Hi Guys,
I'm new to this forum, and I was thinking about having a gaincloan (3886) built for me for a pair of Jordan Jx92s transmission line speakers I am building. I was also thinking about using a LittleDot headphone amp/preamp in the system, but they tell me not to use it with a direct coupled amplifier. I assume that the gainclone is direct coupled, am I right? Is this because the preamp passes DC, so you shouldn't use it with a direct coupled amp? What should I look for in a preamp to make it suitable for using with a gainclone? What about a gainclone with a simple volume pot incorporated into it?
Thanks, Peter
I'm new to this forum, and I was thinking about having a gaincloan (3886) built for me for a pair of Jordan Jx92s transmission line speakers I am building. I was also thinking about using a LittleDot headphone amp/preamp in the system, but they tell me not to use it with a direct coupled amplifier. I assume that the gainclone is direct coupled, am I right? Is this because the preamp passes DC, so you shouldn't use it with a direct coupled amp? What should I look for in a preamp to make it suitable for using with a gainclone? What about a gainclone with a simple volume pot incorporated into it?
Thanks, Peter
If we are referring to Figure 1 in application note: http://www.national.com/ds/LM/LM3886.pdf then yes, LM3886 based gainclone is direct coupled amp. However, nothing gonna prevent you from installing coupling cap at the amp input, and you'll be fine with a LittleDot.
Thanks to the Canadian! (Peter Daniel). Your solution is exactly what the guy who would build the amp just emailed me to suggest. Does adding a coupling cap have much significant effect on the performance of the gainclone?
If anyone is willing to answer, I do have remaining questions, as what I'm reading online is somewhat contradictory:
1) I'm reading that most SS amplifiers are direct coupled. Is this true? If it were true, than Andrew's response (above) disqualifies most people from using most amps! Seriously - why is this not more directly dicussed?
2) I'm surmising that direct coupled has no way to block DC. The input cap recommended by PD blocks DC from entering the amp. Where does the DC originate? Source? Preamp? Power supply in the source, preamp or amp?
3) Somebody wrote that if you have a direct coupled amp you should use a direct coupled preamp. I don't see how that would add any filtering of DC to the amp/preamp combination. Does this make any sense?
Thanks, Peter
If anyone is willing to answer, I do have remaining questions, as what I'm reading online is somewhat contradictory:
1) I'm reading that most SS amplifiers are direct coupled. Is this true? If it were true, than Andrew's response (above) disqualifies most people from using most amps! Seriously - why is this not more directly dicussed?
2) I'm surmising that direct coupled has no way to block DC. The input cap recommended by PD blocks DC from entering the amp. Where does the DC originate? Source? Preamp? Power supply in the source, preamp or amp?
3) Somebody wrote that if you have a direct coupled amp you should use a direct coupled preamp. I don't see how that would add any filtering of DC to the amp/preamp combination. Does this make any sense?
Thanks, Peter
The average gain setting is high enough not to need the colouration of a preamp stage. I went from opamp to valve buffer and back and eventualy came to the conclusion that the best preamp is a potentiometer, or better yet a stepped attenuator.
A low enough frequency signal is as good as DC....
A low enough frequency signal is as good as DC....
Interesting - cats squirrel. The guy building the amp for me said the the input cap should have no effect on the performance! He suggested using a standard polyprop cap. Should I be aiming higher in this application. I know it's a matter of personal taste, but for a budget amp like a gainclone, any suggestions?
Of coarse if size permits I'd kick his behind for trying to start my amplifier chain trough an electrolytic. Even a cheap polyprop cap would be miles better. I don't think you realy need 10uF though, and that wil be quite big and expensive. 3.3uF should be more than adequate, even lower, especialy if your speakers don't go all that low.
Don't discredit the chipamp out of hand, it sounds a fair bit better than most gear under $200.
Don't discredit the chipamp out of hand, it sounds a fair bit better than most gear under $200.
Most SS amplifiers are AC coupled.
The output is usually directly coupled to the speaker. The Dual Polarity Power Supply that is almost exclusively used in ClassAB amplifiers allows the output capacitor to be omitted.
I think it is this capacitor you have mistaken for AC or DC coupled.
A DC coupled amplifier amplifies all frequencies with in it's pass band to the same gain as DC signals.
An AC coupled amplifier blocks DC at it's input and has the DC gain set to 1 (+0dB)
The output is usually directly coupled to the speaker. The Dual Polarity Power Supply that is almost exclusively used in ClassAB amplifiers allows the output capacitor to be omitted.
I think it is this capacitor you have mistaken for AC or DC coupled.
A DC coupled amplifier amplifies all frequencies with in it's pass band to the same gain as DC signals.
An AC coupled amplifier blocks DC at it's input and has the DC gain set to 1 (+0dB)
my very cheap end of the range Conrad Johnson Pre-amp has a pair of 10uF PP output caps.
Yet the audio press criticised the Pre, for excessively restricting the bass end extension due to adopting an output cap that was too small.
No Electrolytics anywhere inside, not even the PSU.
My one amp has 100uf np electrolytic input caps (nothing else fitted)... you should see the poor speaker cones dance trying to reproduce subaudiable frequencies when I put a warped LP on.
I don't realy subscribe to the gainclones with the least amounts of best parts school, that is so common. Sure I started there. But I find these chipamps perform much more gracioulsy when given fixed parameters in how high or low they should extend themselves.
If I get a chance over the weekend I'll upload an example schematic.
I don't realy subscribe to the gainclones with the least amounts of best parts school, that is so common. Sure I started there. But I find these chipamps perform much more gracioulsy when given fixed parameters in how high or low they should extend themselves.
If I get a chance over the weekend I'll upload an example schematic.
Thanks guys. You may be interested in a similar thread I put on audiogon, where Ralph at Atmasphere states that I probably don't really need an input cap to protect my speakers ("The only way most tube preamps are going to make DC is if the output coupling cap fails, not if a tube fails.")
AudiogoN Forums: Direct Coupled Amps and Appropriate Preamps
It's a bit confusing to me, whether I need a coupling cap or not!!! Thoughts?
AudiogoN Forums: Direct Coupled Amps and Appropriate Preamps
It's a bit confusing to me, whether I need a coupling cap or not!!! Thoughts?
belt and braces?
No, if you have all sources capacitor coupled, and they are never going to fail, then you don't need two caps in series. However, if the DC does get through, then bang goes the 'speaker, and whats the use of one 'speaker, can you get another bass/mid range drive unit? The tweeter probably has a capacitor, too.
So my 2p's worth and my philosophy (and my practice) is ALWAYS put in a good quality cap.
No, if you have all sources capacitor coupled, and they are never going to fail, then you don't need two caps in series. However, if the DC does get through, then bang goes the 'speaker, and whats the use of one 'speaker, can you get another bass/mid range drive unit? The tweeter probably has a capacitor, too.
So my 2p's worth and my philosophy (and my practice) is ALWAYS put in a good quality cap.
Peter, unless you know for sure your sources, like DVD players, etc. do not output any DC (sometimes this only happens when sources are powered down before the amp....), an input cap offers your speakers a line of protection...without it, it is DC in and DC amplified out... go ask your speakers how they feel about running off DC.
Here is the filter arrangement I promised. The important parts sits between the input socket and the chip inputs.
I have to admit that it is not strictly my design, but learned from an old electronics magazine, that ran an article on the issue... I'm poor, it came from a library, so I don't remember which one... basicaly this arrangement will limit the chip to only trying to perform work on frequencies we can actualy hear... You could probably breadboard the required bits and insert it in your amp's input chain just to check it out.
I have to admit that it is not strictly my design, but learned from an old electronics magazine, that ran an article on the issue... I'm poor, it came from a library, so I don't remember which one... basicaly this arrangement will limit the chip to only trying to perform work on frequencies we can actualy hear... You could probably breadboard the required bits and insert it in your amp's input chain just to check it out.
Attachments
That is a standard input arrangement for any amplifier.
It contains an RF filter R4 + C4 and a sub-bass filter (=DC blocker) C8 + R2 and a grounding resistor on the input side of the DC blocker.
It is also drawn correctly to show the feedback R6 + R5 + C7 connected to the Signal Ground.
C7 + R5 sets the DC gain to ~1 and also rolls off the AC gain at very low frequency.
Power Ground (GND) is kept completely separate from the Signal Ground (J1-1).
The amplifier measures the voltage difference across J1-1 to J1-2 and sends a copy to the output.
So that the output voltage does not "Float", both the Signal Ground and the Power Ground must be referenced to Audio Ground (the Main Ground Star).
This is the way to connect every AC coupled amplifier.
There are exceptions. But save them for when you can decide why and how the exceptions can give an advantage, i.e. wait till you become an amplifier designer.
It contains an RF filter R4 + C4 and a sub-bass filter (=DC blocker) C8 + R2 and a grounding resistor on the input side of the DC blocker.
It is also drawn correctly to show the feedback R6 + R5 + C7 connected to the Signal Ground.
C7 + R5 sets the DC gain to ~1 and also rolls off the AC gain at very low frequency.
Power Ground (GND) is kept completely separate from the Signal Ground (J1-1).
The amplifier measures the voltage difference across J1-1 to J1-2 and sends a copy to the output.
So that the output voltage does not "Float", both the Signal Ground and the Power Ground must be referenced to Audio Ground (the Main Ground Star).
This is the way to connect every AC coupled amplifier.
There are exceptions. But save them for when you can decide why and how the exceptions can give an advantage, i.e. wait till you become an amplifier designer.
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Standard, but sadly way underused with chipamps. At best you sometimes see an RC highpass. Once again, as cointerintuitive as it might sound this limitation of the operating frequencies, make these chips sound better.
So, Andrew do you like it? I was not quite sure if your response was positive or negative, sure it just got lost in translation.
So, Andrew do you like it? I was not quite sure if your response was positive or negative, sure it just got lost in translation.
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