EQUIPMENT FORUMS >> SE34I.5 >> Racheal, Clipping, and a Phono Preamp Question

Message started by NothingButTreble on 02/11/18 at 02:24:52

Title: Racheal, Clipping, and a Phono Preamp Question
Post by NothingButTreble on 02/11/18 at 02:24:52

I still have much to learn, but with the help of the people here there is hope.

In the Owner’s Manual it states, “With 6N1P input tubes and a standard 2 volt source such as a CD player, the volume control can typically reach 2/3rds before the amp runs out of steam (clips).  With a 6N2P the volume control will typically reach ˝ way up before clipping.  Of course if you have a source with higher than 2 volts of output, the SE34I.3 will clip sooner.”

But in the specifications, it states, “2.5 volts for full output.”

So should the input voltage to the SE34I.5 be 2, 2.5, or something else?

And what voltage output should there be from the phono preamp?  I'm understanding that if it is 2 volts also as with the standard CD player, you won't be needing to change the volume when switching from phono to CD.  

Is there a voltage input threshold where you'd be switching over to the 6N2P tube, which apparently can compensate for the lower voltage somewhat?  And if so, at what voltage for the input?

Any help is always appreciated.

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by 4krow on 02/11/18 at 03:55:48

I know that this will sound like a generalization, yet the best way to find out what works and what doesn't is simply to try these tubes out as needed. Between the two tubes, 6N1P, and 6N2P, there are differences in gain, that much is clear. The case for me however is that I prefer the 6N1P for what I hear to be best to my ears and system. Though I know that the specs state 2.5 volts for full output, 2 volts or less, will easily get you where you want to go. What the output of your phono pre-amp is, can only be realized upon playing. I should say, it is more important how the system sounds given the output and sonic characteristics of the source in the first place.

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by NothingButTreble on 02/20/18 at 23:15:46

Thank you 4krow, however, I'm not really able to try at this point, as I'm needing to get a phono preamp.  

As I've explained before, I am such a newbie that I didn't know it needed a phono preamp.  Now that I've learned, instead of two people on earth who don't know this we're down to one.   :-[  So I know it needs a phono preamp, I just don't know which one.

However, I would like to know at least the theoretical requirements for the Rachael SE34I.5 as far as voltage input, and also how much gain differential there might be from switching to the other 6N2P optional tubes.  Is this huge, is it minor, is it just a slight bit different?

In this paper (2004), it states that "Decware amps are all set to reach maximum power with 2 volts."  So I'm thinking, in the intervening time, for the Rachael that is now 2.5 volts.  But also 2.0 volts is acceptable since the CD players output that voltage?  So what happens at 1.0 volt?  At some point I'd think the 6N2P tube would be required to compensate, but how much can a tube change do if the input voltage is far from the 2.0 volts, or 2.5 volts, that the Rachael needs?

And, I'm still not sure I understand completely, but anything above 2.5 volts and clipping occurs?  Or is clipping dependent on where the volume control knob is set?  Can you input 3.0 volts and have the volume knob very low?  Or will it somehow hurt the Rachael?  Could you put a different tube in and be OK with 3.0 volts incoming?

Any help is greatly appreciated.

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by Archie on 02/21/18 at 00:05:56

So what happens at 1.0 volt?

I think you'll max out the volume and not come close to clipping.  You would be leaving sound volume on the table, i.e., it won't get as loud as it could with higher input voltage.

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by alper_yilmaz on 02/21/18 at 02:19:01

I have an SE34I.2+ which is Rachel SE34I.5's grand grandparent, I assume, so input specs might have changed.  We are using that amp at my girlfriend's, with a Hegel HD2 DAC (with 1 or 1.25V output) which is quite less than enough input.  So in between, we have an iFi micro iTube2, which is a tube buffer/preamp with a max output level of 7.75V.  Actually, I set it at the fixed output buffer mode with the whole 7.75V and the SE34 is working great.  

Similarly, I am feeding my SE84UFO with a Copland DAC/preamp with also some serious output.  The result is magic.  I am feeding my TABOO mkIII with a ZBIT using the XLR outputs of my DAC and the result is quite satisfactory as well.

So, my recommendation would be to use your Rachael with a high-output source or preamp and it is likely to sound much better with more control on bass and nicer mids and trebles.  IMO and IME...  

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by Archie on 02/21/18 at 16:18:36

Or a ZSTAGE in front of Rachel?

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by Steve Deckert on 02/22/18 at 04:24:19

Clipping is always relative.  It is relative to where the volume is set.  It doesn't matter if you run 2 volt source with the volume set in the higher ranges or a 7 volt source with the volume set in the lower ranges. The listen level is the same. Obviously with a 7 volt source if you put the volume in the higher ranges it's going to get super loud and clip the amp.  

Title: Re: Racheal, Clipping, and a Phono Preamp Question
Post by Edsonic on 03/20/18 at 05:58:08

First, let me introduce myself. I have worked in pro audio in various capacities, and after my over-sensitive ears finally gave up, I went elsewhere.

I do not own any Decware gear thus far, but have been interested for some time and my goal is to at least have the SE34I.5 in the mix. The combo of that and the DNA speakers interests me greatly.

To the issue: All the levels spoken of as to output levels are in nominal terms. That is, they are a "reference level." The actual signal itself at any moment can be well below that, or actually averaging that, or well above it with sudden transients or just very loud listening levels. That is, the DAC from the CD is NOT sending a constant 2V to the pre-amp or amp. It's sending whatever V the DAC is told to by the source  at the moment.

For example, " +4 dBu " on the mixing console or " -10dBV " on a consumer tape machine just tell us what " 0 meter " is referenced to. The meter itself and therefore the actual output level can be all over the place.

Same-but-different with a phono stage. We're told a typical p-stage isn't made for a -nominal- input of more than 10 mV, though any decent such device can take more than that temporarily, because that's what 5 mV MM cartridges do on transients, spikes, etc.

The 42 dB of the ZP3, eg., raises that (5 mV)  to 630 mV (.63 V). So then you get it into a pre-amp, with 6 dB of gain, and you will have a -nominal- level of 1.26 V to send to the amplifier. With peaks, spikes, etc. you will definitely get to 2+ V and in the scenario laid out above, some records would send the 34I or other "2.5V input/full power" amps into (short term) distortion on those occasions.

I don't mean to make it complicated, I just wanted to point out that there is a difference between 'nominal' levels and actual levels at any moment, and that output can and does exceed that as a normal course of events.

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