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Old 7th July 2003, 06:24 PM   #11
Variac is offline Variac  United States
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Boy there are a lot of links about this subject, and I'm too ignorant to sort them out.

Heres a semi quote from the Jeff Rowland Concentra thread:
"the Concentra uses the CS3310 as volume control."

This is the chip vol control w/ precision resistors built in, which seems to work pretty darned well on the Concentra.

BUT a lot of people around here wouldn't trust such a thing.
BUT what if it were used to switch as a shunt device- then the signal isn't directly passing through it . Maybe that's how JR uses it? ... Could a simple circuit be worked out for this?
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Old 7th July 2003, 06:53 PM   #12
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Quote:
Originally posted by mhennessy
Check this post...

http://www.diyaudio.com/forums/showt...7685#post97685

Didn't occur to me until recently that this scheme could work well with an inverting GC. The first op-amp could be omitted if your preamp or source has a nice low output impedance...
You also change the gain of the chip this way and I'm not sure how it comes out with higher value series resistors.

I'm using similar setup with my monoblocks, but only with 5 resistors (10k ea. connected in series) for a very limited control range but still useful for me.
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Old 7th July 2003, 09:35 PM   #13
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Hello Variac, I used an 11 step rotary switch to build an 11 step shunt attenuator. This has now been in use for a couple of days and gives me ample control of volume. My original idea of the 255 step, relay controlled attenuator would work, but would be more expensive/complicated to build. Now I`ve built the simple rotary attenuator, I`m quite happy to stick with what I`ve got.
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Old 8th July 2003, 05:27 PM   #14
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Quote:
Originally posted by janneman
Mhenessey,

I saw your post earlier, even commented on this. But now I think it cannot work, because it would be impossible to calculate the resistor valus for monotonic range. You need a ladder network. Did you try to calculate them?

Jan Didden

" Can adders multiply? Yes, on a log table"
Hi Jan,

I've not spent a great deal of time on this, but I can't see why it shouldn't work just fine. Although perhaps you won't be able to get nice 1dB steps - this is my only real question at this stage. I'm guessing that this is what your reference to log tables means?

As a quick "proof of concept", I ran it through Excel (no access to simulators at work!) - here's what came out for a simple 4-bit sequence, using binary resistor values of 10, 20, 40 and 80K - I made the feedback resistor 220K, as this is a typical GainClone value. The 15 steps vary the gain from 32.3dB down to 8.8dB's - a typical GC with 10K/220K has 27dB

The purple line is simply what you'd get from 1dB steps and the blue line shows the calculated response. As you can see, the response is quite nice - there's plenty of resolution at higher settings, and larger step sizes the quieter end - just what you need, IME. The model was for 3 relays initially, and the curve was the same shape. If there is enough interest, I could try and expand it to include more relays tomorrow (if I get any spare time). This would bring more range, which is probably preferable for a real implementation.

Hope this helps,

Mark
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Old 8th July 2003, 05:28 PM   #15
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Quote:
Originally posted by Variac
Boy there are a lot of links about this subject, and I'm too ignorant to sort them out.

Heres a semi quote from the Jeff Rowland Concentra thread:
"the Concentra uses the CS3310 as volume control."

This is the chip vol control w/ precision resistors built in, which seems to work pretty darned well on the Concentra.

BUT a lot of people around here wouldn't trust such a thing.
BUT what if it were used to switch as a shunt device- then the signal isn't directly passing through it . Maybe that's how JR uses it? ... Could a simple circuit be worked out for this?
Hi Variac,

From my experience of the PGA2310, I don't think there's a way of doing this.

Cheers,

Mark
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Old 8th July 2003, 05:35 PM   #16
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Another interesting thing is if there's a difference in sound between amp having 8dB gain and 32dB gain? Reading Joe Rassmusen thread I remember he mentioned optimal gain to be in 30dB range.
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Old 8th July 2003, 05:46 PM   #17
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Quote:
Originally posted by Peter Daniel
Another interesting thing is if there's a difference in sound between amp having 8dB gain and 32dB gain? Reading Joe Rassmusen thread I remember he mentioned optimal gain to be in 30dB range.
The amp with 32dB will be louder


Seriously, how will you tell? If you want to properly compare two amps with different gain, you will have to make up that gain with a preamp (low-gain amp), or lose some gain with an attenuator (high-gain amp). Sure, I accept that there might well be some differences, but with a GC, both these options are likely to affect the sound more than the difference in gain.

I'd be interested to read more - have you got a URL or some search tips?

Cheers,

Mark

PS - Congrats on your venture and first review
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Old 8th July 2003, 06:05 PM   #18
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The easiest way would be to compare it using a buffered, good quality volume control. I believe there will be a substantial difference, as comparing 250k and 300k resistors, inserted in a feedbak loop, was easily detectable. It is also dependant on what level of performance we expect from our GC. If it's only for casual listening or computer based system, then it's not worth investigating.

Here's the post by Joe discussing different gains and possible consequences:
http://www.diyaudio.com/forums/showt...564#post164564
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Old 8th July 2003, 06:59 PM   #19
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Hi Mark,

Yes I was referring to the error you get when trying to get linear-in-dB range with binary steps. But your curves are not that bad. What about using one extra relay to switch the 22ok between two values? You could use the 18-32dB range of the 4 bit thing, which is pretty linear, and use the extra relay to say shunt the 220k with a resistor to lower the gain by 18dB, bringing your linear range to full 32dB. Does that make sense? It would mean you need some logic because you no longer have a nice binary count. Or maybe you do have if the extra step is made 16dB.

Jan Didden.
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Old 9th July 2003, 04:16 PM   #20
Variac is offline Variac  United States
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Mark H,

I like the simplicity of your calcs. After all, if we want "everything plus the kitchen sink" we should just get Apox's.

Also, the minimalist approach seems the right way to go with a chip amp. As Peter said, even a few positions can be quite useful.

I'd really appreciate a schematic that is totally clear, very simple, with parts values so even a gainclone guy could build it!
Who's gonna make a prototype?
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