Messages

1

Tape Tech / Re: REVOX A77 ALIGNMENT QUESTION

« on: March 19, 2010, 10:32:48 AM »

Thank you to all who have replied to my query. You have been very helpfull

I have now got the answer to my question.

I rang a Revox specialist who told me that it was perfectly OK to carry out the adjustments i asked about at 775 millivolts instead of 155 millivolts. Question answered.  Mark

2

Tape Tech / Re: REVOX A77 ALIGNMENT QUESTION

« on: March 18, 2010, 11:04:16 PM »

Dear Sound Signal

Yes, I think it must have been one of your posts I read. Thank you for yor reply.

You way of setting the bias is very interesting.

The problem with the A77 is that some of the other adjustments that are necessary when aligning the machine have to be done at very low voltages, mostly 155 millivolts or -20 db compared to the reference level.   Bias is just one of them.  Others include setting the record level in and out and HF equalization.

As i said in my post it is easy to make a small error when adjusting at these low voltages that is magnified when the level is cranked up. Here's an example.  When balancing the record level in and out at 155 millivolts I get the meter needle to read as close as possible to 155 millivolts on both in and out although the meter scale is cramped. If i then leave these settings and crank the volume  up to show the same ins and outs at reference level [1.55 volts] there can be a difference of 1db or so between the two voltages.

OK its no big deal and it is an old machine and i dont expect perfection. My reasononing for posting my query was twofold. Firstly the meter has a bigger scale at about 775 millivolts [-6db below reference level] and is easier to read, particually the db scale for setting the bias, and secondly i would prefer the A77 to be more accurate in its midrange recording level than miles down at -20 db.

This is all probably splitting hairs but maybe that is what we are here for. I very much doubt that Joe Public would notice any difference in a recording made on a machine that was spot on and one that was a bit out of alignment.

I have aligned my A77 according to the Revox manual and I am very happy with the results. My query is really to find out if there is a more convenient way of doing things if i have to redo the alignment in the future.   Mark

3

Tape Tech / Re: REVOX A77 ALIGNMENT QUESTION

« on: March 18, 2010, 01:29:04 PM »

to Ki

Thanks for your reply.

On the Revox A77 0db is definately 1.55 volts [it used to be 2 volts till Revox revised it]

You are probably right about the built in Vu meters not being accurate enough but I have never used them as a tool when doing any aligning. In any case they do not work in replay mode so it would be impossible anyway. Revox designed the A77 like this, I have always used an audio millivolt meter. I have never tried biasing at 1 khz, i stuck to what the manual said.

Getting back to my question as to whether or not the alignment adjustments could be done at a higher voltage than 155 millivolts [-20 db] Do you think it would be OK to do them at -10db if it were not a good idea to do them at 775 millivolts [-6db]

thankyou    Mark

4

Tape Tech / REVOX A77 ALIGNMENT QUESTION

« on: March 18, 2010, 08:41:06 AM »

I have just completed the alignment of my Revox A77 after changing many of the components on the boards and relapping the heads. No problem, everything works fine but I have a query about the alignment proceedure and wondered if anyone can throw some light on the subject.

The revox manual says that many of the adjustment when aligning should be carried out at a voltage of
155 milivolts which is -20db down from the reference 0db level. I have done this but it is a bit fiddly and you have to be very carefull not to make a small error when adjusting at -20db. For example, reading the db scale when setting the bias is not easy as the scale is compressed.

I have read somewhere on this site that one of the members adjusts the bias on his Revox B77 at 0db and not at -20 db without any problems. Apparently the original reason for adjusting at -20 db was to avoid tape saturation on the tapes that were available 30-40 years ago.

It would be much easier all round if all the -20 db adjustments mentioned in the manual could be carried out at a higher voltage, say 775 millivolts or -6db. In this way small errors of adjustment could be avoided and it would be much easier to read the db scale.

Has anyone tried this or have any thoughts on the subject as I would find yor comments extremely helpfull. Thanks  Mark