Subject: Input stage mods
Date: Wed, 23 Dec 1998 10:46:19 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/23 at 10:46:18, HARPER@SMTP {harper@q3-consulting.com} wrote:
Well, I finally got round to making the input stage mods
to my AtmaSphere M60s that I've talked about, on one
chassis at least.
The results are surprising, and I don't have a good
explanation.
First, what I did. I replaced the driver stage transformer
with a new one from Sowter, that gives 500V, and used this to
get a 600V B+, leaving B- at -320V. I then changed various
component values to get a standing current in the cascode
of 6-7mA per phase, with the goal of operating the 6SN7s
in a more linear region and hence reducing distortion, as
well as increasing overload margins. I also upgraded various components
to handle the higher voltage.
The good news: nothing has blown up (yet), despite having
nearly 1kV inside the chassis.
Distortion measurements on the input stage itself show a marked
improvement: at 1V RMS input, reducing it from 1.6% (measured
on a single channel) to 0.16%, and at -20dB from 0.16% to 0.06%.
So far so good.
But when I look at the output (using the balanced scope probe
to avoid unbalancing the output), things actually get worse,
e.g. 1.2% at 10W as against 0.6%.
Clipping seems to set in at much the same voltage. This seems
to orginate in the input stage.
All this might be easier to measure if I could turn of NFB - I
need to make this easy to do.
Early days - I need to listen for a while and see if I can hear
any difference to justify a day or so spent making the changes, not
to mention $300-400 in parts.
John
======================================================================
John Harper Specialising in the application of
Q3 Consulting Information Technology to
BP32, 06560 VALBONNE, France Telecommunications
phone: (+33) 493 12 24 70
fax: (+33) 493 12 09 89 E-mail: harper@q3-consulting.com
Subject: RE: Input stage mods
Date: Wed, 23 Dec 1998 11:05:44 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/23 at 11:05:43, JERRY$SE@SMTP {Jerry_Seigel@jdedwards.com} wrote:
John,
I posted a possible solution to turning NFB on and off in
http://www.condor-connection.org/asog/faq/fringe/index.html.
Please keep us informed about your experiments.
Happy Holidays,
Jerry Seigel
> -----Original Message-----
> From: Atma-Sphere@ManicReader.com [SMTP:Atma-Sphere@ManicReader.com]
> Sent: Wednesday, December 23, 1998 11:46 AM
> To: Atma-Sphere@ManicReader.com
> Subject: Input stage mods
>
> On 1998/12/23 at 10:46:18, HARPER@SMTP {harper@q3-consulting.com} wrote:
>
> Well, I finally got round to making the input stage mods
> to my AtmaSphere M60s that I've talked about, on one
> chassis at least.
>
> The results are surprising, and I don't have a good
> explanation.
>
> First, what I did. I replaced the driver stage transformer
> with a new one from Sowter, that gives 500V, and used this to
> get a 600V B+, leaving B- at -320V. I then changed various
> component values to get a standing current in the cascode
> of 6-7mA per phase, with the goal of operating the 6SN7s
> in a more linear region and hence reducing distortion, as
> well as increasing overload margins. I also upgraded various components
> to handle the higher voltage.
>
> The good news: nothing has blown up (yet), despite having
> nearly 1kV inside the chassis.
>
> Distortion measurements on the input stage itself show a marked
> improvement: at 1V RMS input, reducing it from 1.6% (measured
> on a single channel) to 0.16%, and at -20dB from 0.16% to 0.06%.
> So far so good.
>
> But when I look at the output (using the balanced scope probe
> to avoid unbalancing the output), things actually get worse,
> e.g. 1.2% at 10W as against 0.6%.
>
> Clipping seems to set in at much the same voltage. This seems
> to orginate in the input stage.
>
> All this might be easier to measure if I could turn of NFB - I
> need to make this easy to do.
>
> Early days - I need to listen for a while and see if I can hear
> any difference to justify a day or so spent making the changes, not
> to mention $300-400 in parts.
>
> John
> ======================================================================
> John Harper Specialising in the application of
> Q3 Consulting Information Technology to
> BP32, 06560 VALBONNE, France Telecommunications
> phone: (+33) 493 12 24 70
> fax: (+33) 493 12 09 89 E-mail: harper@q3-consulting.com
Subject: RE: Input stage mods
Date: Wed, 23 Dec 1998 11:10:41 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/23 at 11:10:40, HARPER@SMTP {harper@q3-consulting.com} wrote:
For what I need, even a switch under the chassis would be OK. But
I'm reluctant to put switches in the signal path if it can be
avoided. So I will probably end up doing something where I can
easily and safely unsolder something to turn of feedback.
I doubt that it makes much difference anyway, since the amount is
so small. Perhaps I should just get rid of it.
John
At 11:05 23-12-98 -0800, you wrote:
>On 1998/12/23 at 11:05:43, JERRY$SE@SMTP {Jerry_Seigel@jdedwards.com} wrote:
>
>John,
>I posted a possible solution to turning NFB on and off in
>http://www.condor-connection.org/asog/faq/fringe/index.html.
>
>Please keep us informed about your experiments.
>
>Happy Holidays,
>Jerry Seigel
>
>
Subject: RE: Input stage mods
Date: Thu, 24 Dec 1998 7:50:52 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/24 at 07:50:52, RALPH@SMTP {ralph@atma-sphere.com} wrote:
Dear John:
The clipping is occurring in the output section. Grid current conditions
cause the voltage amplifier to appear to be clipping at the same time.
-Ralph
>On 1998/12/23 at 11:10:40, HARPER@SMTP {harper@q3-consulting.com} wrote:
>
>For what I need, even a switch under the chassis would be OK. But
>I'm reluctant to put switches in the signal path if it can be
>avoided. So I will probably end up doing something where I can
>easily and safely unsolder something to turn of feedback.
>I doubt that it makes much difference anyway, since the amount is
>so small. Perhaps I should just get rid of it.
>
> John
>
>At 11:05 23-12-98 -0800, you wrote:
>>On 1998/12/23 at 11:05:43, JERRY$SE@SMTP {Jerry_Seigel@jdedwards.com} wrote:
>>
>>John,
>>I posted a possible solution to turning NFB on and off in
>>http://www.condor-connection.org/asog/faq/fringe/index.html.
>>
>>Please keep us informed about your experiments.
>>
>>Happy Holidays,
>>Jerry Seigel
>>
>>
>
>
- You'll be hearing more from us! -
Subject: A1, A2, zero crosings etc...
Date: Mon, 28 Dec 1998 7:41:56 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/28 at 07:41:55, B.LAYER@SMTP {b.layer@vikingelectronics.com} wrote:
Hi All,
Have a hoopy helliday?
Something is bothering me, and I need some opinions.
In a standard ASMS amp with 6AS7G outputs, the grid voltage is held at
roughtly -45 volts for proper bias. It is well known that that source of
power of the ASMS design lies in the wide and linear A2 operating range of
the 6AS7. If the 6AS7 outputs are never driven A2 (into grid current), the
total power of the amp suffers dramatically. If I recall, and M-60 makes
only about 20 watts in pure A1.
So lets apply our hot drive signal of 90V P-P. The grids are now driven to
0 volts and -90 volts on the upper and lower crests of the wave
respectivley. Now let's go into A-2 operation, driving the outputs with a
120V P-P signal. The grids now reach +15 and -105V.
Now, if memory serves me, the 6AS7 cuts off well before -105V, more like
-90V. It should, as it has an amplification factor of ABOUT 2 (more like
1.5 in ASMS service) and is presented with an anode voltage of +135V. The
figures even work out very nicely: 90 x 1.5 = 135V.
Correct me if I'm wrong, but Class A operation does *not* allow the device
to cut off at any point in the cycle; that is the definition of Class A.
So: are the ASMS designs _actually_ AB-2? Think about the definition of
AB-1 operation. An AB-1 design is _really_ a class A design, with extra
headroom FOR POWER. The only difference here is that these devices see grid
current, hence the '2' suffix. But they still can reach cutoff...
Now someone tell me why I'm wrong.
=======================================================================
This message and any attachments to it are subject to copying and are
sent solely for the personal amusement the sender. It may include
information which is technically wrong and exempt from disclosure. If
you receive this communication in any way, please ignore us immediately.
========================================================================
Subject: New E-Mail address
Date: Mon, 28 Dec 1998 22:21:50 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/28 at 22:21:49, TRE@SMTP {tre@ncplus.com} wrote:
This is Teresa and Tre's new e-mail address. tre@venturalink.net
Happy New Year
Subject: Re: A1, A2, zero crosings etc...
Date: Tue, 29 Dec 1998 17:34:30 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/29 at 17:34:30, RALPH@SMTP {ralph@atma-sphere.com} wrote:
>On 1998/12/28 at 07:41:55, B.LAYER@SMTP {b.layer@vikingelectronics.com} wrote:
>
>Hi All,
>
>Have a hoopy helliday?
>
>Something is bothering me, and I need some opinions.
>
>In a standard ASMS amp with 6AS7G outputs, the grid voltage is held at
>roughtly -45 volts for proper bias. It is well known that that source of
>power of the ASMS design lies in the wide and linear A2 operating range of
>the 6AS7. If the 6AS7 outputs are never driven A2 (into grid current), the
>total power of the amp suffers dramatically. If I recall, and M-60 makes
>only about 20 watts in pure A1.
>
>So lets apply our hot drive signal of 90V P-P. The grids are now driven to
>0 volts and -90 volts on the upper and lower crests of the wave
>respectivley. Now let's go into A-2 operation, driving the outputs with a
>120V P-P signal. The grids now reach +15 and -105V.
>
>Now, if memory serves me, the 6AS7 cuts off well before -105V, more like
>-90V. It should, as it has an amplification factor of ABOUT 2 (more like
>1.5 in ASMS service) and is presented with an anode voltage of +135V. The
>figures even work out very nicely: 90 x 1.5 = 135V.
>
>Correct me if I'm wrong, but Class A operation does *not* allow the device
>to cut off at any point in the cycle; that is the definition of Class A.
>
>So: are the ASMS designs _actually_ AB-2? Think about the definition of
>AB-1 operation. An AB-1 design is _really_ a class A design, with extra
>headroom FOR POWER. The only difference here is that these devices see grid
>current, hence the '2' suffix. But they still can reach cutoff...
>
>Now someone tell me why I'm wrong.
>
No-one seems to be stepping up to bat, so...
1) If -45 Volts is the correct bias level, then we have to use mu=2 in the
above formula to be fair: 2x 90 = 180. Why? class A bias voltage = -(.68 X
plate voltage)/mu (-which is 2). You get 45 volts, so mu is functioning as 2
so far.
2) grid current conditions are encountered at a point significantly less
then 0 volts (about -10 volts). We only have a little more room before the
outputs saturate (at least with *our* driver...)
3) It looks like gain and mu have been used interchangably above. This
brings us back to 1).
4) Actual measured cutoff voltage is barely in excess of -100 volts
(probably about 103 to 105 volts- I just used a data-hold meter and averaged
my results), meaning we can go to +10 volts (20 volts into the grid current
window) as a maximum grid voltage. Cutoff occurs just at or just after
saturation, depending a little on the line voltage and the tubes (we used
117 Volts, since that's the spec). So a total input grid voltage swing of
116 volts (not too far from the 120 volt swing mentioned above) is
permissable. In essense, the amp runs just barely outside the AB2 region at
full output. Because no cutoff conditions occur, is class A2 rather then
AB1. Whew!
I hope everyone had a pleasent holiday and from us at Atma-Sphere, have a
happy new year!
-Ralph
- You'll be hearing more from us! -
Subject: Re: A1, A2, zero crosings etc...
Date: Tue, 29 Dec 1998 22:20:52 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/29 at 22:20:51, BLAYER@SMTP {blayer@uswest.net} wrote:
Hi RK, All,
Because no cutoff conditions occur, is class A2 rather then
>AB1. Whew!
Can't disagree with the definitions, I thought cutoff ocurred earlier.
Guess I'll recheck the numbers... It's gotta be close.
Bill
/ / (_)__ __ ____ __
/ /__/ / _ \/ // /\ \/ /
/____/_/_//_/\_,_/ /_/\_\ The choice of a GNU generation.
Subject: Re: A1, A2, zero crosings etc...
Date: Wed, 30 Dec 1998 7:49:36 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/30 at 07:49:35, KCOVI@SMTP {kcovi@ibm.net} wrote:
Any discussion of Class A operation must include the load. For a 16 ohm load it is
true that ASMS amps run on the edge of AB2, or limiting Class A, to which it is
sometimes referred, but for an 8 ohm load the output tubes cut off at much lower
powers, due to the increased steepness of the load line. For example, if an M-60
can make over 60W into 16 ohms running class A, when the load is reduced to 8 ohms,
limiting Class A occurs under 20W.
That we can make as much as 60W into 16 ohms running class A is actually due to the
slow cut-off characteristic of the 6AS7. With normal triodes, operation in Class A
usually results in only a small increase in total supply current at full power,
relative to the current drawn at idle. This feature traditionally made Class A
operation particularly attractive with the poorly-regulated power supplies of a
generation ago. With 6AS7s, however, this is not the case as the average supply
current approximately doubles at full power into 16 ohms. But, given that the ASMS
power supplies are quite stiff, this is not a concern.
Another traditional motivation for Class A operation is that by avoiding tube cut
off, both primaries of a push-pull output transformer are always connected, thus
avoiding the ringing (caused by parasitics) that occurs in Class AB amplifiers when
the current in one primary abruptly goes to zero. This, of course, is totally
irrelevant when you have an OTL amplifier!
It seems to me that running Class A is nowhere near as important with OTLs as it is
with conventional transformer-coupled amplifiers. Probably one of the reasons they
sound so good....
Happy New Year.
- Kevin Covi
Atma-Sphere@ManicReader.com wrote:
> 4) Actual measured cutoff voltage is barely in excess of -100 volts
> (probably about 103 to 105 volts- I just used a data-hold meter and averaged
> my results), meaning we can go to +10 volts (20 volts into the grid current
> window) as a maximum grid voltage. Cutoff occurs just at or just after
> saturation, depending a little on the line voltage and the tubes (we used
> 117 Volts, since that's the spec). So a total input grid voltage swing of
> 116 volts (not too far from the 120 volt swing mentioned above) is
> permissable. In essense, the amp runs just barely outside the AB2 region at
> full output. Because no cutoff conditions occur, is class A2 rather then
> AB1. Whew!
>
> -Ralph
>
Subject: Re: A1, A2, zero crosings etc...
Date: Wed, 30 Dec 1998 11:57:10 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/30 at 11:57:09, HARPER@SMTP {harper@q3-consulting.com} wrote:
Funnily enough, I've been looking at the clipping behaviour quite a bit
lately. I was hoping to get round to making some more test befor responding to
this, but I didn't...
The standard amps clip first in the input stage. That cascode running
on 320V is a delicate balancing act, and it runs out of headroom just
before the output stage does. With my 600V B+ mod, the cascode has much
more headroom and can drive the output stage to its own clipping.
You can see the onset of clipping due to grid current very clearly in
the chassis I have modified so far. In particular, you can see the
cathode follower struggling to drive it and failing. This isn't
surprising. I haven't found any grid current figures for the 6AS7, but
you can bet that once the grid is +ve it will start to be milliamps rather
than hundreds of microamps. The poor follower is running at around 7mA
and suddenly finds itself asked to supply tens of milliamps in grid
current. Obviously it can't do this. (by the way the 6AS& is designed
to operate with *plenty* of grid current, as you can tell from
the big grid dissipators just above the plates. But I have not found
any data for this mode of operation).
John
Practically speaking, therefore, the M60 can't run in A2 (or AB2). To
achieve this you would need a seriously high current drive, for example
another 6AS7 (perhaps running as a plate follower with the cathode
at -120V or so).
It's difficult to measure the grid current directly, at least with
the equipment I have. You could measure the current across the 100 ohm
stopper, but because the output tubes vary so much (in mine I have
measured the standing current per tube varying between 40 mA and 120 mA)
this might be thw rong tube. If you have one stopper per tube you
could measure them all individually, but this is a difficult measurement
to make anyway - you really need a unity gain differential probe,
and I have not yet found one of these on the market.
I did think today of another approach, which is to look at the (common)
plate voltage of the cathode followers. Since they stop running balanced
as soon as grid current starts to flow, you should see evidence
of the grid current at this point. Indeed, this would create feedback
into the input stage as well (as the power supply sags). This could explain
some odd things I have noticed.
Anyway the bottom line is that the output power into normal speaker impedances
(8 ohms and less) is quite a bit less than 60 W, assuming reasonable
distortion levels. I love my M60s but I don't ask them to deliver this!
I will try and make some more measurements over the next few days in
this area. I have been thinking about using active loads on the cathode
followers (using the CCS tube for the input stage, and adding
a 5842 under the chassis to replace it). But I begin to feel I am
"gilding the lily" and may stop doing further enhancements. I did wonder
whether a big decoupling cap (e.g. the 47uF Solen I now have spare after
the 600V mods) on the cathode follower plates might not push the
clipping point up a bit.
John
At 07:41 28-12-98 -0800, you wrote:
>On 1998/12/28 at 07:41:55, B.LAYER@SMTP {b.layer@vikingelectronics.com}
wrote:
>
>Hi All,
>
>Have a hoopy helliday?
>
>Something is bothering me, and I need some opinions.
>
>In a standard ASMS amp with 6AS7G outputs, the grid voltage is held at
>roughtly -45 volts for proper bias. It is well known that that source of
>power of the ASMS design lies in the wide and linear A2 operating range of
>the 6AS7. If the 6AS7 outputs are never driven A2 (into grid current), the
>total power of the amp suffers dramatically. If I recall, and M-60 makes
>only about 20 watts in pure A1.
>
>So lets apply our hot drive signal of 90V P-P. The grids are now driven to
>0 volts and -90 volts on the upper and lower crests of the wave
>respectivley. Now let's go into A-2 operation, driving the outputs with a
>120V P-P signal. The grids now reach +15 and -105V.
>
>Now, if memory serves me, the 6AS7 cuts off well before -105V, more like
>-90V. It should, as it has an amplification factor of ABOUT 2 (more like
>1.5 in ASMS service) and is presented with an anode voltage of +135V. The
>figures even work out very nicely: 90 x 1.5 = 135V.
>
>Correct me if I'm wrong, but Class A operation does *not* allow the device
>to cut off at any point in the cycle; that is the definition of Class A.
>
>So: are the ASMS designs _actually_ AB-2? Think about the definition of
>AB-1 operation. An AB-1 design is _really_ a class A design, with extra
>headroom FOR POWER. The only difference here is that these devices see grid
>current, hence the '2' suffix. But they still can reach cutoff...
>
>Now someone tell me why I'm wrong.
>
>
>
>
>
>
>
>=======================================================================
>This message and any attachments to it are subject to copying and are
>sent solely for the personal amusement the sender. It may include
>information which is technically wrong and exempt from disclosure. If
>you receive this communication in any way, please ignore us immediately.
>========================================================================
>
Subject: Re: A1, A2, zero crosings etc...
Date: Wed, 30 Dec 1998 21:28:14 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/30 at 21:28:14, RALPH@SMTP {ralph@atma-sphere.com} wrote:
>On 1998/12/30 at 11:57:09, HARPER@SMTP {harper@q3-consulting.com} wrote:
>
>Funnily enough, I've been looking at the clipping behaviour quite a bit
>lately. I was hoping to get round to making some more test befor responding to
>this, but I didn't...
>
>The standard amps clip first in the input stage. That cascode running
>on 320V is a delicate balancing act, and it runs out of headroom just
>before the output stage does. With my 600V B+ mod, the cascode has much
>more headroom and can drive the output stage to its own clipping.
>
>You can see the onset of clipping due to grid current very clearly in
>the chassis I have modified so far. In particular, you can see the
>cathode follower struggling to drive it and failing. This isn't
>surprising. I haven't found any grid current figures for the 6AS7, but
>you can bet that once the grid is +ve it will start to be milliamps rather
>than hundreds of microamps. The poor follower is running at around 7mA
>and suddenly finds itself asked to supply tens of milliamps in grid
>current. Obviously it can't do this. (by the way the 6AS& is designed
>to operate with *plenty* of grid current, as you can tell from
>the big grid dissipators just above the plates. But I have not found
>any data for this mode of operation).
>
> John
>
>Practically speaking, therefore, the M60 can't run in A2 (or AB2). To
>achieve this you would need a seriously high current drive, for example
>another 6AS7 (perhaps running as a plate follower with the cathode
>at -120V or so).
>
>It's difficult to measure the grid current directly, at least with
>the equipment I have. You could measure the current across the 100 ohm
>stopper, but because the output tubes vary so much (in mine I have
>measured the standing current per tube varying between 40 mA and 120 mA)
>this might be thw rong tube. If you have one stopper per tube you
>could measure them all individually, but this is a difficult measurement
>to make anyway - you really need a unity gain differential probe,
>and I have not yet found one of these on the market.
>
>I did think today of another approach, which is to look at the (common)
>plate voltage of the cathode followers. Since they stop running balanced
>as soon as grid current starts to flow, you should see evidence
>of the grid current at this point. Indeed, this would create feedback
>into the input stage as well (as the power supply sags). This could explain
>some odd things I have noticed.
>
>Anyway the bottom line is that the output power into normal speaker impedances
>(8 ohms and less) is quite a bit less than 60 W, assuming reasonable
>distortion levels. I love my M60s but I don't ask them to deliver this!
>
>I will try and make some more measurements over the next few days in
>this area. I have been thinking about using active loads on the cathode
>followers (using the CCS tube for the input stage, and adding
>a 5842 under the chassis to replace it). But I begin to feel I am
>"gilding the lily" and may stop doing further enhancements. I did wonder
>whether a big decoupling cap (e.g. the 47uF Solen I now have spare after
>the 600V mods) on the cathode follower plates might not push the
>clipping point up a bit.
>
> John
>
>
If you remove the output tubes you will see that the voltage and driver
circuits run a lot more headroom then with the load of the tubes in place.
We get 65W into a non-inductive 8 ohm load with 117 volts from the wall-
before clipping, which we do not define at an arbitrary level, like some
magazines, but rather at the point where the waveform begins to square off.
If the amps are getting proper line voltage, they should do that. The older
amps (without the 1 ohm resistors in the plate) will sart out at about 56
watts after a two minute warmup and will settle down to 61 watts after about
ten minutes. So if the amp is not meeting these specs either the line
voltage is down, the tubes have lost emmission or the driver has a problem
(see GA review where Charles Hanson measures the power).
We used to bypass the plate resistor for the driver tube but there is no
appreciable effect, so we stopped using the part.
We built a number of amps with beefier driver circuits, but there is a point
of diminishing return as the grid current of the output tubes climbs quite
quickly just above what the 'current' (get it? current? huck huck) driver
does. The MA-2 uses a pair of 6SN7s for this purpose, but the result is
lower distortion, not more power. Anyway the point is to have the tube last
a while and with only 6ma they last for some years. Again in the MA-2,
parralleled sections are used on the bottom of the cascode to reduce
distortion and increase bandwidth (and a higher B+ voltage is used) but the
increase in actual headroom is not profound.
At this point the driver curcuit has seen over 21 years of changes and
refinement- and every driver circuit we have looked at has its own
tradeoffs. The system we use now was chosen for several reasons 1) it uses
only a single pair of coupling caps, and a small value 2)matched tubes are
not essential to operation (although better performance can be acheived 3)
because of 2) reliability is high. In the almost 21 years of business, the
biggest problem we have faced is the Futterman/NYAL reliability legacy. So
the driver topology was chosen for this reason. We feel that further
improvements will be along similar lines- other topologies which are
superior in their ideal forms in practice are way too fiddly and not very
user friendly- crucial for keeping the amp running and keeping our sport
safe and fun!
-Ralph
- You'll be hearing more from us! -
Subject: POWER CABLE EXPERIENCES
Date: Thu, 31 Dec 1998 21:21:34 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1998/12/31 at 21:21:32, ASEK@SMTP {asek@uswest.net} wrote:
Happy New Year to everyone!
This group is good for sharing experiences so we can learn from each
other. I enjoyed the exchange started by John Harper's driver stage
modification, and would like to share my recent experience with power
supply cable.
I did not believe power cable could make much difference as long as it
delivered the current without too much series resistance. My setup,
comprising my home-made copies of MA-1s with 6SN7 driver stages driving
the midrange and tweeter sections of Magnepan MG-20s, a Bryston 4B
driving the bass panels, and a REL subwoofer, draws about 15 amperes and
was making the standard outlet box in our Phoenix house get a little
warm. Primarily for safety, I had two 20-ampere circuits installed for
the system. We live less than two miles from the battery of
television/radio transmitting towers on South Mountain, so I had the
circuits installed with metallic-sheathed wire to a steel junction box.
Each circuit is fed from a different side of the 220-volt step-down
transformer which supplies several houses. We also had an elaborate
surge protector installed at the circuit-breaker panel. I replaced the
spec-grade outlets the electrician provided with hospital-grade units
and shortened the wires in the junction box. I found the ground
connection loose and tightened it (this is always worth checking
yourself if you are confident of working with power wiring).
Running the system from one of these circuits solved the heating
problem, made the supply voltage firmer (as detected by checking the
MA-1 bias levels), and made a subtle improvement in the sound. During
this period, I installed new speaker cables from Silver Audio and the
system reached its highest level of performance yet attained, either in
Boise or Phoenix. However, I was not happy with the appearance of the
extension cords: I had made an outlet box from spec-grade outlets in a
steel junction box with a metallic-sheathed cable for the installation
in Boise, and this was too short to reach the new outlets in Phoenix. I
was using this plus a short, heavy-duty standard extension cord in
Phoenix.
I ordered some AudioQuest AC-12 power cable and made up two new outlet
boxes with aluminum boxes, hospital-grade outlets, and hospital-grade
plugs. I intended to run each MA-1 from a different circuit, and split
the remaining loads between the two circuits.
This made the system sound terrible! The beautiful treble I had
achieved turned to metallic hash! Patricia Barber's _Cafe Blue_ has
wonderful close-up sibilants and cymbals, and these became complete
rubbish. I experimented with different connections and found that
running the CD player and preamp from the old composite extension cord
arrangement restored most of the integrity, but the sound was still
degraded compared to running the MA-1s from the composite extension cord
arrangement along with the CD player and preamp. Running the Bryston
from one of the new extensions tightened up the bass so I left it that
way. Now the Bryston and REL have one circuit and the MA-1s and sources
have the other. Note that I have not replaced the stock power cords to
the CD player and MA-1s, just made ten-foot extension cords with
hospital-grade outlets for the whole system.
I'm not done with my experiments. I intend to try again with flexible
metallic conduit around the AC-12 on one of the new extension boxes, and
perhaps make some long power cords for the Theta Miles CD player and
MA-1s from metallic-sheathed cable. I don't know if my problems come
from the close proximity to the transmitters, or from power supply
interactions with the AC-12 cord. However, it is clear that some CD
players are sensitive to the cable used to connect them to the power
mains in an urban RF environment, and the MA-1s are not completely
immune.
Regards,
Al Sekela
Subject: new e-mail address again
Date: Fri, 1 Jan 1999 23:02:21 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1999/01/01 at 23:02:20, TRE@SMTP {tre@venturalink.net} wrote:
I had not changed my "respond to" address upon my last mailing.
Again the new address is tre@venturalink.net
Happy New Year to All Tre and Teresa
Subject: Bill's ExFactory site.
Date: Sat, 9 Jan 1999 8:38:28 -0800
From: Atma-Sphere@ManicReader.com
Organization: SMTEK
To: Atma-Sphere@ManicReader.com
On 1999/01/09 at 08:38:27, BLAYER@SMTP {blayer@uswest.net} wrote:
Hey all,
Finally! Check out
I'd appreciate any feedback you may have. Please note that the graphics are
slow to load; we know this and are actively working on it.
Note also that the link from the ASOG page is broken, this is due to
filename changes. I'm sure Revrend Gilmore can fix this in a jif, though.
Hope you like it!
+----------------------------------------------------------+
| "The" Bill Layer - Frogtown, Minnesota. U.S.A. |
| Vacuum tubes, Analog, Motorcycles and Other Alternatives |
+----------------------------------------------------------+
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| | | |
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