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41
Amplification (Pre/Power) / Re: Valve Vs Solid State amplifiers
« Last post by zenelectro on December 22, 2017, 11:10:02 AM »
Well I can remember back to when I was a wee one and listening to the old record player with its 5 inch speaker and tiny valve amp and wondering quite how it was possible to get so much sound from such a small box.  A lot of water has passed beneath the bridge since then and yet I still wondered at how big old boxes(usually reflex loaded) with modest valve amps could produce what I considered a much better sound than solid state amps driving expensive smaller box speakers.

Now having read the following piece (reference to another web site) I can begin to understand a little bit more about a thing called for want of a better title POWER RESPONSE. Please read the link as it helps explains a lot of the mystery's surrounding the whole subject.

http://education.lenardaudio.com/en/14_valve_amps_7.html

I like his reference to musicians preferring the valve sound and agree's with his musings.
V

There's a mix of good info and well, not so good.

The transformer section is worth a read:
http://education.lenardaudio.com/en/14_valve_amps_5.html

If you scroll down a bit past half way there is a Pi wound OP tranny used on a KT88 amp. A company I worked at
many years ago actually made that transformer. I remember the sections were individually wound and then
assembled on to the C Core.

Very Trick OP transformer.

I've still got a copy of that amp schematic kicking around somewhere.

The 'semi Pi' winding arrangement shown just above that is done with a combination of split bobbin (2 vert sections) and many horiz sections
is a very nice design, inherently balanced - appears to be copied by EHT amps....

John Burnett is a smart guy for sure. Apparently he was also involved in a precurser to what became AES (with Tom Misner). 

Funny little industry this.

T
42
Amplification (Pre/Power) / Re: How to Build a killer Amp
« Last post by fallsaudio on December 19, 2017, 08:39:41 PM »
Hello to all!
              This amplifier is a rock solid circuit to be use with 2A3, 6A3 , 245, 246 ,PX25 etc. It will provide you with a amazing sound stage and a hi quality sound that a lot of others SE amps fail to do .  But the ux250 a tube that require 10000 ohms or less resistance on the control grid . Yes it will work in there but it will stress the tube and shorten the life of the tube . You can be overcome the problem by remove the coupling capacitor and the plate load resistor to the driver tube and placing a Hi Quality inter stage transformer 1:1 ratio 10K to 10K works great . The primary winding is connect were the plate resistor was and the secondary goes across the grid leak resistor from the grid to the signal earth .I will over the day post a circuit for those who are not sure what to do . :D
Paul
Fallsaudio

If anyone has a problem and need help, I am more than willing to help . Just email me at fallsaudio@yahoo.com
43
Amplification (Pre/Power) / Re: How to Build a killer Amp
« Last post by stevenvalve on December 19, 2017, 08:19:01 PM »
Best to run around 300v/0/300v to the rectifier. 400V/0/400v will probably have to much voltage, especially if you run the 15uf cap on the voltage out of the rectifier. The 15 uf cap is needed to lower the noise floor but it is a case of diminishing returns, a bigger cap will probably not lower it much more anyway, but it will not hurt. The other advantage of the 15uf cap is you get a voltage increase and that will allow you to run a lower voltage mains transformer. The UX250 or type 50 is good for 450 volts, but dont run that because that will shorten the life of your hard to find UX250 globes and could make them sound stressed. I run 250v/0/250v and that gives me around 280v-300v at the valve. the B+ switch is used to let the valves warm up before adding the currant, helps the valves last a lot longer. I must say my UX250 globe amplifier running this circuit is so good it is the end game for me, it really does sound real, but to get it there you must use the right bits and tune it correctly. My PX/4 amplifier is running the same circuit and same parts combination.
  At the moment this amp does have an Impedance to grid problem when using the 50 tube. As it is, the Impedance to grid is 100K and needs to be 10K. It is only a problem with the 50. It will work fine with 2A3 -245 -PX4  45 345 145 valve. There will be an update soon on fixing this problem. With the 45 dont run more than 250 Volts, with the PX4 1930s globe no more than 250volts, up to 300v is fine with the later 1950s ST PX/4 finned or non finned versions. I can run these different valves because i had filament transformers made with AC 2.5v 4v 5v 6.3v 7.5v.
44
Amplification (Pre/Power) / Valve Vs Solid State amplifiers
« Last post by vitavoxdude on December 19, 2017, 03:15:53 PM »
Well I can remember back to when I was a wee one and listening to the old record player with its 5 inch speaker and tiny valve amp and wondering quite how it was possible to get so much sound from such a small box.  A lot of water has passed beneath the bridge since then and yet I still wondered at how big old boxes(usually reflex loaded) with modest valve amps could produce what I considered a much better sound than solid state amps driving expensive smaller box speakers.

Now having read the following piece (reference to another web site) I can begin to understand a little bit more about a thing called for want of a better title POWER RESPONSE. Please read the link as it helps explains a lot of the mystery's surrounding the whole subject.

http://education.lenardaudio.com/en/14_valve_amps_7.html

I like his reference to musicians preferring the valve sound and agree's with his musings.
V
45
Resistors / Re: Resistor games
« Last post by zenelectro on December 19, 2017, 10:51:59 AM »
You also have to consider the value of the resistor - it's really important.

For example, if you have a fairly high impedance circuit, say after the OP of a pre amp tube, then a 100 ohm resistor will
make much lass difference than say a 10kohm resistor.

Other rules can apply also, for example in Cathode circuit, if the resistor is shunted with a cap, as is commonly done you will hear the cap mostly
and then some of the resistor, but not much compared to cap.

Then there are tricks to 'hide' resistors. Often 6922 tubes have grid stopper resistors for stability. Some people don't like the sound of them
in front of the tube. A trick I often use is to wind a thin coil of wire over a carbon comp (A.B.) resistor. At audio freq the wire shorts the resistor out
to nothing.  At freq where it wants to oscillate, the wire becomes an air coiled inductor damped by the resistor.

 I bet you haven't seen that before!

:)  :)   :)
46
Resistors / Re: Resistor games
« Last post by vitavoxdude on December 18, 2017, 11:02:51 AM »
Here is another link to an extensive resistor test in a variety of positions, DAC, Pre amp, Phono and power amp.  Certainly one of the more exhaustive examples and a good read.  You will need to use a translator (google).

http://diytriode.blogspot.com.au/2015/09/1092015-weglowe-rezystory-w-audio.html

 :D :D :D :D :D :D
47
Reel to Reel / Neil Young Auction
« Last post by zenelectro on December 10, 2017, 11:37:27 AM »
Looks like Neil is offloading some nice gear.

Quite an assortment of stuff including a host of Lionel model trains of which he apparently owns a part share in the company.

ATR102 1/2"

https://www.julienslive.com/m/lot-details/index/catalog/243/lot/98626/?url=%2Fm%2Fview-auctions%2Fcatalog%2Fid%2F243%2F%3Fpage%3D19%26http_referer%3Dhttps%253A%252F%252Fwww.gearslutz.com%252F

T
48
Other DACs / Re: Marantz 94 mark 2
« Last post by brenden on December 08, 2017, 01:26:19 PM »
Welcome  from me too John.
     You should have fun modding your 94 mk2  but it is also full of frustrations at times .If you need help with anything ,let me know .
49
Other DACs / Re: Marantz 94 mark 2
« Last post by zenelectro on December 07, 2017, 09:27:27 PM »
Hi everyone.

I also have a CD94 mkii and will be modding soon.

What I never see in reviews about the CD94 MKII is what happens when you substract the signals from 2 DAC where one had an inverted input signal.


Hi John, welcome 

The two signals are opposite (one dac signal goes up +, other goes down -) and are summed in the differential to single ended circuit.

As such only signals that are the same will be cancelled. The call this common mode signals, or common mode rejection. 

Quote

As the clock component at 22.1 kHz is equal in both TDA-1541a and the signals are substracted the clock frequency component is eliminated and you keep the output signal 2x.
Am I right here? ;D


Not quite.

Both DAC's outputs are stepping in opposite directions, so there is no cancellation of the 44.1kHz sample rate (if running zero oversampling).
As stated before, only signals (or noise) that is the same on both DACs will be cancelled. 

Quote


That is why the MKII sounds better. In theory you don't even need a filter because the clock signal is almost not there.


This is not the case - unfortunately. As pointed out above, the 44.1kHz signal 'staircase' of zero oversampling will not
be cancelled at all.
If you still run the digital filter this will be at whatever sample rate the DF runs at, it's 4 x OS in CD94's case = 192kHz.

There's no free lunch unfortunately.

Quote

I will implement a lot of these mods.

Thanks for your explanation.

John
50
Other DACs / Re: Marantz 94 mark 2
« Last post by maessen on December 07, 2017, 04:30:05 AM »
Hi everyone.

I also have a CD94 mkii and will be modding soon.

What I never see in reviews about the CD94 MKII is what happens when you substract the signals from 2 DAC where one had an inverted input signal.

As the clock component at 22.1 kHz is equal in both TDA-1541a and the signals are substracted the clock frequency component is eliminated and you keep the output signal 2x.
Am I right here? ;D

That is why the MKII sounds better. In theory you don't even need a filter because the clock signal is almost not there.

I will implement a lot of these mods.

Thanks for your explanation.

John
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