Vintage Amfiton-002 Hi-Fi amplifier for acoustic guitar - diyAudio
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Old 18th August 2013, 12:31 PM   #1
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Default Vintage Amfiton-002 Hi-Fi amplifier for acoustic guitar

Hi!

I own the vintage Soviet Hi-Fi amplifier Amfiton 002. I would like to use it to amplify acoustic instruments - guitar, ukulele etc. Amfiton 002 has the only one built-in mic preamp, the others are designed for LP, Tape reacorder etc...

Click the image to open in full size.

I want to modify those preamplifiers to make them work with the electret mic, piezo and sound-hole magnetic pickup systems.

So, there is the question here: How to modify Phono preamplifier RIAA frequency equalization circuit in the schematic ???

Thanks for the supporting!
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Old 18th August 2013, 05:10 PM   #2
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Post the schematic.
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Old 18th August 2013, 06:52 PM   #3
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Quote:
Originally Posted by cyclecamper View Post
Post the schematic.

Hi,

I have got some recommendations on the issue, it all is about the CR circle in the phono preamp stage, the capacitors and resistors that should be removed/changed are marked in green.
Thanks!
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File Type: jpg Amfiton correction preamp - stage A1.jpg (214.7 KB, 79 views)
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Old 19th August 2013, 09:37 AM   #4
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Quote:
Originally Posted by Schertler View Post
Hi!

So, there is the question here: How to modify Phono preamplifier RIAA frequency equalization circuit in the schematic ???

Thanks for the supporting!
I think it's more convenient to build a small, simple "flat" guitar-pickup preamp inside this HiFi amp to boost the pickup signal (few mV to line-level (0.1-1V). and feed that (internally) to an unused line input of the HiFi amp. You've got already power supply rails in that HiFi amp so that's easy.
Use high (>10M) input impedance to accomodate piezo pickups if you need to.

YMMV

(I like the Cyrillic script on the amplifier!)
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Old 19th August 2013, 11:44 AM   #5
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Here's the user manual (including schematic) for the classic Leak Stereo 70 amplifier - this has a similar front end to that shown, and provides various option for using microphones etc. with the amp. I've seen many of those amps used as guitar and PA amps in the past, and doing an excellent job at it.

It should be easy enough to modify the Russian amp with the Leak details.
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File Type: pdf Leak Stereo 70 service manual.pdf (882.7 KB, 26 views)
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Old 19th August 2013, 12:23 PM   #6
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I have several ideas of modifying the Amfiton amplifier and currently I decided to build a stereo cabinet and use the amp as it is - factory made stereo. I would not like to destroy the amp's design, drilling and splitting stereo input-outputs and pots etc etc....
I would prefer just to build a very compact 2-3 channel mixer-commutator.... there are many available and this should be much easier than destroying-rebuilding Amfiton... here it is Lilliput mixer http://www.yerasov.ru/PDF/LILLIPUT_3_2.pdf
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Old 19th August 2013, 01:13 PM   #7
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OK, if you want to keep the Amfiton as-is then an external preamp is the way to go.
I'm afraid the Lilliput mixer won't work with ordinary guitar pickups and piezo's. They both require a fairly high input impedance of the mixer or you will lose high frequencies. Perhaps you can add a simple 1x JFET buffer as first stage?
E.g. like this: http://www.till.com/articles/GuitarPreamp/index.html

Last edited by fastfolkert; 19th August 2013 at 01:15 PM. Reason: typo
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Old 25th December 2013, 07:08 PM   #8
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After all, I am completing my acoustic instrument active cabinet, its design uses Bi-amping on a base of the stereo channels etc .......
At this point I've got the issue with my Hi-Fi amplifier's LOUDNESS / Tone Compensation switch ...... how useful and effective this can be with acoustic musical instruments ??? is it worth to add this tone control switch into the cabinet ??
Thank you!
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