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1970s Design Indulgence
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Graham Slee View Drop Down
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Joined: 11 Jan 2008
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2023 at 9:58pm
The Proprius has three things in its favour:

1. no stereo loop (as they're monobloc)

(a plus for depth and width of soundstage)

2. no transformer harmonics

and

3. a regulated power supply

(a plus for everything else!)

Bass content depends on all three and the "lucky mix", meaning Blackstar was a "lucky mix".

However, the 7eventy sometimes exhibits the "never heard that before" and so I'm going to guess that the main culprit is the stereo loop.

Because the 7eventy is now a retirement hobby, I will give it one more shot with a different layout which rids it of the stereo loop.

(that's if John C will pay to have the PCB made Question)
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ICL1P View Drop Down
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Points: 2341 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ICL1P Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2023 at 10:46pm
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Graham, what will the next couple of retirement projects be?
Ifor
=====
Reflex M & ACCESSION M, CuSat50, Majestic DAC, a Proprius pair.
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Sylvain View Drop Down
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Points: 481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 07 Feb 2023 at 11:42pm
For what it worth,  I view " bass " as speaker / cable / acoustic environment / music content dependent.
Proprius is driven with an excellent Interconnect cable design, mine libran and bass radiation on BW 620 (8"cone) in a kitchen diner, no sofa and bass is grand and generous.
70"something Nostalgia with a  very multi strand thick copper speaker cable from Amp to Focal 6" bass cones was very balanced with bass overflowing in it's bottom under speaker vent to cause 20mm MDFvinyl floor to vibrate. 
My only issue is the Stage width and depth for better scale to it's presentation of music.
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Graham Slee View Drop Down
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Feb 2023 at 9:03am
Originally posted by ICL1P ICL1P wrote:

👍
Graham, what will the next couple of retirement projects be?

Already announced are a remote control transmitter and receiver circuit (an unusual one), which might be useful to retrofit to an amplifier or preamplifier project.

And the other being a "line stage", although that tends to suggest a switch and a pot in a box. I feel that the lessons learnt so far in terms of what buggers up the stereo image, could be put to good use in a "proper" preamplifier - what used to be called a control amplifier - a thing with gain that properly drives a power amplifier, and uses real transistors - the basic circuit of which has already been alluded to on here.
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Sylvain View Drop Down
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Points: 481 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Sylvain Quote  Post ReplyReply Direct Link To This Post Posted: 08 Feb 2023 at 10:54am
Seems a DEFINITIVE Reference system to a addP a significant and responsible G UPGRADE Modern Audio source is being   seriously and responsibly contemplated .....Not a " gap in the Market" Audio engineers thinking of this century ......BUT 70's AMP is best Compliment to 21st century music source....AND my experience of two electrocnic Pre amp attached to DAC or DAC Amp is but disastrous to music re production in a domestic environment.....The 2.7 V to 3.2 V of CD Player output needs a Pot in a box but with added thinking of a mature Audio engineer to Musicality NOT a marketeer agent function.....
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morris_minor View Drop Down
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Points: 6017 		Post Options Post Options   Thanks (1) Thanks(1)   Quote morris_minor Quote  Post ReplyReply Direct Link To This Post Posted: 08 Feb 2023 at 11:09am
Many thanks to Ifor for bringing along the amp! As the attached photo shows it's now installed in my living room system hooked up to a pair of KEF LS50s and driven by an Audiolab AV processor/pre-amp with sources of vinyl (Reflex M and Elevator, Yamaha PX-3/Zyx R100) and digital from a Roon driven Squeezebox Classic using the Audiolab DAC. I normally use a sub with the LS50s so will be trying the amp with and without this. Normally the amp I use is a venerable Audiolab 8000A from the era Graham's amp harks back to - so an appropriate comparison in many ways.
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
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Graham Slee View Drop Down
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Points: 16298 		Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Feb 2023 at 11:43am
Interestingly, other stereo amplifiers seem to do exactly the same as the 7eventy as regards grounding, so I'm hoping for a comparison between it and stereo amplifier (instead of between it and the Proprius monoblocs).

I know the Quad 303 uses the Dinsdale mod, but not 10 ohms. It is 2.2 ohms in the 303. I tried the same trick in the 7eventy but could not discern any audible difference.

In other amps (like the JVC ja-s22 a member on another thread allerted me to), the ground is taken to chassis at the input of the power amp, and also from the supply ground. As an integrated, the input grounds are isolated from chassis, with 10n RFI capacitors.

I've tried numerous grounding techniques - some cause hum - but it still seems open to experiment. Still, I cannot see how any of these other amps prevent ground current from one channel being "pulled" via the other.
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