Control Amplifiers?

[sandyk]

2 hours ago, davide256 said:

he only fault I find right now with a fully modded Hafler is transients have a whip crack like accent, otherwise midrange and bass are much improved without a pre in the circuit.

Did these modifications involve the PSU area's filter capacitors ?

 The use of Low ESR electrolytic capacitors can lead to this, as can the inappropriate use of lower value parallel capacitors across large value filter capacitors. Many are overdoing this in their new servers etc. too ,when  adding a lot of low value "boutique" bypass capacitors. 

 

[sandyk]

1 hour ago, davide256 said:

I’m not clear what you are referring to. The bridge board power supply capacitors are 4 pole Jenson capacitors which replaced some fairly large capacitors using a standard diode bridge (about 4x the size of the Jensens) 

 The Jensen capacitors may be exaggerating HF detail a little if the circuit had already been optimised for normal type capacitors

 

Quote

FOUR TERMINAL ELECTROLYTIC CAPACITORS WITH EXTREMELY
LOW INDUCTANCE/IMPEDANCE FOR HIGH FREQUENCIES - Jensen

 

[sandyk]

3 hours ago, davide256 said:

Possibly. But every pre section I’ve ever had has introduced its own signature and limitations. At this point I view them as a no longer needed added whisper chain member if you can passively switch inputs and manage gain elsewhere

 However, at least in this thread, you appear to be basing your conclusion mainly around Vacuum  Rube technology which has MANY dB poorer S/N and Dynamic range compared with the best of Solid State equipment.

 Very few Valve amplifiers would achieve 90dB which is up to 40 dB less than the very best of solid state , and is barely adequate for RBCD, let alone high resolution LPCM and DSD.

[sandyk]

4 hours ago, bluesman said:

You do not need to buy a new preamp under any circumstances.  FIrst, almost all modern preamps have output impedances >20 kOhms. 

 You obviously mean Input Impedances.

The same applies to Power Amplifiers, although there can be a S/N advantage with a Power Amplifier having a lower Input Impedance ,provided that the Preamplifier or even a DAC,  has a low output impedance and adequate current drive capabilities.

 

 The attached may be of interest to some members

Alex

Passive_Preamps.pdf

[sandyk]

51 minutes ago, bluesman said:

hat I meant to say instead of "almost all modern preamps have output impedances >20 kOhms" was that "almost all modern amplifiers have input impedances >20 kOhms". 

Actually, there are many these days that have lower input impedances to achieve an improved S/N which is needed for high resolution digital sources .

The designs from Silicon Chip magazine are fairly representative , with their Ultra-LD Mk.3  from as far back as 2011 having an Input Impedance of a little under 12kohms , and many of the designs by U.K. Amplifier Designer and Author Douglas Self having a 10K input impedance. (Audio Power Amplifier Design Handbook 5th ed - D. Self (Focal, 2009) WW)

[sandyk]

1 hour ago, bluesman said:

Neither a project amplifier in a 10 year old magazine nor one text published a decade ago with content that's even older seems like a sound basis for advising the OP on mating any preamp/DAC and amp he's ever likely to buy. 

 The most recent magazine designs (SC200 etc.) have the same 12K Input impedance as back then .

I think you will find that Douglas Self's series of  amplifier books may be a decade old, but are still considered relevant by most qualified E.Es.

 Furthermore, most Vacuum Tube amplifiers , or Passive Preamps that the participants in this thread seem to prefer will have a much higher output impedance than typical Solid State Preamps OR DACs

 

 The attached graph in the extract from ESP may also be of interest to some

[sandyk]

3 hours ago, bluesman said:

I fear you've been as careless in this quote as I was yesterday. I assume you mean "...most Vacuum Tube preamplifiers".

 Yes. I shouldn't have bothered replying further and let others take what they wanted from our respective replies..

  The simple fact remains that the vast majority of vacuum tube equipment ,even when using transformers at the output. has both higher input and output impedances than most well designed solid state gear. 

Your idea of good enough is quite obviously very different to mine, where we have found in John Dyson's PM group that we are often able to hear differences of a little over 0.1dB in the frequency response area, with even a 1dB variation resulting in quite an obvious difference., dependent on the part of the spectrum it is in.

Quote

A single quoted figure with no reference frequency is probably useless in identifying potential negative interactions, since the preamp's output impedance probably rises at the very lowest frequencies and OI is almost always quoted as the resistance at 1 kHz.  If it reaches a very high value by 50 Hz or lower, it can result in attenuation of the lows in proportion to the rise in impedance by frequency

 

 A well designed Solid State Preamp will have very little difference in output impedance due to the normal use of a series output resistor of typically 100 ohms, especially with  I.C. based designs,  as most opamps do not like directly driving loads of >100pF . My own Class A Preamplifier is a discrete design ,  and is not only DC coupled, it is able to drive a 75 ohm cable or different makes of headphones simply by using the appropriate value of switched in  series output resistors and has a -3dB frequency of 1.5MHz.

(It can even pass VHS quality composite video)

 

( Many headphones such as AKG K701, ATH W1000  etc. comply with the old IEC61938 specification of using a series  120 ohm output resistor)

 

Quote

 I'm partial to more useful works like The Tube Amp Book (Pitman) and Building Valve Amplifiers  by Jones - now in its second edition (2014).

Your idea of more useful  is clearly based on your preference for glowing ancient technology with it's attendant added maintenance costs, using replacement tubes most likely different to those originally supplied, and usually with quite a variance in specifications to the original tubes . 😊

[sandyk]

7 minutes ago, bluesman said:

The added maintenance cost is easily offset by the drastic reductions in our heating bills. 🤪

 

 You fail to take into account the added cost of Air Conditioning in Summer, unless you live in a colder part of the country

 I guess that the hiss from the vacuum tubes is likely to mask the hiss from the A/C when running in Quiet mode though.😉

[sandyk]

Quote

How long do KT88 tubes last?

about 2500 hours

 

Power tubes like EL34's and KT88's are good for about 2500 hours or more. But may go longer in an amplifier with a conservative design. Small signal tubes with numbers like 12AX7, 12AU7, and 6922, and rectifier tubes like 5AR4 may go 10,000 hours. So you get years and years of enjoyment.

 I wouldn't want to also watch TV every night using a system like that at something around $280 for 4 matched tubes !  🙄

 Add to that the slow degradation that occurs without you realising it for quite a while .

[sandyk]

15 minutes ago, bluesman said:

 And those solar panels in the walls generate all our electricity.

 You aren't connected to the A.C. mains grid ?

The largest solar installation that I have seen belongs to Audiophile Neuroscience, but he is also connected to the Mains grid 

[sandyk]

Quote

Preamps of today do not require gain as all quality source components have an output of about 2 volts with a low output impedance.  - Townshend Audio

Generally,  FM Stereo tuners don't ,Tape Decks don't, RIAA Phono Preamps don't, and DTV audio with multi channel  may need as much as 500% amplification. ( I am going by captured .ts streams from USA Late Night Shows which may have 5.1 channels , and some DTV stations in the USA also use multichannel DTS Audio.)

 

 Stuff from the U.K. such as the Graham Norton show, which deserves better for the musical content, appears to have a miserable 128kb/s .aac Stereo. 😝

 

[sandyk]

21 minutes ago, bluesman said:

No need - the tube glow powers the solar panels in our inside walls. The panels power the tubes.  I assembled large arrays of piezo mic capsules that generate power from the vibration of my speakers, and I’ve achieved perfect coupling.  So there are no losses and we use no fuel to heat and light the place, cook etc.  

 

The only downside is the need to play music or videos 24/7/365 to keep it all going.  The day I stop the music, I’ll drive my Chevy to the levee and proclaim it to be Don McLean day.

It's a shame that Michael J Fox isn't up to another Back to the Future movie. They could have found another power source for the Delorean. 🤣

[sandyk]

13 minutes ago, bluesman said:

I bought the last flux capacitors, too. They’re now my preamp’s output couplers - the SQ is amazing!

https://www.youtube.com/watch?v=O35Yy_AFot0