Simple Hifi Home Stereo Amp Builderino

Discussion in 'Shock Brother's DIY Amps' started by kleydejong, Feb 8, 2019.

  1. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    I'd like to attempt a hifi amp build. If this forum is only appropriate for guitar amps, I completely understand and will refrain from posting here, please let me know. I've completed several successful guitar amps now, but for whatever reason I feel a bit uncertain about a hifi amp project. So I'm going to try something simple and see how my knowledge will transfer. This will be from the perspective of a guitar amp maker dipping into the hifi world.

    Build Objectives

    - I play my music off my computer. I run it into an audio interface for Digital to Analog conversion. Then I run that into a solid state receiver. I run that into a pair of Overnight Sensation bookshelf speakers that I built a while back. https://www.parts-express.com/overnight-sensations-mt-speaker-kit-pair--300-706.
    - I want a device that can replace the solid state receiver I'm using.
    - I want to draw on my guitar amp experience as much as possible - meaning 12A*7 tubes in the preamp feeding SE EL84 or 6V6's in the power section.
    - Simple PTP wiring. Not interested in a kit as I can source my own parts.
    - Budget friendly.

    Circuit

    At this point my biggest question is about what type of circuit I should use. I found a nice list of schematics here - http://diyaudioprojects.com/Schematics/. I also made a reddit post looking for input here:

    https://www.reddit.com/r/diytubes/comments/antdqg/diy_hifi_amp_build_need_circuit_advice/

    I got a lot of good input. I'm treating this as a little bit of an experiment. I really don't have a lot of experience in the hifi audiophile world with nice gear. I perceive I could quickly start spending a lot of money on this project, which I don't really want to do. Perhaps I'm shooting myself in the foot, but I'm going to try and be pretty frugal on this build.

    One decision I'm going to make off the bat is to use a power transformer I have sitting on the shelf. In my experience it is best to start with the power supply and work backwards from there. The PT I have in mind is labeled 40-16519. I found some information on that PT here - https://www.amplifiedparts.com/products/transformer-fender-replacement-power-330-0-330-v-120-ma and it is described as being a Deluxe Reverb PT. This provides the following specs:

    [​IMG]

    In a hifi amp everything is in stereo - so I'm thinking a stereo Single Ended 6V6 output section could be ideal.

    My perception is that the output section of a tube amplifier really won't differentiate that much between a guitar amp and a hifi amp - but I could be wrong. I've been reviewing many hifi schematics and find they tend to be more robust in the power supply in terms of filtering to reduce noise. They also tend to use negative feedback or other design choices to keep things clean - especially in the preamp. Lastly I would estimate that the output transformer and speakers used are HUGELY different.

    Looking further I discovered a nice schematic here - http://diyaudioprojects.com/Schematics/SE-6V6-Amp-Lacewood-Schematic/


    [​IMG]

    [​IMG]

    I may make some modifications. I'm thinking a 12AX7 instead of 6SN7 just for familiarity and I already have a stock of 12AX7's. Probably a volume control on the input. I may tweak the rectifier and filtering a bit too.

    Any input or advice going into hifi would be very welcome. Away we go!
     
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  2. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    No stereo building experience to offer, but I know that with the right speaker a tweed Champ or Princeton can sound pretty darn good playing music. Going the single-ended 6v6 route, you may compare those to anything else you look at in the stereo world.

    Sent from my XT1585 using Tapatalk
     
  3. Tom Kamphuys

    Tom Kamphuys Tele-Meister

    Age:
    39
    156
    Sep 18, 2018
    The Netherlands
    Blencowe also has a book about HiFi preamps besides the guitar/bass preamps book.

    Here's an article by him about a hifi amp.
     

    Attached Files:

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  4. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    I have noticed there are some very simple looking single ended circuits not far off from a 5F1 in the hifi world. This gives me hope!
     
  5. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    Of course, Blencowe is a genius! I will review, thanks for the input.
     
  6. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
    That xfrmer is going to make nearly 400v which you don’t need for your b+ listed.

    Also stick with 6v heaters unless you want to build a separate power supply for your heaters
     
  7. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    Would EL34's be more optimal given this PT?
     
  8. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
    With hifi you want everything in your signal chain to be quality components. Get some nice paper in oil caps. The edcors are great output transformers.

    Also noise is important so proper grounding and isolation of psu is important.

    Buy a nos 5u4gb or go ss rectifying as new tubes are unreliable.
     
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  9. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    Wait, I don't think my PT has enough current - never mind.
     
  10. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
    Not sure what the plate voltage range for them is but it might be too hot too. I’m building a preamp with el34 and using that Hammond 270fx as well.

    I think 12ax7 are good to like 350 are they not?

    I would also be surprised if a single 12ax7 per side would be enough for your pre-stage. Most configurations use multiple tubes for buffer/gain/follower etc
     
  11. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    I'm not sure about input gain. I'll be running my music off my computer, DA conversion via an audio interface. I believe it sends a line level signal L+R.
     
  12. kleydejong

    kleydejong Tele-Holic

    649
    Aug 30, 2010
    Orange City, IA
    Regarding my power supply, what if I copied the power supply design from an AB763 Deluxe Reverb that this PT was designed to be used in? I also have a 50ma 4h choke on hand.

    [​IMG]

    Most of the hifi amp schematics I'm looking at appear to have more filtering via a choke before the B+ node feeding the Output Transformer. Is the concern that one filter capacitor isn't enough filtering for a hifi design? Whereas with a guitar amp you can get away with it?
     
  13. Tom Kamphuys

    Tom Kamphuys Tele-Meister

    Age:
    39
    156
    Sep 18, 2018
    The Netherlands
    Guitar amps get away with anything.

    Sag, distortion, noise, hum, limited frequency range, standby switches. As long as they sound good at 11, everybody is happy.
     
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  14. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
    Caps are dc filters mostly and with an opt you won’t transfer dc to a speaker anyway.

    A lot of it comes down to frequency control, caps are also filters and most tubes have frequency ranges beyond hearing and into rf noise.

    Like said above, a guitar amp is made to be nasty while a hifi amp is clean so more components to lower psu noise, filter unwanted frequencies and perform linearly.
     
  15. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
    Here is an amp I built using 6t9 compactron tv audio tubes.
    Power supply
    5EF8D047-D233-48FD-832C-C7EE92ED6174.jpeg
    Amp section (outputs have been stolen)
    AD0895EF-C968-41ED-80FC-28914D69C666.jpeg
    Top
    973E09E7-B7AF-40D9-8F45-DCC7B19F9B66.jpeg
     
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  16. Billnchristy

    Billnchristy Tele-Afflicted

    Sep 21, 2017
    Georgia
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  17. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    You might want to draw a couple of load lines, because I would definitely NOT use 12AX7's. You want good headroom and not too much gain, and 12AU7 would be much more suited. 10K plate and 220 ohm cathode and thank me later...You will still have more than 20dB gain, and with a line level input, it will overdrive the 6V6 by a couple dB.

    Remember that consumer line level is 0.775VRMS but tubes clip at peak-to-peak voltages. Convert line live to P-P and multiply by 10 (20dB) = almost 22Vp-p. A hot level from a CD player output will get distorted, line level is even too hot by a couple dB. Now, isn't math fun?;)

    You could also save some $$ and loose the GZ34 to kick up the voltage a bit and get more juice out of it while giving your input stage more headroom. If your PT can support it, 6L6 will give you all the headroom you need with line level input.
     
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  18. Mongo Park

    Mongo Park Tele-Holic

    606
    Nov 28, 2010
    Winnipeg
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  19. David Barnett

    David Barnett Doctor of Teleocity

    My opinion is that, unless you are in a very small space, a single-ended amp won't be sufficient for the Overnight Sensations. I think something like an EL-34 push-pull design, ~35W/side, may be more appropriate.

    The Overnight Sensations are a very compact enclosure with small drivers and full baffle-step compensation (or else there'd be no bass, thanks to Hoffman's Iron Law...). This means the efficiency will be fairly low. Single ended amps are suited for very efficient speakers.
     
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  20. jsnwhite619

    jsnwhite619 Friend of Leo's Ad Free Member

    Age:
    34
    Sep 10, 2013
    Georgia
    Hook an iPod to your 5f2 and see how loud and clean it is. Should give you an idea of power requirements -- is it close or completely lacking?

    Sent from my XT1585 using Tapatalk
     
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