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How do I best adjust the overall gain of a dual-mono BII/IVYIII combo?
What is the max gain I can get without compromising THD and how/where do I set it?
Sorry to bother but I have fallen in love with a single power gain stage after the BII.
Nic
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What kind of output swing would you like?
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Russ, what is the formula?
Seems the R for I/V in the first stage provides some "gain" by the V=IR formula
Then the second stage is the Rg/Rf type of gain. Total gain is the product of the two.
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Well - I'm not sure. A gain that would compensate for the bypass of the buffer stage on the UcD. There is an app note. Nic Edited by user Friday, March 26, 2010 4:49:09 PM(UTC)
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glt wrote:Russ, what is the formula?
Seems the R for I/V in the first stage provides some "gain" by the V=IR formula
Then the second stage is the Rg/Rf type of gain. Total gain is the product of the two.
The I/V stage should be considered constant, as it is pretty well optimized for the latter filter. Its output is about 8.5VRMS at 0DBFS. You can't really go much higher without signal degradation. It is OK to go a little lower, but I found the results not as good either in measuring or in listening. The formula is basically: Output VRMS = 8.5VRMS * (R / 780) The next stage actually has a loss, not a gain. :) The best way to adjust the output swing is with R13-R16. Here are some values and differential output levels(the SE output will be identical): 180R you get about 2VRMS 221R you get about 2.4VRMS 390R you get about 4.25VRMS 470R you get about 5.12VRMS I would not go a lot higher than that. :) But you could use a 750R resistor and get about 8VRMS which is about 22Vpp. That's a ton of swing. :) Anyway I think you should have the idea now. Cheers! Russ Edited by user Friday, March 26, 2010 7:41:49 PM(UTC)
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Oh Should mention that the above formula is for stereo, in dual mono you will have double the swing, but you will not want to have more than about 7-8VRMS max, and that only into a high impedance of more than 5K. So if your going dual mono and want 8VRMS I would shoot for something like 4VRMS from each half. Edited by user Friday, March 26, 2010 7:49:18 PM(UTC)
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Looking at the uCD app note I would shoot for 4-5VRMS final output. You should be just fine to drive it directly. If you need to, you could go a little higher, but I don't think you will need to.
That means if your going dual mono, you might not want to change the output swing at all. Just go stock. :)
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Russ White wrote:Looking at the uCD app note I would shoot for 4-5VRMS final output. You should be just fine to drive it directly. If you need to, you could go a little higher, but I don't think you will need to.
That means if your going dual mono, you might not want to change the output swing at all. Just go stock. :) Hi Russ, (I'm interested too since I have the same amp modules) If the buffer has a gain of 5 and the "standard" output of IVY is 2vrms, wouldn't output be 10vrms to compensate for the bypass of the buffer? 10Vrms is +/- 14V which is already very close to the supply voltage. Is the reason why you wouldn't recommend going too high is because of power dissipation/limitation in the opamps? Now that I think about it some more, the buffer supplies are +/-12V, so they can't swing more than 12V 12V peak is about 8.5V RMS, is this a safe/good output voltage from IVY? Edited by user Friday, March 26, 2010 10:06:36 PM(UTC)
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I don't understand what you are asking. I did not say to bypass anything. There is no "buffer" per se in the IVY III. Remember the second stage is really acting like differential amplifier with a *LOSS* not gain. Remember its a fully differential amp. :) So 8.5db is about 6Vpeak at each differential output (which sums to 12Vpeak) so it is not swinging all that close to the rails. Edited by user Saturday, March 27, 2010 5:47:49 AM(UTC)
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glt, if you asking about using the old IVY, then I would simply start at something like 470R at the I/V resistor spots(R1-4 on that board). You could easily go up to 750R if you like. Edited by user Saturday, March 27, 2010 5:51:50 AM(UTC)
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I think glt is referring to the buffer/gain stage and its supply on the UcD module (the one I'm bypassing).
I guess the question is really what increase in output VRMS is needed to compensate the loss of gain caused by bypassing the "buffer/gain" stage on the UcD modules.
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OK, I guess is hard to keep context in a running thread, so here is the summary:
1- NicMac (and maybe I) wants to bypass the buffer in the Hypex UCD amp module and use the IVYIII as the sole stage between BuffII and the amplification module
2- That first stage has a gain of ~5 as specified in the application paper from Hypex
3- Now, in order to compensate that loss of gain NicMac asks the adjustment to IVY III
4- I propose that if you loose a gain of 5, then to add it back in the IVYIII, you will have to increase the gain by the same factor of 5
5- Assuming that 2Vrms is "standard" output, then the adjusted gain would be 10Vrms, or 10x1.4=14V peak or 28V peak to peak
6- But wait, the UCD buffer is powered with a 12 V supply, thus the maximum output of the buffer (that we are thinking of bypassing) is 24V peak to peak. This is 12 v peak or 12/1.4=8.57V RMS
Therefore if IVY III can supply 8.25V RMS at 0dB from BuffII, it would have completely compensated for the removal of the input buffer in the Hypex UCD amp. From the data above, this seems to be accomplished with R=750 ohm, which you "do not recommend"
So my questions was, "what is the downside of running IVYIII with outputting ~8Vrms?"
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There is no real downside so long as the impedance does not drop more than say 1K. :)
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Also I should be more clear. I should not have said "I do not recommend" I should have said "Be very careful". :)
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