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Tube pre-amp

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I'm new to tube amps (not new to electronincs) and I found this forum. Been reading the massages for some time now and I thought I'd ask a question myself. I am looking for a schematic of a tube pre amp, but since I'm new I'm having trouble finding sites about the topic. You peolple know some good sites? You would realy help me out!

Thanks !!

Roel Dirks
The Netherlands
The Internet is full of schems of tube preamps. The problem is what are you looking for.
Try this link:
There are several preamps comparred. I own the McIntosh C22 and the SRPP preamp. Both work fine. The original C22 has tone controls, which are made perfect. They have nothing to do with all the other I've seen so far. May be something similar is just the tilt control of Quad.
The SRPP circuit is quite simple, the sound is great, there is no need for global feedback. The THD are very low because of the circuit configuration.
My own oppinion is that if you use a solid state amp, the tube preamp will help you overcome the transistor sounding of your system.
Note that both preamps have pretty high gain. If you don't need high output swing, I suggest a resistor in series with the pot. Lets say 150K and 100K pot after it. I personaly use 226K resistor plus 10K pot. This way my SRPP preamp works like a follower. The input equals the output.
The tubes in the SRPP will last less then these in the McIntosh.
Note that the input and the output of the SRPP preamp are out of phase.



[Edited by Asen on 05-06-2001 at 09:07 AM]
Nice and simple :)

Thanks. Lots of information here. But since I have little experience, are there things I need to look at when building the preamp? On the site it reads: "However, some experience is required or it will end up as an impressive noise generator"
So how do you prevent this?

Also found this site:
It is a preamp a lot like the one on the site you mentioned and it uses the E88CC. I have some of these tubes so it would be nice if this would work.

Thanks again.

Don't be afraid - there's no noise. According to my experience tubes are times quieter than anything else. My preamp has 2mV output noise - there are not any special measures taken.
I'll find time these days and will send you more detailed information. For being with not enough experience I sugest you build a simple preamp, like the SRPP. There are loads of information about this circuit in the net. I'll send you details for the PSU, which is nothing special - 3 RC groups, 400uF is enough for both channels.
To be continued...


[Edited by Asen on 05-07-2001 at 05:15 PM]
Two questions:
1) Are you planning on a phono stage, or just line?
2) How much gain are you shooting for? If you're using a CD player, you won't need much gain...perhaps only 6-12 dB. Some tuners would require more. If you're planning on a phono stage, then it's nice to have some extra gain on hand (perhaps 18-24 dB) in case you get a low-output cartridge and need to take up slack from a phono stage that's a few dB shy. Anything over high twenties is overkill.

Thanks Asen, looking forward to your information, and thank you in advence for your time.

Hi Grey,

It's just for a cd player, no phono. So about 6 to 10 dB will do fine i think. And it is just like Asen said, I am HOPING to overcome some of the solid state sound of my amp without having to build a full tube amp.

I also might add that I am planning on using it also as a pre amp on my Pass ZEN amp, if this is possible.

Any info you can offer me is well noted.

Hi Micke,

Look at: http://www.diyaudio.8m.com/srpp.html

It says something about not exceding the heater to catode voltage. Not sure what it means but it says that in a stereo version you use one tube for both upper parts of the schematic and one tube for both lower parts of the schematic. Can someone else clear some thins up?

Also take a look at: http://www.infomaniak.ch/~bonavolt/lindesrp.htm


[Edited by jaaasgoed on 05-07-2001 at 09:39 AM]
If you're planning on using it with a Zen, then you might need more gain, as the Zen is not the most sensitive of amps. Perhaps 18-24 dB would be in order.
The heater to cathode voltage limit is a number not to be taken lightly. The heater, usually a folded wire, and the cathode, usually a rectangular metal shell, are in close physical proximity to one another, generally touching (they're insulated). While the cathodes are separate, the heater is shared between the two sections of most twin triodes, so you can't run one cathode at a drastically different voltage from the other. If you exceed the rating, you're likely to get an arc between the two, with unfortunate consequences. In a circuit such as the one you are discussing, it's general practice to use one tube for the lower sections, and another for the upper. In this case the heater voltage for the tube handling the upper sections should be lifted to something approximately equal to the cathode voltage (somewhere within the heater/cathode rating--it's not critical). A voltage divider from B+ to ground, tied to one side of a *separate* filament transformer (or a separate winding, if you've got more than one on your power transformer) will do the trick.
You're on the right track.

Yes, you could use 4 tubes if you wanted to, although if you're using twin triodes (12AX7, 6SN7, 6DJ8/6922, etc.) you'll be wasting the unused tube section. However, that would give you the option of paralleling the tube sections for lower noise, distortion, etc. (Hint, hint...)
Dropping a 6SN7 into that 6DJ8 circuit is likely to give you odd results, as the 6SN7 likes higher voltages than the 6DJ8. (I use 450V rails for 6SN7s) That said, the results you got are probably somewhere in the ballpark, as you're getting 21.6 dB gain. The 6DJ8 should probably give you more gain, due to having a higher mu--33 compared to the 6SN7's 20, if memory serves. (I'm at work and don't have my reference stuff handy. I'm sure someone will spank me if I'm wrong.) The 6DJ8/6922 is a wonderful tube, and that circuit looks quite reasonable. I would just about guarantee that it will sound great if you execute it cleanly.
Two things to be aware of:
1) The output impedance will be a bit high. Don't plan on driving long or highly reactive interconnect cables with it unless you add a cathode follower.
2) Being a single gain stage, it will be phase inverting. Reverse the leads to your speakers.

Hi again

About the SRPP:

1. The PSU voltage is not critical. It depends on the tubes you use. In my case I use Tesla ECC88. My PSU output is 180V DC. The consumption is ~10mA per channel. You must calculate the resistors in the PSU using the Ohm’s law. I suggest you to use the free “PSU Designer II” (Duncan’s Amp Pages) – a very useful programme. Here’s the address:


The programme will help you a lot if you decide to use tube rectifiers. There are things you should know so that you don’t damage the rectifier tubes. The software will take care of that. You must remember – the first cap in the PSU shouldn’t be too big. For example – if you use EZ80 the first cap shouldn’t be bigger than 50uF. I use RC filters, but may be inductors will improve the performance of the preamp. I haven’t tried that yet. I haven’t tried tube rectifiers too, but intend to. What I use for rectification at the moment is Fast Recovery Silicon Power Rectifier - BYT12P/1000A in full wave configuration. Special features of this diode are: Multiple diffusion, Low switch on power losses, Good soft recovery behaviour, Fast forward recovery time, Fast reverse recovery time, Low reverse current, Very low turn on transient peak voltage, Very good reverse current stability at high temperature, Low thermal resistance. Some of these features are not of importance in our case.
Special features of the tube rectifier is the soft start of the whole circuit, and the better noise behaviour of the PSU. As I said I haven’t tried it yet but some people report that entirely tubed circuits sound better.
In the PSU I use 2 transformers – one for the tube heating, and one for the high voltage – 20VA each. For the heating I use 9VAC, bridge rectifier (ON HEATSINK), 2200uF, LM317 (ON HEATSINK) and 6600uF. The current through the triodes depends a lot on the heating voltage. I tried a common ground (both grounds connected together) and floating ground (the ground of the heating PSU circuit connected via 3/4 divider to the high voltage). For the second I used 3,3MO and 1MO resistor divider. I didn’t notice any difference in the sound reproduction of the preamp, but I was unable to make an AB test. I must admit – I still don’t know what’s the benefit of the floating ground. May be is connected with the thermal drift of the tubes (the SRPP is sensitive to this phenomenon).
2. About the tubes. Firstly I tried the SRPP with Russian 6N23P dual triodes. This tube is very sensitive to vibrations. Switching the input selector one will hear the grid ringing through the speakers. The next tubes I tried were the Tesla ECC88. I’m still using them. Analogue of the ECC88 is 6DJ8. The military 6922 or E88CC will last longer though.
3. About the gain. The circuit has a pretty high gain, which depends on the MU of the tube you use. Sometimes this is a problem. Ways to solve it are: to put a resistor in series with the input pot or to put a global feedback (I haven’t tried the second one). If you use 500 k resistor for feedback – the gain will be circa 7 dB. I suggest you to measure the highest level your CD player gives (for the purpose I have the Alan Parsons’ test disk; you must find your own way to do that), than measure the input voltage your power amp needs before clipping. Then rearrange the preamp input divider so that the output to be what you’re looking for.
4. About the PCB. I don’t use such. The circuit is so simple that I’ve soldered all the parts directly on the socket pins. I use PCB for the PSU only. Take care for the signal grounding. Use isolated RCA plugs, shielded wire, ground the pot using the wire shield, then connect this ground directly to pin 9 of the tube and to the minus pin of the lower cathode cap.
5. The parts – I haven’t tried different types – just the best I had.
6. The sound – It’s something personal. I’ll say it like that – since I’ve put this preamp in my system I haven’t even thought to pull it out of there. Of course that depends on the components one has. In my configuration I’m content with this preamp.



[Edited by Asen on 05-07-2001 at 05:53 PM]

about your question. There's a quiet good article in the Tube CAD Journal (issue March 2001):
Thake a look, it's about the Italian Hybrid. I've tried the SRPP with different voltages (from 130 to 180). It works in both cases. Performes better with higher voltages. Otherwise distortions are higher.



[Edited by Asen on 05-07-2001 at 05:58 PM]
I haven't heard anything about this regulator. You must use at least 2 (for both channels). If you set the heating voltage at 6.3 - the current through the tubes will be 10mA.
The RC filters are a very good solution if you don't want to use inductors.



[Edited by Asen on 05-08-2001 at 02:12 PM]
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