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Old 22nd September 2012, 12:30 AM   #381
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Hey guys!

I'm strongly considering getting this pre-amp for use in my system. The only thing keeping it from being a slam dunk purchase for me is the issue of microphonics/hum/etc making it into my system that a different pre amp wouldn't have.

I'm going to use this with 87 dB speakers in a near field, but I'm pretty sure pre amp noise shouldn't be an issue thanks to the lower sensitivity.

My *heavy* concern is that I'm planning on running Stax SR-007 headphones with a converter that'll let me run the headphones through my speaker equipment chain: Pre-Amp -> Speaker Amp -> Headphones. Now, these headphones are sensitive enough already (they can be run perfectly well from 3W speaker amps), and considering the drivers are right next to my ears, I'm really worried about noise from this particular pre-amp. Can noise be eliminated almost completely? I'm going to put Herbie's guitar dampers, and probably use TJ45 or Valve Art 2A3 along with Valve Art 274 since I'd read it introduces the least noise.

Basically, can noise the noise be eliminated almost entirely for satisfactory headphone use? And how limited do my tube options look if I'm trying to get a setup quiet enough for such use? Thanks!
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Old 24th September 2012, 07:25 PM   #382
GeirT is offline GeirT  Norway
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Hi Hygienist,
as described earlier in this thread it could be wise to install the Rod Coleman heaters as adviced by others. Reportedly, besides sounding better they also should lower the noise.
I've just built the pre with new DIYsupply heaters but I must admit that noise is an issue (the pre is considerably more noisy in recent days than it was in the beginning - of unknown reasons, nothing being altered in my system).

The pre is very transparent but it has its nits, someones call it as a Ferrari as it needs to be coddled with to perform its best. And in reality the volume control function needs to be done by a remote handset as the encoder (knob) at the pre front is far too unstable even you turn the knob carefully.

So H, it is possible to get good (and noisefree) sounds of this pre but I would say that it not a fail-proof and fussfree design.

But I like it ;-)
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Old 24th September 2012, 07:41 PM   #383
Desmo is offline Desmo  Denmark
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@Hygienist: The preamp has 3 outputs with different gain, the intention of this is, that you use the output that match your amp's gain and your speakers efficiency best possible. I have 88dB speakers, use the middle output and have my volume at 2 - 3 o'clock = perfect.

I have now used the Rod Coleman DHT regulators for some time: No noise, and the sound is quite a lot better. Regarding microphonics that totally depend on the tubes you use...

@GeirT: Check if the ribbon cables are inserted fully. If not that can be the cause of your problem with the volume control. The volume on my preamp (and all others that I know of) works perfectly.
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Old 25th September 2012, 08:41 AM   #384
Desmo is offline Desmo  Denmark
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I quote myself... I was asked in PB about what caps and resistors I have used for upgrade in the Rod Coleman DHT regulators... One of the reasons for choosing the Amtrans caps was, that these are spec'ed for 110 deg Celsius and they are located in a hot area, so better to use caps designed for some heat. The Mills resistors are very transparent, I like them both for amps and cross over use. With the big housing of the 12W type there is relatively large surface area = lower surface temperature of the resistor.

Both the Amtrans caps and the Mills resistors are relatively cheap parts, but good quality. Of course one can try with more expensive and exotic caps and/or carbon resistors etc...


Quote:
Originally Posted by Desmo View Post
I used this one (from his older manual), but without the fuses on the DC side. If you have any doubts about what's best to do/use, then just ask him in the DHT heater thread, he is very helpful...

Click the image to open in full size.

The most critical is the rectifier diodes and especially the first caps after the rectifiers. I used MBR1045 diodes and RIFA PEH200, 10.000uF-40V as C1. The RIFA's are big and a bit expensive, but they can handle 12A ripple, so they are exellent for this purpose. They are the two big white caps in my installation if you look at the pics. I can't remember the manufacturer of the C2 caps, but they are also 10.000uF - 40V types with a ripple capacity for around 4A or so. Check your local supplier and choose caps according to ripple handling - it's all well described in Rod Colemans instruction manual. For the rest of the components I used what I had...

I will recommend the upgrade of R1 and C3 on the regulator modules (there is lot's on this in the DHT heater thread). I used 12W Mills 0.47 ohm resistors and Amtrans 220nF caps. Both are relatively cheap and the sonic improvement in dynamics and clarity is worth it. They can fit like this...


Click the image to open in full size.
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Last edited by Desmo; 25th September 2012 at 08:46 AM.
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Old 25th September 2012, 08:57 AM   #385
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Hi Morten, This is an excellent implementation, and I very much approve of your use of high-quality parts in the rectified-dc section.

I have not tried expensive capacitors in the Regulator (C3). Panasonic ECHU sounded similar to the standard part to my ears, but it is possible that (for a preamp especially) exotic parts are worth the trouble.

Thanks for sharing!
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Old 25th September 2012, 09:03 AM   #386
Desmo is offline Desmo  Denmark
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Hi Rod,

I can't say if it's more critical with these parts (R1 and C3) in a preamp, but both Bjarne and I have upgraded with the same resistors and caps and hear the same difference: Even better dynamics and even more natural sound. This was amazing since these areas was already MUCH improved with your regulators.

I'm glad that I went through the trouble of finding space for the RIFA caps as C1 in the raw dc supply, they don't even get warm to the touch and will last forever in this application. It does not get much better - that's how I like my DIY
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Old 25th September 2012, 09:06 AM   #387
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The C2 caps in your version are Panasonic TSUP series.

10000uF 16V or 35V are suitable for most applications. If the environment is warm, the higher-voltage part handles more ripple:

3,78A for the 16V
4,42A for the 35V version, at 85 deg C.

The Panasonics are certainly recommended.
If you prefer 105 deg C rated parts, the Panasonic TS-HA or -HB is also recommended.

ECOS1EA153DA - PANASONIC - CAPACITOR, 15000UF, 25V | Farnell United Kingdom
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Old 25th September 2012, 09:07 AM   #388
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Quote:
Originally Posted by Desmo View Post
Hi Rod,

I can't say if it's more critical with these parts (R1 and C3) in a preamp, but both Bjarne and I have upgraded with the same resistors and caps and hear the same difference: Even better dynamics and even more natural sound. This was amazing since these areas was already MUCH improved with your regulators.

I'm glad that I went through the trouble of finding space for the RIFA caps as C1 in the raw dc supply, they don't even get warm to the touch and will last forever in this application. It does not get much better - that's how I like my DIY
Thanks Morten, I will look out for the Amtrans cap, and compare!
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Old 25th September 2012, 09:15 AM   #389
Desmo is offline Desmo  Denmark
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You have good eyes Rod..! I just checked the extra caps I bought for ''C2'' and they are indeed the Panasonic TSUP 10.000uF, 35V

What I like about the Amtrans caps is, that they are natural sounding. For use as coupling caps they might not have the hyper details of other more expensive caps, but they are natural and coherent. Good caps for little money. On the downside, they are quite big and therefore hard to fit on the small regulator circuit board. In the UK they are sold here Amtrans AMCH Capacitors homepage
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Last edited by Desmo; 25th September 2012 at 09:18 AM.
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Old 25th September 2012, 09:16 AM   #390
gjm is offline gjm  United Kingdom
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Guys,

I'm still following this! I have little I can contribute but maybe, once our container arrives, that will change.

Y'see, we've just moved from the UK to NZ...
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