hi olav, yes the 240ohm i have talking is the input and output series resistor, now i have no series resitor at the output as ZM told me and replace the 1K input gate resistor with a 220ohm charcroft Zfoil ( stupid expensive but so good!) . i also use some NewclassD regulator i have as power supply . and a LDR as volume pot .. in a word it kills my threshold sl10 preamp..
and everything i had before
and everything i had before
Not really end of summer ...
Hi KatieandDad!
No - a long and warm part is still waiting(down to sunny Spain the 12 of July to enjoy the warmth of the south) - but when the rays of the Sun recedes later this year, and my wife an youngest girl is off on 1 week school-excursion - my soldering-iron will be a little busy. Not to forget my new Alp12P that also is on the list this fall. Need one new speaker beside the Alp10.2.
Have a nice building time everyone!!
Best
Olav
Hi KatieandDad!
No - a long and warm part is still waiting(down to sunny Spain the 12 of July to enjoy the warmth of the south) - but when the rays of the Sun recedes later this year, and my wife an youngest girl is off on 1 week school-excursion - my soldering-iron will be a little busy. Not to forget my new Alp12P that also is on the list this fall. Need one new speaker beside the Alp10.2.
Have a nice building time everyone!!
Best
Olav
Well, here's my completed B1 and matching chip amp, in Par-metal chassis. Huge thanks to everyone who's contributed to this forum -- I've spent forever reading through and figuring all this out. Especial thanks goes to 6L6 for helping me out in PMs, and for his great build thread with nice photos -- I used his idea for the PSU. Thanks also to Steve Slater at Apex Jr., and of course thanks Nelson Pass for the awesome project.
The littlest board is a summing/low-pass filter for a subwoofer output -- thanks goes to AndrewT for suggesting that in this thread.
The littlest board is a summing/low-pass filter for a subwoofer output -- thanks goes to AndrewT for suggesting that in this thread.
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An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I have confused myself regarding gain when going from balanced to unbalanced. Since the B1 provides no gain, I want to get this correct.
I am taking the 2 legs (+ and -) directly from a voltage DAC (AKM DAC on a Behringer DCX). I am doing this by replacing the analog output section with a 1:1 line transformer. When I measure across the outputs (+ and -) on the secondary side I get 1.75 v RMS and the DC has been cancelled. As I should get. When I measure across just one leg I get half the voltage relative to ground. Also, as I should get.
My question: when I go into the (unbalanced) B1 buffer (by connecting the - leg to the RCA shield and the + leg to the RCA center) will the B1 "see" a voltage of 1.75 RMS or will it "see" half that voltage. IOW am I losing 6dB?
I am taking the 2 legs (+ and -) directly from a voltage DAC (AKM DAC on a Behringer DCX). I am doing this by replacing the analog output section with a 1:1 line transformer. When I measure across the outputs (+ and -) on the secondary side I get 1.75 v RMS and the DC has been cancelled. As I should get. When I measure across just one leg I get half the voltage relative to ground. Also, as I should get.
My question: when I go into the (unbalanced) B1 buffer (by connecting the - leg to the RCA shield and the + leg to the RCA center) will the B1 "see" a voltage of 1.75 RMS or will it "see" half that voltage. IOW am I losing 6dB?
there's something wrong.
The transformer balanced output signal is not referenced to ground. It should be floating.
You should not be able to measure half voltage from one pole of the transformer to ground.
If instead of using a pair of B1s, you used another transformer at the input end, then again you would be floating the balanced inputs.
It's when you replace the transformers, at either end, with electronics that the ground references come in. That's the big disadvantage of electronically balanced signal transmission. Transformer coupled signals float and give best attenuation of interference.
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proper wiring of your xformer can be made in 3 ways :
1. ballanced symmetrical - CT of secondary must be connected to DAC audio gnd ; no galvanic isolation (few other possibilities , when CT is connected to receiving end GND -then there is galvanic isolation ; also possible tying both sending and receiving gnd's .......... then there is not galvanic isolation )
2.pure balanced - CT NC , entire secondary is floating
3.unbalanced - one end of secondary connected to gnd , other side is hot ; same choices as #1 regarding connecting out gnd - if connected to both sending and receiving end , there is no galvanic isolation ; if connected just on receiving side , there is galvanic isolation
with appropriately wired switch(es) you can flip between all iterations
search on Jensen site - plenty of useful pdf files , with nice pictures
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I am afraid that I worded my question poorly. I will be tapping directly from the output of the DAC chip and bypassing the existing analogue output (opamps, RC filters etc). I referred to the output of the DAC as being "balanced". I should have referred to it as a differential output.
I will be getting the galvanic isolation when I take the outs of the DAC (+ and -) and I will not be using the center tap on either the primary or secondary side. When I measured the voltage from a single leg, I of course had the voltmeter connected to one leg and a chassis gnd (in that case only).
I am greedy about getting as much voltage out since the B1 provide no gain.
I looked at the Whitlock / Jensen papers and they are helpful.
Hi
I will build the B1 line preamp
I've buy ten 2SK170-BR, but they all have an IDSS of arround 2.7 ma. Is it a too low IDSS to get low noise and low thd ?
I've use a transistor analyser with a precision of 5% to measure the IDSS.
Where can I ad a low pass filter in the B1 circuit ?
Thanx
Paul
I will build the B1 line preamp
I've buy ten 2SK170-BR, but they all have an IDSS of arround 2.7 ma. Is it a too low IDSS to get low noise and low thd ?
I've use a transistor analyser with a precision of 5% to measure the IDSS.
Where can I ad a low pass filter in the B1 circuit ?
Thanx
Paul
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2SK170 are either GR, BL, or V. Real Toshiba GR span 2.6mA to 6.5mA and tend to bunch half that way as random samples. You probably got fakes. Even if they are selected near IDSS samples from bottom of the barrel real 2SK170GR such low transconductance is no good for B1. You would need 7 to 9mA BL samples for good dissipation and trasconductance balance.
P.S. Which transistor analyzer that measures IDSS?
P.S. Which transistor analyzer that measures IDSS?
Hi
How about using two of my 2SK170 in parallel ?
I used a M Cube semiconductor analyser.
Thanx
Paul
Just get the proper fets. If they are fake, this is just the beginning of a nightmare that would otherwise be a super simple build. 2SK170 is not the least bit rare and are available.
Russellc
Shoot them some clean macro pictures front & back, we will be able to advise if real Toshiba, and if they are valid save them for something else. For B1 get BL as Russellc wrote.
P.S. That's 11% error, don't trust the analyzer for any real IDSS matching in the future.