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Post by Deleted on Jul 23, 2013 10:29:22 GMT
It's surprising how much is inside these little devils. Excellent quality though; smooth and neutral, as one would expect. The Alps pot is 100k log; swapping to a lower value could be useful but it works fine in my system with no noises or noticeable HF loss. Regards, Derek Creek OBH-22 Passive Pre-Amp (inside view)
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Post by Deleted on Jul 23, 2013 11:59:21 GMT
Hi Derek Was this designed by Alex Nikitin ? Regards Alex
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Post by Deleted on Jul 23, 2013 12:04:57 GMT
Hi Alex. I have no idea who designed it. Sorry.
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Post by Deleted on Jul 23, 2013 23:17:02 GMT
Hi Alex. I have no idea who designed it. Sorry. Hi Derek Alex Nikitin was the chief designer at Creek in the early 90s. He is also quite a friendly guy, and unless memory fails me , he has also posted in RG. I have previously spoken with him. Kind Regards Alex
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rowuk
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Post by rowuk on Jul 6, 2014 14:01:12 GMT
A couple of holes in the cover, then we add 2 valves (plus a couple of power supply bits) and now we have a REAL preamp!
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Post by Deleted on Jul 7, 2014 0:16:24 GMT
A couple of holes in the cover, then we add 2 valves (plus a couple of power supply bits) and now we have a REAL preamp! Hi Robin It seems rather silly to call a buffer with a little less than UNITY gain, or an attenuator with switched inputs a pre-amplifier, although some may try to justify the term as it is before the amplifier. If you are interested, we may soon see the Class A/HA/Preamp project revisited, with PCBs becoming available from a rather knowledgeable U.S.A. member. This could also depend on whether enough members are still interested in this project. Regards Alex
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rowuk
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Post by rowuk on Jul 7, 2014 16:24:53 GMT
Well, "pre" amp could simply mean "before" the amp too. That would fit in any case. In any other market they would be proud to call buffers: buffers, attenuators: attenuators and devices with GAIN: amps One of the biggest challenges in audio is a common language. We still do not have words to describe "sound" or how a technology applies to "sound". Because there are a great deal of challenged people dealing with audio from a manufacturing, reselling and customer standpoint, all seem to be content with words like "better", "neutral", "transparent", "microdynamics", "high res", "black", "detailed", "grainy", "weight" and further non-descript garbage. I guess we cannot expect more from those who don't practice fidelity in any sense of the word. Pimp my cables! A couple of holes in the cover, then we add 2 valves (plus a couple of power supply bits) and now we have a REAL preamp! Hi Robin It seems rather silly to call a buffer with a little less than UNITY gain, or an attenuator with switched inputs a pre-amplifier, although some may try to justify the term as it is before the amplifier. If you are interested, we may soon see the Class A/HA/Preamp project revisited, with PCBs becoming available from a rather knowledgeable U.S.A. member. This could also depend on whether enough members are still interested in this project. Regards Alex
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Post by Deleted on Jul 17, 2014 10:16:30 GMT
What, this old thread? Regardless of the language used it's still a bargain and definitely hi-fi. I've just bought a back issue of Hi Fi Critic so I could read their review(s) of the OBH-22. Seems the crtitcs loved it. I do to.
If you don't want to call such a device a Pre-Amp then how about 'PVC' or Passive Volume Control? Or 'AARSS' which stands for Attenuator And Remote Source Selector.
Derek
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rowuk
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Post by rowuk on Jul 17, 2014 16:01:20 GMT
What, this old thread? Regardless of the language used it's still a bargain and definitely hi-fi. I've just bought a back issue of Hi Fi Critic so I could read their review(s) of the OBH-22. Seems the crtitcs loved it. I do to. If you don't want to call such a device a Pre-Amp then how about 'PVC' or Passive Volume Control? Or 'AARSS' which stands for Attenuator And Remote Source Selector. Derek I like AARSS. Most of the passives that I have heard deserve the name "SignalConstrictor" however............... Just like the big snake, they kind of squeeze off "life".
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Post by Deleted on Jul 18, 2014 8:37:23 GMT
I fail to understand why and how passives are able constrict the sound. Also people say say things like 'no bass drive'.
My opinion is that most, if not all, active pre-amps change the sound in some way; they MUST do otherwise they'd all sound the same and we know that's not true. So bass 'drive' could maybe be something to do with a power supply effect? I don't know, I'm not an expert as you'll all know. And all active pre-amps will have different sonics in terms of sound stage, imaging, detail and so on. Consider too how much effort people go to in the field of op-amp rolling. Plenty has been written on the which is the 'best' op-amp in a given situtation. I.E ALL op-amps sound different.
Now consider that there are a number of integrated amplifiers where the design is basically just a power amp section with a source selector and volume control at the input end. My now sadly defunct MF B200 is an example of that type of design; all inputs other than MC/MM went to the volume pot and then on to the amp itself.
I like the idea, therefore, of a 'pre-amp' stage that is no more than just the necessary volume pot while doing away with the need for yet another op-amp or whatever. Given one's source is of reasonably low output impedance, you use short interconnects after the pot etc. etc., i.e. if certain basic conditions are met then a passive 'pre' MUST be the way to go.
And if the resulting sound has 'no bass' or 'no drive' then what you're missing is colouration. Nice colouration maybe, but a 'distortion' nevertheless
regards,
Derek
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Post by Deleted on Jul 18, 2014 9:59:56 GMT
Hi Derek It's not quite that simple, as modern solid state amplifiers have much lower input impedances than earlier amplifiers, especially valve amplifiers. This is done mainly to maximise Signal to Noise ratio, and maximise Dynamic Range . It helps that modern digital sources have much lower output impedances than earlier RIAA phono preamps, and much higher output levels (2V RMS is typical) compared with more like 300mV from phono and earlier FM tuners etc. of years ago, so we are able to lower the input impedance of the preamplifier/amplifier. The CD has a markedly improved dynamic range over vinyl, and even with tape where they need to use Dolby C or DBX for example, to get to around 75dB dynamic range. CD which is 16 bit 44.1 kHz has a dynamic range of 96dB, but the newer 24 /96 and 24/192 formats achieve an extra 6dB dynamic range for each additional bit. In the real world, this theoretical Dynamic Range of 96dB +24 dB (120dB) is not achievable, due to preamplifier and power amplifier constraints, as well as ambient noise levels. Johnson noise of input resistors etc. is also one of those considerations, where the higher the resistance value, the lower the signal to noise ratio of the preamplifier/amplifier.
Kind Regards Alex
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rowuk
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Post by rowuk on Jul 18, 2014 16:15:57 GMT
Hi Derek,
there are many reasons why components at their basic level can "change" sound. There are also a lot of bogus claims to sell stuff - especially with the concept of "less is more".
I guess the first step is to determine if you hear differences in audio cables. I personally do not believe in esoteric crap, but there are basic rules, laws of physics that explain why resistance, impedance and capacitance change frequency response. There are also schools of thought that say the shielding is a critical issue in todays hi res/high electronic smog environments.
I have been there, tried all sorts of stuff and can claim to hear at least a bit of it.
In my own system, I have recently tried out various pots and switched attenuators (no LDRS tried yet). My system has valve amplifiers located next to the speakers. There are about 5 meters of cable between my sources and the speakers. The difference between a passive attenuator and a fine active buffer/attenuator is very large. I personally believe that capacitance and impedance have the most to do with this phenomenon. With the passive attenuator, the source has to be able to "drive" the cables to the passive, it has to handle the resistance load from the attenuator and then drive the cables to the amplifier (my valve amps are easy to drive with a 330K resistor to ground on an input valve). The biggest difference is putting the buffer AFTER the attenuator. The difference is perceived extension at both ends of the audio spectrum, the reproduction of the "attacks" and "tails" of each note as well as an interesting effect that kind of changes the playback so that a solo piano or chamber orchestra does not sound any smaller than a large symphony orchestra. With less demanding music created in the studio with no acoustic reference, the differences are hardly noticable. Vinyl and digital are equally affected as my output stages of both of those amps are very similar.
I have received quite a few suggestions for improving my cables, changing the attenuator to another more "magic" type, descriptions of a "diode" effect at each solder or contact junction. Funny enough, these suggestions all came from people that do not know me, don't know what I have or have tried, and for the most part only cut and paste the advertising garbage read elsewhere. Maybe there is merit to the arguments, but these people are in no position to help me believe it.
My personal belief is that we need to star ground/shield to the pre amp, we should keep the cables as low impedance and low capacitance as possible. The best interconnects that I have found are made from good quality balanced microphone cable with good solid connectors. This seems to have the best balance between capacitance and impedance. I attach the hot and earth wires at both ends, and the shield at one end that gets connected to the preamp. The cable is not expensive, it holds up for many years before becoming microphonic (unlike many hundreds of dollars worth of Monster cable that I recently tossed for exactly this reason). It is easy to solder and looks nice too.
If one uses a passive attenuator with very short (and good) cables between good sources with solid output stages and a high impedance amp input, there is probably no gain or loss of fidelity.
I am experimenting with "biasing" the cables - having a DC component present on the interconnects- filtered at the amplifier.
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Post by Deleted on Jul 23, 2014 12:08:05 GMT
I think I covered everything, and showed that I had at least a basic understanding of the situation, when I said (albeit briefly) "Given one's source is of reasonably low output impedance, you use short interconnects after the pot etc. etc., i.e. if certain basic conditions are met then a passive 'pre' MUST be the way to go".
My V-DACii source has an output impedance of c.110 Ohms* and max output level of 2.2V. My power amp has a (quoted) input impedance of 31kOhms and needs just 1V input to achieve its full 120W pc output. My interconnects are 50cm long and are of suitable quality (Van Damm OFC instrument cable).
Rock Grotto has often been a champion of low cost products that punch above their weight. In fact it seems to be the MAIN reason why it's here. There are few (no?) reviews or comments about, say, the latest 50,000 GBP killer power amp. And no-one raves about the newest 900 GBP MC cartridge or the 20,000 GBP turntable needed to do it justice.
Nope, Grotto members get a kick out of finding something inexpensive, championing the cause, often moving on to show how significant improvemnmts can be made with a tweek or two here and there. The Superlux 681s come to mind and the Creek OBH-22 falls into this category.. it's cheap (for a pre-amp) and it's good, nay, VERY good.
I fail to understand why any mention of using passive pre-amps garners such negative views in here. For the sound quality that the Creek and its ilk offers (yes, I have to say it don't I?.. under suitable conditions) it is beaten by only very upper-end pre-amps. It really has no character, which is something to be lauded and appreciated. I wholeheartedly recommend it. If you can find one, and your input/output environment is suitable, don't hesitate to get one.
* Stereophile measurement 99 to 124 Ohms (MF quoted spec = 47 Ohms)
Derek
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Post by Deleted on Jul 23, 2014 13:16:03 GMT
Hi Derek It's rarely a good idea to use a passive preamp as described. The best passive preamps (expensive) use high quality transformers for impedance matching purposes. You would more than likely get better results by having the potentiometer in the power amplifier itself, and let the low output impedance of the source device drive the cable better with negligible HF rolloff. In a typical domestic listening situation as described, (especially if you are married) you may need to use up to 30dB of attenuation, with average power levels of only around 1 or 2 Watts.(REALLY !) Unless you use a relatively low value potentiometer AND very short low capacitance leads to achieve this, you WILL have considerable HF rolloff, and it will then load the source device fairly heavily, which many opamp based designs may not like, resulting in higher distortion . With my 15W Class A amplifier, a typical preamplifier attenuator setting (DACT 2) for me is around 27dB to 30dB, and a few dB less when demoing to friends. My preamp has a maximum gain of just over 3 times.
Regards Alex
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Post by Deleted on Jul 23, 2014 13:36:21 GMT
OK then Alex, I give in. Watch out for my Creek on Ebay. Even though I don't get any treble roll-off I can't be too sure can I? For convenience I'll just ignore the fact that the Creek sounds miles better than my 'proper' pre-amp. Now what am I going to buy instead? It's got to be under 300 GBP though, and better than my X-PreV3 (800 GBP when new in 2009 so allow for inflation)
Seriuosly though, have you read the review of the Creek in HiFi Critic by Colloms et al.? They outlined the potential shortcomings of such a device but in spite of all that they all thought it a great-sounding bargain. Hi-Fi World too. Why were they wrong?
I like the Creek. You tell me I shouldn't like it. I suggest that's all there is to be said.
D
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Post by Deleted on Jul 23, 2014 13:54:59 GMT
Hi Derek I am not saying you shouldn't like it. IIRC, not so long back. Martin Colloms reviewed a passive preamp using transformers, and it was rated as very good indeed. Another problem is that your typical power amplifier (mine too) has way too much gain for 2V RMS CD/DVD players etc, and we need to throw away too much S/N tatio. Don't race in. Try listening to as many different preamps as you can, if you are sure that is what you want to do. Good night from Sydney Au. ! Regards Alex
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rowuk
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Post by rowuk on Jul 23, 2014 18:29:45 GMT
Hi Derek,
I simply tried to reply to your "question" with my experience involving constricted. There are no absolutes in the audio world as we have no interchangeable frame of reference. Not even words necessarily have a common understanding. This is very unfortunate because it is often impossible to discuss anything and be sure that the true intent is conveyed. If I buy a professional oven for baking pizza, it is possible to describe just about everything that it can do to produce a world class pizza. Shit, in the audio world, we can hardly find anyone admitting to using the same interconnects.
My experience with passives was different than yours, that is all that that means. No need to defend your personal experience - I never challenged it.
As far as RG offering advice on good deals, that is most certainly true. And then you find out after you bought it, how much you can rip out and replace. It does keep us busy and out of trouble however.
The longer I deal with audio, the more I discover that better seldom means "more" or "less" of something, rather the synergy with which an entire playback chain is put together and that many of the things that make audio more enjoyable are very explainable when we find a way to discover a common meaning for the "words" that we use.
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