drawback of the limited attenuation range.
At the prices reported by our erstwhile Portuguese bloodhound
, it compares well against the cost of a DIY attenuator and won't have the drawback of the limited attenuation range.
Nuuk said:
Are you sure they are Panasonic, or just a guess?
I got http://babelfish.altavista.com/babelfish/tr to translate http://www.thel-audioworld.de/bauteile/regler/Potis.htm.
This is not the same pot I remember seeing about a year ago? But memory may be failing me. But the translator put text under the picture (the one below the six channel job) showing a pot in pieces. It says:
Interior life
Coal silver course.
5-fold more pinnated
Silberschleifer.
Center tap.
"Coal Silver" it says and "Silberschleifer" - the Silber part of that word is Silver in German, right? So we seem to have the right kind of pot.
The general look of these pots reminds me of a certain Taiwanese manufacturer, so are you guys sure it's Panansonic?
The rest of the description/translation (a bit of a hoot):
The new potentiometer generation in the medium class. Now again revises with specially hardened and smoothed schleifbahn. Thus increase of the sound characteristics in homogeneity and dissolution. A high-quality potentiometer, also for applications of multi-channels, which does not shrink from a comparison regarding sound quality and price/achievement relationship.
Mono, stereo or sixfold. 4 or 5-Kanal is needed, one attaches simply only 4 or 5 channels of the 6-fach-Potis. The resistance value 6x20kOhm/logarithmisch can be inserted as well as into all 10kOhm/log applications. Likewise into most 50kOhm/log applications.
The schleifbahn is similarly different carbon film potentiometers, consists however of a mixture with admixture of further materials, in order to obtain a higher accuracy and life span, than with conventional carbon film potentiometers. In addition these potentiometers are better trimable on synchronisation. A Fuenffachschleifer provides for a precise signal scanning and a full Drehfeeling. All THEL potentiometers are ordered by us with the default to keep a timing error of under 1dB.
Four types available
Technical data:
Synchronisation: type = < 0,5dB; max = < 1dB; Tolerance: 20%;
Axle: 6x10mm; Thread: 9x0,75mm;
All THEL potentiometers with additional center tap
Prices
1x10klin Mono 21x23x20 EUR 13,00
2x10klog Stereo 21x23x26 EUR 22,00
2x100klog Stereo 21x23x26 EUR 22,00
6x20klog 6-fach 21x23x50 EUR 52,00
Joe R.
Joe, I said these pots seam to be made by Panasonic because of this post I found here on the forum:
I'm not sure.
Actually, on their site I didn't find any mention to Panasonic pots...
Anyway, I found your favourite pots.
Or at least, I found the place you were talking about...
carlosfm said:
I'm not sure.
Actually, on their site I didn't find any mention to Panasonic pots...
Anyway, I found your favourite pots.
Or at least, I found the place you were talking about...
carlosfm said:
And well done indeed! Now how about somebody ordering one, I'd say the 100K stereo would do nicely and at 22 Euros is not a huge outlay, and then report back. My guess is that it will be liked a lot and it's very much cheaper than switched attenuators, and much more flexible than a 12 position switch - the 24 used in the DACT (which I use in my big RTP premap) is only just enough.
Thel! Not Thiel nor Thiele. So close and yet so fare...
Joe R
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