Hi Do,
Thanks for the very interresting post you shared!
It is indeed a shame that amp can't be used easily with passive amps due to its low input impedance (unless using transformators etc.). I understand std modern equipment does cope with that and it allows lower noise floor, but a 50k imput as often seen would be far better.
3 questions for you:
1- regarding your findings passive / active pre, I have the feeling there is more here acting sides the active regarding "drive and punch" than trully adressing a frequency response problem. Could it be that your passive had the same frequency response after all and the impedance mismatch wasn't really an issue?
2- Do you intend to test your LDR pre again with your now uprated FO? It would be interresting to find out how it sounds
3- Did you compare your LDR pre vs your DB1 pre on another set-up? Just to make sure in a general case your DB1 wasn't generally more dynamic anyway, hence moving to DB1 adressing indeed some issues but while being more "device related" than impedance mismatch?
Many thanks again for all you share
Claude
Thanks for the very interresting post you shared!
It is indeed a shame that amp can't be used easily with passive amps due to its low input impedance (unless using transformators etc.). I understand std modern equipment does cope with that and it allows lower noise floor, but a 50k imput as often seen would be far better.
3 questions for you:
1- regarding your findings passive / active pre, I have the feeling there is more here acting sides the active regarding "drive and punch" than trully adressing a frequency response problem. Could it be that your passive had the same frequency response after all and the impedance mismatch wasn't really an issue?
2- Do you intend to test your LDR pre again with your now uprated FO? It would be interresting to find out how it sounds
3- Did you compare your LDR pre vs your DB1 pre on another set-up? Just to make sure in a general case your DB1 wasn't generally more dynamic anyway, hence moving to DB1 adressing indeed some issues but while being more "device related" than impedance mismatch?
Many thanks again for all you share
Claude
Hi Claude,
It is not easy to drive a 5K input with a passive preamplifier and I've noticed the same effects on the AMB B24 which has about the same input impedance as the FO 1.4. An active circuit is much better suited. I've done several tests with my gears and I have close to 7 preamps (mix of passive, active with unity gain and also others with lowish gain of 3) and also multiple amplifiers. Most of my amps have 50K input and using them with the LDR is extremely transparent and dynamic. The DCB1 doesn't have any better dynamics I found and it does color a little bit but I like it. I will shortly be testing with the DCG3 which should be really nice since it is Class A and SE design.
The FO sounds really good but you need the proper preamplifier to drive it.
Thanks
Do
It is not easy to drive a 5K input with a passive preamplifier and I've noticed the same effects on the AMB B24 which has about the same input impedance as the FO 1.4. An active circuit is much better suited. I've done several tests with my gears and I have close to 7 preamps (mix of passive, active with unity gain and also others with lowish gain of 3) and also multiple amplifiers. Most of my amps have 50K input and using them with the LDR is extremely transparent and dynamic. The DCB1 doesn't have any better dynamics I found and it does color a little bit but I like it. I will shortly be testing with the DCG3 which should be really nice since it is Class A and SE design.
The FO sounds really good but you need the proper preamplifier to drive it.
Thanks
Do
Thanks Do
Ouch, 5k input impedance instead of the usual 50k! That's indeed sadly a big negative as it makes the FO very difficult to drive for any passive (and I like passive too as don't see the point in any further gain stage). Even some lamp active pre might struggle...
5k is so low, is that what you measured? Somewhere I believed (hoped?) the input impedance of the FO to be 10k, with the possibility to alter that by simply changing one resistor and that going upwards to 20k or even 30k was possible without any real life drawbacks (marginaly more noise but from such a low level to start with). Is that not the case sadly, was I mistaken?
Anyway, let us know how it works with the DCG3
It would be nice to have LC's solution on how to modify the modules to allow passive resistive pres with say very short non capacitive cables...
Many thanks again
Claude
Ouch, 5k input impedance instead of the usual 50k! That's indeed sadly a big negative as it makes the FO very difficult to drive for any passive (and I like passive too as don't see the point in any further gain stage). Even some lamp active pre might struggle...
5k is so low, is that what you measured? Somewhere I believed (hoped?) the input impedance of the FO to be 10k, with the possibility to alter that by simply changing one resistor and that going upwards to 20k or even 30k was possible without any real life drawbacks (marginaly more noise but from such a low level to start with). Is that not the case sadly, was I mistaken?
Anyway, let us know how it works with the DCG3
It would be nice to have LC's solution on how to modify the modules to allow passive resistive pres with say very short non capacitive cables...
Many thanks again
Claude
I prefer a good amp with low input impedance on a bad amp with high input impedance. If you know you need an active stage, you can choose your own and give the character you want with it. If you don't like the idea not being able to use a passive pre, just hide the active stage in the cabinet of the FO and you'll have a high impedance input power amp, being able to cope with any pre, passive or not. BTW, Hypex is following the same idea with their OEM modules.
One drawback of the FO is that the schematics are not available. Experimenting with the input stage could maybe (maybe !!!) raise the input impedance, but I'm sure LC has been studying this. Anyway, I'm very happy with my FOM. And when my fingers start hitching, I'll try with DCG3 or other preamp, but after running the FO for some months, I still don't feel any need to change.
My concern is sound quality: no need for an additional stage as all my sources vary from 13 to 2V output, admittely DIY. I could reduce that to less than 5V, but why...
So it is not a matter of "hiding", but one of adding and SQ.
However, some of your post hints to something that could indeed make sense: having LC developing and non expensive pre (volume just, or volume and a couple of sources) that can match the FO sonic qualities. I know there is this FO volume board à la B1 with an op amp and basic pot. I don't know its sonic qualities but maybe there are more qualitative ways (switched resistors by relays and better buffer) at LC's level to raise it to FO levels?
Perhaps LC has such plan?
The Salas seems outstanting, but at a price and complexity / space. Some Shiit pre seem to make sense to, having something similar as their inside as a module could be great. As of me, I still use my Black Beauty since 15y without a problem...
Just thinking loud, I like it simple, qualitative and non expensive
Claude
That reminds me of Hoffman's Iron law, big, loud, low. You can only pick two
A simple buffer of any kind allows a passive pre to work well. If you don't like op-amps for whatever reason there are other choices.
A good quality op-amp in a unity gain configuration sounds simple, high quality and non expensive so maybe you can have it all
From all your posts it sounds like you are trying to convince yourself to want a First One but it doesn't fit that well with other parts of your chain.
Also remember that the FO M has an input sensitivity of 1.5V so if you have a 13V source you will need to attenuate a lot even when running it flat out.
That reminds me of Hoffman's Iron law, big, loud, low. You can only pick two
=> Nah, one can try harder, wouldn't think so much and just go ahead with std stuff otherwise
A simple buffer of any kind allows a passive pre to work well. If you don't like op-amps for whatever reason there are other choices.
=> no prob with op amps as long as sound is fine
Have even received a FDA today, a SMDL AD18 from my neighbour for eveluation (as I told him to have an ear on it), that's quite integration to extreme... let's see how it sounds vs old tech
A good quality op-amp in a unity gain configuration sounds simple, high quality and non expensive so maybe you can have it all
=> perhaps but still an additonal stage, but would be indeed my B plan, you named it, that is with a qualitative pot and op amp
From all your posts it sounds like you are trying to convince yourself to want a First One but it doesn't fit that well with other parts of your chain.
=> Correct... Could be a nice replacement to the current inside of my DIY amp, I like keeping the outside and upgrading the inside. My main prob is input impedance, rest is straight forward
Also remember that the FO M has an input sensitivity of 1.5V so if you have a 13V source you will need to attenuate a lot even when running it flat out.
=> Yep, but I can adjust my DACs output easily (transistors swaps) to get 3V, so that should hopefully be OK
Thanks
Claude
The Salas DCB1 is 95% Power Supply and just 5% preamp. You could do it with a simpler Power Supply to keep it small. A smaller PS will have an influence on sound, there again we meet Hoffman.
I have a Shiit Gungnir DAC. It's great, really great. I can imagine a Shiit pre would not be a bad idea.
Hi,
I did build a LDR preamp too from BTFSystems LLC - BTFSystems LDR passive preamp and its really sounds great. My diy dac is using a LC zap filter 2 line stage -> LDR pre -> FO M. Sounds great still. I guess maybe the dac stage driving capability has to be considered too whether the passive pre is suitable or not.
No one using LC's Attenuator Gain module which is a simple active pre stage? I am consider trying it but like never heard anyone take about it here. Anyone here tried it?
regards,
ck
I did build a LDR preamp too from BTFSystems LLC - BTFSystems LDR passive preamp and its really sounds great. My diy dac is using a LC zap filter 2 line stage -> LDR pre -> FO M. Sounds great still. I guess maybe the dac stage driving capability has to be considered too whether the passive pre is suitable or not.
No one using LC's Attenuator Gain module which is a simple active pre stage? I am consider trying it but like never heard anyone take about it here. Anyone here tried it?
regards,
ck
I was thinking about schiit Saga for a preamp,but then i read a review from the Hi-fi World April 2017.
Input impedance (DCR) measured
10k Ohms, and output impedance varied
around 2k Ohms, reaching a max of 10k
at full volume and a minimum of 249
Ohms at one position. These figures are
good enough to feed a 10k input on, say,
a power amp., albeit with some loss.
Maybe it´s still good to ok with the First One.
There is no gain via both outputs.
As Schiit claim the Saga SCH-20 has a
gain of x1 (unity) via both outputs, Direct
and Tube. In other words it provides no
amplification.
The Saga SCH-20 measured
perfectly. Even the tube has been given
sufficient voltage to swing a very high
output, although with zero gain and only
3V or so available from modern sources
this is not going to occur in practice.
As Schiit claim the Saga SCH-20 has a
gain of x1 (unity) via both outputs, Direct
and Tube. In other words it provides no
amplification.
The Saga SCH-20 measured
perfectly. Even the tube has been given
sufficient voltage to swing a very high
output, although with zero gain and only
3V or so available from modern sources
this is not going to occur in practice.
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I know there is no gain, but your point wasn't gain but impedance related.
No gain doens't mean anything as of impedance. No gain and passive pre = probably the figures you mentioned, whereas no gain with an active stage (I would expect the tube to be that output stage = low output impedance, nerly constant.
In rough non scientific words, Iimpedance is to drive your following unit without any frequence/phase response issue. Gain is to drive the following unit while being able to reach a given max volume.
If the FO has an input sensitivity of 1,5V (which would be low but well) and your source a 3V output then a pre with no gain will be more than enough to drive the FO to max level.
No gain doens't mean anything as of impedance. No gain and passive pre = probably the figures you mentioned, whereas no gain with an active stage (I would expect the tube to be that output stage = low output impedance, nerly constant.
In rough non scientific words, Iimpedance is to drive your following unit without any frequence/phase response issue. Gain is to drive the following unit while being able to reach a given max volume.
If the FO has an input sensitivity of 1,5V (which would be low but well) and your source a 3V output then a pre with no gain will be more than enough to drive the FO to max level.