[Ted Fletcher]

Ha Ha Ha! It’s great to be right now and again!
I have received this very nice old P2 (made in 2003) and the fault was exactly as I thought…. the capacitors in the output stage had been destroyed…. most likely by over-voltage, and the most likely cause of that is someone plugging the output into a mic input with phantom power on it!
So Neil, it’s all fixed…. don’t do it again!

[Ted Fletcher]

The sales address gets to me, or you can use my personal address [email protected]

[Ted Fletcher]

Yes, it’s:
The Sound House,
Hunsdon Road
Torquay TQ1 1QB
I will have a look at it for you.

For general interest, I have seen this sort of problem two or three times before….. (weak output, very low level) and it was mystifying at the time, but was traced back to BBC installations where there were microphone inputs on jackfields…. with 48V phantom power! An accidental insertion of a jack plug could put phantom power up an output, sometimes with disastrous results.
The moral is, keep phantom power away from everything else! 😯

[Ted Fletcher]

Sounds like it could be a cabling problem…. You should be running the output balanced; If my memory is right there’s jack outputs, and you need to either use standard unbalanced jacks or balanced (3-pole) jacks. If the ‘ring’ is left disconnected, then the output may be low and thin.
If it’s not that, then it sounds like a real fault….. I fix all faults on gear of my design at a fixed rate…. #25 plus the cost of sending it back to you. I’m happy to look at it.

[Ted Fletcher]

I can certainly let you have the schematics for the 828, but I only have details of the series 2 version…. but that’s likely to be the one you have.
As for pots, these were ‘Omeg’ pots and I don’t use them or hold any stocks any more, but you might find them in RS or Farnell.
I will email you the circuits and layouts.

[Ted Fletcher]

I will try to give a really definitive answer here, because it’s an important subject…..
Is it the same compressor? Yes and no! The elements of the compressor are the same; the rectifiers, the attack and release circuits and the optical elements, yes, but they are connected in a different way.
The P10 was designed as a 2-channel device where each channel could be used independently. When the ‘LINK’ button is pressed, the audio from the lower channel is routed up to a parallel compressor in the upper channel where it shares a common attack and release circuit with the top channel, but the audio routes through a separate optical network…… so it’s a true stereo compressor, BUT the centre image relies on the accuracy of the optical cells.
By contrast, the P38 and P38EX convert the audio into ‘sum and difference’ mode and then compress both through a stereo compressor similar to channel 1 (stereo mode) of the P10. After compression, the audio is ‘de-matrixed’ back into left and right audio. This arrangement gives technically perfect image centering no matter what happens anywhere in the audio. If there is a slight imbalance in the compressor circuit, the effect will be to modify the width of the image, NOT any left/right shift.

I consider the P38 and P38EX far superior for mastering; not only is there a perfectly stable image, but also there is control of width and balance. The compressor is easy to use, without having to set up individual in/out gains and there are the other functions (sidechain and partial compression) on the EX.

There’s nothing wrong with using the P10 as a stereo compressor…. it’s very good! But only if you don’t have a P38!!

[Ted Fletcher]

BTW, I gave you a wrong type number….. the one I meant was MC33078 This is a good sounding dual that’s very forgiving.

[Ted Fletcher]

I don’t think we ever manufactured a fixed balance TBU; although we might have played around with some very early ones in 1972/3…. Come to think of it, it is possible that the TBU1 was manual balance.
Certainly the TBU2 was an automatic TBU, it worked by minimising sidetone during the moments when ‘transmit’ was taking place. It worked very well on local ends, but, as with all those analogue auto systems, they could never cope with the delays inherrent in digital transmission. The TBU2 had auto correction for both level and phase, and I believe this was where I started to use a partial ducking circuit.
It worked reasonably well, and was a competitor of the Studer unit.
In the early 80s I used a more sophisticated version of the TBU2 with very fast acting balance, in communications systems for money brokers. These multi-line ‘broadcast’ systems were very successful until everything went digital!
I’m afraid I don’t have any pictures of these old units.

[Ted Fletcher]

I don’t even know what a ‘matchpack’ is! No we certainly never made one. 😳

[Ted Fletcher]

Hmmmm a bit of a problem here….. I would suggest the quickest way is to replace the chips in the offending channel; it’s doubtful if its mechanical. If the crackles vary with input gain control, then it’s the front-end chip, and that’s the most likely. Replace with the same type, or if it’s a dual, I suggest using MC33378 as an alternative to TL072. It’s best not to go for the lower noise modern equivalents as you could run into stability issues.
I’m sorry I don’t have circuits for the later 828S mixers.
As a last resort, I can probably fix it for you, but sending a mixer to Torquay is fraught with risks.

[Ted Fletcher]

The P10 insert is after the whole input section…. it’s after the mic and line amp, the polarity reverse and the variable phase.
Both insert send and insert return are balanced, but can be used unbalanced with no problems.

[Ted Fletcher]

The ‘Brick’ was the first of my ‘Voice Channel’ units (hence ‘VC’). It was smaller than the conventional 2U rack unit but the circuit was almost identical to your VC1. It has become a legend because of the really clean and smooth sound it produced with the less-expensive Chinese mics. I’m thinking seriously of re-issuing it.
The meter in your unit is made by ‘Monocor’ in Germany. I’m sorry, I don’t have spares for that meter, nowadays we have our own meters made for TFPRO.
I’m really sorry I can’t help on this one. 😥

[Ted Fletcher]

No yours is not a ‘false’ one!
There were 4 distinct versions of the VC1; the first one was derived from the ‘brick’, it was the one with all the controls in a single line.
It was a transformer input mic amp, a compressor and a harmonic exciter. Some of those had the gold lettering like yours.
Next came the green version in your picture, this was again a transformer input mic amp, compressor and exciter, but with a slightly different layout, mainly for ease of construction. The we changed the exciter into an EQ and called it the VC1Q. Very soon after that we introduced an all solid state mic amp and called it the VC1QCS.
They were all very successful and reliable…. and I know that most are still in service today.

[Ted Fletcher]

In terms of circuitry they are almost the same.
The mic amp is a neat little discrete transistor class-A design that sounds very good… it’s streets better than the later IC mic amps that everyone now uses (except myself and a couple of other designers). And don’t forget, these mixers were built to a very exacting spec. and had to pass both the IBA Code of Practice, and the BBC spec for on-air continuity mixers.
I have had a look and I don’t have circuits for these mixers. 😥

[Ted Fletcher]

Thanks for those pictures…. brings back memories.
The AM21 modules most likely were originally at one of the ILR radio stations. The 8-track routing maroon module is later, yes could have been from ‘The Manor’….. but it was a long time ago!

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