View Full Version : Pre amp matching
Yesterday I bought a glass house passive pre that I had owned previously.i also collected a trafomatic elegance 2 power amp (300B) in the hope of using them both together.
The pre has to be wound around 3/4 of the way to get any sound and with the pot fully open I still only get a low to moderate level of volume.. No distortion or similar even with the pot at full vol.
Is this just a matching issue? I heard the power amp working at the sellers using a naim all in one type thing as the pre.
Is it just a case that this power amp needs an active type pre??
hifinutt
19-05-2018, 05:57
i was just pondering that question myself , having tried rather a lot of pre amps like you guys have too
i have only heard of being only able to turn vol knob a few mm and its too loud
https://www.pinkfishmedia.net/forum/threads/glasshouse-passive.215410/
Power amp is not sensitive enough for a passive, you will need an active pre or a buffer with gain betwixt the passive and the power amp.
You haven't got anything I could try just to prove the Power amp have you Mart?
I've a couple of integrated amps where the pre amp can be split from the power amp. A Harmon Kardon and an XTZ. Not world beating pre amp sections but will drive any power amp. You're welcome to have a borrow.
Cheers Mart i only want to prove it's working ok. I'll drop you a Pm
I think you need to take the source into account as well mate. If it has a low output then an active will be required, if it's powerful then a passive may be appropriate. This all ignores impedance matching. If it is a valve stage with unusually high output impedance it may be losing gain driving the passive (though realistically this is not very probable). What is your source driving the amps, and If you trust it why not connect it direct to the power amp and play some known quiet music to see how loud it is? For gawds sake don't choose anything noisy or you could do the speakers some mischief!
Gain and output are not standardised across manufacturers so these compatibility issues seem rather too common.
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I'm using a chevron paradox dac but it was just as quiet using my old pioneer PDS9o5 CD player
Ok, Chevron is off my radar but the Pioneer would be up to the task. Are you sure the tubes in the power amp are all sound?
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walpurgis
19-05-2018, 08:34
Slightly left field, but I have a very nice sounding Moth Series 30 active pre-amp that has high output and drives insensitive power amps very well. I have too many pre-amps and the Moth is not in use at the moment.
George47
19-05-2018, 08:53
The power amplifier has a sensitivity of 0.5V rms which with the output of your CD player of 2V is enough signal to overload your power amplifiers. There needs to be more data to see if the impedances are mismatched. If it is an impedance mismatch then a simple buffer circuit could solve the problem. Persevere as the power amplifier is excellent and a passive preamp gives a tremendous purity to the sound which your SET can take full advantage of.
Ok, Chevron is off my radar but the Pioneer would be up to the task. Are you sure the tubes in the power amp are all sound?
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I have a Chevron Paradox DAC as well and have used it via a passive preamp (Tisbury not Glasshouse) into many different power amps and never had to open up the pot (certainly not past 12 o/c).
How long are your interconnects? Try shorter ones (say 0.5m each side).
Following not for the feint hearted: if you have a 3.5mm to RCA cord try connecting your phone/ipad/tablet directly to the power amp. But ensure (double and triple check) that volume is zero on the phone/ipad/tablet and then very gradually bring the vol up. You should not have to bring the vol up much to get adequate output.
Primalsea
19-05-2018, 20:34
Was the Glasshouse pre a kit? Could be wired wrong as your source should have plenty output to drive the amp to full output.
walpurgis
19-05-2018, 20:35
Good point.
I've used the passive with other bits of kit when i owned it previously and it's been ok. (Quad 909).
What is a buffer circuit by the way.
Thanks for the info so far chaps
walpurgis
19-05-2018, 20:43
I believe the Quad 909 has high input sensitivity and does not need much driving. A pre-amp that works with it may not have enough output in other situations.
This is why I stick to integrated amps!
Lawrence001
20-05-2018, 08:10
And why I stick to well matched pres and powers!
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Lawrence001
20-05-2018, 08:13
How about the Velleman pre on here in Take5's sale of Vinny's old system?
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I've used the passive with other bits of kit when i owned it previously and it's been ok. (Quad 909).
What is a buffer circuit by the way.
Thanks for the info so far chapsAs far as I can see from what's written above, the input level your power amp isn't unusual. That's why I wondered about the valves in the amp. If you have a few spares, including a valve rectifier if it has one, it would be worth a swap to at least eliminate that variable.
Since youve had this exact passive before I assumed you'd know it's input and output arrangents.
Re. Buffers they offer high input impedance and low output impedance which makes them a useful interface between bits of kit. They usually have no gain and are considered more or less transparent depending on your point of view.
Their main use is to present a high impedance input to a source with a highish impedance output stage (like some valve preamps) so gain is not lost there, whilst presenting a very low impedance output to drive the low impedance input stage of a power amp (like pro equipment, class d amps, and the like), ensuring gain is not further lost there.
However solid state sources tend to have low output impedances, and valve amps high input impedances, so it's fairly unlikely to be of benefit in your set up, though passives can muddy the water a bit...
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chris@panteg
20-05-2018, 10:06
Also many solid state amplifiers these days have much lower input impedance in the line stage, typically about 20k, I've learned that it's best to avoid using any valve pre or phono stages which have a high output impedance with the above mentioned, say around 4 to 5k, it just won't sound right.
I'm going to try the Velleman. I have to say it sounds lovely ...just quiet!
Good choice. It's a nice unit
Dropped the Velleman in. Still need a lot of volume knob travel compared to the norm but I have a good usable amount of volume now ��time to see what 300Bs bring.
Lawrence001
20-05-2018, 20:58
Dropped the Velleman in. Still need a lot of volume knob travel compared to the norm but I have a good usable amount of volume now ��time to see what 300Bs bring.That was swift work when I suggested it I didn't think you'd get it so quick, how far away are you?
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Time to check the valves I think
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Only an hour or so.OMG! Until the end of the world? I only have 12 minutes left...
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I'm going to try the Velleman. I have to say it sounds lovely ...just quiet!
Just to avoid confusion.
When steve said this, he wasn’t meaning the Velleman. he didnt have it at that time!!
He has simply borrowed it to try with his power amp. It is still for sale, and available.
Steve, I didnt notice any need to crank it way up to get to listening levels. That was with the Quad 63s and my little Quad 306.
Ps great to catch up.:)
That's correct sorry for any confusion. It was the passive that was quiet, the velleman is spot on. Lovely (and heavy!!) Little thing.
Sorry if this has already been suggested, but if you bought the Glasshouse pre as a 'used' item it might be worth checking if a previous owner has adapted or fitted any pre-attenuation resistor set-up.
I have a 50k stepped attenuator passive (not Glasshouse) and had no problems driving the 0.5v required for an SS power amp other than not being able to turn it past the first few steps without rattling the windows. To remedy this I needed to add a pre-attenuation set - using a guide offered on the Goldpoint website.
Ok I've confirmed there is no issue with the passive pre.. .it sounds fantastic. So...basically the power amp sounds like it's in a reduced output set back mode. No distortion or anything like that. Sounds beautiful...just quiet. As it's both channels I'm wondering if it's the central valve rather than one of the output valves.
walpurgis
22-05-2018, 09:21
Input impedance/sensitivity?
I've heard off the designer who states that it needs a high gain pre amp as it is a 3v input sensitivity. Obviously that doesn't mean much to me... :D but it may explain things?
How do I find a high gain pre amp?
walpurgis
22-05-2018, 10:14
How do I find a high gain pre amp?
Quad?
Or, I could lend you my Moth Series 30 to try. It sounds very good with my valve monos.
I've heard off the designer who states that it needs a high gain pre amp as it is a 3v input sensitivity. Obviously that doesn't mean much to me... :D but it may explain things?
How do I find a high gain pre amp?
That is a very very low input sensitivity indeed. My amp is 0.4V input sensitivity!
Bear in mind that the higher the preamp gain, the higher the noise and distortion, so it should still be kept as low as possible.
Thats great, thank you. Would a croft micro 25 do the job?
hifinutt
22-05-2018, 13:31
i am not an expert but elite audio have a 12 month old vtl 2.5 which is 1295 on ebay and 1795 on their site !!
it has adjustable gain
https://vtl.com/products/preamplifiers/tl-2-5i/
8dB or 14dB (user selectable)
https://www.ebay.co.uk/itm/VTL-2-5i-Pre-Amplifier-current-model-huge-saving-rrp-3500/253583127255?hash=item3b0abb72d7:g:S04AAOSwfoNaaKc E
George47
22-05-2018, 17:28
I've heard off the designer who states that it needs a high gain pre amp as it is a 3v input sensitivity. Obviously that doesn't mean much to me... :D but it may explain things?
How do I find a high gain pre amp?
That certainly does explain it and of course, passive preamps are not feasible. Oddly enough all the amps on their web page including the Evolution 2 (300B) all have reasonable sensitivity. I assume it is an older model. Going for an active preamp means the world is your shell-like. Valve or SS? Budget? etc...
Around £600 max really as I was originally planning to use it with the £165 glasshouse! Thinking Croft 25 unless sonething tasty comes along at a bargain price.
George47
23-05-2018, 21:23
Around £600 max really as I was originally planning to use it with the £165 glasshouse! Thinking Croft 25 unless sonething tasty comes along at a bargain price.
Guys at Stereophile loved it: https://www.stereophile.com/content/croft-acoustics-phono-integrated-integrated-amplifier-stephen-mejias-comments
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