AR SP8 mk2 high output volume

Yep, let’s go full circle and get dizzy again, just ditch the AR and use the A30 the way it was meant to be used. And if you don’t like what the source is giving then, change it instead.

AR output stage circuit diagram. https://ibb.co/Chrcx4t

OMG- while you are at it, jumper out R-30, C25 and C26. This will allow the feedback to include everything that occurs at the output of the preamp. I would also consider eliminating the C24 bypass cap and replacing C10 with a good quality part of the specified value (bypass caps tend to smear the signal when bypassing a larger coupling cap). D18 really doesn't protect the tube during warmup, but it does affect the sound so removing it is a pretty good idea. ARC left a lot of performance on the table in this design...

BTW this preamp is old enough that the power supply filter capacitors should be replaced if you want it to be reliable. If not replaced, the preamp could develop a hum, but could also suffer a power transformer failure and that is an expensive part to replace if you can even find it (ARC does not stock it anymore- they purged older parts like this years ago).

Here is another alternative, leave the A30’s volume up full, or again better still take it and the input selector out, and replace it with a 100kohm resistor to ground.

And then get full 6db shaved off the AR preamp’s gain, by a tech to do this.
Parallel R39 (another 39kohm) resistor across R29 (also a 39kohm) resistor, this makes it 19.5kohm, more feedback less gain is the result could sound a bit cleaner also.

AR output stage circuit diagram. https://ibb.co/Chrcx4t

@Georgehifi do not see in any review of the A30 R what you comment as a novelty

https://ibb.co/J7fFmwm

Puresound A30R https://ibb.co/mX2M6CM

@Georgehifi  do not see in any review of the A30 R what you comment as a novelty. In fact, now a remote control is incorporated and it is expressly said that it can function as an excellent power amp by raising the potentiometer to the maximumIgehifi

New Features (from original A30)

⦁ Twin power transformers for cooler operation and reduced noise floor

⦁ Output transformers have improved laminate material/windings for greater bandwidth

⦁ Remote controlled volume control and mute

⦁ Luxurious high gloss black finish

⦁ Updated styling

Thanks again for your contributions. I just ran a new test with the A30 working as an integrated amp and I certainly like it better when I put the AR SP 8 on. All sound becomes bigger and more controlled..

Just found this, the newer Puresound A30R model which among other things like 2 power tranies, now also sports a new 4th input call "fixed"
This suggests to me now it can be used as a "proper poweramp" with the volume control and input switching out of circuit when the "fixed input" is used by another preamp or sources with volume control.
https://ibb.co/J7fFmwm

Cheers George

The worst area of rolloff is typically around the middle of the control range

That will be for linear pots, with logarithmic pots it’s more like 1-2 o’clock as we have here with a 100kohm "A" taper pot. If this amp were to used as a poweramp, it would be better for the volume control to be removed and a 100kohm resistor in it’s place to ground, and the gain dropped by 50% by a tech, Then there will be no series resistance causing any HF filtering. And a + could very well be a tighter bass with lower gain/higher feedback, which was it’s only area of question in reviews.

"beautiful sound with minimal distortion, but not too well-controlled bass"  

Cheers George

Good to know the A30 volume pot does not degrade the signal when set lower than full. I learned something.

@audite84  The volume control is a 100K device. Combined with the input capacitance of the voltage amplifier tubes (which are essentially 6SN7s) there will be a high frequency rolloff. This is called Miller Effect. But in this case the values have been chosen well so that the rolloff is occurring well outside the audio band. The worst area of rolloff is typically around the middle of the control range; on paper at least its affecting things around 90KHz and above.

Whatever, Ralph's told you as well, you can see the forest for the trees, and not worth the effort.

Have they told me? Yes, there have been different opinions and arguments, all very valuable. You had your answer and others theirs. But I’m not going to apologize for this ...... it’s a forum DISCUSSION.. if you feel dizzy stop following.

I would like to know your opinion and if you consider its high output volume a problem with this power amp. AR SP 8 mk2 Problem is the volume control is too low, Very sensitive amp. I can’t use much volume control.Does this affect the signal quality.

This is what you asked, you’ve been told, now your making everyone dizzy.

in fact I made that query, and it was not me who began to question about the possible degradation of the signal because we are talking about an integrated amplifier. I think is you who does not mind looking at what is said here, because here more things are being said than what you say.

I just received a direct response from the creator of the A30 Guy Sergeant, who had asked this question about the signal degradation when you use the potentiometer of the device as a power amp.

This is what he said:

If you use the potentiometer at full or nearly full that effectively takes it out of circuit. It presents a high resistance (100 Kohm) so the signal takes the easier path into the amplfier itself.

@georgehifi Do you think I’m lying when I say that I like what I hear when I connect the AR?

Not in the least, but you started this thread asking for answers to your high gain problem, you now have them and don’t care to look at what’s said here, and not just by me. Like I said your going round in circles.

Cheers George

@georgehifi Do you think I'm lying when I say that I like what I hear when I connect the AR? It's very easy for me to use the A30 as a built-in amplifier and keep the AR as a collector's item. Can I also buy a Dac with variable output or does this also contradict Nelson's Bible?

What is evident is that there is a discrepancy between people who, like you, are interested in helping and I am grateful. You affirm that using two potentiometers compromises quality but does not say to what extent it compromises it, or what should I hear anomalous as a consequence of that.
I remind you that the origin of this problem is that Guy Sergeant, the manufacturer of the A30, has put in his instruction book that this integrated amplifier can function as an EXCELLENT power amp, just by setting the potentiometer of the device to the maximum. This gives me to understand that if there is any compromise with the quality of the signal, it may be minimal.
Grateful for your help, but not for repeating the same thing many times, it becomes more true.

Good to know the A30 volume pot does not degrade the signal when set lower than full. I learned something. 

@Georgehifi I will not make decisions because they are necessary to respect the Nelson Pass Bible.

I'm saying that the easiest cheapest way out of your high gain predicament, with "gods" recommendation to back it up.
 
Unless you want to have sound quality compromises, by having two volume pots in the siganl path or voltage dividers ( Rothwell attenuators)  at the inputs of the A30 both causing impedance mismatching problems.
 
But seeing this AR pre seems to be some sort of cherished attachment, and your not keen to dump it
Then the A30 needs to be mod'ed properly, input switching and volume potentiometer disconnection, with 100kohm loading resistor to take it's place to ground and a 50% gain lowering, all done by a tech with view on stability still, is the only other way out!!

You can't have your cake and eat it too. So suck it up and do one or the other. because your just going around in circles unless you do.

Cheers George

@Georgehifi I will not make decisions because they are necessary to respect the Nelson Pass Bible. In hifi there are many factors at play and I believe that Nelson Pass will be compassionate if in my house I am satisfied with a result that alters one of his commandments, and that according to other colleagues are saying, and according to what I am listening it is perfectly audible and satisfactory by the reasons being said. I respect your reasoning, but It is much easier than going to a technician and if we add everything that includes the sum of factors that influence the final result, it would be necessary to be very sure that this Nelson Pass mandate prevails over all other factors and responds to a perfectly palpable injury from my chair.
if this AR + Puresound A30 set won’t sound very good to my ears, I wouldn’t have worried about excess gain at all. thanks really for your help

@atmasphere , that is what I said, or....what I meant. A volume control / switcher, straight, without a gain stage ( passive ) to the power amp section. If I was not clear, I apologize.

Quite often George and I disagree, but not here.

@mrdecibel  This 'integrated' amp does not employ a separate gain stage for a preamp section. Its a power amp circuit (a variant of the Williamson circuit) and simply has enough gain that any source with a maximum output of 1 volt (such as an old school cassette deck) can easily drive it to full output. 

BTW I do not recommend tampering with the feedback resistor- such things can lead to oscillation

tenoris OP

This is why I say get a tech (not yourself) to disconnect the Alps passive, change the gain with the feedback to half of what it is, as he will scope it and compensate for stability.
And then once that is done you can use your AR preamp which you are so insistent on using, with the volume up around or over 12 o’clock. And this is what you searching for.

Cheers George

This just keeps going around in circles, if you don’t like the sound when it’s used as an integrated, change the source to one you like, instead of coloring it with that premp, and then having your problem of way too much gain.

Just look at the specs of the A30, it’s at FULL POWER already with ONLY 0.5v (500mV) input from a source. Most sources today put out well over 2v!!!

So just use it as is with it’s own passive volume control, and remember Nelson Pass saying to you ("psychological need" to turn it up more) than when the AR pre is in and then sell it.

Nelson Pass,

“We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.”

Cheers George

It seems the integrated amp is similar in design, to a power amplifier, connected to a passive unit ( this A30 amp design, is becoming very popular ). What the OP is saying, imo, he does not like passive, as much as the AR's tube line stage, and prefers the extra gain, like many people, that do not like passive. It just so happens, the amp has it's own volume control ( no different than many pro amps having input attenuators ), but still going through a preamp, with gain, or even a passive device, with multiple inputs ( something I am very accustomed to ). Enjoy !, and be well....

when I put the AR I notice a plus in terms of presence and forcefulness of the music

OK. I asked simply because with a high level signal like a CD player I would not have expected adding additional circuitry would have helped out.

Thank you all very much for these valuable contributions.
@atmósfera the one hand it seems good news that the passive attenuator of the A30 does not degrade the signal, but what I do not understand is your question because it seems that the AR is not fulfilling its function as a preamplifier. I gather this because you ask me strangely if I notice any improvement. Is it that the AR is not fulfilling its function like any other preamplifier?
The Puresound as integrated works quite well but when I put the AR I notice a plus in terms of presence and forcefulness of the music

@tenoris

Having looked at the schematic supplied by @imhififan I agree that essentially this amplifier is actually a power amplifier supplied with three inputs and a passive volume control.


Since the control is 100K and given the characteristics of the input tube, you can successfully operate the volume control to reduce the level of signal coming from the ARC without degradation.

However if the sources are high level (in other words not phono), I am still having trouble seeing what good the ARC can do for you unless the sources are not physically fairly close to the amplifier. It seems that you are saying that it nevertheless sounds better this way- so I am curious, what improvements are you hearing?

BTW I do not recommend tampering with the feedback resistor- such things can lead to oscillation, and if the schematic is correct there appears to be little or no compensation for a variety of frequency poles present in the amplifier design- by increasing feedback, any one of these poles could cause the amp to be unstable.

@georgehifi thank you very much for your advice. If you take it to a technician, you could also complete the operation by reducing the gain at any of the Puresound inputs.As I have already mentioned.

Sorry but no, again introducing series impedance at the A30 inputs is not on, with no thought for impedance ratio matching (min 1:10) between stages.
Best would be to completely take the Blue Alps out of the circuit (not just turn it up or bridge it out) introduce a metal film 100kohm input resistor to ground , and then reduce the gain by 1/2 of the total preamp tube stage with feedback resistance of R14 on imhififan circuit diagram.

Cheers George

@georgehifi thank you very much for your advice. If you take it to a technician, you could also complete the operation by reducing the gain at any of the Puresound inputs.As I have already mentioned, I have followed the manufacturer’s instructions, which in the Puresound instruction book says not only that it can work as a power amp but that it can also do it in an excellent way, textual words.

@audite84 with the volume of the Puresound at maximum it continues to work, so I do not understand why if we put it at 1 there is more degradation of the signal. It is true that if the manufacturer indicates this, this reason must exist, except that it is written thinking that most of the current preamplifiers need more volume.

OP, 

If the Puresound A30 is to be used as an amplifier (i.e. driven by a separate preamp), its volume control should be fully turned up. You are definitely degrading the signal if it's at 1 o'clock.

As mentioned, given the mismatch between the AR and the A30, it would be best for you to use the A30 as it is, an integrated amp.

Tube rolling is one thing you may look into if you're looking for a particular sound. Start with the driver tubes if you wish. 

If anyone interested, this is the schematic of the Puresound A30

http://lampizator.eu/AMPLIFIERS/CHINA/bewitch%206550/IMG_5576.jpg

IMO, leave the Puresound A30 and AR SP8 stock, just simply set the Puresound A30 volume knob at 12 or 1 o'clock is the best solution.

I used to have an Audible Illusions Modulus 2 pre-amp, the line stage of which provides 30dB of gain! Did Art Ferris ever update his design?

AR SP8, has 4 12AX7's , 1 AT7 and 1 6922.
yeah you could swap  a  pair of 12AX7's, and employ   12AU7's in that circuit.
have Richard remod it  for you

https://www.arcdb.ws/model/SP8

Interesting subjecft. I was going to posta topic on this subject of **preamps with high gain** = maybe too much gain
Here is my situation,,I just picked up a used Jadis DPL, , has 1 AU + 1AX + a cd buffer stage. anyway,
I had Richard Gray look over the LINE STAGE (Richard says a pre is actaully a line stage with a phono section),, anyway,, he says there are issues with the design,, that the 12AX7 is giving too much gain in the circuit = meaning at just 1/4 turn of vol knob, and the db level is quite significant,,, so I left him the DPL to look over,,,like 1 hours later he writes,,*Ok just did this and that and this,,,** when Richard gets a task, he goes right to it,,although it is a quite simple circuit and lots of open space to work. In 1 hour he had some mods completed...
I will not know the results as my speakers are being repaired, with new voice coils on the Millenniums and 2 of the W18’s need refoaming,,both I plan to do myself, its easy.
, so you may want to ck out if you can mod the 12AX7 toa 12AU7,, a AX has a mu of 100, a AU of 15.
Richard is anxious to have me test it, but can’t till new xovers arrived from Madisound in 2 weeks.
I’l;l posta YT vid when all upgardes/mods are completed.
Send the pre to Richard and have him mod it for you.

tenoris OP
This amp cannot be used as just a poweramp it’s always got the volume control in the signal path, at best it can be said it’s a poweramp with fixed input level controls and source selection.

There is "no rca power amp input" on the back of this amp, as the pic shows, https://ibb.co/fNVJzTb , it only has Tape CD and AUX, aux is also an input for any low level source, but it is not "poweramp input". If it were the passive volume control on the front would not work, and you say it still does.
So once again for the best sound just use it as a Integrated amp which it is, and flick the AR pre.

Or take it to a tech and get the A30's volume control and iput selector fully disconnected then it will be a poweramp, and still use your AR pre, but your going to be back in the same boat with too much gain, with the AR volume down around 9 o'clock.  

Cheers George

Thank you all very much, you are very kind. Let's see, I'm using the A30 as a power amp because I have tried this option and have noticed improvements in the scene and in the sound presentation. I know two more people who also do it with satisfactory results. My ears do not perceive degradation, although this does not mean that there is not. Undoubtedly both devices are very good separately and I like to have them, I will try with the Aux input but I am afraid that they are all the same and the manufacturer does not indicate anything about it, only says that the A30 can work as an excellent power amp, which I hints that the AR could be a travel companion.

There's no power amp input on this, just use it as an integrated and flick the AR.

https://ibb.co/fNVJzTb
Cheers George

I am using the Puresound A30 as a power amp because it is a possible option and so indicated by the manufacturer.

I have just tried to use the Puresound attenuation as you have indicated and the result is quite satisfactory, with this volume at 1:00, I can have a tour in the AR between 10 and 11 as a high volume level

@tenoris
If the above two statements are correct then you might be using the wrong input- use the one marked 'amplifier' rather than something like 'AUX'.


If this amp can be used as a power amp it will have an amplifier input, and that will reduce the gain such that the ARC can be easily used.


If it does not have an amplifier input, then what the manufacturer told you is incorrect, and there really isn't any advantage I can see from using the ARC- it should sound better just running the amp by itself with its own volume control.

tenoris You said it was a poweramp, in your opening post
Ralph is correct the A30 is an integrated!!!
1 o’clock is fine, just use it, it’s probably a passive in front of a poweramp any way, it uses a genuine Alps "Blue Velvet" volume control which is very good.

https://ibb.co/hH8kYpj
.
https://6moons.com/audioreviews/puresound/16.jpg

You are degrading using two preamps, sell the AR pre.


Cheers George

.Since we are somehow allowing some signal degradation by using both volume controllers, I wonder if it doesn't matter if the Puresound's volume is located in one place or another.

I have just tried to use the Puresound attenuation as you have indicated and the result is quite satisfactory, with this volume at 1:00, I can have a tour in the AR between 10 and 11 as a high volume level

On the other hand ; what do you think of the Rothwell attenuators? For their price I think they deserve a test.

Since your A30 has a volume control knob, no need to add another attenuator to the signal chain to further degrade the signal !!!

@atmósfera@atmósfera I am using the Puresound A30 as a power amp because it is a possible option and so indicated by the manufacturer.
As @imhififan indicates, I'm going to try to attenuate the A30's volume control.
On the other hand ; what do you think of the Rothwell attenuators? For their price I think they deserve a test.

Why are you using a preamp? Your amplifier is an integrated amp. 

😯

@tenoris
Why are you using a preamp? Your amplifier is an integrated amp.

If its for the phono, use the tape output of the ARC instead of the main out- problem solved.

Does this affect the signal quality or is it just a drawback?I just want to know if it's something I need to worry about.

Although  Puresound recommended turn the volume all the way up to use it as a power amp, it is OK to adjust the volume knob on the A30 to stay at 12 or 1 o'clock to reduce gain, and use the AR SP8 as a preamp.

Even better to use the Schiit Sys straight into the amp, if the amps input is 30kohm or higher like the OP's 100kohm A30.

Cheers George

This Schiit SYS is worth a try. I use one between my CDP and preamp to lower the output and it works great!
https://www.schiit.com/products/sys

Thank you very much for these answers, they are very useful!

tenoris
Does this affect the signal quality

Yes very much so, as Nelson says below, your throwing away much of the sources output level by turning down the volume of the AR, so the tube gain stage of the AR preamp can make it back up again, which means noise figures are worse, with added distortion.

Perfect reason to go direct if you dac has volume or  just get a good passive.

Nelson Pass,

“We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.”

Cheers George

You can try an in-line attenuator. AR do a mod to change the feedback and lower gain so you might ask them as a last resort. You could also try replacing the 12AX7 tubes to 5751 as they have 70% of the gain. GE black plate triple mica.