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Old 24th April 2013, 07:29 AM   #801
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Wow Oliver! Nice to see a new version of the Tube-I-Zator (V. 3). Nice features added to it. I don't remember the size of the V. 2. What is the size difference between the 2?
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Old 24th April 2013, 09:01 AM   #802
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Quote:
Originally Posted by headrott View Post
Wow Oliver! Nice to see a new version of the Tube-I-Zator (V. 3). Nice features added to it. I don't remember the size of the V. 2. What is the size difference between the 2?
Thanks headrott. The size of the V3 is the same, so everyone could change it without problems
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Old 24th April 2013, 11:16 AM   #803
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Originally Posted by dvb-projekt View Post
Thanks headrott. The size of the V3 is the same, so everyone could change it without problems
Well, you had to go and say that huh Oliver? Well, I will have to find the time and collect the parts to install and I will be doing this upgrade. I especially like the soft start feature. Thanks again Oliver.

Greg
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Old 24th April 2013, 01:41 PM   #804
tmas is offline tmas  United States
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Hi Headrott,

How is your DAC working out for you? What value of I/R resistor did you finally settle on?
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Old 28th April 2013, 04:32 AM   #805
DQ828 is online now DQ828  Australia
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Quote:
Originally Posted by noizas View Post
Hi Crom,

sadly to say, but both I/V (more correct name should be I/U) resistor values 20R or 56R compromise TDA1541 linearity and resolution.
However to detect those problems you need perfect set of your ears, loudspeakers and amplifiers , else you need to measure THD somehow.

Value of I/U resistor is possible to calculate from TDA1541A datasheet:
1. "Notes to the characteristics: To ensure no performance losses, permitted output voltage compliance is 25 mV maximum." - here is P-P values, not RMS.
2. "full scale current: 4 mA (nominal)" - current is negative here.
3. ""zero scale current: 25nA (nominal)"- actually 0 mA.

So there is two ways to calculate maximum correct value of I/U resistor by Ohm law R=U/I :

A. If you have no constant 2mA current injection circuit -
R=[-25mV]/4mA=6.25R , because current is only negative here.

B. If you have constant 2mA current injection circuit -
R=[+-25mV or 50mV P-P]/4mA=12.5R , because current is swinging +-2mA around 0 (compensated by CCS).

So, why most of diyers use I/U resistor for TDA1541 in range 20R - 60R ?

It is because of noise issue as well as amplification factor.

Lets take circuit with CCS 2mA injection, so we have signal of U RMS=0.7*25mV=17.5mV, and we need to amplify it to:
1. For CD player output level (2V RMS): K=2000mV/17.5mV - about 114 (even more than 12AX7 in grounded cathode way can provide, not even mention SRPP - half of mu).
2. For level of professional audio (+4dBu, or 1.23V RMS): K=70 (still not achievable with SRPP and 12AX7 tube, but almost here )
3. For level of customer audio (-10 dBV or 316 mV RMS): K=18 (easily achievable in SRPP with 12AX7 and almost achievable with medium mu tubes as 6N1P or 6DJ8, etc).

But choosing tubes with medium to high mu, do not forget standing current in SRPP - more standing mA you have, less the output will be taxed for charging capacities of interconnect cables and input of preamplifier.
This is also related with output impedance - as usual medium mu triodes have less plate resistance than high mu triodes, so damping factor of interconnection would be better.

Best wishes
Saulius
So for a complete novice at such things, does this mean, the higher the I/U resistor value (say 56 Ohms) the larger the signal will be, but at the expense of THD?
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Old 3rd May 2013, 01:38 PM   #806
DQ828 is online now DQ828  Australia
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What is the input & output impedance of this board?
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Old 3rd May 2013, 01:57 PM   #807
noizas is offline noizas  Lithuania
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Originally Posted by DQ828 View Post
So for a complete novice at such things, does this mean, the higher the I/U resistor value (say 56 Ohms) the larger the signal will be, but at the expense of THD?
Yes, you are right.


Quote:
Originally Posted by DQ828 View Post
What is the input & output impedance of this board?
It depends on tube you use in SRPP and other factors - power supply voltage, current flow per tube, etc. It is possible to calculate impedance by Tubecad program made by John Broskie.
Anyway, you can send me parameters of your SRPP, I will calculate impedance figure for you if you really need it.
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Old 4th May 2013, 01:51 AM   #808
DQ828 is online now DQ828  Australia
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Quote:
Originally Posted by noizas View Post
Yes, you are right.




It depends on tube you use in SRPP and other factors - power supply voltage, current flow per tube, etc. It is possible to calculate impedance by Tubecad program made by John Broskie.
Anyway, you can send me parameters of your SRPP, I will calculate impedance figure for you if you really need it.
That would be great thanks, what parameters do you need?
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Old 4th May 2013, 08:00 PM   #809
noizas is offline noizas  Lithuania
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Quote:
Originally Posted by DQ828 View Post
That would be great thanks, what parameters do you need?
Tube type (6N2P, ECC83, etc), Rk and voltage of power supply.
Also Rload (resistor which is loading output capacitor - if you have installed such thing).

There is attached report in PDF for 12AX7, at it's max current 2.5mA, 300V supply.
As you can see Zoutput is quite high - about 30K (if loaded with 1M Rload).
So this setup of SRPP has to be loaded with high input impedance pre-amplifier, at least 100K, better - more than 200K.
Attached Files
File Type: pdf Test Report SRPP 12AX7 300V 2_5mA.pdf (8.8 KB, 30 views)
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Old 5th May 2013, 09:30 AM   #810
Crom is offline Crom  United Kingdom
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Quote:
Originally Posted by noizas View Post
300V supply.
Very interesting conversation on impedence guys - reading with interest!

I think the recommended input voltage setting was 150...I am probably demonstrating my ignorance here but seeing as this tube's vmax is much higher, is there any sonic advantage to increasing the voltage?
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