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Old 16th October 2008, 03:21 PM   #781
sparky6 is offline sparky6  Canada
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Default Re: Re: B1

Quote:
Originally posted by stein2


B1 is a buffer stage, no gain in signal. If you think but not sure if you need gain, take a single pot, add some coax with terminals at both ends and try with passive volume only between your source (CD for example) and power amp. If you get enough output from source to fully drive the power amp, B1 should do. If you can go with the single pot all the way and feel that the amp lacks output power, then, some gain in the control/preamp unit would help. In that case, you might consider NS10 with a proper, modern shunt PSU... like some of us did

I suppose I should have mentioned that the Goldpoint is a series stepped attenuator type passive "preamp". What I'd like to know is what the advanatges of an active buffer stage over just a good quality passive would be. I'm quite happy without an active preamp so far, but I'm not sure what I'm missing by not having a buffer. I was considering trying to squeeze the B1 into the Goldpoint by leaving the PS caps in the PS.

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Old 16th October 2008, 03:40 PM   #782
Zen Mod is offline Zen Mod  Serbia
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Default vaistinu konza!

Quote:
Originally posted by juma



Ma jok, to je lokalna fora - Munze Konza (Zemun Zakon) ! Vaistinu Konza (Zakon) ! (tako se pozdravljaju i odpozdravljaju zemunci na satrovackom)
A dal'je tuzemstvo ili inozemstvo - ostaje da se vidi !

Anyway, I don't think that noise scheme will work here - it's quite different from Broskie's implementation in Aikido preamp. Furthermore, B1 doesn't need it - it has a very good intrinsic PSRR already. I know what would make you happy - nice, hot, glowing 6SN7 as WCF

me modestly ( as always) thinks that even B1 will benefit from that sort of noise injection , but - it will be audible , that's pretty questionable ;

interesting you're mentioning Broskie's site - even if it's certainly treasure , I always had difficulties reading it , just because I simply can't make mental map of site .... too many things in one place , I resume ;
hehe - I'm probably used to old , hard copy based , reading ; what's sometime limiting to me is fact that PC screen have just one page .....

"injecting noise" have many faces ..... - first one , known to me , was in reading and constructing tube stab ( too back in time and space ) , where upper resistor ( in resistive divider , connected from output rail to ground , feeding error amp first grid) was deliberately bypassed with small cap ;
then I have thoughts that main reason is for decreasing gain of that stage in/on higher frequencies , but later I discovered beneficial influence of that cap even on lower frequencies ;

interesting - seems that all electronics is made of simple blocks and tricks ..... rare ones are capable to mix them in sorta unusual way ;

that's why this forum is known as Papaboard ........ not under any other name

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Old 16th October 2008, 03:46 PM   #783
stein2 is offline stein2  Serbia
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Buffer is "buffering" between two stages thus allowing optimal impedances/loads to occur at output of the previous stage to the following stage. For example, a cathode follower has gain of 1 or less but if well made almost infinite input impedance and very small output impedance which allows a fairly long cable to be used from the preamp to the power amp and therefore making it easier for the preamp to deliver the right kind of signal to the next stage. Passive attenuators usually only create mess at the input of the power amp. For example, F5 has no capacitors at the input, only one 1k in series and a 100k in parallel, adding just a passive attenuator, the input impedance of the amp varies with the change on the pot position... That can although does not have to necessarily ruin the performance of the amp.
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Old 16th October 2008, 09:40 PM   #784
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i have built a B1 but have need of a B2-can anyone doodle out a schematic for me? thanks bubba
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Old 17th October 2008, 02:30 AM   #785
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Quote:
Originally posted by bubba177
i have built a B1 but have need of a B2-can anyone doodle out a schematic for me? thanks bubba

Hah! Where in MO are you, bubba?

Does anyone have a BoM in excel or some other format with columns for price, qty, part# and such for Mouser or Digikey? I'm lazy, what can I say What's the approx parts cost using the Master's original parts (using perfboard). I searched for it, but couldn't find anything.
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Old 17th October 2008, 02:51 AM   #786
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Read a bit more of the thread and then ask questions.
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Old 17th October 2008, 03:30 AM   #787
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umm what? lol, I didn't mean a BOM & parts cost estimate for the B2, I know bubba was joking. I searched for "list", "parts list", "BOM", and "cost" and couldn't really find what I'm looking for. I've read the Mr. Pass' ETM article but I'm a very visual person and like my parts lists organized like this ...I mean I know I could go thru the article and make one but I figured someone had already done it, plus I should be doing more important things right now, like my Differential Equations take home test ugh
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Old 17th October 2008, 04:45 AM   #788
BFNY is offline BFNY  United States
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Quote:
Originally posted by pinkfloyd4ever
I searched for "list", "parts list", "BOM", and "cost" and couldn't really find what I'm looking for. ...I mean I know I could go thru the article and make one but I figured someone had already done it, plus I should be doing more important things right now, like my Differential Equations take home test ugh
I think most folks just use existing parts on hand, there are so few. Plus you are not going to find the JFETS needed at Digi-key or Mouser, not the Toshiba ones at least. If you you non-boutique parts including coupling caps, it will be maybe $10. tops plus the enclosure, pot, switch, jacks, t-x, JFETs and board. What you use for the latter group of parts will depend on how fancy, or not you want to make it, and will determine over 90% of the cost. Those choices will be personal and different for most.
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Old 17th October 2008, 08:37 AM   #789
steenoe is offline steenoe  Denmark
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Default Re: B1

Quote:
Originally posted by sparky6
Hi all,
What would be the advantages over passive?

Thanks...
Maybe none, maybe a lot. It all depends. In an attempt to explain the impedance issue (Z), here you go: For the purpose of understanding what is going on with the Z's, you can view the output Z of your preamp and the input Z of your poweramp as resisitors; series resistors in fact. You know that voltage will be dropped across a series resistor, right?
Now if the largest value of those series resistors is the output Z of the preamp (passive or active, doesnt matter) the largest amount of voltage (your precious signal!) will be dropped across that resistance. The smaller part will be dropped across the input Z of your poweramp. That doesnt sound like a good idea, does it?
Let's say, as an example in rough figures, that your preamp outputs 10V and has an output Z of 1k and your poweramp has an input Z of 100r, what will happen? Well, you will nearly throw away 9 volts in the preamp and only 1V in the poweramp.
This is where the buffer and impedance matching comes in. The B1 has a very low output Z.
The figures are just for illustrative purposes and very approximate, and the explanation is rather simplistic, but what...
So, do you need one? Build one and you will find out.

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Old 17th October 2008, 09:20 AM   #790
AndrewT is offline AndrewT  Scotland
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Following on from Steenoe's explanation.
If the interconnect cables and next stage have some capacitance, then this forms a low pass filter with the output impedance of the source.

eg. Rs=1k0 (output impedance), Capacitance of cables 200pF/m and 2.5m long along with 680pF at the input of the next stage, gives C=1180pF.
The F-3dB of the Low pass filter is 135kHz.
Many builders/designers suggest that this filter should be between 160kHz and 500kHz to minimise it's effect on the audio band frequency response.

If a 100k passive pot is added between the two active stages the Rs, for the next active stage varies upto 25k. This reduces F-3dB to 5400Hz. Nothing short of a disaster in reproducing the sound in anything close to High Fidelity.
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