Audio Research Reference 75

[microstrip]

Originally Posted by TOGA

Dear Dafos,
Well, I can't say it is 100% reliable as it is a rumour. But I heard info from a friend of mine who is big ARC fan. About the name 150SE, that is what I call it, I don't know the real name yet. For me, I rely so much that I might wait for it. Unless Ref75 prove it doesn't have power deficit I will buy it before year end. But If I feel I need more power, I definitely wait for this non-existence-for-now new 150 watt.
Toga

They would be repeating history. At the middle 90s Audio Research had two mono models: the VT150SE (with two large front meters and nice buttons ) and the VT150 for people who could not afford the SE - no front plate and no nice meters, just a miserable small meter to control bias. I have to say I was very happy with the VT150 - great sound with my Quad ESL63!

[TOGA]

Ok, forget about cables for awhile, what I have at other room is Kimber 8TC, dealer
has Transparent Ultra. So I will use my SS Reference cable.
Installation completed. amp has 100 hours on it. But now has minor problem.
Right channel of amp play way louder than left channel. Bias is spot on.
Left channel as so sound a bit distorted, similar sound to cassette tape being recorded far too strong beyond +0dB. Is this because of incomplete pathway
for balance connection ? like not all three pins are connected inside.
Waiting for dealer to come back to have a check. Oh and I don't see
digital tube hour meter inside.
Sound ? yes it has great potential. power driving Magico is absolutely fine
for my purpose. meter as moving around 1/4 way from peak most of the time.
Can't say more until can make it sound level equal between two channels
Toga

[TOGA]

Hi again, not a good news, due to unknown reason that cause problem I mentioned in last post. They will take it back tomorrow. They promised to let me borrow Ref 150 instead tomorrow, which I gladly accepted, so that I will know what the extra 75w bring.
For now, I can tell that this 75watt baby is really powerful, with good deep bass. mid and high is ARC tube's hallmark, so it has to be good, and it is. Overall sound is smooth, musical and so refined. This new feeling is very similar to when I replaced Moon P8RS with ARC Ref40, it brought a nice taste of tube in the right amount.
I also can confirm that using 8 ohm output tap make it sound more snappy and faster.
while 4-ohm tap make a soft,plush and laid back but can be boring sound in my system.
There are 4 tubes as you know and also 4 separate bias for each tube, is this mean I
don't need a matched pair in the future ? as I seems to be able to adjust bias for each tube individually.
Right now center of sound is emerge in the space between center ch. and right ch. , yes it is that far off. (I checked with mono mode, swapped cables and can confirm that it's the left ch. of the amp that cause this.) So .. cannot tell about sound stage quality.
Not able to write more until get a properly functional one tomorrow.
Toga

[Dafos]

Toga, you will need matched pairs of output tubes, most especially for each channel. Because of the push pull nature of the amp, using unmatched tubes will make proper biasing very difficult to achieve. You will notice that increasing the biasing current on a weak tube will result in the over biasing of it's partner tube. On the other hand, once you compensate by reducing the bias on the strong tube, there will not be enough biasing current for the weak tube. This is based on my own personal experience when my dealer supplied me with weaker tubes (still supplied by ARC but with lower designated values) to replace the tubes that went bad when the output coupling caps of my amp failed.

[TOGA]

Thanks Dafos.
There is one thing that I wanna do when i get my own amp.
The signal cables from XLR connectors run toward circuit board at the front thru one inch wide
Space between Two very hot tubes. This will make these wires very hot too.
Thinking about wrapping wires in this area with some thermal sleeve.
I may be too nuts for this idea. . May be.

Talking about ref75 that has problem since new.
I ve got two bad Levinson 432 out of the box.
A failure soft start board on Moon W7M.
A blown caps on Arc REF40 and now ref 75 that has one channel ill..
They are not highly reliable at all for these expensive toys.

toga

[SundayNiagara]

High Definition = High Performance!

[TOGA]

faulty Ref 75 is gone back to dealer. Now with Ref 150.
Similar sound, but seems more difficult to maintain. all adjustment must be done with
cover off. the cover of 150 is in silver, 75 has one in black. 250 in silver.
is that mean we can choose color of cover ? Or design teams keep changing their mind.

[metaphacts]

Originally Posted by TOGA

faulty Ref 75 is gone back to dealer. Now with Ref 150.
Similar sound, but seems more difficult to maintain. all adjustment must be done with
cover off. the cover of 150 is in silver, 75 has one in black. 250 in silver.
is that mean we can choose color of cover ? Or design teams keep changing their mind.

You can order it either way. ARC gives you the ability to match your new unit to an ARC piece you may already own. That even includes matching a decades old piece. The choices are yours.

[TOGA]

Thanks Metaphacts,
I guess all the Ref 75 dealer have in stock are with black cover.
Actually R150 with silver top looks nice. I like it. It just doesn't match with Ref40's black plastic top. Now I am impressed with the quietness of R150 fans. Biasing procedure of R150 is a bit more complicate than R75's.
Toga

[Masterlu]

Sweet!