Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Thu Aug 11, 2016 1:05 pm

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Post n°1

Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Thu Aug 11, 2016 1:05 pm

Hi, all. I have a question. Would it be possible to use my Audio Analogue Bellini as a pre-amp for my ST-35? I am asking, since I don't want to risk and damage my beloved ST-35. I have a PAS 2, but when I turn the volume knob past the 10 hour mark, the volume stays the same, and goes higher again at the 12 hour mark...........

Thanx in advance for the help.

by peterh Thu Aug 11, 2016 3:47 pm

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Post n°2

Re: Audio Analogue Bellini as pre-amp for ST-35?

by peterh Thu Aug 11, 2016 3:47 pm

gatchaman wrote:Hi, all. I have a question. Would it be possible to use my Audio Analogue Bellini as a pre-amp for my ST-35? I am asking, since I don't want to risk and damage my beloved ST-35. I have a PAS 2, but when I turn the volume knob past the 10 hour mark, the volume stays the same, and goes higher again at the 12 hour mark...........

Thanx in advance for the help.

A new volume pot for the pas2 might be good.
No preamp will damage your st35 , don't worry.

by gatchaman Fri Aug 12, 2016 3:17 am

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Post n°3

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Fri Aug 12, 2016 3:17 am

@peterh:

Thanx for your reply. Is installing a new volumepot difficult? What brand can you recommend?

by GP49 Fri Aug 12, 2016 3:34 am

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Post n°4

Re: Audio Analogue Bellini as pre-amp for ST-35?

by GP49 Fri Aug 12, 2016 3:34 am

If you do not use the LOUDNESS function in your PAS, there is an inexpensive switching-type volume control, available from an eBay seller in China, that sounds very good and works very well. Read about it in this thread:

https://dynacotubeaudio.forumotion.com/t2931-user-report-dact-type-21-stepped-attenuator-250k-for-tube-amp#25100

I can't quote an eBay item number, as it has changed since that thread was posted. Search for it by name at eBay.

It is the standard volume control in the SP12 and SP14 preamps, which attests to its quality.

The same seller also offers a version for those who wish to retain the loudness function.

by gatchaman Fri Aug 12, 2016 5:21 am

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Post n°5

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Fri Aug 12, 2016 5:21 am

Thanx for pointing that out, GP49! I found the seller on Ebay, do I need to get the 250k version?

by peterh Fri Aug 12, 2016 5:46 am

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Post n°6

Re: Audio Analogue Bellini as pre-amp for ST-35?

by peterh Fri Aug 12, 2016 5:46 am

gatchaman wrote:Thanx for pointing that out, GP49! I found the seller on Ebay, do I need to get the 250k version?

Excuse me for filling in :
Yes you will need the 250K version.

tubes4hifi also had these pots, i understand that that pas stuff is moved to another seller.

yes : http://www.tubenirvana.net/pas3-spare-parts.html

But they had both the "loudness" and without versions.

Personally i found "alps" on ebay i long time ago, 250k and with loudness.

Last edited by peterh on Fri Aug 12, 2016 5:48 am; edited 1 time in total (Reason for editing : link to tubesnirvana)

by Peter W. Fri Aug 12, 2016 8:51 am

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Post n°7

PAS VC Option

by Peter W. Fri Aug 12, 2016 8:51 am

The original control is a tapped 250K dual-pot *AUDIO TAPER* volume control. As the human ear does not hear volume increases in a linear fashion, audio taper controls show small increases in the first 'half' of the travel, increasing logarithmically thereafter. It may be the case that your present VC is a linear-taper control, meaning that you would perceive very little increase until the very last bit of travel.

It is NOT rocket science to replace the control. If you can solder and follow directions, it is quite easy and clearances within the unit are quite reasonable. I have done such a replacement in less than 20 minutes after the unit was opened and the iron hot.

You need to ask yourself if you want to retain the Loudness Contour option. Again, as the human ear is not a linear device, the contour option was added to boost bass a lot and treble a bit at very low volumes so that your ears perceived the full bandwidth. Many audiophile/phools react in horror at such a concept, but if you consider the actual results, it is quite a reasonable option. If you do want this option, you will have to find a tapped (4th lead per element) VC.

Look up item number: 301189273741 on eBay for one option.

There is some good support for going as low as 100K, but no higher than the 250K. That would be your choice, and also may give you more options in finding what you need.

Keep in mind that David Hafler used the cheapest parts from the lowest bidders in his kits (excepting tubes and transformers), so it is no surprise at all that these controls fail. Nor did Dynaco have a "factory" until bought out by Tyco - they used Drexel students on piecework for "factory assembled" items. Again, no surprise that QC was all over the map in those days, and why a carefully assembled kit is a better bet than otherwise even today.

by gatchaman Fri Aug 12, 2016 1:30 pm

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Post n°8

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Fri Aug 12, 2016 1:30 pm

Thanx all of you for the help and gining me some extra info. I am going to order the replacement and see if I can manage to get the job done. I think driving the ST-35 with a PAS 2 might be better then with my Audio Analogue Bellini.

by **Bob Latino** Fri Aug 12, 2016 3:34 pm

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Post n°9

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Bob Latino Fri Aug 12, 2016 3:34 pm

gatchaman wrote:I think driving the ST-35 with a PAS 2 might be better then with my Audio Analogue Bellini.

As much as I love Dynaco tube gear, the original PAS-2 or PAS-3 in stock form is not that great of a preamp. Weak power supply, tone controls in the circuit that can't be switched out etc., etc. From a sound quality point of view, almost any modern preamp will sound better than the original Dynaco PAS-2 or PAS-3 > even a PAS that has been modified. If you A and B your PAS preamp with your Audio Analogue Bellini, I would be willing to bet that the Audio Analogue Bellini will sound better.

Bob

by Peter W. Fri Aug 12, 2016 3:43 pm

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Post n°10

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Peter W. Fri Aug 12, 2016 3:43 pm

Bob:

FULLY agree that the PAS is simply not that great. But, a few things:

a) In the X version the tone controls can be switched out, or, rather, they are out-of-circuit when in the null position. These iterations are also have better impedance matching for SS amplifiers, another legitimate criticism of earlier versions.
b) Yes, Hafler used the cheapest, chintziest controls and switches he could find. But, they may all be replaced for relative pennies.
c) It has a rather better than average *tube* phono stage.

Making you absolutely proper, accurate and correct in your statement, 'cept that the AAB is solid-state, not tube.

by Roy Mottram Fri Aug 12, 2016 9:27 pm

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Post n°11

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Roy Mottram Fri Aug 12, 2016 9:27 pm

we don't like to admit it, but GOOD SS does sound better than really bad tube gear. Tube gear is usually inexpensive to fix.
But as I've pointed out several dozens (if not hundreds) of times, getting a PAS2 or 3 or 3X to be competitive with modern sound gear will cost 2-3X what it's actually worth !!!
Ask Stew if he likes his new JFET phono pre I built for him, to replace his old PAS preamp . . . ( Stew, are you out there somewhere . . .)
I've rebuilt several dozen PAS preamps for way over $800 (plus the cost of the preamp itself) and I've also build dozens of MUCH better new tube preamps for under $600 that were FAR superior!

by gatchaman Sat Aug 13, 2016 2:33 am

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Post n°12

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Sat Aug 13, 2016 2:33 am

This is very interesting. What are your recommendations for pre-amps instead of the PAS 2?

by **Bob Latino** Sat Aug 13, 2016 7:31 am

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Post n°13

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Bob Latino Sat Aug 13, 2016 7:31 am

Check out the Tubes4hifi preamp kits at the link below ..

Tubes4hifi preamp kits ..

Bob

by stewdan Sat Aug 13, 2016 6:46 pm

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Post n°14

JFET Preamp

by stewdan Sat Aug 13, 2016 6:46 pm

Hi Roy --- the JFET Phono Preamp is exceedingly Clean and Quiet sound wise and to my ears does sound better than the stock PAS. However, It did not replace the PAS Phono, since I still listen to it every now and then. The only "complaint" that I have about the JFET, is that it has no ON/OFF Switch, but I can live with that.

by Guest Sat Aug 13, 2016 8:09 pm

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Re: Audio Analogue Bellini as pre-amp for ST-35?

by Guest Sat Aug 13, 2016 8:09 pm

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Last edited by PeterCapo on Fri Dec 04, 2020 11:58 am; edited 1 time in total

by Guest Sat Aug 13, 2016 9:33 pm

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Re: Audio Analogue Bellini as pre-amp for ST-35?

by Guest Sat Aug 13, 2016 9:33 pm

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Last edited by PeterCapo on Fri Dec 04, 2020 11:58 am; edited 1 time in total

by Dogstar Sat Aug 13, 2016 11:10 pm

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Post n°17

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Dogstar Sat Aug 13, 2016 11:10 pm

I like the AF2 Tube Buffer I built from the kits offered by Glass-Ware. It makes my VTA ST-120 sound very good. That web site has lots of different preamps and one of those will be sure to satisfy your tastes.

I was using a Cary SLP 100 which I still have and do put into the mix every once in a while but to be honest I think the tube buffer is more open and three dimensional than the Cary.

The only thing the Cary has over the Glassware AF2 is the remote but I could have built it with one had I not wanted to keep the cost below $200.

by gatchaman Sun Aug 14, 2016 10:39 am

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Post n°18

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Sun Aug 14, 2016 10:39 am

Thanx for all the thoughts!

@PeterCapo : This is what happens. When I listen to music, and I turn the volumeknob higher, the volume increases until 9 o'clock, then stays at the same level volume until I reach 12 o'clock and the volume starts to increase again. Hope this makes sense? I am used to when you turn the volumeknob higher the volume increases, without any pauzes.

by audioregenesis Sun Aug 14, 2016 11:25 am

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Post n°19

Re: Audio Analogue Bellini as pre-amp for ST-35?

by audioregenesis Sun Aug 14, 2016 11:25 am

The response exhibited by your volume pot is not uncommon in the PAS, as well as some other vintage preamps. This is related to the way in which the pot is constructed, and the degree to which it is experienced depends upon which version of volume pot your PAS contains. Dynaco did not use the exact same pot. throughout production. I have seen four variations with somewhat different construction. This is also why some PAS owners complain about terrible volume tracking while others seem to have no problem.

Although the volume pot. is supposed to be be completely logarithmic in operation, it is not actually constructed that way. Instead, it consists of two linear tracks, connected together, that attempt to somewhat simulate the log. response. This is commonly done to reduce cost and complexity and is not just a "Dynaco" thing. The point at which the two tracks are joined is also the point from which the loudness tap is taken. In the construction process, that connection point also involves a small conductive patch that the pot. wiper travels over. When it does, a flat spot in the response is exhibited and the volume does not change until the wiper has passed over the conductive portion and back onto the carbon track of the pot. On some pots the conductive patch is quite small and the volume flat spot not too noticeable. On others, such as yours, it is larger and the flat spot is quite evident. If you routinely operate your PAS in that area and find the condition unsatisfactory, the only remedy is to replace the pot.

by gatchaman Mon Aug 15, 2016 2:31 am

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Post n°20

Re: Audio Analogue Bellini as pre-amp for ST-35?

by gatchaman Mon Aug 15, 2016 2:31 am

@audioregenesis : Thanx for your explanation of my situation. I just have to figure out now if it troubles me that much, knowing that the volumeknob acts the way it does. Just happy to know it is part of the game, and nothing is broken. Choices, choices, LOL!

by ViperZ Mon Jun 18, 2018 9:19 pm

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Post n°21

Re: Audio Analogue Bellini as pre-amp for ST-35?

by ViperZ Mon Jun 18, 2018 9:19 pm

audioregenesis wrote:The response exhibited by your volume pot is not uncommon in the PAS, as well as some other vintage preamps. This is related to the way in which the pot is constructed, and the degree to which it is experienced depends upon which version of volume pot your PAS contains. Dynaco did not use the exact same pot. throughout production. I have seen four variations with somewhat different construction. This is also why some PAS owners complain about terrible volume tracking while others seem to have no problem.

Although the volume pot. is supposed to be be completely logarithmic in operation, it is not actually constructed that way. Instead, it consists of two linear tracks, connected together, that attempt to somewhat simulate the log. response. This is commonly done to reduce cost and complexity and is not just a "Dynaco" thing. The point at which the two tracks are joined is also the point from which the loudness tap is taken. In the construction process, that connection point also involves a small conductive patch that the pot. wiper travels over. When it does, a flat spot in the response is exhibited and the volume does not change until the wiper has passed over the conductive portion and back onto the carbon track of the pot. On some pots the conductive patch is quite small and the volume flat spot not too noticeable. On others, such as yours, it is larger and the flat spot is quite evident. If you routinely operate your PAS in that area and find the condition unsatisfactory, the only remedy is to replace the pot.

Hi George, sorry about resurrecting an old thread - I have exactly the same problem as described. The volume tracks ok up to 12 o'clock, but still not "loud enough", then between 12 and 1 o'clock it jumps a bit to quite significantly louder volume. You mention logarithmic vs linear. My understanding is that the original pot is 250k x2 gangs linear pot with loudness pin. Thank you

EDIT: I think I might answer my own question - the 250k log should work?
https://www.ebay.ca/itm/1pc-Potentiometer-250K-Log-ALPS-Audio-Amp-Volume-Control-Pot-Stereo-W-Loudness/201881296077

by Dogstar Mon Jun 18, 2018 11:07 pm

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Post n°22

Re: Audio Analogue Bellini as pre-amp for ST-35?

by Dogstar Mon Jun 18, 2018 11:07 pm

I put an ALPS 50K log potentiometer in the Tubelab SSE amp I built...sounds good ...but as suggested by others go with the 250K log potentiometer for your application. You will need the PC board for ALPS pots and I'd also recommend the connectors as well.

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