{"id":2953,"date":"2013-12-28T15:04:56","date_gmt":"2013-12-28T15:04:56","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=2953"},"modified":"2014-01-02T09:34:21","modified_gmt":"2014-01-02T09:34:21","slug":"iriaa-test-box","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2013\/12\/28\/iriaa-test-box\/","title":{"rendered":"IRIAA test box"},"content":{"rendered":"

Testing RIAA stages is a real challenge. However, with current testing gear becoming affordable to us thanks to the development of PCs and sound card interfaces, now you can \u00a0test your RIAA stage without further excuses. There are software-based solutions to implement IRIAA \u00a0transfer curve for looking at a flat frequency response of our RIAA stage, but they are not free or easy to implement unless you are skilled on data manipulation on your PC. You can also build your own analogue IRIAA stage. In fact, Morgan Jones suggests a great way of implementing this in his great “Building Valve Amplifiers” (Second Edition) which was \u00a0recently released. I recommend the book highly, albeit I will not fall in the trap again of buying the e-book version. I was highly\u00a0disappointed\u00a0with the e-book release of 4th edition of “Valve Amplifiers”. I guess I will just use my Kindle for reading plain books instead.<\/p>\n

The circuit proposed by Morgan Jones is inspired on Hagerman’s paper<\/a> (thanks Gary B for providing the link) which includes an IRIAA stage for same purposes:<\/p>\n

\"Extracted<\/a>
Extracted from “On Reference RIAA Networks” by Jim Hagerman<\/figcaption><\/figure>\n

Morgan Jones changed Hagerman’s design component values to fit to the 3.18uS Neuman pole instead of 3.5uS and combined 1% and 0.1% resistor tolerances to improve the accuracy of the IRIAA response. You can get the\u00a0essence of the circuit from the above diagram.<\/p>\n

I modified the circuit proposed by Morgan Jones slightly to fit my requirements and in particular I added the additional resistors to simulate DL103’s output resistance of 40\u03a9.<\/p>\n

I had a nice strong mints sweet metal box from Marks & Spencer and used it ast the housing for the IRIAA stage. A BNC adapter also was added to the input to ensure I could hang the IRIAA box from either the waveform generator or the SC interface:<\/p>\n

\"Inside <\/a>
Inside the IRIAA box <\/div> <\/div> <\/div>
\"MC <\/a>
MC and MM outputs <\/div> <\/div> <\/div>
\"IRIAA <\/a>
IRIAA box <\/div> <\/div> <\/div> <\/div>
\"Input <\/a>
Input connector <\/div> <\/div> <\/div>
\"Inside <\/a>
Inside box 2 <\/div> <\/div> <\/div>
\"Inside <\/a>
Inside box 3 <\/div> <\/div> <\/div> <\/div> <\/div>\n

Building this box takes just a couple of hours and you will be amazed with the results you can achieve. I wish I could post the diagram but I don’t have Morgan Jones’\u00a0permission\u00a0so I hope this post encourages you to buy the book if you weren’t still convinced to do so.<\/p>\n

This IRIAA stage has two outputs. One for MC and the other one for MM. You can see the ideal frequency response below:<\/p>\n

<\/p>\n

\"IRIAA<\/a>
Ideal MC and MM outputs from the IRIAA stage<\/figcaption><\/figure>\n

 <\/p>\n

At low frequencies, the MM output will go down as low as 70dB, whereas the MC will attenuate as much as nearly 100dB.<\/p>\n

I did a quick sweep MLS frequency test on my workbench and here are the results achieved:<\/p>\n

\"IRIAA<\/a>
MM IRIAA frequency response test<\/figcaption><\/figure>\n

You can see from the MM output the accuracy is really good. You can test your RIAA stages with acceptable accuracy, which is what we need at the DIYAudio level.<\/p>\n

Just as an example, the below test shows my work in progress MM RIAA stage which is actually being converted to MC given the recent acquisition of the DL103 cartridge:<\/p>\n

\"RIAA<\/a>
RIAA test<\/figcaption><\/figure>\n

You can see from the IRIAA-RIAA response that the curve remains flat between +\/- 0.1dB. You can get a more accurate measurement with individual frequency measurements but this was good enough to demonstrate the value of the IRIAA box.<\/p>\n

An invaluable piece of testing gear for measuring our RIAA phono stages \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"

Testing RIAA stages is a real challenge. However, with current testing gear becoming affordable to us thanks to the development of PCs and sound card interfaces, now you can \u00a0test your RIAA stage without further excuses. There are software-based solutions to implement IRIAA \u00a0transfer curve for looking at a flat frequency response of our RIAA … Continue reading “IRIAA test box”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[449,448,162,67,5],"tags":[509,513,512,511,510],"class_list":["post-2953","post","type-post","status-publish","format-standard","hentry","category-riaa","category-riaa-stages","category-source","category-thd","category-valves","tag-iriaa","tag-morgan-jones-building-valve-amplifiers","tag-riaa-measurement","tag-riaa-phono","tag-riaa-test"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-LD","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/2953","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/comments?post=2953"}],"version-history":[{"count":10,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/2953\/revisions"}],"predecessor-version":[{"id":2974,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/2953\/revisions\/2974"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=2953"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=2953"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=2953"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}