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Old 10th Dec 2018, 12:26 am   #21
teetoon
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Shaun, for some reason your post 19 wasn't there when I last commented.
I have to say once again, the EQ connects to the tape loop not the pre-power.

Do you realise that the pre out also comes after the volume control so any adjustment you made while recording would affect the record level. You would also have no control of volume coming back from the graphic to the power amp and any extra noise in the signal path would be as though you had the volume control fully open.

I don't know how to say it without offending anyone (which is the last thing I want to do) but I have been setting up this kind of equipment since the 70's in both home and professional environments and can assure you that I am giving you good advice

Do you have the manual for the graphic as this would confirm exactly what I am saying.

I would definitely ditch the DBX though as this is just complicating things for you and a Revox doesn't need it.

I'll sit back and wait for the mud to come flying now .

David.
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Old 10th Dec 2018, 2:17 am   #22
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

A high proportion of amplifiers have recording and replay connections for tape recorders. Sometimes this is implemented as a tape monitor switch, sometimes by having dual source switches, one for listening, and one for recording. A lower proportion of amplifiers have loop-out connections between their preamp and power amp sections.

If you have a graphic equaliser and an amplifier without those pre-power amp links, then the tape connections are the only place you can insert it into your signal path. This then ties up your tape connections and you therefore need an equaliser with appropriate tape switching if you want tape facilities. This means that when you'e using tape you have to make the switch selection on the equaliser, not the amplifier.

Some equalisers lack the tape switching and are designed to just connect in in place of the pre-power amp links. This leaves the tape facilities in the preamp working normally for your tape machines. You've said you want to use the equaliser on the signal feeds to your B77 (I don't understand why, because it would record tapes with eq on them set for your current room and speakers. If you move, change speakers or rearrange the room, all your tapes will be equalised wrongly) But it's a free world and it's your choice. The pre-power connection for the equaliser won't do this, so you'll have to live with the need to throw switches on the eq when you're replaying.

Where you'll find two Davids agreeing is that a Revox B77 really doesn't need DBX. The recorder is sufficiently good that the benefit from DBX is reduced substantially and the recorder is sufficiently good that it makes the DBX problems a lot easier to hear.

I've been a professional electronics designer since the early seventies, so I've tended to do my own amplifiers etc, but never a graphic equaliser - slide pots give me the heebie jeebies. I've used parametric equalisation instead.

David
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Old 10th Dec 2018, 2:42 am   #23
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Hello David. Re EQ'ing the recording, Shaun has said this is to correct poor quality source material and nothing to do with room acoustics so, say for example, you were playing a 78, you could filter some of the very high frequency hiss or if you had a poorly mastered CD there maybe a nasal quality to it which could be tamed by a tweek in the 2-3khz range maybe.

I think people get confused by the idea of room eq'ing as this never works unless you use pink noise and a calibrated mike and spectrum analyser to show the peaks in the room. Even then it's only going to tune the listening point where you had the mike set up. It always sounds wrong to me and I have always tuned by ear.

The biggest mistake most people make with a graphic eq is to do the smiley face setting or start pushing everything up until all you've done is increase the overall volume. Even I was guilty of that when I got my first graphic (a Rotel 7 band in 1980) but if you really listen and switch the eq in and out it soon becomes obvious which settings are better and which are just making it louder or harsher.

Atleast we agree on the DBX as you say. The last time 2 Davids agreed on something was in the Lib Dem's wasn't it ?

David.
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Old 10th Dec 2018, 9:02 am   #24
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Yes, it would make sense for adjusting poor source material for recording. Graphic equalisers usually amount to a lot of active filters feeding a multi-input summer and can be a bit noisy. Some designs used L-C resonators with pot core inductors, but still had a noisy multi-input summer but the active filters won out under pressure from the accountants. I think graphic equalisers are best kept out of circuit except when they are needed. OK if it has a bypass switch that does what it says on the can.

I've had a play with equalisers at home. I have decent microphone and a couple of spectrum analysers which cover audio and one of them even has a tracking generator built in. Pink noise is a lot kinder on your speakers than a fixed amplitude swept tone. Swept tones make your neighbours wonder if you've got an exotic bird, but short bursts of pink noise sound like gunshots which is an impression you don't want to create nowadays. White noise and a cross-correlator will get you the impulse response of your setup without any cruel transients hitting your speakers. Transient tests fire the damping foam pieces out of the transmission line ports on my speakers!

I worked in a lab where a call of "Hey, David!" got about seven heads peering over the partitions. Agreements were common. Unfortunately I share a surname with another David, a golfer who won the US masters and became the boss of the American Ryder cup team, so my name has caused the taking of rather a lot of mickey over the years. Golf courses are no-go areas, though I do ride in an annual horse race across one

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Old 10th Dec 2018, 11:46 am   #25
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

David, Thank you. Alas I am not as good with description as I am with pictorial presentation so when I have time to digest this (I am currently waiting upon specialists to rectify a problem with three generators so that I can sail) I will knock up a sketch of what I understand should be the linking of each piece whereupon if you have time and the inclination you could offer your own if mine isn't what you had in mind. I'm getting slower in my old age. Many thanks for your kind participation. Shaun.
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Old 10th Dec 2018, 11:48 am   #26
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Quote:
Originally Posted by teetoon View Post
Shaun, for some reason your post 19 wasn't there when I last commented.
I have to say once again, the EQ connects to the tape loop not the pre-power.

Do you realise that the pre out also comes after the volume control so any adjustment you made while recording would affect the record level. You would also have no control of volume coming back from the graphic to the power amp and any extra noise in the signal path would be as though you had the volume control fully open.

I don't know how to say it without offending anyone (which is the last thing I want to do) but I have been setting up this kind of equipment since the 70's in both home and professional environments and can assure you that I am giving you good advice

Do you have the manual for the graphic as this would confirm exactly what I am saying.

I would definitely ditch the DBX though as this is just complicating things for you and a Revox doesn't need it.

I'll sit back and wait for the mud to come flying now
Oh hell. I just replied to you and the page that followed showed many more responses so I'll go through those now.
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Old 10th Dec 2018, 9:43 pm   #27
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Shaun, no worries there. I think the delay in posts appearing is because you are new and posts need to be approved before they are seen.
Don't give up we'll get you there

David. Interesting points there and yes I remember the pot cores in some of the early graphics. A friend had a Maplin design that used them. It didn't do a lot except increase hiss, the sonic improvements were too subtle for him. I'm sure they can do better when implemented correctly but since the late 70's they all seem to use chips.

Your mention of swept tones reminds me of sound system installs where you wind the sig gen up and listen for vibrations, then go and screw down the offending item

David.
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Old 10th Dec 2018, 11:09 pm   #28
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Just to be fair to double ended noise reduction systems like Dolby and DBX, for best performance they assumed very accurate record/replay alignment. It was stated in the literature. This wasnt too hard for those who worked in recording studios every day as they (hopefully) already had that discipline of tape machine maintenance and alignment in place, and they used pro tape machines which were designed for easy access to alignment trimmers etc.

Much harder for home listeners and music lovers with their consumer gear which generally wasnt designed for easy alignment and who usually didnt want to go beyond the front panel of their tape machines.

Just a mild roll off of the treble in a tape machine due to slight overbias could mean, when Dolby was engaged, a much bigger roll off in treble, plus encode/decode artifacts. This gave Dolby and DBX a bad name amongst consumers, while Dolby and DBX continued to be used without these problems in the recording industry.

Unless you were prepared to undertake very careful maintenance and alignment of tape machines, maybe Dolby and DBX werent worth it.

Whether Noise Reduction was needed depended on the dynamic range of the material you were recording. Recording radio broadcasts or even LP's wasnt too hard as the dynamic range was already controlled so even cassette recordings of them could sound acceptable. But raw live performances could easily outstrip even an open reel tape machine's capacity. Eventually, digital recording allowed effortless recording of big dynamic live concerts etc, without the extra cost and complexity of Noise Reduction.

Tim
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Old 11th Dec 2018, 9:41 am   #29
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Also the recording industry used Dolby A which is a quite different beastie to Dolby B and C.

The idea behind DBX, right at the beginning was that a uniform compression ratio across the full dynamic range shouldn't need careful alignment for level. But this goes out the window when you want to operate close to the limits of the dynamic range of the tape.

David
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Old 11th Dec 2018, 11:41 am   #30
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

The glaring omission of dbX, to mind, was its single-band approach, which inevitably led to breathing effects on things like bass guitar and solo piano. Dolby's four band layout in the A system rendered its operation inaudible when properly lined up. You could fiddle with a dbX line-up for a month of Sundays and still have the huffing and puffing to contend with.
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Old 11th Dec 2018, 2:37 pm   #31
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

That's inevitable with a single band system. You have only one parameter to vary and you have to vary it to suit everything at once.

Anyway, here we are several decades after the origins of all these things and if we want sound with low noise we only have to throw enough bits at it. The problem has been solved. However, for people whose religion prevents them from using anything digital, the problem is still there, but then, it's a self-inflicted limitation.

Playing about with these old noise reducers for fun is one thing, but having to use them because there's no alternative ended some time ago. Similarly I couldn't understand anyone wanting to have dentistry 1950s style. In some areas actual progress has been made.

David
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Old 11th Dec 2018, 4:11 pm   #32
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

I believe DBX was used quite a lot professionally but more in smaller studios and on narrower track formats such as 8 track 1/2" /16 track 1", and of course Portastudio cassettes, which formats were already noisier than wider track formats in the more well equipped studios which probably used Dolby A.

https://en.wikipedia.org/wiki/Dbx_(noise_reduction)

I remember as a musician recording at one of our city's top studios in the late 80's. They used a 1/2" 8 track Otari machine at 15ips with DBX I. I do recall hearing some breathing on my isolated bass tracks in the control room but once part of the overall mix, and certainly on the final customer cassette copies, the breathing tape noise was inaudible.
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Old 12th Dec 2018, 9:25 am   #33
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

To Davids (that's both) and to all contributors, thanks. My brain is fried. I have noted everything and done further reading.

There are arguments both for incorporating the eq. in the 'pre out' 'pre to pwr.amp.' loop and for not doing so, that argument being amplifying eq. noise with a weak signal that's then going to be to amplified just adds noise.

I find the idea of using that route odd because the signal going to the tape, if taken from the eq, changes with amp. controls BUT all the publications state that if the amp. does not have a tape monitor provision as mine doesn't (Revox H5) then it's the only route, the normal route - as you have mainly stated - being feeding the eq. from the amp. tape out whereupon in my case I'd send the eq. signal to the tape machine (no need to discuss the return route here I think).

As for the dbx I take heed of what you have said and will try it after the eq. signal to the tape and will determine if it worth keeping.
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Old 12th Dec 2018, 4:32 pm   #34
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

The reason why most graphic equalisers have a "tape monitor" switch is this.

Not all standard integrated hi-fi amplifiers (i.e., a pre-amplifier, controls and power amplifier in one box) or receivers (i.e., all the above plus a radio tuner) have a disconnection point between the preamplifier and power amplifier. However, they (nearly) all have a tape loop; both to ensure against creating a feedback loop if a two-head recorder is used, and to allow off-tape monitoring if a three-head recorder is used.

The selected source (tuner, phono, CD player, VCR .....) is fed to the "tape record" outputs. The "tape monitor" switch then selects between this, and the "tape playback" inputs. If your tape recorder has three heads, and its monitor switch is set to "T" for tape, then the signal that returns to the amplifier is what has actually been recorded onto the tape and picked back up from it. When listening to any other source, the tape loop is bypassed.

If there is no other insert point between the pre- and power amplifiers, then the tape loop is the most sensible place to connect a graphic equaliser. Otherwise you would need a separate switch box, and maybe a phono preamplifier. The equaliser then provides its own tape loop: the equaliser proper is fed from either the amplifier's "tape record" outputs, which are also sent to the "record in" inputs on the tape deck, or the tape deck's "playback out" outputs, and the equalised signal is returned to the amplifier's "tape playback" inputs. As a bonus, disengaging the "tape monitor" button on the amplifier allows you to listen to the unequalised sound.

It's also possible for there to be multiple tape loops, either at the amplifier or the equaliser. In this case the switching arrangements are a little more complex, as you can have "source", "tape 1", "tape 2", "dub 1→2" or "dub 2→1" modes.

If your amplifier has a proper insertion point between the preamp and power amplifier, though, you may as well use this, as connecting an equaliser is really its intended purpose.
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Old 12th Dec 2018, 9:10 pm   #35
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

And so the mis-information keeps coming.
The clue is- PRE - POWER. It is not for a Graphic EQ. If it was it would be labelled TAPE ADAPTER / PROCESSER.

Find the manual for the graphic to see how it connects.
Also the manual for the amp to see how to monitor a tape recording.

If I hadn't wired up this sort of set up before I would not advise you.

Julie, With all due respect, have you ever connected a domestic graphic eq to a pre-power connection point ? How do you control the volume coming back from the tape deck as the power amp in is direct to the power amp. I know the Revox B77 will have output controls but what if it was a normal cassette deck being used ?
Please don't take offence as none intended.

David.

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Old 12th Dec 2018, 9:30 pm   #36
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Quote:
Originally Posted by Radio Wrangler View Post
Anyway, here we are several decades after the origins of all these things and if we want sound with low noise we only have to throw enough bits at it...Playing about with these old noise reducers for fun is one thing, but having to use them because there's no alternative ended some time ago.
Quite so. I have some pretty obscure boxes dotted about whose sole purpose now is the correct replay of tapes with variously obscure processing. Ironically enough, Dolby A encoding is now used in some circles for processing vocal tracks...
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Old 12th Dec 2018, 10:27 pm   #37
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

After doing a bit of research, I am beginning to smell a rat here.

See this: http://audiokarma.org/forums/index.p...lizers.688898/

Dated 2015.

Another here:http://audiokarma.org/forums/index.p...emotes.696145/

I fear the advice is falling on deaf ears. Sorry.

David.

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Old 13th Dec 2018, 12:10 am   #38
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Keep asking the same questions of different people until you get the answer you wanted in the first place? But if you know the answer already, why ask?
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Old 13th Dec 2018, 2:15 am   #39
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Default Re: Revox H5 Preamp 'Out' & 'Power in' Purpose & Use

Just to put this to bed. See image. It says, and this is from the Kenwood manual, The GE 1000 is designed to be connected in your system's TAPE MONITORING PATH.

From the horse's mouth. Thankyou and Goodnight

David.
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Old 13th Dec 2018, 4:22 pm   #40
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Julie, With all due respect, have you ever connected a domestic graphic eq to a pre-power connection point ? How do you control the volume coming back from the tape deck as the power amp in is direct to the power amp.
The tape deck will be connected to the amplifier, not the equaliser; and the amplifier's volume control will be in circuit, whether it is upstream or downstream of the pre-power insert point.
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