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Preamp or no?

olds1959special

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I had a D0100 pro Dac going to a Schiit Saga S to four mono block amps but I ditched the preamp and am going straight from dac to power amps using a pair of splitters. I use the volume control of the dac. Is there any reason to keep my pre amp?
 
I had a D0100 pro Dac going to a Schiit Saga S to four mono block amps but I ditched the preamp and am going straight from dac to power amps using a pair of splitters. I use the volume control of the dac. Is there any reason to keep my pre amp?
A preamp is an additional layer of safety that protects from various volume mishaps.

Currently, if you accidentally set the DO100 Pro to DAC mode, then it's possible that you'll damage your speakers and/or your hearing.

In terms of sound quality, only two scenarios exist where a simple preamp can improve things:

-Your DAC->Amp connection is underdamped, stressing the DAC.

-Your can hear hiss with the DAC connected, but it goes away when you plug it out of your Amps.
 
if I remember correctly, in the tests done on ASR of various Dacs with volume, the best performances were obtained at maximum volume. So this would already be a good position if you want to listen to digital: exploit the best performances of the Dac and use a preamplifier for volume control....provided that the preamplifier is transparent enough obviously....
 
A preamp is an additional layer of safety that protects from various volume mishaps.

Currently, if you accidentally set the DO100 Pro to DAC mode, then it's possible that you'll damage your speakers and/or your hearing.

In terms of sound quality, only two scenarios exist where a simple preamp can improve things:

-Your DAC->Amp connection is underdamped, stressing the DAC.

-Your can hear hiss with the DAC connected, but it goes away when you plug it out of your Amps.
How do I know if the DAC-amp connection is underdamped? I am using RCA splitters to separate the signal from the dac to the four amps. I don't think I hear any hiss issues, and the volume is always remembered from the last setting and there is no full output DAC mode, except for setting the volume at 99.
 
A preamp is an additional layer of safety that protects from various volume mishaps.
Indeed. But that's about it, too. These days there's a bunch of DACs that make numerous classic preamps green with envy in the performance department (pretty much all but those with 4-gang volume pots), and the DO100 Pro is one of them. Those DACs that have linearity issues at low levels that could spoil the fun (generally of the R-2R variety) generally do not sport a volume knob.

If the volume setting is remembered reliably, you have nothing to worry about. There have been a few instances of documented oopsies with certain models. It goes without saying that issues in this regard is something that manufacturers should have an eye out for by themselves.
 
Indeed. But that's about it, too. These days there's a bunch of DACs that make numerous classic preamps green with envy in the performance department (pretty much all but those with 4-gang volume pots), and the DO100 Pro is one of them. Those DACs that have linearity issues at low levels that could spoil the fun (generally of the R-2R variety) generally do not sport a volume knob.

If the volume setting is remembered reliably, you have nothing to worry about. There have been a few instances of documented oopsies with certain models. It goes without saying that issues in this regard is something that manufacturers should have an eye out for by themselves.
I tried a Topping DAC once (don't remember which one) that freaked out and started outputting loud white noise one time, but it seems the D0100 Pro has been fine so far.
 
How do I know if the DAC-amp connection is underdamped?
You can calculate the damping factor with Amplifier input impedance divided by DAC output impedance.

This should be at least 10, but ideally 50+.

Keep in mind that with two Stereo Amps connected to one Stereo DAC output via splitters, the input impedance is cut in half.

Same with four Monoblocks.
 
You can calculate the damping factor with Amplifier input impedance divided by DAC output impedance.

This should be at least 10, but ideally 50+.

Keep in mind that with two Stereo Amps connected to one Stereo DAC output via splitters, the input impedance is cut in half.

Same with four Monoblocks.
I don't have the input impedance specs for the Kenwood L-05M's. It just says Input sensitivity: 1V. The DAC output impedance is 100 ohms according to the specs online.
 
I don't have the input impedance specs for the Kenwood L-05M's. It just says Input sensitivity: 1V. The DAC output impedance is 100 ohms according to the specs online.
The L-07 was 50 k ohm input impedance. They are very similar so that is likely what the L-05 is. Same 1 volt sensitivity for both.
 
The L-07 was 50 k ohm input impedance. They are very similar so that is likely what the L-05 is. Same 1 volt sensitivity for both.
Based on this, the damping factor should be 250 in my setup so I guess I'm okay?

50k input impedance / 100 ohms output impedance / 2 = 250
 
Basically, it depends on the noise contribution of your preamplifier, all other things being equal.

The LO-5Ms have a residual noise of (rated) ~28uV, but most of the examples I've owned (quite a few including 7 of their bigger brother LO-7m/mk2) have way in excess of that. Usually you will see 50-100uV. They are 47 years old and unless you've completely rebuilt with matched semis (unlikely), yours could be even worse. You will hear that as hiss in the tweeters.

I would always use a preamplifier, but you also want to know what noise it generates at the typical listening levels you use, along with the connected loudspeakers and their efficiency.

This is the input stage of your Kenwoods:

1725672157347.png


They are, of course a DC coupled amplifier and as such, you need to ensure the output offset of your D/A converter remains very low. Competent D/A converters will be capacitor coupled, but that doesn't rule out switch-on and switch-off transients tripping your DC protect on the power amps. The LO series amps will happily offset your woofers with DC up to the trip point of the internal protectors...
 
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Basically, it depends on the noise contribution of your preamplifier, all other things being equal.

The LO-5Ms have a residual noise of (rated) ~28uV, but most of the examples I've owned (quite a few including 7 of their bigger brother LO-7m/mk2) have way in excess of that. Usually you will see 50-100uV. They are 47 years old and unless you've completely rebuilt with matched semis (unlikely), yours could be even worse. You will hear that as hiss in the tweeters.

I would always use a preamplifier, but you also want to know what noise it generates at the typical listening levels you use, along with the connected loudspeakers and their efficiency.
This seems to contradict what AnalogSteph says above. I'm not sure what noise my pre-amp generated, it's a Schiit Saga S. I wanted to discuss this here to see if my ears are correct in feeling there is an improvement, even if there is a little less oomph in the bass and weight of sounds, there is more clarity overall.
 
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This seems to contradict what AnalogSteph says above. I'm not sure what noise my pre-amp generated, it's a Schiit Saga S.

If you didn't hear any noise before or after, then it's of little interest.

Basically, whatever noise your Saga generates is amplified by the Kenwoods by their gain.

Preamplifier noise invariably is dictated by the volume postion and/or internal gain in most cases. The D/A converter is likely not the weak point with residual probably around 1-2uV or so. The only time D/As betray themselves is when heavily attenuated, but we are talking at such low levels they are really only of academic interest. Not a usual usage scenario.

Mostly people "hear" an improvement when you pull something out of a chain. Mostly its imagined (they subconsciously think the playback chain must be somehow more "pure" when you pull out something and it still works) and often it can be detrimental to remove something like a high quality preamplifier due to risks and actual degraded performance.

But just do what works for you. As I said, I'd never run a high powered system with expensive speakers attached and trust a cheap <insert country of origin here> D/A converter to always remember its volume setting from one power cycle to another.
 
I guess I can always check the volume before hitting play when I power up.
 
I'm not sure what noise my pre-amp generated, it's a Schiit Saga S. I wanted to discuss this here to see if my ears are correct in feeling there is an improvement, even if there is a little less oomph in the bass and weight of sounds, there is more clarity overall.
While that comparison is hard to make without matched levels, you may still have gotten an improvement but not exactly the way you might think - the Saga S sports both exclusively RCA inputs and a 3-prong IEC power jack, which is a combo that makes me quite nervous with regard to potential ground loop issues, depending on what your DAC is connected to.

Your speakers are quite insensitive at 84dB/2.83V/m, so power output is more likely to be an issue than the noise floor.
Given the slight woofer and mid-tweeter sensitivity mismatch and room for improvement in their integration plus presence of 4 power amps, semi-activating them with a DSP crossover could be a fun project. Probably not entirely cheap though if you want to remotely retain your DAC performance.

How are the 4 amps being used now? They don't seem to support BTL, so do you have 4 speakers to go along with them?
 
In my DSP-based multichannel multi-SP-driver multi-amplifier fully active stereo audio setup, I intentionally use four HiFi-grade "integrated amplifiers" (and active L&R sub-woofers having volume/gain controller) to dedicatedly and directly drive each of the SP drivers, i.e. sub-woofers, woofers, midranges, tweeters and super-tweeters.

What would be the pros of using "HiFi preamp" or "HiFi integrated-amp" in this type of DSP-based multichannel audio system?
I wrote rather redundantly and intensively in my post #931 on my project thread;
I wrote in my post #931 on my project thread as follows;
Here in this post, please let me emphasize again about the pros and merits of relative gain (i.e. tone) control not only in digital domain but also in analog domain using pre-amplifiers or integrated-amplifiers (in my setup). I recently wrote again in my post #56 on a remote thread like these;
Yes, as for safe and flexible tone controls (or I can say "relative gain controls among the multiple SP drivers"), my stance (policy) at least, is that we are encouraged to utilize the "best combination" of "DSP configuration in digital domain" and "analog domain tone controls using HiFi-grade preamplifiers and/or integrated amplifiers".

We need to note (and to respect for) that analog domain tone controls (relative gain controls among the multiple SP drivers) give no effect nor influence at all on the upstream DSP configuration (XO/EQ/Gain/Phase/Polarity/Group-Delay). I believe that this is a great merit of flexible tone controls in analog domain. We know well, on the other hand, in case if we would like to do the "tone/gain controls" only within DSP configurations, such DSP gain controls always affect more-or-less on "XO" "EQ" "phase" and "delay" of the DSP settings which will leads you to possible endless DSP tuning spirals every time; within DSP configurations, XO EQ Gain Phase and Delay are always not independent with each other, but they are always interdependent/on-interaction.

Just for your possible reference, my DSP-based multichannel multi-SP-driver multi-amplifier active system has flexible and safe analog level on-the-fly relative gain controls (in addition to upstream on-the-fly DSP gain controls) for L&R subwoofers, woofers, midrange-squawkers, tweeters, and super-tweeters, all independently and remotely. My post here shows you a typical example case for such safe and flexible on-the-fly analog-level tone controls. This my post (as well as
this post) would be also of your interest.


Of course, I know well that I (we) can also perform such relative gain control using DAC8PRO’s 8-channel output gain controllers. I do not like, however, to change the DAC8PRO’s output levels frequently on-the-fly (while listening to music) due to safety and inconvenience concerns; I like to keep DAC8PRO’s analog out gain level always at constant -4 dB which should remain to be usually “untouchable” in my case.

One of the very unique aspects/features of my multichannel audio rig is that I fully utilize four HiFi-grade “integrated amplifiers” plus L&R active subwoofers, each of them have its own gain (volume) controller for safe and flexible relative gain (tone) control in analog domain even on-the-fly i.e. while listening to music.

In this perspective, my posts #438 and #643 should also give you better understandings. Furthermore, my posts #317(remote thread), #313(remote thread) would be also of your reference and interest.
 
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so power output is more likely to be an issue than the noise floor.

Not so with the LO-5Ms. They are monoblocks and mains noise (and residual) is always an issue with these either in three core (earthed) or two core (US style two pin unearthed). It is such an issue that the amps (and the Kenwood LO-7C preamp) came with earthing terminals and a (too long) connecting earth wire to bring the chassis' to a common potential. But then you get long ground loops from SE gear. LOL. Plug them into separate power outlets in a room and it gets worse, especially with the earthed versions.

1725674564552.png


Basically, they need to be plugged into a common power strip, with short power leads and tie all the chassis' together via a short ground connection. The entire design for placing the amps at the speakers was unfortunately ill thought out for a single ended design with long interconnects.

At least Kenwood had fitted and supplied special outer collared screw-thread RCA plugs which not only looked cool, they prevented destruction if someone pulled on an RCA plug while powered up. I wish more companies used those plugs. Like these:

IMG_3621.jpg
IMG_3622.jpg
 
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While that comparison is hard to make without matched levels, you may still have gotten an improvement but not exactly the way you might think - the Saga S sports both exclusively RCA inputs and a 3-prong IEC power jack, which is a combo that makes me quite nervous with regard to potential ground loop issues, depending on what your DAC is connected to.

Your speakers are quite insensitive at 84dB/2.83V/m, so power output is more likely to be an issue than the noise floor.
Given the slight woofer and mid-tweeter sensitivity mismatch and room for improvement in their integration plus presence of 4 power amps, semi-activating them with a DSP crossover could be a fun project. Probably not entirely cheap though if you want to remotely retain your DAC performance.

How are the 4 amps being used now? They don't seem to support BTL, so do you have 4 speakers to go along with them?
Two amps per speaker, one for lows, one for midrange and highs.
 
Would rewiring the power-amp with a 3-wire AC cable achieve acceptable results?

Yes and no. The Australian delevered LO-5m and LO-7ms were fitted with a three pin earthed lead and of the 7 I had and restored, they all had a bit of mains residual. Some were switchable voltage two pin and some were switchable voltage three pin earthed. The earthed units were better in isolation, but when connected to another earthed/grounded source, loops were created. A floating two pin unit ends up with the chassis being at some potential until the RCA is connected and then it's not a true ground/earth due to the resistance of the long patch cable shield.

1725692345676.png


The "special" connector RCA lead were 15M long for each amplifier, so were the trigger cables and the earth leads (x2) for connection back to the preamplifier which was provided with two dedicated earth points. It didn't really help that the chassis was comprised of several compartments screwed together with earth points at several locations including wrapped around the input RCAs and the speaker ground.

I came to the conclusion after many years with lots of LO series gear that it was a brilliant concept, with lots of careful engineering and expense thrown at it, but they failed to consider how the systems would perform in a typical domestic setup. The LO-7C and LO-07CmkII preamplifiers were pretty much the finest measuring preamps I've ever touched. But they were a bit fragile as time wore on and difficult to work on due to the construction.

The power amplifiers (LO-7m) were rated at 150wpc@8R. My examples achieved 190W@8R and 289W@4R. Under 4R they current limited.

I think monoblocks are really only a good option if you use balanced cabling and signaling. The amplifiers end up a distance from the preamp/sources and often in a different set of power outlets.

My personal opinion is single transformer power supplies with adequate current capabilities for both channels are often a better option than so-called dual-mono twin transformer amplifiers. The same goes for separate true monoblock amplifiers connected to a common source. The exception being dual secondary transformers- they seem to have none of the hum issues of a chassis with twin transformers and most of the benefits of separate supplies. That's my experience anyway. YMMV.
 
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