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Receiver as preamp for SET tube amp?


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On 1/13/2021 at 9:28 AM, richieb said:

Why compromise the magic of SET with the preamp section from a receiver? Like JMON said it will work but I can’t believe is the best solution or the end game sound you’re looking for. 

Thanks for your input. Don’t want to compromise the sound, just looking for the convenience of the preamp functionality with the Marantz in front. Listening to them together and separate, I don’t hear any significant differences so far. This might be a temporary solution...

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Personally I would never put a receiver anywhere near a nice SET amp. I think it defeats the purpose. I'd save my pennies for a nice simple tube preamp. If you don't have any other means to listen go for it but I'd make it temp. I've committed far worse sins.

 

I rotate stuff around but I usually listen to Jubs - 45 SET AMP - George Wright Preamp  - EAD DAC - EAD CDP - MUSIC SERVER or for vinyl GW Phono pre.

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  • 6 months later...

I've been using a Marantz SR7013 AVR as a DAC and preamp to my Jolida Fusion 3502P for a year now, and after rolling in some good NOS tubes, I love it. I have a bypass switch so I can use the AVR for movies, and the Jolida for stereo, straight into my Cornwalls. 

Bonus: the AVR has Audyssey room correction. Best of both worlds. 

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  • 6 months later...
On 8/3/2021 at 7:59 PM, JohnW said:

I've been using a Marantz SR7013 AVR as a DAC and preamp to my Jolida Fusion 3502P for a year now, and after rolling in some good NOS tubes, I love it. I have a bypass switch so I can use the AVR for movies, and the Jolida for stereo, straight into my Cornwalls. 

Bonus: the AVR has Audyssey room correction. Best of both worlds. 

I'm needing to do the exact same thing as you have did, what is the bypass switch you are using?

I have a marantz sr5015, vta st-120 tube amp, and klipsch belle's, having simple bypass switch would be perfect! Essentially I have to share the belle's with my wife/kids/tv, but I hate unplugging things when I want to run the tube amp. 

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On 2/7/2022 at 8:13 AM, KASTLROCK said:

I'm needing to do the exact same thing as you have did, what is the bypass switch you are using?

I have a marantz sr5015, vta st-120 tube amp, and klipsch belle's, having simple bypass switch would be perfect! Essentially I have to share the belle's with my wife/kids/tv, but I hate unplugging things when I want to run the tube amp. 

This is exactly what I use: https://www.ebay.com/itm/SPECIALTY-AV-2-Amplifiers-Receivers-to-1-Pair-Speakers-Selector-Switch-Combiner-/224545913401?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

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  • 9 months later...
On 2/9/2022 at 1:32 AM, JohnW said:

Thank you for sharing this. For some reason I didn’t get a notification of your reply. How does this wire up? and is there something in the receiver menu that needs to be toggled on/off when going from the internal amp to the external? I’m assuming the switch box is wired into the Marantz L&R pre-out. It really sounds exactly what I’m wanting to do. Using the Marantz as the Dac/preamp, is the volume controlled by the Marantz or the amp. I have yet to hook my tube amp up as it can be easily damaged from misuse, not warmed up or just left on as I’m sure you know. Do you use an EQ at all by chance. Thanks-Mike. 

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1 hour ago, KASTLROCK said:

How does this wire up?

 

Plug two amplifiers into device; "Amp A" for one of your power amplifiers and "Amp B" to any other power amplifier. Hook one set of speakers to the "Speakers", the front switch's for each speaker both "L" and "R" have "Amp A" and "Amp B" selections separately so one could use Amp A for one "L" and Amp B for "R" or vice versa.

 

Fun fact since these are just switches you could run it in reverse with one amplifier powering two sets of speakers. This time the speakers would be speaker "A" and speaker "B".

 

 

1 hour ago, KASTLROCK said:

is there something in the receiver menu that needs to be toggled on/off when going from the internal amp to the external?

 

Depends on your receiver. Some older receivers had RCA jumpers externally where the preamp and power amp sections split, no internal settings just run the preamp out to the tube amp. Most receivers have some sort of "preamp out" which should just be the front end section of the receiver. This is important because the power stage section is the one that will color the signal the most at low levels with higher harmonics.

 

I'd probably still check the preamp out on an FFT analyzer to see how the output looks. As others have mentioned many have SET amplifiers that have no negative feedback and they like it that way for the extra low order harmonic distortion, mainly 2H. If the receiver's output contains higher harmonics at low levels then they are only going to be amplified by the power amp and mixed in with the original signal. It's not the distortion SET lovers want, it's a nasty irritating distortion that causes listening fatigue over time.

 

Thankfully most reputable receivers "preamp out" will be fairly nice opamps that are so squeaky clean it won't impart nasty distortion like an output stage run at low powers. I've seen too many receivers running so cold that at low output power, like under 1 watt will have nasty harmonics from crossover distortion. These are the lower end receivers typically mass produced and run cold to get past warranty.

 

If you know a good tech one can even have their "preamp out" section of the receiver modified to run in Class A mode which greatly improves the sound. With many opamps it's as simple as tying a resistor from the output to the rail.

 

1 hour ago, KASTLROCK said:

is the volume controlled by the Marantz or the amp.

 

If the amp has a volume control than typically you set that to maximum volume and use the preamp section of your receiver for volume and tone controls.

 

1 hour ago, KASTLROCK said:

I have yet to hook my tube amp up as it can be easily damaged from misuse, not warmed up or just left on as I’m sure you know.

 

As a general rule of thumb it's good to be more safe than sorry but this is often greatly over exaggerated by far to many, especially if it's a low power SET amplifier. You can turn a tube amplifier "on" without it being hooked up to speakers as long as you don't run a signal through it. With no load on the power tubes there can be large voltage spikes that can break down the insulation of the output transformer. Of course if you have a 2 watt SET amp and the B+ is 250v and it's a modern hi-pot tested output transformer I doubt anything will be damaged even if you run a signal through it with no load. Most good amplifier designs will also have a loading network at the output to compensate for rising impedance with frequency on speaker loads, this filter should load the output enough to save the iron. Now if you have a vintage high powered tube amplifier with over 500v on the plates than running a signal through it with no load is asking for trouble. The higher B+ allows higher swings in the output transformer that may break down 60 year old winding insulation.

 

Easy thing to remember, if you turn a tube amp on with no speakers don't play any music through it and no harm should come. I don't know why anyone would play music through an amp with no speakers hooked up but people do dumb stuff.

 

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  • 2 weeks later...
On 12/5/2022 at 11:37 AM, KASTLROCK said:

Thank you for sharing this. For some reason I didn’t get a notification of your reply. How does this wire up? and is there something in the receiver menu that needs to be toggled on/off when going from the internal amp to the external? I’m assuming the switch box is wired into the Marantz L&R pre-out. It really sounds exactly what I’m wanting to do. Using the Marantz as the Dac/preamp, is the volume controlled by the Marantz or the amp. I have yet to hook my tube amp up as it can be easily damaged from misuse, not warmed up or just left on as I’m sure you know. Do you use an EQ at all by chance. Thanks-Mike. 

Sorry, I've been away from this for a while. 

Yes, you simply use the Marantz L&R preouts. Volume is controlled by the Marantz. I don't use an eq per se, but I do use the Audyssey room correction. You can turn it off by using switching to Pure output. 

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