Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: grovesyblues on January 03, 2024, 04:28:36 am

Title: Need help to understand this Phono Circuit
Post by: grovesyblues on January 03, 2024, 04:28:36 am

Hello All, I have an Audio Innovations Series 1000 Preamplifier, this is a passive Preamp with a Tube based Phono Stage. I bought it new in 1985 and it's still working fine, but I have never understood what the circuit is and how it works. My tube knowledge is some what limited as I studied digital electronics in my early days. I keep looking at this circuit and comparing it to other designs on the web, however I can not find anything like this circuit. I would love to understand how it works and what technique(s) have been used. Can anyone explain how this circuit works, just for personal interest more than anything else.

Many thanks to anyone that replies.

Cheers
Simon

Title: Re: Need help to understand this Phono Circuit
Post by: kagliostro on January 03, 2024, 05:28:51 am

May be of interest ?

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.diyaudio.com/community/attachments/tc-srpp-pdf.948461/&ved=2ahUKEwizuYWXjsGDAxVy9gIHHd34ALYQFnoECBUQAQ&usg=AOvVaw06Cqgzl2p6os3eYKdyADKH (https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.diyaudio.com/community/attachments/tc-srpp-pdf.948461/&ved=2ahUKEwizuYWXjsGDAxVy9gIHHd34ALYQFnoECBUQAQ&usg=AOvVaw06Cqgzl2p6os3eYKdyADKH)

Franco

Title: Re: Need help to understand this Phono Circuit
Post by: grovesyblues on January 03, 2024, 05:50:28 am

Hello Franco, thank you very much, exactly what I was looking for. I did think it sort of looked Push Pull like but with no output transformer I excluded it. The article said very popular in the 90s which is about the right timing, Audio Innovations were leading the valve resurgence in the late 80s when I bought this unit. This is a very good clear article, thank you taking the time to reply and posting the link.

Kind regards
Simon

Title: Re: Need help to understand this Phono Circuit
Post by: WimWalther on January 03, 2024, 08:38:15 am

For those not wishing to download a PDF file, the gain stage is known as an SRPP design.

Title: Re: Need help to understand this Phono Circuit
Post by: kagliostro on January 03, 2024, 10:52:00 am

Yes, SRPP

or

Quote

This circuit has many names: SRPP, SEPP,
Totem Pole, Mu Follower, Mu amplifier,
Cascoded Cathode Follower, and its original
name, the Series-Balanced amplifier (Feb.
1943, US patent 2,310,342. Just what "SRPP"
means is uncertain; maybe it stands for Series
Regulated Push-Pull amplifier or Single-Ended
Reflexive Push-Pull amplifier.

Franco

Title: Re: Need help to understand this Phono Circuit
Post by: PRR on January 03, 2024, 12:32:11 pm

https://www.tubecad.com/may2000/