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Old 14th Nov 2020, 6:27 pm   #121
Richardgr
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Default Re: Adding a selectable line input to valve radiogram

Just for my understanding, you need some gain for some inputs to the amplifier? Do you have an approximate idea what signal level is ideal, and I what comes from the source?
Could it an impedance issue, your input presenting a lower impedance?
Where are you injecting the input in the circuit?
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Old 14th Nov 2020, 6:39 pm   #122
barretter
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by Rich400 View Post

To clarify the RIAA curve just describes the non linear relationship of bass in the output of the cartridge. By building in an adjustable low pass filter into the circuitry Of my modification I can either increase or reduce the bass level. This will adjust graphically the RIAA curve.
Sorry for not being clearer on this point.
There are 2 RIAA curves introduced in 1954, one for 78rpm coarse groove and one for 33/45rpm microgroove records. Both involve reducing the bass and increasing the treble when making the stampers used to produce the discs. This distortion has to be removed in playback by increasing the bass and reducing the treble which is what the built-in RIAA stage in post 1954 pre-amps does as well as highly amplifying the low output of moving magnet cartridges. What you are doing is not at all clear.
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Old 15th Nov 2020, 12:20 am   #123
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Default Re: Adding a selectable line input to valve radiogram

If you want to use an Ortofon OM Pro S it will have to have its own dedicated pre-amplifier. The Ronette BF40 has an output of 800 millivolts, the Garrard GC8 has an output of 800 millivolts for 78s and 200 millivolts for 33/45s ; the output of the Ortofon is 5 millivolts. The Ronette and Garrard cartridges have to have an input resistance of 1M whereas the Ortofon has to be loaded with 47K. The Ronette and Garrard sort of do the necessary equlization by themselves but the Ortofon needs an electronic circuit to do the needed equalization and amplification. There isn't any way you can feed a line source into the RIAA circuit used for the Ortofon.
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Old 16th Nov 2020, 2:45 pm   #124
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by barretter View Post
Quote:
Originally Posted by Rich400 View Post

To clarify the RIAA curve just describes the non linear relationship of bass in the output of the cartridge. By building in an adjustable low pass filter into the circuitry Of my modification I can either increase or reduce the bass level. This will adjust graphically the RIAA curve.
Sorry for not being clearer on this point.
There are 2 RIAA curves introduced in 1954, one for 78rpm coarse groove and one for 33/45rpm microgroove records. Both involve reducing the bass and increasing the treble when making the stampers used to produce the discs. This distortion has to be removed in playback by increasing the bass and reducing the treble which is what the built-in RIAA stage in post 1954 pre-amps does as well as highly amplifying the low output of moving magnet cartridges. What you are doing is not at all clear.
Hi not a problem, as what I am doing is working well thanks.
I was referring to the adjustment of the RIAA curve from the cartridge and similarly inverting this effect from the modern line signal to the amp.

To clarify, the amp is expecting a signal at its ext input from the deck cartridge into the chassis, which has high mid/treble characteristics (RIAA characteristics). It was not configured for any other ext input. Now I am inputing a modern line input, i need to tailor the treble and bass values accordingly (reduce the bass component) for the amp to respond correctly. I also have to adjust the overall level slightly (reduce) as it is slightly higher than the ceramic cartridge level.

I have successfully completed this now, and the sound is surprisingly good.

However at this stage i wish to add a small adjustment to the final signal to the amp to compensate for the small differences in outputs from different Cd/server recorded levels.

This may seem a lot of trouble to some, but now i have fitted VU meters you would be surprised how much these differ. While I am doing these mods, it would be nice to have a panel mounted control to trim the occasional very low output recording so the amp does not have to be cranked up.

Regrettably the passive method i am using to condition the signal (RIAA bass/treble adjustment) as described above is taking a very small loss away from the signal (which now seems to equate to the cartridge level). Unfortunately the level will have to be slightly amplified to trim these recordings as the resultant level from my passive conditioning has not left me any headroom to turn down (adjust).

I can find small amplifier boards than can be panel mounted, but to get a small amplification they are usually intended for lower end systems, and I do not want to compromise the surprisingly good audio i am seeing here to get a sensible FSD.

My question is to find a quality panel mounted amp that can perform this, and if anyone knows of one available.

Before I started this project I would have been happy with low end functional kit to do the job, but now I have this up and running I am frankly astounded at how good this sound is coming from the Yamaha WXAD-10 (via my INNUOUS server)

So I intend to work this through maintaining this surprisingly excellent sound.

I hope this makes more sense to you.

Last edited by Rich400; 16th Nov 2020 at 3:05 pm.
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Old 16th Nov 2020, 2:59 pm   #125
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by barretter View Post
If you want to use an Ortofon OM Pro S it will have to have its own dedicated pre-amplifier. The Ronette BF40 has an output of 800 millivolts, the Garrard GC8 has an output of 800 millivolts for 78s and 200 millivolts for 33/45s ; the output of the Ortofon is 5 millivolts. The Ronette and Garrard cartridges have to have an input resistance of 1M whereas the Ortofon has to be loaded with 47K. The Ronette and Garrard sort of do the necessary equlization by themselves but the Ortofon needs an electronic circuit to do the needed equalization and amplification. There isn't any way you can feed a line source into the RIAA circuit used for the Ortofon.
Hi again Barretter

Yes you are quite right, I have a SPA9 phono preamp (MM) to do this.

The Ortofon OM Pro S will be on an interchangeable headshell (4HF), for modern 33/45's, and the channel select will be on the new rotary switch fitted to select amp input between the following:-
1. The new ext input (with RIAA bias adjustment as described)
2. The headshell for the Orotfon (with SPA9 in circuit)
3. Headshell for GC8 mono ceramic cartridge (with no signal correction).

This is all in place and seems to work out ok, i just need to find a way to provide a small amplification trim to the ext input as described in my previous post.
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Old 16th Nov 2020, 3:22 pm   #126
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Default Re: Adding a selectable line input to valve radiogram

The Garrard GC8 is not a Ceramic type - it's a Crystal, and you might have the high-output version.
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Old 16th Nov 2020, 9:04 pm   #127
Rich400
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Default Re: Adding a selectable line input to valve radiogram

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The Garrard GC8 is not a Ceramic type - it's a Crystal, and you might have the high-output version.
Hi thanks again for your contribution Edward

Largely irrelevant though, as I am not interfering with the GC8 input signal as I have said above.
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Old 16th Nov 2020, 10:44 pm   #128
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Default Re: Adding a selectable line input to valve radiogram

I don't really understand what you are getting at when you talk about "adjustment of the RIAA curve from the cartridge and similarly inverting this effect from the modern line signal to the amp" or "RIAA bias adjustment".
For a start if you have lots of 78s from before 1954 they won't have been cut with RIAA pre-emphasis but with each record company's patent pre-emphasis and the same goes for pre-1954 microgroove discs. Which de-emphasis to use is a complete minefield which is why the RIAA (Radio Industry Association of America) introduced their standard in 1954 and succeded in having it adopted by most of the world's record-issuing companies by the time stereo came along.
As far as I can see the only components in the disc input circuit are a couple of 1M resistors which are presumably the correct loading for the two ceramic/crystal cartridges. Is there any circuitry further down the line before the main amplifier which could contribute to equalization of the signal from these cartridges?
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Old 18th Nov 2020, 4:49 pm   #129
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by barretter View Post
I don't really understand what you are getting at when you talk about "adjustment of the RIAA curve from the cartridge and similarly inverting this effect from the modern line signal to the amp" or "RIAA bias adjustment".
For a start if you have lots of 78s from before 1954 they won't have been cut with RIAA pre-emphasis but with each record company's patent pre-emphasis and the same goes for pre-1954 microgroove discs. Which de-emphasis to use is a complete minefield which is why the RIAA (Radio Industry Association of America) introduced their standard in 1954 and succeded in having it adopted by most of the world's record-issuing companies by the time stereo came along.
As far as I can see the only components in the disc input circuit are a couple of 1M resistors which are presumably the correct loading for the two ceramic/crystal cartridges. Is there any circuitry further down the line before the main amplifier which could contribute to equalization of the signal from these cartridges?
Hi Barretter
You seem very well read about the historical aspects of record recording standards, thanks for sharing this with me.

To clarify, as far as the phono system entering this amp, this will be via two separate H4F head shells one with the original GC8 78/45 reversible cartridge and the other a new moving magnet cartridge with a robust tracking weight for 33/45 stereo use. The GC8 input is now switched into the amp in its original unchanged level and conditioning and requires no further discussion as this is operating satisfactorily playing all my 78's.

The MM cartridge headshell will be input to the amp via the SPA9 pre-amp. This pre amp has RIAA conditioning, and I have yet to assemble this part of the project.
Hopefully this will also be suitable, and as it stands i do not have any current questions on this.

With regard to the new EXT input (WXAD-10 wifi) I am satisfied I have managed to provide suitable signal conditioning in the form of high/low pass adjustable circuitry prior to the signal entering the SRG600 amp. I am able to tune this signal to respond to signal bias expected by the amp previously (occasional RIAA bias conveyed from the cartridge). To remind you I am using the phono input to the amp and switching the various inputs pre conditioned as previously described. This is working satisfactorily as intended and works well. I do not have further questions here either.

My question was to source a small adjustable amp to trim the differing signals strengths in the final connection to the amp.
The older CD's (via WXAD-10) seem to have lower outputs and I would like to be able to trim these to the same level at the final stage so the amp sees the same level as the newer higher level signals.

It is a simple request to source a line level amp which only has a small adjustable gain so I don't have to couple something together.
It appears no one knows of something suitable so it looks like I will have to do this!

I hope this clarifies my question.

Last edited by Rich400; 18th Nov 2020 at 4:55 pm.
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Old 18th Nov 2020, 8:19 pm   #130
Richardgr
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Default Re: Adding a selectable line input to valve radiogram

I get a bit confused when you say 'trim'. I am thinking you mean 'gain' there?

How about one of these wee beasties ...
Tube preamp buffer
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Old 18th Nov 2020, 9:14 pm   #131
Edward Huggins
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Default Re: Adding a selectable line input to valve radiogram

As well as "Trim", the OP is using other words/phrases that I do not understand.
What does "Conditioning" and "RIAA Bias Adjustment" mean please?
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Old 18th Nov 2020, 9:57 pm   #132
Rich400
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Default Re: Adding a selectable line input to valve radiogram

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Originally Posted by Richardgr View Post
I get a bit confused when you say 'trim'. I am thinking you mean 'gain' there?

How about one of these wee beasties ...
Tube preamp buffer
Hi Richard
Yes I can see why you suggest ‘gain’ works well there!

Thanks for your amp kit suggestion, a nice little unit there!
Perhaps the adjustment pot would be working at the bottom of the range but looks like it would do the job.
Thanks again for another positive contribution!
Richard
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Old 19th Nov 2020, 11:47 am   #133
Rich400
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Default Re: Adding a selectable line input to valve radiogram

Quote:
Originally Posted by Edward Huggins View Post
As well as "Trim", the OP is using other words/phrases that I do not understand.
What does "Conditioning" and "RIAA Bias Adjustment" mean please?
Hi Edward
Conditioning is applied to a signal this refers to changing the characteristics of it.

The RIAA signal from the cartridge has a bias towards mid/higher frequencies. That is when RIAA standard was applied at the recording stage, the bass component was minimised to permit shorter track length. The amplifier in my SRG600 is expecting in its original EXT input this type of signal, so when a full range signal is applied the output sound would be incorrect. To enable the amp to work correctly the signal has to be ‘conditioned’ through high snd low pass filters (Bass and Treble for you) this adjusting the RIAA bias.
It’s nice to give something back to you Edward again, if there’s anything you don’t understand just ask.
Regards
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Old 19th Nov 2020, 1:50 pm   #134
Edward Huggins
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Default Re: Adding a selectable line input to valve radiogram

Thank you for this detail. It's just that the wording you are using is not typically used by vintage electronics engineers.
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Old 20th Nov 2020, 4:02 pm   #135
barretter
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Default Re: Adding a selectable line input to valve radiogram

Quote:
Originally Posted by Rich400 View Post
Quote:
Originally Posted by Edward Huggins View Post
As well as "Trim", the OP is using other words/phrases that I do not understand.
What does "Conditioning" and "RIAA Bias Adjustment" mean please?
Hi Edward
Conditioning is applied to a signal this refers to changing the characteristics of it.

The RIAA signal from the cartridge has a bias towards mid/higher frequencies. That is when RIAA standard was applied at the recording stage, the bass component was minimised to permit shorter track length. The amplifier in my SRG600 is expecting in its original EXT input this type of signal, so when a full range signal is applied the output sound would be incorrect. To enable the amp to work correctly the signal has to be ‘conditioned’ through high snd low pass filters (Bass and Treble for you) this adjusting the RIAA bias.
It’s nice to give something back to you Edward again, if there’s anything you don’t understand just ask.
Regards
Richard
The amplifier in your radiogram is not "expecting" an "RIAA conditioned" signal.
The RIAA "conditioning" (or "deconditioning", I suppose) is performed by the way the ceramic cartridge works in combination with the 1 megaohm resistors. After that the now "conditioned" signal is fed to the grid of the first ECC83 valve which amplifies it so as to overcome the losses in the treble and bass tone controls, then to the second triode of the ECC83 for further amplification and negative feedback from the output transformer, then to the phase splitter and finally to the push-pull output stage. You need to input your external line stage after the two 1M resistors but it might overload the first triode of the ECC83 so you probably need to attenuate it somehow.

Last edited by Station X; 20th Nov 2020 at 5:14 pm. Reason: Typo corrected.
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Old 20th Nov 2020, 4:43 pm   #136
Edward Huggins
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Default Re: Adding a selectable line input to valve radiogram

Ah, I now see the OP is not using the word "Bias" in the electronic sense, but in the literal sense. It's a rather esoteric way of explaining an electronic characteristic!
Again, all my 60 years experience of the theory of crystal/ceramic cartridges working into a high-impedence input (c.1 meg ohm load) tell me that no form of EQ adjustment is needed - it is performed by the inherent piezo/mechanical virtues of the cartridge per se.
So why do these Posts seem to wander off into attempting to change these inherent characteristics by some form of variable EQ/Gain? I just don't get it. HELP!
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Last edited by Edward Huggins; 20th Nov 2020 at 5:04 pm. Reason: typo
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Old 20th Nov 2020, 5:23 pm   #137
barretter
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Default Re: Adding a selectable line input to valve radiogram

Quote:
Originally Posted by Edward Huggins View Post
Ah, I now see the OP is not using the word "Bias" in the electronic sense, but in the literal sense. It's a rather esoteric way of explaining an electronic characteristic!
Again, all my 60 years experience of the theory of crystal/ceramic cartridges working into a high-impedence input (c.1 meg ohm load) tell me that no form of EQ adjustment is needed - it is performed by the inherent piezo/mechanical virtues of the cartridge per se.
So why do these Posts seem to wander off into attempting to change these inherent characteristics by some form of variable EQ/Gain? I just don't get it. HELP!
He's using a magnetic cartridge for his microgroove records so he needs a separate RIAA preamplifier for them. Otherwise he seems to think that the frequency correction for the 78s is performed by the input circuitry of the amplifier rather than by the characteristics of the ceramic cartridge in conjunction with the 1M resistors. Thinking of the tone controls as filters seems to be the root of this.
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Old 21st Nov 2020, 12:54 am   #138
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Default Re: Adding a selectable line input to valve radiogram

The last thing that I would do is to claim any technological superiority within this thread [perish the thought ] but as Edward says, it's all getting a bit strange in terms of an unknown terminology and 137 posts I think it's very much a product of the Forum being quite different these days as I mentioned recently. (See the "10 Reel to Reel Wanted" thread-posts #6 and #22 for example!].

https://www.vintage-radio.net/forum/...d.php?t=173235

When following a scientific approach to vintage radio restoration a detailed obsessive technique may indeed help but on the other hand, less can be more and looking at process, rather than content, might just help. You never know!

Dave

Last edited by dave walsh; 21st Nov 2020 at 1:21 am.
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Old 21st Nov 2020, 1:32 am   #139
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Default Re: Adding a selectable line input to valve radiogram

You have to know when to stop, sit back, and just listen to some music.

It's sort of important, because all subjects are bottomless without some self-imposed limit.

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Old 21st Nov 2020, 1:43 am   #140
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Default Re: Adding a selectable line input to valve radiogram

A wise man speaks. I really don't like to criticise audio [phool] enthusiasts in the usual way it's done. They are not so far from us in a way after all but my aim is to always just to get to hear the material., I've known a few people with really great kit who, primarily, listened to frequency response records

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