Aside from more inputs, what benefits would a preamp confer upon the already amazing 8600? I know I could buy one and find out, but I’m hoping to hear from those who have tried adding a preamp and observed either an improvement or a degradation in sound quality. I have a decware zen switch box in order, so the input problem will be solved. But would an active pre add or detract from a pure 8600? If it depends, what should I look for in a pre that will mate well? So far my philosophy has been less is more - just get as many components out of the way as possible. But maybe the 8600 is really designed to be fed by a line stage preamp.
Sources are Lehman audio Black Box phono pre and a Luxman DA-06 DAC. Thanks in advance.
Sources are Lehman audio Black Box phono pre and a Luxman DA-06 DAC. Thanks in advance.
I found the TU-8600S somewhat lacking in bass compared to my push pull EL34 DIY amps. Adding a preamp cured it. I’m now pairing my 8600S with a vintage Counterpoint SA2000 hybrid tube preamp.
The downside is that the 8600S has too much gain, so it amplifies the noise from the preamp, making it audible near the speakers. Turning the volume knob to 2 o’clock position or lower eliminates the noise. I don’t like using a preamp to amplify the signal only to attenuate it again, but it still sounds very clean. It is a major improvement in the bass department.
The downside is that the 8600S has too much gain, so it amplifies the noise from the preamp, making it audible near the speakers. Turning the volume knob to 2 o’clock position or lower eliminates the noise. I don’t like using a preamp to amplify the signal only to attenuate it again, but it still sounds very clean. It is a major improvement in the bass department.
TU-8600 has input sensitivity of 320 mV/50 kOhm for full output. With any 2V rms source younger than 20 years it is already quite sensitive as usual with tube amplifiers. So no it definitely does not need a superfluous preamp and it definitely does not need any more gain. In fact you should forget about adding any more gain as (too much) gain is evil and serves no purpose than amplifying noise and making volume already loud at very low volume settings. Those that use phono would be better off upping the output level of just the phone preamp.
*What TU-8600 needs is extra inputs when one has more than 1 source. Retrofitting that would be a nice challenge. The way it is developed forces many to exhibit the bad habit of adding an extra active device solely with the purpose of source selection (and getting too much gain as a bonus). A switch box would be sufficient but absolute best would be more inputs. As it already has volume control anyway it then would be a complete integrated amplifier.
*What TU-8600 needs is extra inputs when one has more than 1 source. Retrofitting that would be a nice challenge. The way it is developed forces many to exhibit the bad habit of adding an extra active device solely with the purpose of source selection (and getting too much gain as a bonus). A switch box would be sufficient but absolute best would be more inputs. As it already has volume control anyway it then would be a complete integrated amplifier.
Last edited:
A Sparkler Audio model S506 “switchgirl” ― Input Selector will do the job... $275 ..
TU-8600S is an integrated Amp. You do not need any preamp. Also TU-8600S is not a HIFI amp. If you want MSG Bass you will be very very disappointed...
If you have a proper setup , I will say 8600S is an emotion amp...It will touch your inner heart...
Paul you are 100% correct...
TU-8600S is an integrated Amp. You do not need any preamp. Also TU-8600S is not a HIFI amp. If you want MSG Bass you will be very very disappointed...
If you have a proper setup , I will say 8600S is an emotion amp...It will touch your inner heart...
Paul you are 100% correct...
Last edited:
Also agree jean-paul. IF the 8600 were like the 8200 in that regard it would be perfect. I also use the sparkler audio switchgirl before the TU8600 to switch between my phono and DAC, although I would have much preferred the input select to be built into the TU8600 itself, particularly as the switchgirl is a powered device that requires another AC plug. I've heard that beresford and luxman have decent and transparent passive switch boxes that do not require external power. I haven't been game enough to mod the TU8600 PCB and case to add a second input and switch.
On second thoughts: adding a small relay board and a second pair of RCA connectors (I don't think a third pair is possible) and replacing the existing PCB mount RCA connectors also for chassis mount ones would not be that hard. So 4 of the same type good quality chassis mount female RCA connectors. When using a small relay board directly in front of the relay board a small source selection toggle switch (similar to the power switch) can be used at the right side of the volume control without breaking the "looks". Output wires of the relay board can be connected to the pads where the old PCB mount RCA connectors were soldered. This would be technically and likely also sonically a good solution. I think engineering is a better method than adding useless gain as common error.
When using tape to prevent scratches a skilled worker can make the slot for the switch the nice way. With a small relay board input wiring will still be short as possible and far away from everything. It can be powered from filament power. If one is very concerned about the looks one could give up on the phones output and use that hole for a IR receiver and have the inputs switched by IR remote control.
When using tape to prevent scratches a skilled worker can make the slot for the switch the nice way. With a small relay board input wiring will still be short as possible and far away from everything. It can be powered from filament power. If one is very concerned about the looks one could give up on the phones output and use that hole for a IR receiver and have the inputs switched by IR remote control.
Last edited:
I also use the Sparkler switch. Solves the problem elegantly. You can get one through Victor at vkmusic.ca.
I went for the Decware Switch Box because I could opt for a remote control volume. The lead time there is over four months...
For many, this would be a super simple DIY project...but not me, I need a kit and instructions.
But the point of this thread was to understand the pros and cons of adding a preamplifier to the 8600, aside from the additional inputs.. It seems consensus is that it only adds noise, but, being the internet, I’m willing to bet some have done it and prefer it sonically.
For many, this would be a super simple DIY project...but not me, I need a kit and instructions.
But the point of this thread was to understand the pros and cons of adding a preamplifier to the 8600, aside from the additional inputs.. It seems consensus is that it only adds noise, but, being the internet, I’m willing to bet some have done it and prefer it sonically.
That is a decisive factor 
Also counts for online suicides, online drug advices etc. Some have done it and preferred it.
If no additional inputs are necessary why add a preamp? This is a common error in tube circles. With 320 mV input sensitivity for full output there is already too much gain. I see this so often that I always ask what the purpose is but I never have gotten a good answer. Mostly to "do something" or "everybody does it". With 2Vrms sources and 320 mV sensitivity there is nothing to be gained except a nervous situation and nice surprises when switching sources. The idea that added stuff would win from a straight wire is also common. In all other disciplines in audio people are not busy at all with adding useless gain in a situation with sufficient gain
Practically no one needs a preamp for decades now unless one has an old phono pre with low output. Then it would be better to have that one upgraded.
Also counts for online suicides, online drug advices etc. Some have done it and preferred it.If no additional inputs are necessary why add a preamp? This is a common error in tube circles. With 320 mV input sensitivity for full output there is already too much gain. I see this so often that I always ask what the purpose is but I never have gotten a good answer. Mostly to "do something" or "everybody does it". With 2Vrms sources and 320 mV sensitivity there is nothing to be gained except a nervous situation and nice surprises when switching sources. The idea that added stuff would win from a straight wire is also common. In all other disciplines in audio people are not busy at all with adding useless gain in a situation with sufficient gain
Practically no one needs a preamp for decades now unless one has an old phono pre with low output. Then it would be better to have that one upgraded.
Last edited:
TU8500 is a good match for TU8600
I finished building the TU8500 last night and started listening with the TU8600S instead of directly connecting my source components. I couldn't believe my ears - more dynamics and low level detail compared to direct connection.
Here is my theory on why this is so...Wikipedia says consumer audio manufactures must supply 2v (peak-to-peak) line level outputs but actual music level is more like 0.3v (0.6v p-p). Feeding this directly into the TU8600, the signal is reduced by the input volume control before it gets to the driver and gain tubes and the grid of the 300B. The power transfer curve of a 300B tube shows that as plate voltage increases, plate current will increase much higher beyond a certain threshold. 30v will create 23 mA of current (0.7 watt) while 50v will create 58 mA (2.9 watt). (The 300B plate drives the speakers further down the chain.) If the grid voltage is too low the 300B is not operating in its optimal power range. Low level music detail is amplified at a lower gain than higher level music. Perhaps using the TU8500, which provides 3X gain, is providing enough grid voltage to operate the 300B in its linear range.
In summary, this turned out to be the tonic I needed to make my system boogie. The built-in phono RIAA EQ preamp sounds pretty good too. Will have to compare vs. my more expensive standalone phono preamp.
I finished building the TU8500 last night and started listening with the TU8600S instead of directly connecting my source components. I couldn't believe my ears - more dynamics and low level detail compared to direct connection.
Here is my theory on why this is so...Wikipedia says consumer audio manufactures must supply 2v (peak-to-peak) line level outputs but actual music level is more like 0.3v (0.6v p-p). Feeding this directly into the TU8600, the signal is reduced by the input volume control before it gets to the driver and gain tubes and the grid of the 300B. The power transfer curve of a 300B tube shows that as plate voltage increases, plate current will increase much higher beyond a certain threshold. 30v will create 23 mA of current (0.7 watt) while 50v will create 58 mA (2.9 watt). (The 300B plate drives the speakers further down the chain.) If the grid voltage is too low the 300B is not operating in its optimal power range. Low level music detail is amplified at a lower gain than higher level music. Perhaps using the TU8500, which provides 3X gain, is providing enough grid voltage to operate the 300B in its linear range.
In summary, this turned out to be the tonic I needed to make my system boogie. The built-in phono RIAA EQ preamp sounds pretty good too. Will have to compare vs. my more expensive standalone phono preamp.
I leave the TU8600 volume control at max (0 ohm). My preamp volume is at 9:30. I am using LS35A clone speakers which have a low sensitivity of 84 dB. If you are using high efficiency speakers I can understand you need to set the TU8600 volume control to 9 or 10. I was typically at 12 to 1 position with direct connection.
I've read comments suggesting power amps should not have volume controls at all because they add noise. It seems to me if you reduce the input signal level by 70% (estimate at 9 position) you will reduce the maximum voltage available to the grid that controls the amount of power produced by the 300B plate. Another consideration is that the output capacitors of the TU8500 (upgraded to Mundorf) will meet the input volume control resistor in the TU8600. I thought an RC network acts like a high pass filter. It would be interesting to increase/decrease both volume controls to hear the end result (if any).
I had looked into the Schiit Freya and Saga but decided the TU8500 was worth a try even though it doesn't have remote control for volume & input selector.
I've read comments suggesting power amps should not have volume controls at all because they add noise. It seems to me if you reduce the input signal level by 70% (estimate at 9 position) you will reduce the maximum voltage available to the grid that controls the amount of power produced by the 300B plate. Another consideration is that the output capacitors of the TU8500 (upgraded to Mundorf) will meet the input volume control resistor in the TU8600. I thought an RC network acts like a high pass filter. It would be interesting to increase/decrease both volume controls to hear the end result (if any).
I had looked into the Schiit Freya and Saga but decided the TU8500 was worth a try even though it doesn't have remote control for volume & input selector.
I don't really get this explanation. I assume the volume control in TU-8600S is installed between the input jack and the amp itself, just like in any other Elekit amp that I saw. In that case, all AC and DC voltages are the same everywhere in the amp at the same output volume, no matter whether being driven from a preamp or not.
The sonic difference may well be coming from the absolute phase inversion introduced by the TU-8500 or volume mismatch.
You are correct about location of volume control in TU8600. The volume control of TU 8500 is closer to the output. I was suggesting a low level signal might cause the 300B to operate near the bottom of its power transfer curve where the gain ratio is less than one. Other comments in this thread suggests 320 mV is sufficient to drive the TU8600 to full volume. As for phase inversion of TU8500, didn't see this in the specs. I could check with a scope to confirm.