ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #40 on: April 27, 2016, 07:43:02 AM »
I imagine with the output amp.

Well, the output amp  (and an output Tx) will definitely add more gain but I can't see the reason of having such a small gain in the input amp. Unless it's not a mic preamp, I'm definitely missing something :)

From what I remember of the manual, the internal operating level is -10dBV (where 0dBV = 0.477V into 200 ohms). The smallest input level is -50dBv so the gain needs to be 40dB. The amp has 25dB and the transformer secondary taps give up to 15dB for a total of 40dB.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


Re: Hayes Middlesex Pre/Channel
« Reply #41 on: April 28, 2016, 05:35:49 AM »
From what I remember of the manual, the internal operating level is -10dBV (where 0dBV = 0.477V into 200 ohms). The smallest input level is -50dBv so the gain needs to be 40dB. The amp has 25dB and the transformer secondary taps give up to 15dB for a total of 40dB.

Cheers

Ian

Thanks for chiming in IAN. If I remember well the transformer is 1:3 (or something like that) so I'm not sure how it can give 15dB of gain but I get the idea. Do you believe there's an attenuator somewhere and if so, what would be the best place to have it? If it's between the transformer and the input of the amp , it would change the impedance, right?

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #42 on: April 28, 2016, 09:53:30 AM »
From what I remember of the manual, the internal operating level is -10dBV (where 0dBV = 0.477V into 200 ohms). The smallest input level is -50dBv so the gain needs to be 40dB. The amp has 25dB and the transformer secondary taps give up to 15dB for a total of 40dB.

Cheers

Ian

Thanks for chiming in IAN. If I remember well the transformer is 1:3 (or something like that) so I'm not sure how it can give 15dB of gain but I get the idea. Do you believe there's an attenuator somewhere and if so, what would be the best place to have it? If it's between the transformer and the input of the amp , it would change the impedance, right?

Check out the document in this post:

http://groupdiy.com/index.php?topic=61769.msg783662#msg783662

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

L´Andratté

Re: Hayes Middlesex Pre/Channel
« Reply #43 on: April 29, 2016, 03:47:51 AM »
Check out the document in this post:
The man,who document, that wasn´t there...
Apart from the dark mysteries surrounding this console, it´s cool looks and rather prominent former users, does it actually sound so special as to justify the hype (sorry for my ignorance, of course it does, but is anyone here, actually having heard it in real life)?
The circuits are very simple looking, not a bad thing at all, but evoking recollections of my early fuzz face experiments... ;D
« Last Edit: April 29, 2016, 03:59:57 AM by L´Andratté »
"Why not get an assistant to work the faders? Real vintage! And maybe cheaper... ;)"

L´Andratté

Re: Hayes Middlesex Pre/Channel
« Reply #44 on: April 29, 2016, 06:19:28 AM »
..., does it actually sound so special...

Now, the more I look into it I really like to find out for myself.
BC109 is readily available, ACY21 not so, but 2N222 (not 2N2222), a germanium PNP that is supposed to work as equivalent, for acceptable expense.
Brian Sowter thankfully makes In-/Output transformers (as stated above), sadly at the doubtlessly justified price of 91 GBP each, which is not an impulse buy for me atm... Hmmm *Brood*
« Last Edit: April 29, 2016, 06:23:06 AM by L´Andratté »
"Why not get an assistant to work the faders? Real vintage! And maybe cheaper... ;)"

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #45 on: April 29, 2016, 07:31:53 AM »
As to the sound, I think the key aspect is that it is all class A, just like the classic Neve designs of the 70s. The circuit details are not terribly relevant. That and the use of transformers are in my view the two main contributors to the sound.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

leadbreath

Re: Hayes Middlesex Pre/Channel
« Reply #46 on: April 29, 2016, 08:56:30 AM »
Its definitely not a circuit with massive amount of gain, I know of someone who has added an extra gain stage after the output amp to increase gain.
f**k marlbro's and weed ill stick to smoking germanium and silicon

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #47 on: April 29, 2016, 09:55:56 AM »
Its definitely not a circuit with massive amount of gain, I know of someone who has added an extra gain stage after the output amp to increase gain.

The basic mic pre input sensitivity seems to be -50dBu which is more than adequate for the majority of uses of the mixer. They were not trying to record small acoustic signals at large distances with ribbon mics. They mostly used condensers for which -50dBu sensitivity is plenty.

Cheer

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

leadbreath

Re: Hayes Middlesex Pre/Channel
« Reply #48 on: April 30, 2016, 02:30:47 AM »
Quote
The basic mic pre input sensitivity seems to be -50dBu which is more than adequate for the majority of uses of the mixer. They were not trying to record small acoustic signals at large distances with ribbon mics. They mostly used condensers for which -50dBu sensitivity is plenty.

Cheer

Ian

true...
f**k marlbro's and weed ill stick to smoking germanium and silicon

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #49 on: April 30, 2016, 05:57:01 AM »
Quote
The basic mic pre input sensitivity seems to be -50dBu which is more than adequate for the majority of uses of the mixer. They were not trying to record small acoustic signals at large distances with ribbon mics. They mostly used condensers for which -50dBu sensitivity is plenty.

Cheer

Ian

true...

OTOH, if you are designing a mixer for use in a TV studio or film set, where the mic has to be out of shot, then you might need the 80dB gain available from a Neve channel.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


Michael Tibes

Re: Hayes Middlesex Pre/Channel
« Reply #50 on: April 30, 2016, 07:10:11 AM »
No comp/limit  at the moment unfortunately, my source has said that he has a loads of drawings from that company but only managed to find the ones I mentioned so far in relation to the "numbers" desk.

Awesome Info!!  :) :)

So the comp different from the ..413 (which we know already)?

If I get things right then this should shed some light on the relevant history:

http://www.waves.com/behind-abbey-road-studios-emi-tg12345-consoles
http://www.musictech.net/2014/07/emi-tg12345/

Michael

Re: Hayes Middlesex Pre/Channel
« Reply #51 on: March 01, 2019, 12:53:34 PM »
hi, sorry if i exhume this zombie thread but i don't think is necessary to open a new one.
so, i've build this two stages with the acy21 as output and bc549c as the other four trans and an oep a262a3e wired 1:12 and i have about 50db of super flat 20hz to 20khz gain but i've omitted the output transformer. IT IS VERY NOISY too be usable as preamp, is it normal for this circuit?  is there something that i can do to improve the SNR? use the original transistors? oh, and i've used one 10k pot at the input after the transformer and one 10k pot after the output amp. beautiful shhhmooth sound anyway.

thanks!

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #52 on: March 01, 2019, 01:19:03 PM »
There is no reason why this preamp should be very noisy. First check with just the first stage. You should have close to 50dB max gain. Short the transformer input and measure the noise level at the output. It should be -70dBu or better.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

JohnRoberts

Re: Hayes Middlesex Pre/Channel
« Reply #53 on: March 01, 2019, 01:44:56 PM »
Well, the output amp  (and an output Tx) will definitely add more gain but I can't see the reason of having such a small gain in the input amp. Unless it's not a mic preamp, I'm definitely missing something :)


From what I remember of the manual, the internal operating level is -10dBV (where 0dBV = 0.477V into 200 ohms). The smallest input level is -50dBv so the gain needs to be 40dB. The amp has 25dB and the transformer secondary taps give up to 15dB for a total of 40dB.

Cheers

Ian
That is a little weird use of dBV... 

0dBm (1 mW) is indeed 0.477V @ 200 Ohms, a power level with 0dBm=1mW.

dBu was commonly voltage wrt 0.775V without specific impedance qualification.  dBV was voltage wrt 1V again without impedance qualification...   -10dBV was (is?) a very popular semi-pro recording equipment 0VU reference level (0.316V) again independent of termination.

I recall another dBV ( x) voltage reference with stated OdB voltage reference level included inside parenthesis. For this case that could be stated X dBV(.477V). dBV without stated reference implies a 1V voltage reference.

I've seen dBv used interchangeably with dBu (voltage ratio wrt 0.775v)

Of course there are any number of variants in popular dB usage.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: Hayes Middlesex Pre/Channel
« Reply #54 on: March 01, 2019, 01:53:42 PM »
There is no reason why this preamp should be very noisy. First check with just the first stage. You should have close to 50dB max gain. Short the transformer input and measure the noise level at the output. It should be -70dBu or better.

Cheers

Ian

yes Ian thanks, if i short the trx it disappears. so why all that noise? meanwhile one of the channel started motorboating, a bad cap?
« Last Edit: March 01, 2019, 02:25:04 PM by xazrules »

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #55 on: March 02, 2019, 12:53:00 PM »
yes Ian thanks, if i short the trx it disappears. so why all that noise? meanwhile one of the channel started motorboating, a bad cap?

It is just picking up stuff in the air. Mic pres do that if there is nothing connected to their inputs. They are pretty sensitive.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Hayes Middlesex Pre/Channel
« Reply #56 on: March 03, 2019, 07:02:44 AM »
yes i see, changed the steup ratio of the transformer improved things, but are there some techniques to make the amp see a costant load? i ask this because if i want to use only the line in (summed to the input beetwen trx and amp with a series resistor) with no mic connected the SNR worsen..

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #57 on: March 03, 2019, 03:44:33 PM »
yes i see, changed the steup ratio of the transformer improved things, but are there some techniques to make the amp see a costant load? i ask this because if i want to use only the line in (summed to the input beetwen trx and amp with a series resistor) with no mic connected the SNR worsen..

If you changed the step up ratio of the transformer downwards then the noise would go down simply because the gain has gone down.

I don't understand your method for including a line input. Can you post a schematic showing how you do it.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Hayes Middlesex Pre/Channel
« Reply #58 on: March 04, 2019, 03:17:59 AM »
yes this is how i summed mic and line togheter. if both the inputs are connected the noise performance is perfect, but if i remove a mic from his input it worsen.

ruffrecords

Re: Hayes Middlesex Pre/Channel
« Reply #59 on: March 04, 2019, 03:58:03 AM »
OK, now I understand. I have not seen a line input summed like this before. I think the problem is it is not really summing because the impedance appearing across the transformer secondary depends on what is plugged into it. With a mic plugged in this impedance is the mic impedance reflected to the secondary. This appears in parallel with the 10k pot and so attenuates the line input signal and the overall noise. With no mic plugged in the reflected impedance in parallel with the 10K pot is a lot higher so there is less attenuation so the noise appears to be higher.

The normal way to this would to to use a switch to connect the 10K pot wither to the line input of the mic transformers secondary.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'