Topic Options
ICL1P wrote:
Copyright © 1998
Cadman Enterprises Ltd
Welcome to the Graham Slee Audio Products Owners Forum  Open to all owners plus those contemplating the purchase of a Graham Slee HiFi System Components audio product and wishing to use this forum's loaner program: join here (Rules on posting can be found here) This website along with trade marks Graham Slee and HiFi System Components are owned by Cadman Enterprises Ltd |
1970s Design Indulgence |
Post Reply 
|
Page <1 278279280281282 333> |
| Author | |
Graham Slee 
Admin Group 
Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Online Points: 16097 |
 Post Options
 Thanks(1)
 Quote Reply
 Posted: 09 Feb 2023 at 12:24pm |
I'm sure you've followed a Ford where the indicators come on and the rear light on one side or the other stops working? That's due to corrosion where the bulb wiring is grounded to the body, so it pulls current through another bulb. But that's because Ford insist on doing things cheaply. Apols to Ford owners. In power amplifiers the stages that do the current for the load have separated grounds (uncommon negatives if you like), so that one channel doesn't do a "Ford" with the other. And the 7eventy has separated grounds where you'd expect them, but as you found, separation wasn't as good as a monobloc. And that's because the voltage stages also used the "time honoured" grounding technique as illustrated by the Decca guy, Artus, followed by everybody else. It is thought that the voltage stages consume such little current that it doesn't matter, but I have always thought that it does. After all, it is still current, and if one channel's voltage amp requires a few milliamps more, and the other channel's voltage amp doesn't (due to the stereo mix) then it can pull current (or pinch current) through the other channel. But this is considered to be so small as of no consequence. Except, the ground (-ve connection) for each side also carries the residual of the signal harmonics, so will add or subtract from the other's residual, adding distortion to the other channel. You see, we still measure stereo like we measured mono. There are no tests for stereo loop distortion, except for crosstalk, but that's a misleading test. Having said that, crosstalk now measures -97dB (in other words, bl**dy good). S/N unweighted is 67dB; CCIR 20Hz - 20kHz is 79dB; and A-wtd. is 80dB (take your pick). In addition, in THD sweep tests, both channels track each other very closely, which wasn't the case before unless the ground wiring runs were tweaked each time. So it does matter that the stereo ground loop is tackled even for the low current voltage stage. And so, I must mark everybody else (except the particular JVC amp) as must try better. A case where research means research. Whether the 7eventy sounds better or not, who can say.  |
|
|
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
|
|
 |
|
|
morris_minor
Moderator Group 
Joined: 27 Mar 2012 Location: Surrey Status: Offline Points: 5904 |
Post Options
Thanks(0)
Quote Reply
Posted: 09 Feb 2023 at 12:50pm |
|
I see the moniker "7eventy" is gaining traction
|
|
|
Bob
Majestic DAC/pre-amp Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50 2 x Proprius + Spatia/Spatia Links |
|
|
|
|
Fatmangolf
Moderator Group
Joined: 23 Dec 2009 Location: Middlesbrough Status: Offline Points: 8623 |
Post Options
Thanks(1)
Quote Reply
Posted: 09 Feb 2023 at 7:07pm |
|
It is a sound name Bob. Grounds and sound...
|
|
|
Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
|
|
|
|
morris_minor
Moderator Group
Joined: 27 Mar 2012 Location: Surrey Status: Offline Points: 5904 |
Post Options
Thanks(2)
Quote Reply
Posted: 17 Feb 2023 at 12:08pm |
|
So, I've had the 7eventy amp hooked up for 10 days now and have had time to form some opinions.
As I mentioned earlier, the amp is fed by an Audiolab 8200AP which acts as a pre-amp for a Reflex M/Elevator combo, and DAC for an old Squeezebox Classic promoted (or down-graded, depending on how you look at it) to a Roon endpoint. Speakers are a pair of passive KEF LS50s, and listening was done with and without a sub (with the Audiolab settings changed appropriately).  Very first impressions - borne out by repeated listening - was that the sound was dynamic and detailed, neutral rather than warm and cuddly. The stereo soundstage was wide, and depth information seemed to improve the longer the amp was left on. Vocals had an impressive immediacy and orchestral timbres were realistically conveyed. Taking Graham's advice I dialled the meters down slightly to 17 (from 20) and though the change was subtle the sound did seem to "relax" a bit without losing impact or definition. The normal amp in this system is an Audiolab 8000A, and using the sub with the 7eventy I had to turn the bass level down a bit compared to the setting I'd been using with the Audiolab. I'm not at all sure why as the roll-off for the LS50s was set to the same for both amps. However most listening was done without the sub and the LS50s set to full-range. Music I tried included Alan Parsons Project albums, Sade, some Pink Floyd, a lot of Zero 7, many jazz albums, and orchestral and choral music. One particularly revealing LP is Vaughan Williams' Mass in G minor from Kings College Cambridge with its striking acoustic - relayed by the 7eventy and LS50s with as much clarity, depth and definition as the Proprius pair and PMC floorstanders in my study system. As the amp is hooked up to my AV system and TV, using it with the Disney+ Obi-Wan Kenobi series (sub on, of course) provided a truly immersive, window-rattling experience. Looking at the comments from Ian and Ifor, it's apparent I didn't have the same impressions! I haven't compared the 7eventy to the Proprius amps, not have I ever compared my 8000A to the Proprius. (Maybe this means I'm getting less of an "audiophile" as time goes on and I just like listening to music?). I think the problem hifi equipment has is that it's all very dependent on both the other components in the system and the preferences (and prejudices in some instances) of the listener. You can only tell it like it is for you - as the saying goes "your mileage may vary". Also unlike Ian and Ifor i didn't notice any difference between vinyl and digital. I'm quite willing to accept, though, that my hearing is not what it was! The bottom line is that I'm in absolutely no rush to return to using the 8000A, though I'm waiting to find out who is next in line for the 7eventy audition. Graham's long and exhaustive development of this amp has produced a fine product that deserves to have a future. |
|
|
Bob
Majestic DAC/pre-amp Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50 2 x Proprius + Spatia/Spatia Links |
|
|
|
|
Sylvain
Senior Member 
Joined: 18 Jan 2010 Status: Offline Points: 457 |
Post Options
Thanks(1)
Quote Reply
Posted: 17 Feb 2023 at 2:30pm |
|
this almost match my experience of 70's .....it is very good on vocal Phil Collins anwould not say contrary natural and intimate ....bass evident but possibly dependent on speaker design and ancillaries but i felt the high frequencies of the Focal inverted dome dispersion succinctly BUT perhaps my choice of music, studio registered, but felt stereo imaging though the silence in between the speakers are sometimes to be appreciated. Yes Indeed, this 70's deserve to emancipate among the best well considered, developed analogue amplifier for todays 24bit music.
The Graham selected and specified transformer may have assisted the better, more natural and blissful vocals Mid range frequencies than toroidal.
|
|
|
|
|
ICL1P
Senior Member
Joined: 04 Aug 2012 Location: Faringdon, Oxon Status: Offline Points: 2324 |
Post Options
Thanks(0)
Quote Reply
Posted: 18 Feb 2023 at 12:38am |
|
Good to hear Bob.
|
|
|
Ifor
===== Reflex M & ACCESSION M, CuSat50, Majestic DAC, a Proprius pair. |
|
|
|
|
Graham Slee
Admin Group
Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Online Points: 16097 |
Post Options
Thanks(1)
Quote Reply
Posted: 22 Feb 2023 at 3:23pm |
|
Dynamic Quiescent Current AC theory is easy. After all it's simply trig'n'geo metry! I mean, we do have scientific functions and formulae to be able to create equations to which we only need to add values. But that assumes we have a clue what we want to model... I really like the contradiction in my title above. What I think we really need is to know the quiescent current (or emitter resistor voltages) at the very instant the signal stops. It should be obvious that if set quiescently, then at the moment signal is applied, more current flows in the output stage, which causes heating in the output stage, which causes more "quiescent" current to flow. Therefore, the quiescent current set statically must be wrong? Could this be why Bob reported that the amp sounded more relaxed by turning the quiescent down from 20 to 17? I definitely think so. By the way, what units do 20 and 17 describe? The meter is marked in uA (micro-amps), but they are actually giving the average voltage of the emitter resistors in mV (milli-volts). To be continued when I get my head around this.
|
|
|
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
|
|
|
|
|
Post Reply
|
Page <1 278279280281282 333> |
Tweet
|
| Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You can vote in polls in this forum |
Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.
This page was generated in 0.235 seconds.
Copyright ©2001-2018 Web Wiz Ltd.
This page was generated in 0.235 seconds.